(Login gpence) Member from IP address 75.35.239.230
I didn't want to steal Dennis K's thread, so to show respect I started a new one.
Yep ... sorry guys ... another long-winded George post.
I'm not an engineer, this is the info about the 351C combustion chambers the best I understand it and can remember it. I don't want to get into an argument with anyone. I understand the whole small block Chevy/squish thing as taught by Smokey Yunick and repeated over an over in magazines, by SEMA, etc is hard to get out of your head once you've been indoctrinated. What Smokey taught in regards the small block Chevy may very well be true, but it just doesn't apply to the 351C, the cylinder heads aren't even close to being the same ... apples and oranges.
I respectfully submit the following to the open minded members of the 351 Cleveland forum.
Both varieties of the 351C cylinder head, quench combustion chamber and open combustion chamber, are poly-angle cylinder heads. The quench combustion chamber head is simply a poly-angle head with some small quench areas added on either side of the valves ... it is not a wedge style combustion chamber. Eventually you'll learn to think of the two styles of 351C heads in the same terms, instead of thinking of one as different or superior to the other.
The combustion chambers of Fords poly-angle heads are shallower than the combustion chambers of a true hemi-head, and this gives them two important advantages: (1) the first advantage compared to a hemi combustion chamber the 351C combustion chambers have less volume and can achieve adequate compression with pistons having flat tops, or smaller domes. Since the pistons have flat tops or smaller domes they are lighter, and they interfere with the propagation of the flame front less. (2) The second advantage compared to a hemi combustion chamber the shallow depth and poly-angle shape of the 351C combustion chambers promote better mixing of the fuel air mixture making them much more detonation resistant, this is true for both the open combustion chamber head and the quench combustion chamber head. This is also one reason for the 351C's higher volumetric efficiency.
Like a hemi head, the flame front in the 351C combustion chamber propagates at a rate, in a direction and above the piston in such a way that makes more horsepower than the flame front propagation of a wedge head.
Detonation occurs when a stagnate pocket of fuel air mixture self-ignites within the combustion chamber before it is ignited by the flame front; the source of ignition is normally pressure or temperature. The shape of a wedge combustion chamber, like the combustion chamber of a small block Chevy or a small block Ford, promotes the formation of such stagnate pockets in the area furthest away from the spark plug, which is shielded from the flame front by the large flat surface of the cylinder head, known as the squish area. The squish area of these heads is almost ½ the width of the cylinder itself. To prevent detonation with this combustion chamber design the clearance between the piston and the squish area at top dead center must be kept relatively small, thereby forcing any pocket of fuel air mixture out of hiding and towards the flame front. In comparison, the fuel air mixture in a 351C combustion chamber is dynamic or active over a significantly greater area of the combustion chamber; this is due to the relatively shallow depth and the poly-angle shape of the combustion chamber.
Squish promotes turbulence or swirling/tumbling of the fuel air mixture, it also squeezes fuel air mixture away from the edges of the cylinder and directs it towards the center of the combustion chamber where it will be ignited by the flame front. As a motor increases in speed (rpm) the piston reciprocates faster and faster within the cylinder, there is a point in which the turbulence created by the pistons motion makes the turbulence created by squish unnecessary. As a generalization then, squish becomes less important in the prevention of detonation as the speed of a motor increases. Whether or not squish is needed to improve horsepower at higher motor speeds shall be dependent upon how efficient the shape of the combustion chamber is at promoting swirling of the fuel air mixture within the combustion chamber. Wedge shaped combustion chambers are notoriously poor in this aspect whereas the shape and depth of the 351C combustion chamber (both quench and open chambers) promotes better mixing and swirling over a larger area.
Squish is not the only means by which detonation is avoided in the design of a combustion chamber, as in the case of the 351C for example, the poly-angle shape and shallow depth of the combustion chamber combats detonation. The design of the water jacket is also capable of combating detonation. The coolant path of the 351C cylinder head was specifically designed to increase coolant flow and reduce the temperature around the exhaust valve.
Torino Pat:
The Ford Off Highway Parts manual, 351C section, pages 8-9 states the quench chamber head promotes better low rpm torque and makes it easier to raise the motors compression ratio (see above). These are the only advantages ascribed to the quench combustion chamber head by Ford. The intake ports and valves of the M code and Q code heads are the same size and shape. There is nothing in the design of the Q code heads that would make their ports flow less than the ports of the M code heads. If a person is going to assert that the open combustion chamber heads flow worse than the quench combustion chamber heads the burden of proof should be upon them to prove their point, not me, because there is no physical reason why this should be the case.
To my knowledge no piston manufacturer offers an off-the-shelf piston with a dome designed specifically for the open combustion chamber heads. If there are problems encountered with the open combustion chambers in drag racing I would tend to believe the piston domes are the most likely culprits, not the combustion chambers themselves. Obviously there are domed pistons designed specifically for the quench combustion chamber heads, and the quench heads will make it easier to achieve a certain compression ratio. So from that outlook, the quench heads are a better choice and a good recommendation.
One last note about this ... my interest is street cars, not drag racing. I wasnt there and I dont claim to be experienced in the realm of building full boogie drag racing motors.
In the 1970s I helped a gentleman modify his 1972 Q code motor. He wanted to raise the compression without resorting to using quench combustion chamber heads. We had the decks leveled, and then the block was milled until the decks were the same height as the piston domes, i.e. it was zero decked. We had the heads milled until the combustion chamber volumes measured 70cc (milled about 0.025 inch). This machine work gave his motor a true 10.0:1 compression ratio at all 8 cylinders. We installed the D1ZZ-BX camshaft and headers. On the dyno his motor made about 355 peak horsepower. Over the years I assembled several motors with almost identical specs excepting for the cylinder heads ... I always used M code heads instead ... they all made 350 to 360 peak horsepower on the same dyno. I must admit, I was leery about building a 10.0:1 compression ratio motor with open combustion chamber heads, I was worried about detonation because detonation was a big issue in that era. I was relieved when we found the motor was no more prone to detonation than the motors I assembled with quench combustion chamber heads.
For those of you who have never seen this before, I thought you might enjoy seeing the small block Chevy cylinder heads that "almost were". In the same era that Ford dropped its racing program and abandoned further development of the 351C as a race motor, Chevy also dropped the development of these cylinder heads ... and for the same reasons ... to focus their budget and time on tailpipe emissions and passenger safety.
(Premier Login blizzardND) Forum Owner 64.21.236.34
Lets see if we can get some addl. input from our old timer 351C Ford Builders
September 6 2011, 8:49 AM
Well thought out and explained in a way that even I understand.
Over the years, I've run both open and closed chamber heads on the same car, same shortblocks for that matter; and like you point out, they run very much the same, really not even noticeable.
Question for ya George...
I've often thought that the open chamber 4V head looks very much like a Hemi head and really don't understand why its not called a Hemi head, other than back then MOPAR was using that name in their marketing, and that chamber design was used on the more pedestrian 2V head, so I'm sure Fords marketing folks passed over the whole idea.
Really even MOPAR's Hemi head are not a true Hemi, so the Ford 351C head is just a bit shallower than that. Maybe we should just roll back 5-6 years on this forum and go back to calling them "Cannon Ball" heads. Because when you flip the, over on your work bench, you now have a place to store 4 cannon balls.
Has anyone ever seen a set of custom popup pistons for the Open Chamber 4v's? (or even 2v's?)
Great history, and I think the whole topic helps remind us what a special slice of automotive history the 351 Cleveland was.
Thanks for taking the time George, I know you spend a lot of time on these "mini dissertation" which may seem unappreciated, but I think we all learn, and do indeed appreciate the time you spend on your "classroom presentations"
Never Pet a burning dog, and don't fry bacon naked... Gary Busey on Celeb Apprentice.
Blizz ... Cleveland heads are not hemi heads, they are too shallow to be hemi heads.
Chrysler may have had the rights to the name Hemi, I don't know. But Chrysler also invented the canted valve head, and referred to their canted valve motors as "Poly-Spherical". Motors with canted valve heads are supposed to approach the performance of motors with hemi heads without the expense of hemi heads. A poor man's hemi you see.
So somebody coined the term poly-angle head, very similar to Chrysler's poly-spherical.
I know for a fact there are engine builders & head porters who prefer the open chamber head. These folks must have their own custom dome designs ... I doubt they're using the off-the-shelf domes pictured in that post; I find the off-the-shelf selection a bit disheartening. But the Cleveland is a historic motor, yesterday's news. We are lucky to have the new products available for it that we've got.
Re: Lets see if we can get some addl. input from our old timer 351C Ford Builders
September 7 2011, 1:23 AM
Relative to the polyspherical/hemi/semi-hemi combustion chamber question, note in recent magazine articles the 'new' 5.7-liter Chrysler Hemi has added two oddly familiar small 'eyebrow' quench areas canted on the top & bottom of their combustion chambers, reportedly for 'more efficient' burning. Sure looks like a 1970 Cleveland closed chamber..... The EFI 5.7 also now uses dual plugs- mostly for emissions, I think.
wydendorf (Login winkmiester) Member 4.154.133.234
Re: Lets see if we can get some addl. input from our old timer 351C Ford Builders
January 29 2012, 3:46 PM
Here ia a way to put things in a better perspective for the time that the 351c came about at Ford. Back then there were basicially just Regular Leaded and Premium Leaded Gasoline at all Gas Stations except Sunoco, which did have different grades at that time (I think 180 to 260 as I recall) but they were the only one. When you bought a car, It had either a Regular gas (meaning Low compression) or a high performance (Premium gas was necessary because of the higher compression) engine. Most 4 Barrel carb engines from Ford at that time were Premium Gas engines and most 2 barrel carb engines were Regular gas engines, meaning the higher compression 351c 4v was made to run on premium gas and the 2v 351c was made to run on regular. At that time, Ford could produce the two different versions of the 351c by just putting different heads on the same short block and simplify their assemby of engines. In the late 1960's and early 1970's, The U.S. government had a big push to control exhaust emissions I have a friend that started as an Engineer at Ford in 1973 and he said at that time all engineering efforts were on emissions and that racing efforts were all on the back burner. The government was breathing down the necks of the big Three about exhaust gas emissions and that all efforts were placed in that area. In about mid year 1971 all high compression engines were lowered because of the emissions deal and the fact that there was a push for unleaded gasoline and catalytic converters that came about in 1975. When The Government started pushing for unleaded gas and catalytic converters all the compression ratios were lowered because of removing the lead which increased the octane rating on the gas. High octane leaded gas was to be discontinued so the automakers produced everything with a lower compression ratio to run on unleaded. As far as drag racers prefering one head over another, It would all depend on the class intended. I have a couple of friends that run the open chamber heads because they are running a certain class in NHRA Super Stock and the horsepower rating with the open chamber heads is lower so they can run with less weight in the car. Some of the closed chamber head engines were refactored with more horsepower because they ran fast and make it harder to be competetive in a heavier car. The quench head engines seem to run fast in very light cars(under 2800 lbs)
www.lifterboretools.com
This message has been edited by winkmiester from IP address 4.154.133.234 on Jan 29, 2012 3:49 PM
1) In regards to the quench heads not burning a fuel and air mixture as well as the open chamber heads, Are you for the grove technology and should it be used on the quench heads?
2) As a result of the things you listed, I was under the impression that the Aussie heads would be, not necessarily a better flowing head, but as a result of the quench combustion chamber, would give more performance and power. According to Torino Pat the only difference would be, the ability to safely increase compression and thats it, No difference or benefit? In that case since Im lowering the compression in my motor to around 9.5cr I would have been just as well off with the original open 2V heads?
I know that Im lowering my compression to work with the cam I installed, and I understand that, but if the cam was more aggressive, what then?
Thanks for helping to understand the differences.
Brent Lykins, B2 Motorsports (Login blykins) Member 72.4.3.130
A more aggressive cam will let you get away with a little more compression....
September 6 2011, 9:33 AM
...however, it also shifts the hp/tq curves to the right, which in turn takes away from power on the bottom end. Of course if you keep shifting the curve to the right, then the cam puts the powerband up out of the range of the cylinder heads and you have a dog of an engine on both low and top ends.
Thanks again George. That is a very interesting article for sure. While this is a little different situation, a number of years ago I was thinking of installing a blower kit from Dick Landy to fit the 351c, one of the things we talked about was heads and what he told me was from there testing they consistently made better hp with the open chamber head.He attributed the extra hp to the bigger combustion chamber volume which favors blown applications? He said under normal circumstances he didn't think there would be any difference? just some more things to think about!
Thanks for another excellent post, George. Well written as usual.
Yes I would agree that the open chamber cleveland head is similar to a hemi head. I also would say that a hemi head is a poor choice for a pump gas motor that needs to be detonation resistant on modern fuel. A hemisphere is a good shape for a combustion chamber, but typically in order to get a proper compression ratio you need a domed piston, so the chamber ends up shaped more like a new moon (crescent) than like a sphere. That isn't a good shape for a combustion chamber, because the flame front has farther to travel.
Now, Ford designed their semi-hemi Boss 429 heads in a better way, with quench pads on the sides to reduce chamber volume while keeping the chamber more compact. The hemi's strength is flow, not street performance. I would argue that's why most modern heads have small, compact (and wedge shaped) combustion chambers and typically have quench areas. I'm not going to say the wedge is the best shape for a chamber, because it isn't - however I believe a more compact shape is generally better. The hemi chamber shape isn't the best for a street build, but it is great for a 10/10ths racing build with a blower running high boost and the chamber on the edge of hydro-locking.
Did Ford recommend the same ignition timing for open and closed chamber heads? I think ignition timing is a good indicator of how good a chamber design is. I understand that even the Cleveland quench chambers require a lot of spark advance - the better chamber design is part of why CHIs and other modern heads produce more power (and require less ignition advance).
The 351C combustion chamber design is not a hemi, its a very shallow poly-angle combustion chamber that works very well fueled by gasoline. With nothing to coorborate my assumption, I have always assumed its the chamber's shallow design that allows it to function as well as it does. My comments apply to both the quench chamber version and the open chamber version.
The best 2 valve combustion chambers seem to be the shallow ones don't you think? Shallow chambers require valves with low angles of inclination, they unshrowd the valves, and they seem to be good at swirling the mixture. Shallow chambers do not hide any part of the chamber from the flame front. So even though the 351C open chamber heads are not compact, they actually work fairly well.
I agree the latest high swirl combustion chamber designs are generally very good. By the way, the high swirl combustion chamber design originated with Harry Weslake and may go back as far as the 1930s.
I have found that the open chambers turning point is about 9.7/10.0-1 compression. With proper timing and curve, colder plugs, good octane, and the right jets it does not detonate at all and makes really good power.
Andy
Right, I'm sorry George I missed that point you were making. Yes I agree with you that the open chamber in theory could be better than a hemi in that the chamber is more shallow, and better than an inline valve head because flow is better.
I always assumed that an open chamber head would have an advantage in flow over a closed chamber head, due to less shrouding of the valves. If the flow is equal, then I would think the closed chamber wedge shape would generally be superior to the open chamber due to greater detonation resistance and a more compact combustion area provided by the quench pad. However as I alluded to in my first post, all wedge chambers are not created equal. Also, manufacturing tolerances used in mass production of engines circa 1970 might not do the best job taking advantage of the quench features. That would be left for aftermarket performance builds.
I'm still wondering if anyone can compare preferred ignition timing between the two types of heads? I think that provides good insight into how efficient the combustion chamber design is.
Edit: One other thought I had is that you can gain some insight into how good the open chamber design is by looking at how many modern engines use a similar design.
This message has been edited by 70vert from IP address 97.127.93.245 on Sep 6, 2011 7:44 PM
The quench combustion chamber is still a poly-angle chamber, just like the open combustion chamber. It has a bit of "squish" on either side of the valves, but not much. Just enough to boost low rpm torque and reduce the chamber volume. It is not a wedge chamber. Both combustion chambers achieve their detonation resistance the same way, via the shallow depth of the chamber and the poly-angle surfaces. The smallish "squish" surfaces present in the quench style chamber does not make it more detonation resistant than the open style chamber.
Ignition timing is about the same for both quench and open versions.
George,
So there is no benefit at all to CC or OC? Was this an oops on Fords part spending research dollars for nothing? I would have thought there was at least one better thing these CC heads would do.
(Premier Login blizzardND) Forum Owner 64.21.236.34
Re: 1.94" exhaust valves, Am I reading that right?
September 6 2011, 4:53 PM
How 'bout the 2.23" intake valve on the BOSS 302? What happened to them in '70 and why are they never mentioned for use with the bigger displacement 351C or bigger stroked engines?
George??
Speaking of bigger engines, another question of mine for a long time. "How much alike are the 351C heads and the 429/460 heads was one develped then just transfred to the other?"
-blizz
Never Pet a burning dog, and don't fry bacon naked... Gary Busey on Celeb Apprentice.
I do remember reading an explanation for the smaller intake valve in 1970 ... unfortunately I can't find that explanation in my stack of stuff ... but going by memory I believe the smaller valve helped the port work better at lower engine speeds ... especially when used in a 302 cubic inch motor. Joe is the techie ... he'll have the hot dope.
Blizz ... use the bigger valve in strokers? ... Homie didn't do strokers in the 1970s and 1980s.
The Cleveland cylinder head is Ford's second generation canted valve head ... it differs from the 385 series head in ways that in my opinion were improvements. The transverse valve angles (side cant) of the 385 series head are 15 degrees, in the Cleveland those angles were 9-1/2 degrees. The 385 series combustion chamber appears very "wedge-like". It is shallower than the wedge heads in that era, but it is "deeper" than the Cleveland combustion chamber. The Cleveland combustion chamber in contrast leaves no doubt that it is a poly-angle combustion chamber, it has no wedge characteristics at all.
I'm just a newbie around here. And I'm a newbie to building 351 Clevelands. This forum has been very helpful to me and I wanted to say "Thank you!" to everyone.
I also wanted to pass a special thank you to George for this article, as well as the many great articles on his Facebook page. I've learned a great deal which I hope to apply to my Cleveland performance street build.
The picures of those experimental Chevy heads are cool to the tenth power. They kinda look familiar, don't they?
The open chamber was an oops - poor design. It isn't an improvement over closed chamber and in fact doesn't function as well. It's more difficult to get a higher compression ratio and there's no quench.
The 351C has shallow poly-angle combustion chambers. Be proud of that fact. Its one of the things that gives the 351C the superior volumetric efficiency it has. Understand your motor, there are fundamental differences between a poly-angle head and a wedge head ... they are very very different. Don't apply wedge head thinking to a poly-angle head.
The 351C open combustion chamber head is superior to any wedge combustion chamber design. It makes as much power as the quench chamber version ... its not prone to detonation any more than the quench chamber version. Poly-heads don't depend upon squish for their power and resistance to detonation, those characteristics are achieved by the shallowness and poly-angle shape of the combustion chamber. The two versions of the 351C head were developed at the same time, the quench version was designed mainly to decrease chamber volume, that's all.
The canted valve head that Chevy was developing in 1969 also had an open chamber design. They didn't feel the need for squish, and it was a racing head!
edited to clarify my meaning and curb my enthusiasm
i know of some strong running open chambered engines
I am not doubting the power output of an open chambered head
But i have personally had 2 barrel clevelandengines. One in perticuar in a 1972 gran torino
that Detonated. you might think it was out of tue, maybe a little bit.
but this car would smoke alot of basic 350 4 barrel chevys , that were in lighter cars.
and must we not for get all the 77 to 82 ford pickup out there with 351m 400 engines
that seemed to pink all the time.
so yes a cleveland head will detonate
sorry george i disagree there
Miller Mylan (Login 417strokers) Member 70.77.66.15
Open chamber not the cause of detination
September 8 2011, 12:44 AM
I like you had the idea that the reason the 400 engine was detinating was the style of the cumbustion chamber. i slaped a set of closed chamber heads on the 400 and got the same results. After a close look at the 400 engine We found the pistons stop more than .070" from the top of the bore with a.040 head gasket this leaves more than .110" squish clearance With this much clearance there is mothing to force the charge to the center of the cumbustion chamber this is what is causing detination,not the shape of the heads.
ok so your saying you zero deck the block that a 400 in a ford pickup wont detonate?
I am not buying that
it might make it less prone to detonate
but i bet it will,
I have a 79 ford bronco with a 400 .030 zero deck a small dished piston,
heads shave .050 a home ported
with a speed pro CS 1021R cam
edelbrock performer intake and 600 cfm holley
tune to the best of my ability
this is a beast engine.
from idle to 4500- 5000rpm.
the brakes will not hold it back, when its on fast idle
and it does detonates
not bad mind you but it does
This message has been edited by pewterboss351 from IP address 75.135.225.165 on Sep 9, 2011 12:54 AM
Miller Mylan (Login 417strokers) Member 70.77.66.15
Stock ford 400 has no chance!
September 9 2011, 1:06 AM
The way the stock ford 400 is made it has no chance. I never used the stock heads on the block after the clearance was corrected but I know the heads can't be the culpert because Closed chamber heads had the same problem! I have talked to many builders and they all say large squish clearance can cause serious problems from over heating the rings and ringlands to interfering with Proper chamber filling. I am sure the 400 would be a kick ass engine if it were "O" decked using stock heads! I don't know if fords idea was in serch of clean air but it made for a sad combination
I've hot-rodded a 400. Rather than mill the decks I decided to do all the correction with the pistons since the dished pistons required replacement anyway. So I ordered up one custom set of forged pistons having flat tops with a 351C 4V valve notch, standard ring set, 400 wrist pin set up for a pressed pin installation and 1.685" pin height. These piston saved having to mill the decks, mill the heads, or install bushings in the rods for 351C pins. They gave the motor a nominal 0.030" deck clearance. I topped the block with standard head gaskets and 1972 Cobra Jet heads (open chamber) having nominal 75cc combustion chambers. The result was nominal 10.0:1 compression ratio. I installed a Shelby dual plane intake manifold with spacers, topped it with a 780 Holley from Ford. The cam was my usual D1ZZ-BX hydraulic cam. This was an unbelievably strong "muscle car" motor powering an F150 with 4.11:1 gears. No sign of detonation, no pokey performance. It was a beast.
I don't mean to imply the 351C can't detonate ... the point I would like to make is the shallow poly-angle combustion chamber doesn't rely upon "squish" to prevent detonation, this is why the open chamber version of the 351C head is no more prone to detonation than the quench chamber version. There are some members who are under the assumption that the open combustion chamber will detonate easier than the quench combustion chamber, or is even prone to detonation, and that the open combustion chamber cannot possibly make as much horsepower. But those assumptions are largely unfounded and influenced by the fact they apply wedge combustion chamber characteristics to the 351C combustion chamber. To those who think that way I write the open combustion chamber heads can make as much power and they don't detonate (any more than the quench heads).
It is of course possible to get any engine combination so far outta whack that it will rattle, ping and detonate.
In the case of the 351M & 400 I think Miller hit the nail on the head, the extreme amount of deck clearance in the later versions of those motors destroyed the shallow combustion chamber's ability to swirl the mixture around. Stagnate pockets of air & fuel are what cause detonation.
Sometimes what we refer to as detonation isn't really detonation. Having worked on old Fords ... I can point a finger at one aspect that causes problems ... worn out or gummed-up centrifugal advance mechanisms that get stuck at full advance. Of course that's not really detonation, that's just too much advance. Pre-ignition (pinging) is another issue that's not related to combustion chambers. Ignitions and carburetors that are out of "whack" will of course create detonation sounding problems. Lean air-fuel mixtures, weak ignition modules, worn out spark plugs or cross-firing ignitions will do this.
All these problems occur when things are outta whack. But wedge heads are another situation. By their very design the portion of the cylinder farthest from the spark plug, directly below the squish area of the head, is completely shielded from the flame front. Pockets of stagnate fuel and air collect there easily at low rpm. Wedge head motors can go into detonation even when everything is well maintained and seemingly working properly. This situation will not happen with a 351C unless ... as Miller pointed out ... the deck clearance is extremely large.
...and that's what I was afraid of with one of the OP's (Dennis K.) threads. Stacking .066" of gasket on top of a piston .030" in the hole doesn't make for a good situation, even with OC heads. Not only could it cause intake manifold fitment issues, but I don't think that would be a good model for complete flame travel...let alone a sound way of tackling an engine assembly issue.
Brent Lykins
B2 Motorsports, LLC
This message has been edited by blykins from IP address 74.130.231.121 on Sep 8, 2011 3:56 AM This message has been edited by blykins from IP address 74.130.231.121 on Sep 8, 2011 3:53 AM
I did express a preference for dished pistons. My comment about the thick head gaskets is that they wouldn't hurt the motors horsepower potential. I am in full agreement with you that its not ideal engineering.
I've seen the head gasket approach work in conjunction with the 302C heads. Its probably on the ragged edge of too much clearance, the quench heads in this circumstance adding turbulence thats not there in the situation of a 351M or 400. That is admittedly just the assumption of an old inebriate.
As far as I'm concerned these Australian 302C heads are more trouble than they're worth for most applications here in the US. Folks use them under the belief they need the quench style chamber to make power and avoid detonation, which is not accurate. They'd be better off milling 0.060" off a set of US 2V heads (0.060" is Ford's max recommendation) reducing their chamber volume by 12cc. The 1970 351C 2V cylinder heads have smaller 76 cc combustion chambers, they'd end up with nominal 64cc chambers which is right in the ball park of where they should be. Let's not forget the Trick Flow alloy 2V heads which flow better, have the proper combustion chamber volume and the combustion chambers are of the high swirl variety. Plus they look racy which is worth 2 seconds in a bench racing session. I'm rambling.
Bottom line Brent ... you're right, the thick head gasket is not an ideal situation. We're in agreement for once.
I think this is the most appropriate spot in this epic thread (thanks George! Fun reading ) for me to throw in my thoughts/limited knowledge.
Alright, so my experience with OC heads is somewhat unorthodox and might not be appropriate to the conversation, but perhaps it means something.
My motor is a .030 over, 2V OC headed, turbo-fed torque machine. I used 0.072" copper head gaskets(no o-ring.. just copper spray RTV!). The block was zero decked, so I have 0.072 piston-head clearance. The heads I used were also milled, but I don't know how much - never measured the volume. I used the gaskets to decrease the static comp ratio. My guess is it is somewhere in the 8.75:1 range. It could be much higher, depending on whether they were decked for flatness or for compression ratio. They did have double springs installed when I got them.
The cam is a small hydro, wide LSA cam with a slight exhaust bias. http://www.summitracing.com/parts/SUM-5201/
I run ~9psi, with a rather small turbo (67mm with a .81A/R turbine housing on a Q-trim wheel), no intercooling. It spools hard, 9psi by 2500rpm or so. Even with the wide LSA, boosted, "detonation-prone" heads, I have not had any hint of detonation - I've even run 89 octane through it without issue.
So I think I'm in George's camp on this one, the closed chambers were done mostly for increased compression, not detonation resistance. I wonder if the slightly better flow of the OC head due to less shrouding would offset any increased compression allowed by the quench?
Examples of other OC headed motors? Well, for one, pretty much any modern engine. While most have some amount of quench pad, nothing comes close to the massive quench pad of the cleveland closed chamber. Look at the LS motors, the ford modular motors, that previously-mentioned Chrysler 5.7 Hemi head.
Ford 4.6 4v:
Chrysler 5.7 "hemi" (interesting that the quench pad is not flush with the deck surface...pistons are flat-tops as well)
Honda K-series:
I know most of you aren't up on your 4-cyl imports, but those Honda heads are pretty impressive. Some versions run 11.7:1 compression and top out at 8700rpm, making 100hp/L naturally aspirated.
I'm not sure where this sudden promotion of the open chamber head is coming from. Yes, I am a Cleveland enthusiast - let's try not to make this personal and stick to discussing the engine.
Could you compare and contrast the closed chamber and open chamber 351C builds you are currently running, George?
Regarding "it's not a wedge" - to me it sure looks like a wedge. Edit: the yellow document you attached to your first post has the word "wedge" in it. I understand that a few degrees of cant in the valves improves flow and allows larger valves to be fitted, but I still see the closed chamber as being roughly a wedge. It's a lot closer to a wedge than a hemi is, and that's a good thing. You can call it what you want, but the difference between the Cleveland chamber and a wedge chamber as it pertains to combustion cannot be large in my opinion. That is the advantage as I see it to the Cleveland head, better flow than an inline head, but better combustion/compression ratio than a hemi style head.
This message has been edited by 70vert from IP address 64.244.192.35 on Sep 8, 2011 12:01 PM This message has been edited by 70vert from IP address 64.244.192.35 on Sep 8, 2011 12:00 PM This message has been edited by 70vert from IP address 64.244.192.35 on Sep 8, 2011 6:39 AM This message has been edited by 70vert from IP address 64.244.192.35 on Sep 8, 2011 6:36 AM
My "Lets Clear This Up" comment wasn't aimed at you. Your comments in a previous thread made it clear your opinon wasn't going to change! So I wasn't trying to engage you in a debate. I can see however how you might have felt my comments were aimed at you, so for that I hope you'll accept my apologies.
I merely restated the intentions of my first post in a stronger way. To make sure my readers understand the point I'm trying to make, to rattle cages, knock the fence sitters off the fence. To at least provoke thought on the subject and to plant seeds of change in receptive minds.
My postion is not a reversal on my part. I'm not changing direction, over the years I've dropped subtle hints, referring to the Cleveland's heads as "hemi" heads, etc. I realize this is a controversial subject for some people. Dennis' thread simply prodded me into making this week the week I dropped the bomb, stirred the pot, whatever.
I always had a preference for quench heads for my street motors, because Ford states clearly low rpm torque is the advantage of the quench chambers. I only helped one guy do a 10.0:1 conversion with open chamber heads, he did the work I just stood around drinking his beer. That motor worked fine, it made as much power as my quench motors, and it didn't detonate even though it had the same compression ratio as my quench motors. But in the 1970s & 1980s quench heads were inexpensive and easy to find, there was no reason to use open chamber heads and pass up the low rpm torque of the quench heads.
I haven't worked on other people's machinery in a long time, but I have consulted, advised, and assisted with other people's projects for many years and continue to do so.
After retirement (next year I hope) I plan to drive my Pantera around North America, interviewing other Pantera owners, snapping pictures of their cars, and sharing stories of my encounters in Pantera International magazine. I'd love to visit with members of this forum too. I am currently collecting parts for a new motor for my Pantera. It shall be a daily driver type motor that must be reliable and get good gas mileage. My goal for the motor is 400 to 450 horsepower, in other words, no big deal. It shall consist of a standard stroke short block with Scott Cook heads and intake, and a hydraulic cam. It may be the last motor I ever build, I've promised my oldest son he can have the remaining Cleveland parts when I'm done, he wants to build a Cleveland for his Fox body Mustang. He likes the charging Rhino too.
Please accept my apologies for misinterpreting, George.
I do have an open mind, but I need strong evidence in a case like this!
I think the fact that no aftermarket company has made an open chamber aluminum head for the 351C is good evidence as to whether the open chamber is better than the closed chamber. Perhaps an overly simple argument, but I tend to align with this guy known as Occam..
Edit - one more thing - Chevy developed that open chamber head, but they didn't use it. The project wasn't stopped at the drawing phase. They had actual parts and the means to test them - and they didn't use them in production or racing cars. I would be very surprised if there wasn't more of a reason than lack of funding.
This message has been edited by 70vert from IP address 97.127.93.245 on Sep 8, 2011 7:56 PM
In my opinion a "true" Hemi head has a deep spherical chamber (no quench pads) and the valves directly in line at the north/south poles (like the classic Chrysler/Keith Black 426 hemi). The modern DCX Chrysler hemi head is similar to the classic head with the north/south valve placement, but with slightly recessed quench pads. The Ford Boss 429 hemi isn't technically 100% a true hemi (but damn close) since the valves are rotated a few degrees off of the dead center north/south poles, and some have quench pads, some don't. The new Jon kaase Boss 429 street hemi head chamber kinda looks somewhat his 426-460 P-51 head's chamber, but rotated more so the valve placement is similar to the normal boss 429 valve placement.
The factory angled valve heads thought of as "twisted wedge" or "semi hemi" stuff (351-C, 429/460, and big block chebby) while not a "true" inline valve wedge chamber (inline east/west valve centerlines), are also not anywhere close to being a true hemi valve chamber layout either (as in north/south valve centerlines). I always just think of them as neither wedge nor hemi, but a completely separate class of their own. And while it's true the 351-C open chamber might have a somewhat spherical shape (no quench) it's not a true 1/2 sphere as the roof of the chamber is too flat/shallow. And the valve placement is nowhere near a north/south hemi layout.
The big block chebby head while available in what was called both open and closed chambers, was never really a true "open chamber" because it still has quench pads. The bbc "open chamber" is really just a real big fat "D" shaped chamber with quench pads. And the bbc closed chamber is more of super skinny "D" shaped chamber (really more of an oval with flat sides) with bigger quench pads.
If you look at the Pro Mod class, all most 100% of the blown alcohol cars use a "true" classic open chambered hemi head/valve layout (aka KB 426 hemi). While some of the gas/nitrous P/M cars use either some form of an updated twisted wedge/semi hemi layout (BBF, BBC) with an exaggerated "figure 8" chamber, or the updated Boss 429 ford "almost true hemi" layout. The new Sonny Lenard (sp) monster cubic inch "chebby hemi" head is making big power numbers with & w/o nitrous. But I haven't yet seen if they are a true hemi, or more like the Boss 429 hemi layout.
As for the 351-C open vs closed chamber debate I think there is in fact some HP/torque difference to be had in a high compression race engine (w/wo a power adder) even if both are at the same static compression. The open chamber piston will be a little heavier with a bigger dome. And the quench properties of the closed chamber mixing air/fuel better & helping fight detonation is a plus, especially with nitrous use. But it might be less of a difference between the two on a turbo motor because of the increased air speed/velocity the turbo brings to the table to help mix the air fuel.
I know one guy who many years ago basically did his own 351-C open vs closed head "test" on his 67-68 nitrous Mustang. His thinking at the time was that the open chamber head & flat top piston had more room inside for more nitrous vs the closed chamber head & flat piston thus making the car faster. Only problem was the motor made less power NA with the open chambered head, so in the end it actually needed the extra added nitrous just to keep up with the closed chamber head and less nitrous. I think his best with the closed chamber heads & less nitrous was around 6.60's-6.50's in the 1/8 mile. When he first switched to the open chamber heads it slowed down to 6.90's with the same nitrous and had detonation flecks starting to show up on the plugs. He then added a ton more nitrous and finally got it back down to the 6.60's range.
This message has been edited by D.I.L.L.I.G.A.S. from IP address 207.200.116.14 on Sep 8, 2011 1:26 AM
all these respected, high performance motors, having combustion chambers that make power without squish.
The best way to describe the 351C chamber is a poly-angle, or a shallow poly-angle. I believe the chamber's shallowness is what makes the chamber work as well as it does.
David I always appreciate your drag racers perspective, I'm not a drag racer yet many of the guys here are into drag racing. You don't post often enough. I'm glad this topic grabbed your attention.
My hope is that the guys who up until now have applied wedge chamber thinking in building their 351C motors will start to view the combustion chamber differently. If we can get over that hump, there's still some new tricks for forum members to consider.
I want to thank George and everyone for all the insight that has been given in regards to this topic. I kinda feel responsible for the thread starting with all my many questions and Im glad I did. This information is like "Gold" and I just wanted to say........."My name is Dennis and Im addicted to the 351C."
Does the combustion chamber in the picture below look vaguely familiar? Its the
combustion chamber of a mid-1950's Chrysler Poly Spherical canted valve head.
The Chrysler Poly Spherical head was the first canted valve head, the one Chevy
and Ford copied. The combustion chambers of the big block Chevy and the big block
Ford don't resemble this too much, but the Cleveland is a dead ringer.
Real world notes for the thread:
4V Open - .012 deck, 214/224 hydro cam, 9:1 measured, 5500 shift point, 36 total timing, Autolite 25 plugs - no signs of detonation
2V open - .000 deck, 226/230 hydrocam, 9.5:1 measured, 6200 RPM shift point, timing locked @ 38 - slight specking on Autolite 25 plugs, clean on Autolite 24s.
4V closed - .000 deck, 238/248 solid flat, 10.5:1 measured, 6800 RPM shift, timing locked @ 38, Autolite 24s - clean plugs. Showing plug specks on that motor meant check the exhaust evac valves for failure.
302 - GT-40 iron head, 60cc chamber, 216/228 hydro cam, 5500 RPM shift, timing locked at 36. Engine was run at .012 deck, 9:1 - no detonation signs. Ran it a couple of seasons then pulled it down and zero decked the shortblock - no other changes, compression 9.5:1. Car picked up .2 and 2 MPH in the 1/8 from just the deck cleanup.
Note - I run/hold all our motors at 180~200F.
EDIT - based from 91 minimum, 93 better premium fuel. Cars are more consistent with 93 but will run on 91.
This message has been edited by Falcon67 from IP address 209.165.224.67 on Feb 17, 2012 11:57 AM This message has been edited by Falcon67 from IP address 65.182.95.67 on Sep 9, 2011 9:24 AM
heres an idea
Ok Drag racers heres your chance to shine
If you drag race a 351 cleveland
why not post your times and mph
please include
your car
weight
cubic inches
compression ratio
cam type
heads
tranny
gears rear tire size
the results should be interesting
My old Cleveland drag cars. This was the late '80's & early 90's, back before all these cool modern aftermarket 351-C stroker kits & alumimum heads were available. The Ranchero basically had 2 "low buck" (by today's standards) combos. The Mustang on the other hand had in effect a cobbled together mismatched "junk-pile" Cleveland made from the usable parts leftover from the Ranchero's broken rod 351-C, another busted Cleveland, and some swap meet parts. Everything used a closed chamber 4V head.
70 Ranchero: Old beat up & rusty 3600/3700 lb street/strip daily driver "beater".
Street/strip combo: +.030 2 bolt block, Stock crank & rods, +.030 TRW flat tops, CC 351-C heads, Felpro head gaskets, small Isky hyd cam #431302 .510 lift & 302* adv dur, Strip Dommy intake, 780 vac & 850 dp carbs, NOS cheater with 16 hole plate (tried 125, 150, 175 jets), cheap Black Jack headers, Mallory Unilite dizzy, FMX trans, stock converter & 3500 "Banana" converter, Crappy 28 x 11 Firestone slicks, 3.00/3.77/4.11/4.56/4.88 gears. Pulled motor when block's bottom dizzy pilot hole got chewed/galled up from a clogged oil passage coming from the front cam bearing.
Best N/A ET = 8.20's (iirc) with ??? gears + 850 dp. Best 175 jet nitrous ET = 7.10's (iirc) with ??? gears + 850dp.
Strip combo: +.030 2 bolt grouted block, .002/.005 deck, ARP main + head studs, stock crank & rods, +.030 TRW 12.5 dome pistons, CC 351-C heads milled .080", copper head gaskets, Crane "oval track" #cra-521421 .639"/296*/260*@.050, Strip Dommy intake, 850 dp + 1150 dommy carbs, NOS cheater (tried 150, 175, 225 jets), Hooker comp headers, Mallory Unilite dizzy + Hifire box, FMX trans & 3500 "Banana" converter, Crappy 28 x 11.5 Firestone slicks, 5.14/5.67 gears. It had decent power all through the power range shifting around 8000/8500, It had about 180/190 lbs cylinder pressure. Broke a stock rod & parked the 'Chero to get the Mustang running.
Best N/A ET = 7.70 with 5.86 gears + 850 dp. Best 225hp jet nitrous ET = 6.70 with 5.14 gears + 1150 dommy.
69 Mustang: Full chassis 2x3 frame, 2500/2600 lbs (wild guess), rear ladder bars & front A-arm/Pinto spindle, coil overs, fiberglass front end, factory steel from windshield back, Lexan windows.
Free "too loose" bore +.030 2 bolt block w/grout added after, stock crank & rods, used/worn ancient +.030 TRW 12.0 dome pistons w/cracked skirts, CC 351-C heads milled .080", Felpro head gaskets, way too much duration mystery "swap meet" solid cam, Strip Dommy intake, 850 dp, NOS cheater (tried 125, 150, 175 jets), Hooker header kit, Mallory Unilite dizzy + Hifire box, C-6 trans & too loose 8" GER + too tight 10" TCI converters, 33.5 x 15.5 Firestone slicks, 5.14/6.00 gears. Shifted around 7500. It was way down on power N/A and only had about 130 lbs average cylinder pressure. Broke one of the mismatched stock rod & bent a few others.
Best N/A ET = 6.50/6.40 range with 6.00 gears + 8" converter + 850 dp. Best 175 hp jet nitrous ET = 6.02@119 mph with 5.14 gears + 10" converter + 850 dp.
And because I'm always an attention whore when it comes to my old crap, here is some ancient video of both cars (lol). Slow by today's standards, but at least I had fun.
Not my car but a friend's. He had a street/strip early model 351-C/4speed powered Mustang I narrowed & back-braced a 9" housing for back in the early 90's. This was probably one of the fastest (if not the fastest) actual "true street driven" Cleveland in the DFW area at the time. It had a simple 6 point roll bar, subframe connectors, full stock interior, stock rear frame rails, ladder bars, leafsprings for years then later replaced with coil overs.
At it's fastest with stock block/heads it had Cleveland somewhere in the 377-390" range using a stock 2 bolt 1/2 grouted block bored .030", stock offset ground crank, stock bbc rods, flat top pistons, Crower roller cam (I never new the size). CC 351-C heads with aluminum intake port stuffers & raided steel exhaust port floor stuffers (home made) welded in place, a Strip Dommy with raised port floors, older NOS cheater plate system, a Liberty 4 speed clutch type trans, single disk clutch, unknown rear gears, slicks were somewhere in the 28/29x10.5 range. After fighting cam problems with this new combo for a few track outings, Crower finally sent him one that was a perfect match for the combo. If I remember correctly it's best 1/8 mile ET was in the 6.15/6.18 range with just 1 ancient 16 hole plate system at somewhere around maybe 2900/3100 lbs. That was damn quick for a stock block/head flat top street driven Cleveland back in the early 90's
A good friend of mine is into mud bogging, he bought a truck from a nearby town that had s Cleveland in it and was known for kicking butt in the stock class. There was a few issues with the engine so he brought it over to get things fixed. When we pulled the heads we were surprised to find o/c heads, it also had the old trw pop up pistons. The pistons were .010 down the hole and were in excellent shape. We added a little more cam and the new gaskets and bolted it back together. That thing was strong and with the light weight of the c motor compared to the 460's he won his class 2 years in a row! He even ran the stock exhaust manifolds. I was of the belief the o/c heads were not the way to go till I seen this engine run.
Miller Mylan (Login 417strokers) Member 70.77.66.15
Not fast but Cleveland
September 10 2011, 5:38 PM
I have owned Clevelands since they were born and raced most, here is Three I can still remember the set up ,not the fastest but i was the most impressed with it for going fast for cheep,
1969 mustang Hardtop 351 cleveland M code Fresh but all stock, C4 Auto with ranger 2.8 converter. Ford 8" with 4.11 posi and a few after market parts listed,Hooker headers,Torquer. holley 780, comp 972 springs. Melling Hydraulic cam and lifters duration @ .050 224 intake 234 exhaust lift .538 intake .562 exhaust. screw in stude and crane rockers 26 x 8.5 x 15 MT ET Drag slicks. I know this is not super fast but The car was a 16.00 second car before i added the Cam, Carb and Intake With Good converter and a shift kit there was an easy 2 tenths in thia car
launches were Food brake to max stall 2500 rpm
Shifts were 5600 trap rpm was 5400
Its best time
60 = 1.72
time = 12.80
Mph = 107.23
I have had a 64 Falcon, and a 71 Maverick with clevelands that ran 11.00 at 120 mph but they had lots of good parts and were not cheep to run
The falcon was a richmond 5 speed car 5.14 gears 13x32x15 goodyear eagles rpm 7200
best time
60 = 1.34
time = 10.92
Mph = 123.11
The Maverick was a C 6 Auto With 5500 stall 5.14 gears 12x30x15 M/T et drag it should have had a trans brake to lift the engine up on to the cam I was never impressed with the performance of this set up 7500 rpm shift points
best time
60 = 1.55
time = 11.22
Mph = 124.75
Wedge verses Poly - understanding combustion chambers a little bit
September 10 2011, 6:45 PM
A Wedge Combustion Chamber has the cross sectional shape of a wedge, due to the angle of the valves
This combustion chamber does not control how the flame front impacts the piston dome very well
It creates an area of "dead space" shielded from the flame front, below the large squish surface
This area is a source of detonation and reduces volumetric efficiency. This is why the small squish
clearance is so important in these motors
The Chrysler poly spherical head didn't have a "dead space" and had no squish area. The valve angles
are smaller, the chamber is relatively shallow. The chamber cross-section is not wedge shaped. The raised
areas surrounding the valves adjust chamber volume, allowing the motor to utilize flat top pistons rather
than domed pistons which were required by their hemi motor. Like a hemi the shape of the combustion chamber
is designed to focus the flame front on the center of the piston dome
The 351C chamber is very shallow, the valve angles are merely 9-1/2 degrees. There is no dead space. The
chamber cross-section is not wedge shaped. This shape evenly distributes the flame front over the entire
surface of the piston dome.
Engine designers realize the combustion chamber is the heart of an internal combustion engine. The best
designed intake port in the world cannot produce superior torque and horsepower if it is supplying fuel
and air to a cylinder with a poor or average combustion chamber. The 351C had the highest volumetric
efficiency of any mass produced push-rod (OHV) V8 not solely because it had well designed ports and large
valves, but also because it had a well designed combustion chamber. Although it may not be intuitive, what
you are looking at in the picture below is one of the best performing combustion chambers of any mass
produced push-rod V8.
The 351C quench chamber is nothing more than the open chamber with raised areas on either side of the
valves primarily there to adjust chamber volume, although the turbulence this creates also improves low
rpm torque. Since the smaller chamber is very well centered in the cylinder, the flame front is focused
upon the center of the piston dome.
Chevy LS7 combustion chamber, even though the head still uses in-line valves, this is not a wedge combustion
chamber, valve angles are only 12-1/2 degrees, the chamber is very shallow and it does not have a wedge shaped
cross-section. There's no dead space. The small amount of squish is for adjusting chamber volume, possibly for
creating turbulence, but not for preventing detonation.
If you use a 351C 4V powered vehicle for a grocery getter ... the eggs aren't going to make it home!
This message has been edited by gpence from IP address 75.35.239.230 on Sep 10, 2011 9:38 PM This message has been edited by gpence from IP address 75.35.239.230 on Sep 10, 2011 9:36 PM This message has been edited by gpence from IP address 75.35.239.230 on Sep 10, 2011 6:51 PM
Ok Drag racers heres your chance to shine
If you drag race a 351 cleveland
why not post your times and mph - 10.074@132+ mph
please include
your car - xf falcon sedan
weight - 3200lbs
cubic inches - 359
compression ratio - 11.62
cam type - solid flat
heads - 2v cast iron
tranny - c4 footbrake
gears rear tire size - 4.56 , 29 x 10 tyre
the results should be interesting
Miller Mylan (Login 417strokers) Member 70.77.66.15
Re: LS7 motors
September 12 2011, 10:22 PM
The thing about the LS7 that is funny ,Ford droped there windsor engine for the POS TRITON and Chevy picked up on it and made an ossem engine that holds its own. If fords engine guys had pulled there heads out of there buts they could have built a Strong push rod engine 20 years ago. When I first seen the LS engine in peices Thought it was a ford .
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