It appears this cam is one of those cams that has long gentle ramps, most cam grinders would rate the advertised duration of a cam like this at 0.006" tappet lift, but Edelbrock chose to use the 0.004" lift figures instead. This makes the advertised duration, overlap and valve event data useless ... this is not as big of a cam as it looks like.
Looking at the duration at 0.050" and the valve lift figures, this looks like a hot street cam. A little hotter than a ubiquitous 280° cam. I would expect the average duration to be about 291° (286° intake, 296° exhaust) and the overlap about 67°. The valve events are about 80° BBDC exhaust valve opening and 70° ABDC intake valve closing . 112° lsa is OK, about as wide as cam grinders go these days. The lobe centerlines are good too. Not a bad cam, I just wish Edelbrock would have been more honest with the advertised duration figures.
If I were having the cam ground for me I would specify 114° lsa, reduce the overlap by 4°, open the exhaust valve 2° earlier, close the intake valve 2° later.
Lot better choices out there for the same or less money....
October 25 2011, 5:05 AM
Even comparing apples to apples on advertised duration, it's a little on the lazy side. I've never seen an Edelbrock cam that really floated my boat. A 10° spread on intake/exhaust is a bit dramatic in my opinion as well. I like the 112° LSA.
Lots of variables in there, especially with the engine. Is it 351 cubes or stroked? 4V heads? Which intake?
My idea of a "street cam" is something that will let the engine peak at around 5500-6000, with a really nice sound, but not overly fussy and dirty on idle/off-idle situations. You can get away with a little more with the lightweight of a Cobra, but you have to watch your toes with the 3.3 gear.
I'm assuming we're talking about a traditional 4V 351 setup, and if I had to pick something off the shelf, I would go with something like a Comp 270H (I also assume we're talking about flat tappets here). If I could go custom, I would go with something using their XTreme Energy lobes, around a 224-226° duration with a 2-4° split between intake/exhaust. Ground on a 110°, installed on a 104°.
When specing a cam, I model the engine in Dynomation, run the cam timing
iteration routine then check to see if there's anything close to the
optimized cam available off-the-shelf. Dynomation has a database of cams
that it will also check against to see if anything is close (user specified
variance around the cam timing specs). Given the cost difference and what's
involved in doing a cam swap, I tend to lean towards a custom grind, unless
there is something pretty close available off-the-shelf.
A lot of the flat tappet stuff from Crane, Lunati, etc., are way over the price of a custom flat tappet cam from Comp. Comp Cams' lobe catalog is pretty extensive, but if they don't have exactly what I want, I usually go to Bullet. Same with the roller stuff. You usually pay less than $50 difference between a shelfer and a custom stick.
sorry gave you half the info, its stock stroke 30 over 351, open 2V heads, performer 351 2V intake, 600 cfm holley vac secondaries, roller rockers, it's currently on flat tappet comp cams 268H, would do a head swap at same time to either aussie quench 2V's or more likely AFD 2V.Tubular headers and 4" sidepipes (no balance pipe, but merge style header to sidepipe construction)
....typically the horsepower curve will shift a little to the right. So not only should you make more horsepower by going to the AFD head, but the peaks should be a little higher as well, even with the mild 268H cam. If that's what you're looking to do, then it may not be necessary to go through another camshaft break-in, and you could just degree it (if you haven't done so) and optimize the cam timing.
However, if you're wanting to try something different, the recommendations in my first post would still be applicable.
Event Timing: Whoever designed this cam for Vic was familiar with the 351C, the exhaust valve opening and intake valve closing are very good, or to put it another way the intake lobe and exhaust lobe centerlines are very well placed in relation to one another and to the overall valve event. Some off the shelf cams screw this up.
Dual Pattern Cams: A dual pattern camshaft having the same "average" duration as the duration of a single pattern camshaft will also have the same overlap for a given lobe separation angle (average duration is the sum of the advertised intake duration and the advertised exhaust duration divided by two). Therefore when comparing cams of similar duration the average duration of dual pattern cams should used to insure a valid comparison. Many make the mistake of comparing camshafts based on the intake event duration.
Many aftermarket Ford camshafts are of the dual pattern variety. The usefullness of a dual pattern camshaft as an off-the-shelf general purpose cam for a variety of applications is hit or miss. Designing a cam that balances intake and exhaust gas flow can only be accomplished if it is designed for a specific motor using complex modeling, reams of data, lots of measurements and dynamometer testing. To assume as some do that a specific amount of extra exhaust duration is required for an engine because its a Ford is unfounded and presumptive. For an example Brent said he likes 2° to 4° extra exhaust duration. All hot-rodded engines are different. Ed Iskenderian insisted that a dual pattern cam was useful for motors equipped with restrictive exhaust systems, but not much else, I prefer to follow his advice in this situation.
A single pattern cam has the advantage of more intake duration for a given amount of overlap. I prefer single pattern camshafts for motors which will be equipped with headers and a relatively free flowing exhaust system (low back pressure - i.e. loud - mufflers). If the balance between the intake and exhaust is not quite right, you'll never know; but there's no guarantee that an arbitrary spread in duration of 2°, 4°, even 10° would be the right amount either.
On the other hand, if I know ahead of time that a camshaft shall be used in a motor with a restrictive exhaust system I believe it is advantageous to select a camshaft configuration offering about 10° more exhaust duration than intake duration. That's a large spread, true, its kinda like going Quail hunting with a bazooka. My attitude in selecting that amount is if I'm going to spec a dual pattern cam, I'm going to jump in with both feet rather than pussy foot around with a few degrees. But I'm also willing to admit my 10° is every bit as arbitrary as Brent's 2° to 4°. Even though my preference is a 10° spread between intake duration and exhaust duration, the reality is a cam lobe catalog may not have the perfect pair of lobes to allow this, so we hope to find a pair of lobes with a spread in the ball park of 10°, and settle for a spread of 8° to 12°.
If you think 8° to 12° is a large spread, Ford's GT/Cobra Jet camshaft had a 20° spread between intake and exhaust duration; 270° intake duration and 290° exhaust duration. By the way, you'll find if you add 270 and 290 and divide by 2 the Cobra Jet cam was another ubiquitous 280° camshaft.
One last point; if I intend to specify a 280° camshaft for a motor, and decide to use a dual pattern cam because the exhaust system is equipped with quiet mufflers, I don't add 10° degrees to the exhaust lobe (290°) to make its duration 10° longer than the intake. I subtract 5° from the intake lobe (275°) and add 5° to the exhaust lobe (285°) in order for the average duration to remain 280° (275° + 285° ÷ 2 = 280°).
...for restrictive exhaust flow theory, but I don't really buy into it.
It's true that some heads flow a lot less on the exhaust side (lots of guys use the magic 70% number as a standardd); the FE being one of them. However, as a knee jerk reaction, guys will throw 8-10° of exhaust duration in there just for good measure, not thinking about overlap and reversion.
This can work in certain situations, while being harmful in others. Extra exhaust duration will certainly add peak numbers to a dyno run or possibly boost an ET, but you have to watch for street manners. Dynos don't have airbags or turn signals.
Extra exhaust duration can also add more "chop" to an idle, which is what a lot of guys crave and want. However, you can get carried away here....i.e. Comp's Thumpr cams, which are one of the biggest flops out there in my opinion.
A few of my ballpark rules...
*Street engines get single pattern cams or I will add a few degrees exhaust duration as stated above. I've never stuck a 10 degree spread in there, even on race engines. Emphasis is on a cleaner idle, a good torque curve, and good throttle response. Unless I think DCR will go nuts or I'm tight on intake valve clearance, I'll usually run cams pretty far ahead, usually to at least a 106 ICL, if not a 104. I will also look at the overlap numbers. I have some "not to exceed" parameters in my head that I use when I pick cams. I don't really subscribe to the "x° of overlap is perfect and if you go to x+1° then it will all far apart" way of thinking.
*Race engines get what they get. On serious competition stuff, I'll use some very aggressive lobes and I'll usually add about 6-8° duration on the exhaust side to help the engine hang on a little longer if it's necessary on the top end. Reversion doesn't matter. Clean idle characteristics aren't in the picture either. Cam timing doesn't get advanced as far on drag engines as it's more critical to not shock the driveline and to shift the powerband towards the higher end if possible.
I think ole George was insinuating that what I "like" was somewhat arbitrary, but what I "like" works well for me, so I'll stick with it. If you speak to several different engine builders and several different cam designers you'll get several different opinions. It doesn't mean that there is a wrong opinion in the mix, it just means that there are several ways of going about doing things.
When I choose a cam, I'll look first at .050" intake duration only. Based on the size of the engine, the head parameters, car weight, rearend gears, intake manifold, brand of cat food the guy buys, etc., then I'll choose an intake duration based on experience, gut feelings, and maybe a few simulators thrown in just to get a good fuzzy feeling. My gut feelings are usually pretty stinkin close though.
From there, I pick how aggressive of a lobe that I want and I'll start looking at advertised durations to match how wild I want it to be. I'll also take a peek at a DCR calculator at this point just to make sure the rest of the planets line up.
When I get to that point, I'll look at lobe separation angles and will pick one based on the engine's intended purpose and application. Stroker engines get consideration here, as well as engine vacuum, torque curves, requested idle characteristics, etc.
I think I love selecting cams more than any other stage of the build. The cam is really the heart of the engine and the entire build plays off of it. Plus when I get an email from the customer, stating how excited he/she is to hear the idle, feel the torque curve, or feel how the cam comes on at higher rpms, etc., it makes it all that much better.