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Edelbrock RPM porting...opinions wanted..long

August 10 2017 at 9:45 PM
Dustin  (Login HarleyJack)
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I am finally getting the ol boy together. Took some time and laid out all the ports on the intake. Dye, blue, scribe the works. So after it's laid out here is what I see: Roof matches spot on, sides could lose 1/8" per side, the floor floor could lose 1/4". Thats what it would take to match the heads dead on. IF I did it I would keep floor up an 1/8". My conundrum is looking at the intake I think that much off sides will get close to breaking into the push rod tubes. Also it appears to me it will be more bellmouthing than blending/opening up. I read up on an old post that Joe C worked one over and have Jays book. Curious if the work would work and how much fruit is in the labor...from those that have done it. Research indicates mixed results. Let's here some opinions ....I am talking myself out of the job!

Engine Specs(on here many pages back)
445
Hyd Roller 227/227 .591 lift
9.3:1 Comp
BBM Heads
Non-Adjustable Rockers

Dyno'd @ 480/547

 
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Tom P
(Login tomposthuma)
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Re: Edelbrock RPM porting...opinions wanted..long

August 10 2017, 10:31 PM 

If you want to port the sides (don't do the floor) without fear of breaking through you could get some thinwall tubes, copper, stainless or whatever doesn't matter, that fits snug in the pushrod holes. Then you can grind until you hit the tube.

 
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John
(Login jetstuff)
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Porting ...

August 11 2017, 5:31 AM 

I'd leave the floor alone, depending on the casting, you'll hit the pushrod tube holes sooner or later, I did my porting, then epoxied some thin wall brass tubing I got at the local hobby shop (also available online ) back in the holes. Be careful about making the pushrod holes in the manifold smaller, or you'll play hell getting the pushrods to clear the manifold.

I think this is the tubing I used, not sure if I had to open up the holes first, it's been a while ....

https://www.onlinemetals.com/merchant.cfm?pid=1551&step=4&showunits=inches&id=84&top_cat=79

Hope this helps, John

 
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Kevin M
(Login kmccullah)
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I wouldn't go too crazy

August 11 2017, 9:42 AM 

Smooth things up a bit and run it would be my opinion. The RPM flows over 300 out of the box. Seems like plenty for your combo.
Kevin M

"They can't arrest us all"

 
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Joe-JDC
(Login Joe-JDC)
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If you are only mismatched by 1/8" on the sides, then

August 11 2017, 11:13 AM 

I would suggest only going into the port about 1/2" and blend out to the scribe marks on the sides, and leave the floor alone. Don't open up the ports any further back than 1" at most, and you do not need to open them up to the pushrod tube size. Just a simple blend will be able to speed the air up and work well with heads up to 300 cfm. Joe-JDC

 
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Dustin
(Login HarleyJack)
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Blend

August 11 2017, 2:18 PM 

Thanks for all the replies FErs...Joe- that is what I was thinking honestly. Looking at the overall runner design and size I lean more toward doing nothing at all vs. matching it all the way around. I know having a step from floor into the head is best but it is a pretty big step. My concern was bell mouthing the end of the runners and possibly hurting velocity without gaining much flow at all. Guessing a minor bell mouth is not bad. The design of the RPM limits a lot of manipulation...works good as is...IMO and so far proven.

What about trying to touch up certain runners and leave some alone? From research on your old thread( I believe) it appears they are not all that balanced with some(2,3) being higher flow than others. I would think increasing on the existing imbalance could be bad longevity wise for the engine/equal fueling of cylinders for the street.


 
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Ross
(Login Bad427stang)
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Not Joe, but actual cylinder fill is real tough to balance (long)

August 13 2017, 5:43 AM 

Joe of course does an incredible job of balancing flow, and he has shown us many times how to equalize. That should indeed increase power, and with a knowledgeable hand like his, will help the whole curve. This post is not questioning that at all.

However, your comment of longevity and equal fueling, first, unless you have a situation of a significantly lean cylinder driving detonation, there won't be any negatives to a bit of a difference in cylinder fill from one to another, and more importantly, it's really tough to say you could manage it, even if you wanted to, and I purposely didn't say flow, specifically talking what the chamber sees. Joe's balance certainly helps, especially when ports are significantly restricted before he touches them.

However, each runner is a different length in a V-8 and therefore will be tuned a bit differently, at best there are pairs or 4 that match. This creates different cylinder fill based on resonant tuning and rpm, even differences in the header primary pipe and which cylinder it follows in the firing order, change cylinder fill, even if the ports flow the same amount. It is not a problem, but it is there

I can go full geek on you to show the math happy.gif I measured a Street Dominator to apply Ramcharger's intake resonance tuning testing from the 60's. There are many ways to calculate, but this is the easiest formula. It was pretty good work and it can show why runners continue to get longer on modern EFI cars too.

To figure out the RPM where a port is tuned (for resonance wave benefits only, not cam profile or port flow performance) an RPM is calculated based on the reflecting wave of the valve opening and closing in the intake port

L = 80500 / N

L = duct length (inches) from Plenum (the first reflection point) to the back of the intake valve (INPUT)
80500 = Constant based on the speed of sound
N = Engine RPM for maximum tuning effect (OUTPUT)

With a Street Dominator measured with a head, I got 11.75 and 8.75 as the inner and outer averages. All manifolds will be different and likely dual planes will have closer spreads than single planes

That resulted in an RPM peak tuning of the inner 4 and outer 4 ports

SD Out SD in
N 6843 RPM 9189 RPM

Quite a difference on when each intake runner comes up on resonant peak. However, that doesn't account for ANYTHING other than resonance. The actual RPM peak of the port is also affected (and far MORE so in most of the curve) by intake cross section, primary exhaust effects, overlap, cam design, overall airflow, crankshaft design, valve and chamber design, you name it. However, it shows, even if every part in your engine matches, intake runner lengths (and header primary pipes and cylinder firing pairs) are different, so you have different cylinder fill at any given point

I look at intake flow balance as giving the intake the ability to make the power and eliminate flow capability as a serious variable, but at any given RPM, a long runner will still behave a little bit differently than a short runner, and in fact, although different runners technically lower the peak RPM, they flatten the curve which is great on the street

As I read my own post, this isn't telling you do anything LOL I am only trying to say that it isn't a reliability worry as much as it is a power benefit to balance flow...and even when you do...a function of packaging and design in an engine guarantees actual fill for any single cylinder will be different anyway.

and to reiterate, Joe is awesome and balancing flow is awesome happy.gif just trying to address the comments that there will always be an inequality by design and unless you have some sort of horrible lean condition, it won't hurt the engine.
[linked image]
---------------------------------
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed


    
This message has been edited by Bad427stang on Aug 13, 2017 5:49 AM


 
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Dustin
(Login HarleyJack)
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Cylinder fill and math lesson

August 13 2017, 6:59 AM 

Ross,
Step away from the coffee! It has side effects! Seeiously, thanks for the info. I have found Joes old info on flowing/moddifying an RPM. In looking at that data you see the difference and "imbalance". Your explanation brought to light the one dimensional view I had. My concern was, being carbed, that fuel is not managed like in an injected application. In my mind i was thinking more flow would mean more fuel to those cylinders and less to others. I am of the opinion that one, there are others, of the main reasons modern cars go so long is injection/fuel managment. So my concern was making an issue worse and having a negative impact on engine life. I want the ol boy to be a heavy lifter but last! It was a good excersise and appreciate the math and explanation. More a person can learn the better they can build. Btway where did you come up with formulas? You secretly an M.I.T. student! I will touch up the ports/clean up the flash a bit. Looks like I was overthinking and underthinking it! Hows the new build? Find the noise?

 
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Ross
(Login Bad427stang)
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That's funny!

August 13 2017, 9:24 AM 

Honestly, I am a closet math geek. Started in flight school ironically, not in college, and many days deployed in the past 22 years gives me lots of time to do mental gymnastics happy.gif

As far as my 445, haven't even looked at it, USAF and side work has kept me very busy. The 396 toy motor is coming along well, finished the worked Streetmaster, got the pistons and rods done, the crank is going to be a fun one, was balanced for big bolt CJ rods and HEAVY TRWs, now going light 360 rods and short/light Diamonds with metric rings. My hunch is it's going to take some grinding and drilling to balance for the new combo.

Once I get the short block wrapped up, I need to decide on heads and then I will swap with the 445 and figure out the noise. I sure hope something left a mark in the 445, it hasn't yet!

[linked image]
---------------------------------
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed


    
This message has been edited by Bad427stang on Aug 13, 2017 9:26 AM


 
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Dustin
(Login HarleyJack)
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396 FE

August 13 2017, 12:58 PM 

Yeah I bet you right about the balancing. Glad to hear it's coming along! Be curious to what you find once the day comes to pull the 445. I am gonna have to freshen up my math skills aparently! Still a lot to learn! Wish I could spend a month or so at Kuntz. Like learning but so many variables that go unspoken. Secrets to the trade and such that you have to witness/learn because it never makes it to a book or a forum. Anyway, my intake is done. Best I could do with tools i have. Just have to clean the heck out of it. Really hard to improve on that particular intake. Fits those bbm heads pretty darn well and the design of intake runners limits any major gains in my opinion. Basically its final touch type work. Got a lot more material off than I anticipated and made a nice mess! I ever start doing porting for a hobby I am going to build a booth! I looked like the tin man after that ordeal! I will have mine back together in the next two weeks I hope. Then its C6 time! Another first.

 
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