[hdpontiac]

I have a question on my edelbrock heads I'm wondering if the head cc can be changed from 72 cc which they are right now to around 82-85 cc without changing head is that something that a machine shop can do don't want to by new heads any help is appreciated.

[Skip Fix]

You can get to 75-76cc pretty easy just using a head gasket and opening up the chamber like the "notches" are in the block the gasket has.
Wanting to drop CR? Bigger dish?

[nas t eh]

Pretty sure the better Pontiac head specialists convert/upgrade those 72 cc heads to a 85cc heart shaped combustion chamber all the time. The only problem is finding a shop that isn’t booked well into next year.

[steve25]

So your saying your block is assembled Already?

The way Edelbrock got to the bigger chamber size they offer is the same route that the factory took, they machined the chambers deeper and used shorter valves.
In terms of making the best power and efficiency your better off with the 72 cc heads and dished pistons to get to your compression ratio you seek.

Also the deeper chamber heads can not be ported to the same level of peak air flow if your looking for such.
This effect is due to the reduction in short turn height in the ports of the bigger chambered heads.
If you can’t rework the pistons because the motor is together then I would first see if I could sell those heads and buy the larger chamber version.

Basically making a chambers perimeter bigger to gain volume will only server to increase the motors propensity to ping and knock.

This is a main reason why the deepening of the chambers is the way to go to drop your compression.

[Schurkey]

...and a thicker head gasket kills quench/squish, also leading to potentially more knock/ping.

[HWYSTR455]

Butler uses the bare 72cc heads when using their' CNC porting programs, they can do it IF the casting is a certain generation. Believe the first generation ones don't have enough meat for some of their' programs.

Call them and ask. They will accept customer's heads and CNC them. If you are unsure of the generation, they can make the determination at initial inspection.

There were some casting issues in the early runs of the first generation as well.

Recommendation: It costs the same to run just a chamber program as it does the base 315cfm program, so might as well do that.

They can do a 'modern' chamber too, but again, believe it's relevant to the generation.



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[HWYSTR455]

I hear a lot of talk about quench around here, but just to say, many other manufacturers' heads have no quench and run fine, with no det.

How do you measure quench on a hemi head?



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[PAUL K]

Originally Posted by HWYSTR455

How do you measure quench on a hemi head?



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By it's octane tolerance.

[HWYSTR455]

Originally Posted by PAUL K

By it's octane tolerance.

Then it's too late, the engine is already together so you can't change it.

Technically, you can measure quench on a hemi head, it's based off the dome of the piston used.

Point I was trying to make is that quench doesn't particularly make or break an engine, there's a lot of leeway. I believe too many just regurgitate what they've read. Many wedge head engines have horrible quench but still perform well. Without det.

Will quench make a difference in det or not when you're on the edge? Probably, but it's not going to help bring a 13:1 engine into pump gas territory.

Does quench help when trying to make peak power in a competition engine? Absolutely.

Can there be too much quench? Absolutely. Believe the 'generic' amount is .035, but that's just from memory, would have to check to be sure.



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[Stan Weiss]

Originally Posted by PAUL K

By it's octane tolerance.

Good morning Paul, When developing a new port. Do you look at the swirl curve and use that as part of of the processes?

Stan

[Stan Weiss]

Looking at Dr Blair's work. What you are looking for is squish velocity. Squish velocity is not only a function of piston to head clearance but also squish ratio (amount of quench area to bore area). In other words the larger my squish ratio the more piston to head clearance I can have to get the same squish velocity.

Stan

[PAUL K]

Originally Posted by HWYSTR455

Then it's too late, the engine is already together so you can't change it.

Technically, you can measure quench on a hemi head, it's based off the dome of the piston used.

Point I was trying to make is that quench doesn't particularly make or break an engine, there's a lot of leeway. I believe too many just regurgitate what they've read. Many wedge head engines have horrible quench but still perform well. Without det.

Will quench make a difference in det or not when you're on the edge? Probably, but it's not going to help bring a 13:1 engine into pump gas territory.

Does quench help when trying to make peak power in a competition engine? Absolutely.

Can there be too much quench? Absolutely. Believe the 'generic' amount is .035, but that's just from memory, would have to check to be sure.



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Understood.... But you can have too much quench and too little quench.. The Hemi is an excellent head because of it's air flow capabilities but completely fails (sometimes) due to it's combustion chamber design.

The optimum quench area is ideal for a specific application. That should be the goal for any build.

"Many wedge head engines have horrible quench but still perform well" ..... I think it depends on what one's definition of "well" is or what "well" is compared to.

[PAUL K]

Originally Posted by Stan Weiss

Good morning Paul, When developing a new port. Do you look at the swirl curve and use that as part of of the processes?

Stan

Good morning Stan, I spent a lot of time twenty some years ago working with swirl, when it was the "thing to do". We found techniques that would improve swirl and everytime it was a win but also discovered when modifying an existing head we were limited to how much we could improve things. Same deal as "wet flow" it's more helpful when designing a cylinder head than developing a port.

[Skip Fix]

swirl and dimples to stir up the boundry layer!

[PAUL K]

Originally Posted by Skip Fix

swirl and dimples to stir up the boundry layer!

Lol!

[Stan Weiss]

Originally Posted by Skip Fix

swirl and dimples to stir up the boundry layer!

Skip,
No, dimples but a bur finish in places does seem to work.

Stan

[Steve C.]

Related, Jim McFarland published quite a bit in Circle Track magazine including tech material on dimpling.

https://www.motortrend.com/how-to/en...ixture-motion/

https://www.motortrend.com/how-to/en...y-faster-burn/

One of Jim's piston designs here:
https://i.postimg.cc/9MQf7Zxq/Jim-Mcfarland-piston.jpg


( Information provided in this post does not represent any endorsement. And unless specified it is not based on personal experience and is offered for general interest only )


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[Skip Fix]

Jim and I discussed that several times. A lot of articles in Circle Track magazine. He was a Texas guy, Steve I think Austin. Some of his circle track motors in the articles were built by a shop near Dallas.
I told me he helped develop the Torker 1 for Pontiacs.

[PAUL K]

I thought Jim was the guy in charge of the Torker project. I've always been curious as to why that manifold is usually and under performer but managed to pass Edelbrock's dyno evaluations.

[Steve C.]

Jim was native Texan and he earned a degree in mechanical engineering from the University of Texas. When I lived in Austin his home was not far from where I lived.
I collected a bunch of his published Circle Track tech material and spoke with him a few times. He was a true gentleman.

https://www.motortrend.com/news/jim-mcfarland-obit/

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