[Randy Allen]

I have a set of the original design Edelbrock heads with 72cc chambers. Is it possible to enlarge the combustion chamber to 87, 93 or 100 cc’s. If so, what vendor does the work and what’s the approximate cost.

The dilemma I face is that even with new 87cc E-heads I need a bigger combustion chamber.

I’m currently running 6X-4 heads with 93cc chambers that have been flowed to 257cc and yield 9:65:1 compression.

I’d like less compression and greater flow to support a growth in CI from 468 to something larger.

Thanks for your assistance.

[leeklm]

Keep in mind most combinations with aluminum heads will support 11:1 cr or even a little more on pump gas

Sent from my SM-G965U using Tapatalk

[steve25]

With the greater heat loss from aluminum heads you could go up to 10.25 compression and run the same octane fuel you are now and not have a knocking or pinging issue assuming your Cam is not too small.
On the Edelbrock and other off the shelf aluminum heads they make the 72 CC chamber deeper to get to the 87 CC range and to convert your 72s to 87 is no small job!
I would sell your heads and see if you can find a used set of 87 CC Edelbrocks or kRE heads.

[ta man]

You will have to figure on what cu inch and what piston dish you will eventually have?
Don't be afraid of compression with the aluminum heads. Mine is at 10.8 to 1 and I routinely run 89 octane

[ta man]

For reference I have a 79 cc chamber on a 466.

[ta man]

Dave Bisschop has opened up many of the original heads as well.

[Steve C.]

Years ago I had a conversation with Dave Bisschop regarding static compression ratio on aluminium heads. He felt you can't protect all of these engines once they leave your shop so he often purposely kept it conservative for most that don't want (or shouldn't) push the envelope and stay on top of the tune, bad gas, weather, etc.

In that conversation with conservative in mind and regarding Edelbrock cylinder heads. Based on his dyno testing at the time, he stated 10.25 max for Edelbrock 87cc castings and 10.5 max for their 72cc castings. The difference being the chamber depth between the two. This was his opinion with the chamber design of the Edelbrock round port heads at the time. Not the newer "heart shaped" design.

Edelbrock heads with a revised combustion chamber design and the KRE D-port heads design it's a different story and a higher compression can be run.

Article that might be of interest:

How combustion chamber design relates to engine performance
https://www.motortrend.com/how-to/02...stion-chamber/


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[Steve C.]

SD Now Offers Custom Chamber size options on Edelbrock heads.

http://www.sdperformance.com/newsStory.php?newsID=38


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[Randy Allen]

Originally Posted by Steve C.

SD Now Offers Custom Chamber size options on Edelbrock heads.

http://www.sdperformance.com/newsStory.php?newsID=38


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Thanks Steve. Having worked for Tom for 10 years I had never seen that article. I suspect he wrote in within a year or two after moving from Mopar muscle.

I guess I can call SD and discuss opening up the 72cc heads but suspect that starting from 87 cc heads with a thicker head gasket would achieve the same or an even lower effective compression.

I’ll await more great suggestions and then have a follow-up question.

Thanks,
Randy

[Steve C.]

From the internet....

For every action there is a reaction. Thicker gasket will lower compression, but increase quench area.


"Chamber volume is the major component in determining static compression ratios. Situations where quench must be sacrificed in order to keep compression in check to satisfy a competition rule or accommodate existing parts, do arise. Increasing head gasket thickness is an easy and affordable way to reduce compression. However, reducing quench will also reduce efficiency and lessen resistance to detonation."

https://www.enginelabs.com/engine-te...ston-and-head/
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[Half-Inch Stud]

Alternate idea: since my ported 48s are nice and done, the Flattoped 455+030 needed more cc, so i opted for the Cometic 0.080" thick. Spendy butt hay, cheaper than dished slugs.

My 455+060 has the RAIIs and the dished slugs for 9.0:1. with 0.045" gasket. 87 Street, 89 Octane Strip, ping free. Good MPG!

455s' Quench zone ought be fine since the 4.21" stroke has more slug velocity than the 3.75" stroke for same stock quench VOLUME. Not worried. Such a doubled quench volume becomes moot soon above high idle.

[steve25]

Like I said, to get that much of a CC increase the chamber needs to be machined deeper.

This requires pulling out the valve seats to do that, then new ones need to be. Installed and a valve job done.

Since this work sinks the valves deeper then the push rod geometry needs to be gone over again and the spring pressures need to be reset.

Making the chamber deeper also shrouds the valves and reduces the air flow some what unless chamber work is done to counter act that.
I would just keep your heads as they are or maybe send them out to have CNC work done to unshroud them more to the tune of adding like 5 more CCs and then get your new pistons that have a 20 or so CC dish.

You absolutely do not want to run anything more then a .050” thick head gasket to keep detonation and knock at Bay!

A 10.5 compression will let you run the crappyest 89 with no issue and allow a good amount of street happy vacuum advance to be run.

[78w72]

if youre changing pistons for bigger CI, the pistons could be dished to get to your desired compression a lot cheaper & easier than changing the head chamber size. ross did that on my butler provided stroker kit for not much extra, think it was about $100 ~5 years ago.

[steve25]

Especially with a dished piston which has far less flat surface area then normal, you want to run the thinnest head gasket you can .

A Easy to get these days Fel Pro 1016 would be my pick!

[Formulajones]

Tony Bischoff did this sort of work on dad's old Edelbrock round port heads when he built the 571.

However dad had a set of 87cc chamber heads to start with, and Tony opened up the chambers substantially so he could keep the piston dish to a minimum and still have a pump gas friendly compression ratio. It came out to 10.84:1 with a 4.750 stroke and 4.350 bore and has been running perfectly on 91 octane pump fuel for several years now.

[steve25]

It makes me wonder if/ how much 1st generation Edelbrock wedge chambers can be changed into the more burn friendly Heart shaped 2nd gen chambers while they are taken out to a bigger size from 72?

[Formulajones]

Could probably be done and keep the compression friendly on the smaller engines. A little welding wouldn't be impossible to achieve it too but it starts getting costly.

Don't believe it's doable on a 571 though, can't imagine a heart shaped chamber that measures over 100cc for a pump gas compression ratio but maybe. Had to start with 87's anyway.

Not convinced they turned out inefficient either like so many preach, as the engine loved 34 degrees on the dyno and more killed power. They didn't need 36-38 or more like you often hear about. A lot of that I think also had to do with the quench and the custom piston design that Tony came up with.

[Steve C.]

New CNC machined heart shaped chambers with improved spark plug location for Edelbrock heads.


http://www.sdperformance.com/viewPro...p?productID=38

http://www.sdperformance.com/listPro...?categoryID=25


SD Performance has more 5 Axis CNC Porting and Combustion Chamber Programs for Pontiac heads then anyone and we are constantly working on more and improving existing programs in our never ending search for more pure Pontiac power. If you already have a set of Edelbrock heads we can apply all our packages or just porting to your existing heads as well, drop us a line for more details.

( As typical this post does not represent any endorsement by me personally. And unless specified it is not based on personal experience and is offered for general interest only)

[afgun]

Right on SD's website...

"If you already have a set of Edelbrock heads we can apply all our packages or just porting to your existing heads as well, drop us a line for more details."

[Steve C.]

Yes, as I mentioned above.

However a fwiw, from what I understand the wait list can be quite long.


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