[MerrittE]

Thanks for all of the info guys it seems like most of what I was finding was related to the early edelbrock heads without fast burn chambers. Here is a write up I found from Rocky Rotella which discusses the newer fast burn chambers. I actually have this book and it is excellent but with so much information I completely forgot all about this paragraph lol. Still I know there are a lot of decisions to be made on the cam choice but I may bring that up under a separate post. It seems the choice of 72cc chambers and 18cc dished pistons will put me right at 10.59 to 1 and if needed I could run a thicker head gasket.

https://www.cartechbooks.com/blogs/t...ac-v-8-engines

Most every other cast-aluminum Pontiac cylinder head available on the aftermarket today features a fast-burn combustion chamber. These castings tolerate slightly more compression ratio. I recommend a target compression ratio of 10.5:1 when combining the Edelbrock Performer D-port or KRE D-port with 91-octane pump fuel. Some builders have reported successful results running a static ratio as high as 11:1, but I consider those specialized applications and certainly wouldn’t recommend that for everyone

[OCMDGTO]

Both engines in my sig are 10-1, no regrets here

[Steve C.]

I've posted this before, here again for interest.....

Years ago I had a conversation with Dave Bisschop regarding static compression ratio on aluminum 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.

Tom S made a good point here....
"If your not going to race it,why take any chance when driving around in traffic on hot summer days.Your ass dyno will never feel the .6 of a point.JMHO,Tom"

I can relate this. About 20 years ago I did a 4.210 stroke 462 with 87cc Edelbrock heads. On my machinist bench they were 313cfm at 0.600" lift.
However when I ordered custom pistons there was a mistake made and the static compression ratio ended up at about 9.7
On the engine dyno with a Performer RPM intake & custom HP950 carb it made 589 ft.lbs torque at 4400 rpm and 580 hp at 5800 rpm.
For the most part it was street only and I'm sure my ass would have not noticed the difference with a bit more compression.
For interest only, it ran 10.948 at 123.59 mph at the track.


.



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[slowbird]

Originally Posted by Steve C.

I've posted this before, here again for interest.....

Years ago I had a conversation with Dave Bisschop regarding static compression ratio on aluminum 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.



.

That's interesting. I always felt the larger chambers were less tolerant, good to see Dave felt the same

[hgerhardt]

Originally Posted by torqjunki

Can you post up details on the 248/254 cam your running please sir? Working on similar combo.

Here you go. As you can see, it's ground 5 deg advanced, so I installed it straight up.

Also, all of my experience with this engine is with the older E-heads. Both my 87cc and 72cc heads are 27+ years old. In fact, other than replacing the valve springs a few years ago, It hasn't been apart in 25 years.

[65 Lamnas]

Originally Posted by MerrittE

..and if needed I could run a thicker head gasket....

That'd be a bad idea......people just don't understand squish and/or the negative effects of running a "thicker" head gasket.

[slowbird]

Originally Posted by 65 Lamnas

That'd be a bad idea......people just don't understand squish and/or the negative effects of running a "thicker" head gasket.

People say that but I have yet to see any real testing that backs it up. I know quite a few engines running thick head gaskets than the normal .040 with issues.
Not saying there isn't some truth to it but I'm not sure it's as bad as people say.

[Stan Weiss]

The greater the squish clearance the less velocity / mixture movement. The velocity for a given squish clearance will vary with CR. This is not the only way to get mixture movement. But how many flow sheets have you seen that show swirl and / or tumble?

Stan

[65 Lamnas]

Originally Posted by slowbird

People say that but I have yet to see any real testing that backs it up. I know quite a few engines running thick head gaskets than the normal .040 with issues.
Not saying there isn't some truth to it but I'm not sure it's as bad as people say.

I don't know "how bad" it is either. Like you, "I've heard" and I've read" and I also know of engines running around with thick head gaskets that are "turds". Chances are good they have other issues than just too much squish.

I'm probably not ever going to "tune" or lower my engine's compression ratio by changing head gaskets, which is what a large segment of folks think is acceptable.

I'm not going to run any tests to prove "squish matters", I'm going to stick to the accepted guidelines. One thing I know from analysis is that mixture motion right before combustion is a good thing.....

[Steve C.]

Might be of interest...

Quench: Unlocking Performance Squished Between the Piston and Head

https://www.enginelabs.com/engine-te...ston-and-head/



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[hurryinhoosier62]

Originally Posted by 65 Lamnas

If the 72cc heads are the fast burn chamber and your block is zero decked, I'd say "go for it". 11.0:1 is totally doable with 92 octane.

Depending on which cam you use…

[hurryinhoosier62]

I’ll go with what Ken Crocie says: one point higher than what an engine with iron heads can run without detonating. Example: if you are running 6X-4 heads milled to 85cc on a 455 with a 9.5 to 1 c/r and a cam that allows for cylinder pressures not to peak above 180psi you can safely run a 10.5 to 1 c/r with 85 cc E-heads. The “421” I’m in the process of building for my ‘64 Catalina will have a static c/r of 9.98 to 1. I may give up a bit of top end power, but engine longevity is worth it in a street engine.

[torqjunki]

Thanks!! I like it. I don’t see LSA

[torqjunki]

That was to hgerhardt.

[Steve C.]

Calculate Over Lap and Lobe Separation Angle

http://www.wallaceracing.com/calc-cam.php



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[65 Lamnas]

Originally Posted by 65 Lamnas

...Chances are good they have other issues than just too much squish....

"too much squish." isn't clear, should have said, "too much squish area".

[65 Lamnas]

Originally Posted by Steve C.

Might be of interest...

Quench: Unlocking Performance Squished Between the Piston and Head

https://www.enginelabs.com/engine-te...ston-and-head/



.

Good article...thanks for sharing...

[65 Lamnas]

Originally Posted by hurryinhoosier62

I’ll go with what Ken Crocie says: one point higher than what an engine with iron heads can run without detonating. Example: if you are running 6X-4 heads milled to 85cc on a 455 with a 9.5 to 1 c/r and a cam that allows for cylinder pressures not to peak above 180psi you can safely run a 10.5 to 1 c/r with 85 cc E-heads. The “421” I’m in the process of building for my ‘64 Catalina will have a static c/r of 9.98 to 1. I may give up a bit of top end power, but engine longevity is worth it in a street engine.

Depending on which chamber you use…

[MerrittE]

After digging deeper I am going to scrap going with the ported heads they are just going to be too much for what I want to do and I’m going to drop the compression down as well to 10:1. Thanks for all the great advice!

[hgerhardt]

Originally Posted by torqjunki

Thanks!! I like it. I don’t see LSA

It's there on the cam card, you just have to do some math to see it. (109+119)/2 = 114.

What I like about this cam is how well the engine likes to rev. 4" stroke (434 cu in.). Enough torque to get wheelspin (with 255-section tires) by hitting the gas at 55 mph in 2nd gear (which is pretty ridiculous on the street!). So it makes good torque plus has that nice, high-RPM lunge (shift at 6500).

And even though these 72cc heads have the old combustion chamber, max power happens at 31 deg total timing. With the old 87cc heads, I needed 37 deg. So good quench combined with high compression seems to work here. (11.4:1 on the 72cc and 9.7:1 on the 87cc)
Note that I did not just swap heads when going from 87 to 72. I also decked the block to make it parallel to the crank but also got the pistons slightly above the deck (forgot exactly how much). So I increased compression plus quench at the same time.