[MerrittE]

Hi guys, I’ve dug through a lot of the older posts but nothing is popping out to me as a clear answer. I have a 428 build that is currently in the machine shop with the intention of putting it in my street cruiser Firebird with a goal of a 91 octane pump gas easy driver with power disc brakes that can hustle. It is .30 over at 4.155 and I will be using a 4.25 stroker crank. I had planned to use 82cc Edelbrock heads with 22cc dished pistons which would put me at 10:1 CR. My machinist wants to use a set of edelbrock 72cc 325 ported heads and a set of 18cc dished pistons which will put me at about 10.6:1 CR. What are your thoughts is this still in the safe zone for a summer daily driver? The reason for this setup is someone ordered it but never paid so he is giving me a pretty good deal on it.

[Stan Weiss]

Originally Posted by MerrittE

Hi guys, I’ve dug through a lot of the older posts but nothing is popping out to me as a clear answer. I have a 428 build that is currently in the machine shop with the intention of putting it in my street cruiser Firebird with a goal of a 91 octane pump gas easy driver with power disc brakes that can hustle. It is .30 over at 4.155 and I will be using a 4.25 stroker crank. I had planned to use 82cc Edelbrock heads with 22cc dished pistons which would put me at 10:1 CR. My machinist wants to use a set of edelbrock 72cc 325 ported heads and a set of 18cc dished pistons which will put me at about 10.6:1 CR. What are your thoughts is this still in the safe zone for a summer daily driver? The reason for this setup is someone ordered it but never paid so he is giving me a pretty good deal on it.

What are the spec for the cam you plan on running?

Stan

[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.


.



.

[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

[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!

[tom s]

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

[tooski]

I gather it's a 428 block that you are stroking to 461. I'm not a high experienced tuner, but I think I do ok. At any rate I have 406 at 10.1 cr. Runs well on 91. slight detonation on 89. I also have a 461 at 10.5 cr with a bit of detonation trouble on 91. I plan on turning either one into a 433 with a hair under 10 cr.

[steve25]

He s giving you a so called good deal on heads ported to a level that you do not need for your stated usage!

Tell him thanks, but no thanks.

[i82much]

what if you used a 4 inch stroke crank with the 72 cc heads? just because it is a driver doesn't mean you can't let it snort a little ... what's your pain tolerance? do you need a sleep number bed and silk pajamas or are you a guy that throws a wool blanket on the ground and sleeps like a baby?

[Stan Weiss]

Can someone else do the math?

If I use 72 cc heads 18cc dish and .038" head gasket I get 10.593:1 CR

If I use 82 cc heads 22cc dish and .038" head gasket I get 9.398:1 CR

Stan

[i82much]

did someone cut 87 cc heads to get you 82? i don't think they make 82 ....

[JEC3039]

I'm with Stan -

Assuming zero-deck, a Fel-Pro 0.039 gasket at 9.4cc and a top ring land of 1.14cc:

for the 82/22 combo I get 9.25

for the 72/18 combo I get 10.40

[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.

[Steve C.]

As eluded to above. Edelbrock heads with a revised 'heart shaped' combustion chamber design you could consider a higher compression ratio.

Related article that might be of interest:

https://www.hotrod.com/how-to/0209hp...oogle_vignette


.

[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…

[steve25]

I would have no problem with a fast burn chamber running 10.5 to 1.
Another plus is the lesser amout of CCs above the piston the higher the idle vacuum will be.

[Steve C.]

Two additional considerations regarding the use of the 325cfm heads.

The choice of intake manifold and with it the discussion involved with port matching it to the intake port size. Example, a Butler 325 cfm heads uses a 1.180 x 2.35 tall gasket

Camshaft lift vs. Cylinder head flow limits....

Note at what lift is that 325 cfm head rated at. I will assure you it is well over 0.600" valve lift. Probably closer to 0.650" or higher.

.

[MerrittE]

Thanks for the feedback I misspoke the heads I originally planned to use were the 87cc version. If going with 72cc heads would 18cc dish heads be safe or should I go to 22cc dishes. I haven’t decided on a cam yet and that will definitely be something I would value input on too. I planned to go roller with butler scorpion rockers and cross wind or torker two intake. Originally I was looking at the butler 500 pump gas package.
This will be backed up by a 4l80e with probably the stock converter and an upgraded rear end but I haven’t landed on a ratio yet. Sorry for the jumbled post but I had to hit the road for a family deal that came up in the middle of this. Thanks for all the advice and I will check out the links above tonight.

[65 Lamnas]

Originally Posted by MerrittE

Thanks for the feedback I misspoke the heads I originally planned to use were the 87cc version. If going with 72cc heads would 18cc dish heads be safe or should I go to 22cc dishes. I haven’t decided on a cam yet and that will definitely be something I would value input on too. I planned to go roller with butler scorpion rockers and cross wind or torker two intake. Originally I was looking at the butler 500 pump gas package.
This will be backed up by a 4l80e with probably the stock converter and an upgraded rear end but I haven’t landed on a ratio yet. Sorry for the jumbled post but I had to hit the road for a family deal that came up in the middle of this. Thanks for all the advice and I will check out the links above tonight.

72cc heads > 16-18cc piston dish > 0 deck block for optimum squish, if at .030 and 4.25 for a 428 block, then that's about 10.6-10.8.....no problem on 92 octane with the "good" chambers. A ported HO intake would be nice with a stock converter if you need hood clearance, or else an RPM. I'm guessing it might be "soft" down low with the T-2 and a stock verter around town.