[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

[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


.

[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.

[performerrpm]

if you havent bought pistons already, then i would definitley buybthe ported ones if the price is right...never know when you might want to do more later. buy the pistons that puts your cr where you want it.

[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.

[hgerhardt]

My 428 with Ross flat tops and zero-decked block and 72cc E-heads is 11.4:1 and is happy with 91 octane. Cam is 248/254 @.050 and 114 LSA.

So much of this is dependent on cam timing. It's the dynamic CR that's important, not static. Dynamic CR is determined from when the intake closes on the compression stroke. The later the intake closes, the less dyn CR you'll have.

An example: this engine with the same cam originally had 87cc E-heads (9.7:1-ish) and I accidentally figured out that it ran better on 87 octane than 91. With the 72cc heads, throttle response is sharper, and I picked up around 1/2 sec in 1/4 mile. Much happier motor!

[Cliff R]

The last 455 I built for the Ventura was 11.3 to 1 compression. Squish .039", 74cc KRE heads ported to 295cfm. I used the older version of SD's Old Faithful cam, 289/308, 236/245 on a 112 LSA with the ICL at 109 degrees.

It managed all grades of pump fuel w/o detonation. I typically tried to keep 92-93 octane in it for the "warm and fuzzy" but it really didn't care. The only issue I ever had with it was in the heat of summer on 87 octane. If I was well heat soaked once it a while it would "run-on" when shut down, but in all other scenarios it was fine.

At the track it actually slowed down on race gas, clearly showing it didn't need that much octane the way it was set-up.......

[torqjunki]

Originally Posted by hgerhardt

My 428 with Ross flat tops and zero-decked block and 72cc E-heads is 11.4:1 and is happy with 91 octane. Cam is 248/254 @.050 and 114 LSA.

So much of this is dependent on cam timing. It's the dynamic CR that's important, not static. Dynamic CR is determined from when the intake closes on the compression stroke. The later the intake closes, the less dyn CR you'll have.

An example: this engine with the same cam originally had 87cc E-heads (9.7:1-ish) and I accidentally figured out that it ran better on 87 octane than 91. With the 72cc heads, throttle response is sharper, and I picked up around 1/2 sec in 1/4 mile. Much happier motor!

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

[78w72]

I have a 400/467 with the original chamber 72cc E-heads & butler 4.25 crank, ross pistons, block decked to .005. With the pistons at 14cc dish the cranking compression is around 10.5-10.7, old faithful 1.0 roller cam... I run 91 octane no ethanol with no detonation at all, it can even run on 89 with no audible detonation but it will run on a bit at shut off on hot summer days. Been in use for 10+ years with lots of low 11 second drag runs.

With aluminum heads & a good tune these engines can easily run 10.5 on 91 gas.