compression ratio wih alloy head

[early2drsedan]

what kind of compression can you run with edelbrock heads and still be safe to run 91 oct gas thanks delete post

 

[440 PHIXX]

Just a guess… 9.5:1. Not sure if you have 93 there but you could probably go above 10 then.

 

[33 IMP]

It depends ENTIRELY on what camshaft you use. Wilder cam=more compression, mild little cam=less compression.
270° at .050, can probably run 11 1/2 to one. Maybe 12.
210° at .050, it will probably rattle itself to death with 10 to one
Typical 225/235 at .050, I would probably shoot for 9-9.5 to one.

 

[justcruisin]

There are a few variables, not the least as said with cam events but also elevation, engine temp, quench, even weight of car comes into it etc. But 10:1 with a cranking compression of 165psi at sea level 35 degrees total timing and 180 degree temps is safe with a quench motor - presuming 84cc edelbrocks on a BBM.

 

[early2drsedan]

your saying more more comp but 270 at 50 11.5 to i maybe 12. 1 but 210at 50 9.5 dont make scince 270would be wilder cam

 

[sabre67]

following

 

[19polara64]

Wilder cam bleeds off cylinder pressure

 

[33 IMP]

your saying more more comp but 270 at 50 11.5 to i maybe 12. 1 but 210at 50 9.5 dont make scince 270would be wilder cam

The 270° at .050 is a MUCH wilder cam than a .210° at .050, so much wider spread of opening and closing events, so less time for compression, meaning you can, or HAVE to, run more static compression. Static compression ratio, and dynamic comp ratio, have to match the cam used.

 

[PRHeads]

When it absolutely, positively has to run on pump gas.......I don’t push the envelope in terms of static CR.

 

[33 IMP]

I ran an aluminum head flat top zero deck small block, at around 11.5 to 1, on california 91 cat pee, and it ran good. But! It was in a very light car, with LOTS of rear gear, and a 265 at .050 solid roller.
Put the same motor in a 3500 lb b-body with no converter, 3.23 gears, and a 225° cam, and it would have detonated itself to death in about a thousand miles.

 

[BSB67]

If you do not fully understand the principles discussed in Posts #3, 4 and 8, then you should follow the advice in Post #9, which is probably what was recommended in Post #2

 

[RemCharger]

If you do not fully understand the principles discussed in Posts #3, 4 and 8, then you should follow the advice in Post #9, which is probably what was recommended in Post #2

Well put.

 

[lewtot184]

I put my engine together with 9.8:1 pistons and 84cc edelbrocks. I figured maybe a half point increase with carbon build up. I use an old fashion asymmetrical cam that probably bleeds some cylinder pressure. I've never had any problems with 93 octane and it would probably be ok with 91. Don't push the limits!
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