[PunchT37]

Climate and elevation plays a lot in static compression choice.

[mgarblik]

Originally Posted by charlie66

So, with a carburetor and a MSD distributor with vacuum advance and a 6al box is 10.5 to 1 still a save zone for 91 octane for street driving?

Yes, I feel with a pretty good tune up you will still be in the sweet spot. Not personally familiar with your camshaft but the basic specs. you posted don't scare me. Around here, 91 octane is the highest you can get with zero alcohol. 93 octane is available with a 10% alcohol blend.

[Steve C.]

I may have missed which cylinder heads were going to be in use here.

This for conversation....

Remember the combustion chamber design is a big factor.
If Edelbrock heads, are they the old style Edelbrock design or their newer 'heart shaped' design that allows a higher compression.
If KRE d-port aluminium heads they have the improved 'heart shaped' chamber design.

Keep in mind this statement, "The design of the combustion chamber influences the performance of the engine and its anti-knock properties. The layout and shape of the combustion chamber has a bearing on the thermal efficiency and performance as well."


A tidbit.... Many years ago when I was planning a previous 462 build with old style Edelbrock aluminium cylinder heads without the heart shape chamber I contacted Dave Bisschop about compression ratios. At the time based on his dyno testing he was recommending a maximum of 10.25 compression with the 87cc Edelbrock chamber design as cast and 10.5 compression with the 72cc Edelbrock chamber design as cast. This was a general recommendation for engines leaving his shop to be used under all types of driving conditions, unknown gas quality, unknown camshaft parameters, and not knowing how the end customer would tune and operate the combination. Obviously under the right conditions it could be higher but like many professional engine builders there not going to suggest pushing it for most people with a lot of unknowns.


.

[Dragncar]

10.5 and never look back. I would go higher but I pay attention to things.
Butler used to put out engines with 9.9- 1 CR. Jim told me it gave some room for guys who did not keep up on their engine or did not know a lot. He did not want complaints.

[charlie66]

Originally Posted by Steve C.

I may have missed which cylinder heads were going to be in use here.

This for conversation....

Remember the combustion chamber design is a big factor.
If Edelbrock heads, are they the old style Edelbrock design or their newer 'heart shaped' design that allows a higher compression.
If KRE d-port aluminium heads they have the improved 'heart shaped' chamber design.

Keep in mind this statement, "The design of the combustion chamber influences the performance of the engine and its anti-knock properties. The layout and shape of the combustion chamber has a bearing on the thermal efficiency and performance as well."


A tidbit.... Many years ago when I was planning a previous 462 build with old style Edelbrock aluminium cylinder heads without the heart shape chamber I contacted Dave Bisschop about compression ratios. At the time based on his dyno testing he was recommending a maximum of 10.25 compression with the 87cc Edelbrock chamber design as cast and 10.5 compression with the 72cc Edelbrock chamber design as cast. This was a general recommendation for engines leaving his shop to be used under all types of driving conditions, unknown gas quality, unknown camshaft parameters, and not knowing how the end customer would tune and operate the combination. Obviously under the right conditions it could be higher but like many professional engine builders there not going to suggest pushing it for most people with a lot of unknowns.

.

There new chambers with the plug moved over to the exhaust valve

[VCho455]

I would add one should consider the intended usage of the vehicle when making this decision. Are you think it would be cool to drive cross country something like Power Tour where you will be fueling up at unknown facilities? Then being conservative with the compression ratio would be beneficial.

Years ago went to Hot August nights in an Iron headed 455 GTO that ran 12.00s with a 9.7 compression ratio. Car ran great on premium gas around town and at the track. Unfortunately we decide to take side trip to Lake Tahoe on the way home. We got fuel on the way out of Reno and half way to Tahoe we were along side the road dialing the timing back trying to stop the pinging and trying to decide if we should just turn around or try and continue on. We eventually limped into Lake Tahoe at 40 to 45 mph and got more gas which helped to dilute the bad gas we got earlier. But it was a painful trip up that mountain.

[carcrazy]

Running 10.9 on my 462 with ported round port eheads, 242/248 solid roller cam. 93 octane works fine. My other 462 with kauffman D ports is set up at 10.4 with a 236/242 hydraulic roller. Also running 93 but could probably run 91.

[Formulajones]

It's going to come down to the whole package, engine temps, and your ability to tune it.

I have a bunch of different combos here.
11:1 with iron heads, 10.5:1 with iron heads, 10:1 with iron heads, 2 setups with 10.7:1 with aluminum heads, 10.5 with aluminum heads and 10.4 with aluminum heads.

They all run and race on 91 pump gas with 10 percent ethanol with no issues.