Highest 'Practical' Compression For A Street Motor

[Road_Runner]

What if any consensus is there here about what is a practical compression ratio for a streetable high HP motor?  I'm looking at stroker kits for the 383 and depending on overbore, pistons, heads used the compression ranges from 9:00 to 1 to around 11:00 to 1.  I'm definitely planning on aluminum heads, possibly the Indy EZ heads that use std intake & exhaust ports and I know Chryco tends to add a full point compression-wise for aluminum heads so does that make anything less than 11 to 1 too low?  I don't want to be detonating on 92/93 octane but I also don't want to leave any HP on the table running too low a compression.  I know cam choice effects this too, so feel free to enlighten me on best cam choice as well.

Thanks in advance, Jim

[Chryco Psycho]

Depending on Altitude & cam choice as long duration cams bleed off cylinder pressure you can get as high as 10.5 on Iron heads & 11.5 with alum heads the other factor is combustion chamber shape to resist detonation so it is variable

[Road_Runner]

Depending on Altitude & cam choice as long duration cams bleed off cylinder pressure you can get as high as 10.5 on Iron heads & 11.5 with alum heads the other factor is combustion chamber shape to resist detonation so it is variable

Let me see: Atlanta is approximately 1050 feet above sea level, long duration cam very likely but again with max streetable HP the goal, very willing for recommendations there as well, most likely flat top pistons and I believe the Indy heads have 75cc close chamber designs.  The problem is 440Source's chart shows only 10.3-1 Compression with their kit and 75cc heads so I'll either have to go with someone elses kit, mill down the heads a bunch or piece my own kit together.  I'm thinking 10 to 1 is too low for my goals.

Thanks, Jim

[dodj]

combustion chamber shape to resist detonation

The stock head, 452's etc, are not  good in this respect?

[Chryco Psycho]

the 452 heads are open chamber & do not have quench so yeah I have seen them detonate at low compression under load 

[Supercuda]

Ideal quench area will be only .040" deep; with the big, open chambers you get nowhere near enough quench. This is why the 915s have always been popular. 10.5:1 on iron is a good number, although you can get away with as much as 11:1 if you feel like doing some engineering. With aluminum heads, I would be more of a 12:1 guy. 11.5:1 is good, but the aluminum really sucks the heat out of the chamber, and you can get away with more compression. As previously stated, cam events will dictate how much compression you can really use. Choose a compression ratio, and spec your cam from there, or figure out how much cam you want, and order your pistons based upon that. Duration adds lope, and saps low-end power; high lift with a short duration will sound tame, but make great power. It has a lot to do with what you want to achieve, and the experts at the camgrinders can help you figure it out.

[djwhog]

10.1 good ball park on the crappy gas, if you ae even more closer to a stock cam even 9.5 is pushing it, however, big cams, lots of overlap 11.1 is very do able.

Aluminm heads you can and need to go up about a point too all things given.

And not just piston ratio, but overall calculated ratio with heads, deck etc figured into the mix.