Hi everyone.

This post is aimed at N/A engines only.

Most people like to bump static compression ratios in their LS engines up into the 11 to 11.6 to 1 static compression ratio and sometimes even higher.
The higher you push you static compression ratio the larger the cam you will need to use to bleed off the dynamic compression ratio to run on pump gas.
By increasing the static compression ratio this also means that the dynamic compression ratio also increases well into the 8 to 1 dynamic compression ratio zone. Great for power increase.
Lots of factors need to be looked at here for everything to work in harmony.
1 fuel octane used
2 air temperature
3 quench
4 weight of vehicle and if towing loads
5 altitude for air density
6 cam size especially inlet valve closing point

Obviously depending on the engine meterial iron vs aluminium, block and heads the risk of deterioration becomes a major factor as static compression ratio increases.
Iron bblcks and heads like around 8.2 to 1 max dynamic compression where an aluminium block and heads can run into the 8.8 to 1 dynamic compression ratio on pump gas.
Obviously the higher you push the dynamic compression ratio the higher fuel octane you will need to use.
So an aluminium LS will run perfectly fine upto 8.5 dynamic compression ratio on 91 pump gas 91 octane likes upto around 8.55 to 1 dynamic compression ratio with a light vehicle. Past the 8.55 to 1 dynamic compression ratio you should really start looking at running 93 octane gas. 93 octane seams to like 8.6 to 8.8 to 1 dynamic compression.
Iron block and heads you need a lower dynamic compression ratio compared to an aluminium block and heads combo.
You also have to look at how much quench you have too.
The tighter the quench the more forgiving the engine is to deterioration.
if you run between. 038 to .043 detonation is keeped at bay more than if you run say .050 to .060 head gasket.

This is the information I've learned from years of dealing with performance engines over 30 years.

I'd like to see what others have have done and what static and dynamic compression ratio people are running on what octane fuel.

 

The 355 in my El Camino has iron Vortec heads, .045" quench, a Crane 2032 cam (270 advertised, 67 IVC from what I could find), and 10.2:1 static. The dynamic calculators put it at 8-8.5:1 depending on the calculator. I run it on 93.

 

I wish I was more tech savvy in figuring out dynamic compression. I get lost in inputting numbers. Long story, mental health issues.

My single cab Sierra weighs about 3700 lbs, runs an LS3 Aluminum 4.070 bore standard deck with 12:1, heads milled .009, cometic .040 head gaskets, a 238-252, 113+4 Cam on ,93 with 25° degrees timing on Me Ported LS3 Heads . Haven't dynoed or track tested but runs very strong.

​​​​​If anyone can help, I'd appreciate it. GOD BLESS AS YOU SEEK HIM.

 

That is about right that you will need pump 93. On hot days and going up hills it might ping from detonation

 

If E85 is an option (technically pump gas these days) you can really lean on it without worrying much in my experience. I just milled .100 off the tiny 61cc heads on my JY 5.3 build. Threw in a pretty mild cam too. Came out to 13.37:1 with a DCR of 10.53. Runs like a champ. Locals are running 14:1+ here on BBC combos.

 

I am trying to decide how to set up my build with compression ratios now. I have the block and the heads all set up, I got them 2 various sources and will have the shop spec them.

Because it is a weekend car that will see track time and we only have 91 easily available here I think I want to stay below 11:!
mostly here just to follow this post and see what others are doing.