I live in colorado which is around 6,800 feet above sea level. I was talking to a guy about my LT1 set up and told him i was going to be running 11.6:1 comp (prob a lil less) and he has a similar set up on his lt1. He said he was having a hard time running 10.9:1 and that I wont be able to run 91 oct without any problems. Im having a hard time believing this. What do you guys think. Ill list my setup.

Eagle SBC 383 Stroker
Keith Black FLAT Top Pistons -7cc valve relief’s
LE1 head 58cc
Fel-Pro LT1 Head Gaskets .039
Custom grind cam (dont have exact numbers right now) slightly larger then the LE1 cam from Lloyd Elliott.

Im not sure how close to 11.6:1 ill be running. I dont have all the parts yet and cant measure. What do you guys think given your experience.

 

You're only putting 80% of the air in the cylinders compared to what you would at sea level. That makes your SCR behave like its 9.3:1.

In actuallity, its the dynamic compression ratio (DCR) that determines what fuel your engine needs, so you need to check that. But directionally, your engine will be processing 20% less air than at sea level, combustion chamber pressures will be 20% lower, etc.

 

You should be fine. I freaked when I moved to Colorado Springs and regular was 85 vs 87 octane and 91 was premium vice 93/94. However, altitude will reduce octane requirement so running your car on 91 is like using 93/94 at sea level.

Mike

 

What was your CR?

 

On the vette 11.25

However, my 5.9RT would ping on 91 at sea level but ran fine in the Springs

 

Is there any one that thinks that I will have big trouble with this compression ratio???

 

Did you check the dynamic compression ratio? Static compression ratio means very little with respect to fuel requirements. When you check the DCR, AND make the correction for the altitude, you will have your answer.