boost and octane

[Guest mck2]

Has anyone experimented with octane requirements at various boost levels? For example, if a car has no detonation on 89gas at 7psi, what would it need at 10psi? or 15 psi?

[Mudge]

There should be simple math out there on static compression ratio and octane requirements as well as timing, too bad I dont know a thing about turbos!

[SleeperZ]

It will all depend on how effective your intercooler is at reducing the intake charge temperature.

 

You could run no ic and have to run race gas at 12 psi, but if you have an intercooler that reduces intake temps 100 degrees lower than without the ic, you could run 91 octane.

 

It's not the amount of air in the cylinder that will dictate if the mixture will detonate, it's how hot it is. Naturally, the air from a turbo gets hotter the more you compress it, but if you have an effective intercooler, you could run 20+ psi and run pump gas.

[240Z Turbo]

other variables to consider are the efficiency of the intercooler and the efficiency of the turbo at the various boost levels. I used to run 19psi daily on an 8.1:1 motor and run 17-18psi daily on my 8.6:1 motor all on 93 octane. TimZ runs 24psi daily on his 7.4:1 motor and 94 octane gas. Your ability to tune also plays an important role in your ability to run alot of boost. AFR's on pump gas should be in the 11.5:1 range at high boost and pump gas. Timing will vary depending on the motor, but I run about 22deg at 18psi and used to run about 24deg with my other intercooler. When I used to run a starion intercooler I could only run about 13-14psi on pump gas and just by swapping to the larger Bell intercooler I was able to run about 5psi more boost just because of efficiency.