Boost Vs: Octane Question
- Thread starter Rob Pod
- Start date
dgoodhue
BuSTeD 4.3
Re: Boost Vs: Octane Question
It is not that simple of a question. The cylinder head design, pressure (note this is not intake pressure), and temperature determine when gasoline will pre ignite. Changing timing, camshaft (timing), turbo's, intake flow, pistons (slightly different cr) all affect this.
A stock turbo peak efficiency is at 14psi; higher boost pressures it starts to heat up the intake charge. For a stock turbo, heads, cam, usually you can get about 17psi on a good running motor on a stock timing. (some can get more/some less). Because inefficiency of the stock turbo at higher boost pressure, the stock turbo peaks out in the 18-20 psi range without additional cooling (alky). With higher octane gas your most likely would want to add more timing. To get the most out of your engine, you really need to experiment with increasing the timing or boost one at a time and monitoring with it scan tool, AFR, and ideally reading plugs after a run.
It is not that simple of a question. The cylinder head design, pressure (note this is not intake pressure), and temperature determine when gasoline will pre ignite. Changing timing, camshaft (timing), turbo's, intake flow, pistons (slightly different cr) all affect this.
A stock turbo peak efficiency is at 14psi; higher boost pressures it starts to heat up the intake charge. For a stock turbo, heads, cam, usually you can get about 17psi on a good running motor on a stock timing. (some can get more/some less). Because inefficiency of the stock turbo at higher boost pressure, the stock turbo peaks out in the 18-20 psi range without additional cooling (alky). With higher octane gas your most likely would want to add more timing. To get the most out of your engine, you really need to experiment with increasing the timing or boost one at a time and monitoring with it scan tool, AFR, and ideally reading plugs after a run.
TrendSetter
Organ donor in training
Re: Boost Vs: Octane Question
Too many variables.
I run ~25 psi on 93 but i have a ls motor with a water/air ic.
Too many variables.
I run ~25 psi on 93 but i have a ls motor with a water/air ic.
Re: Boost Vs: Octane Question
that's a lot for 93 octane period. Any alky injection in there?
that's a lot for 93 octane period. Any alky injection in there?
jharrison
New member
Re: Boost Vs: Octane Question
Fuels are formulated based on compression ratio, which needs to be considered when choosing a fuel. VP's 110 is good up to 12:1-13:1, their C14 is good up to 14:1, and their C16 is good up to 17:1. These formulas will help figuring out what your compression ratio is based on the boost you are running. Add that to your base compression which depends on your pistons. You can change compression also with cams and timing, but you get the picture. As it was said before, too many variables.
1 psi boost = .5 point CR (effective CR)
1 point CR = 2 psi boost (CYLINDER PRESSURE)
1 point CR = 2% HP
1 psi boost requires 1-1.5 octane (minimum)
Fuels are formulated based on compression ratio, which needs to be considered when choosing a fuel. VP's 110 is good up to 12:1-13:1, their C14 is good up to 14:1, and their C16 is good up to 17:1. These formulas will help figuring out what your compression ratio is based on the boost you are running. Add that to your base compression which depends on your pistons. You can change compression also with cams and timing, but you get the picture. As it was said before, too many variables.
1 psi boost = .5 point CR (effective CR)
1 point CR = 2 psi boost (CYLINDER PRESSURE)
1 point CR = 2% HP
1 psi boost requires 1-1.5 octane (minimum)
TrendSetter
Organ donor in training
Re: Boost Vs: Octane Question
no alky, just conservative timing, 11.5 afr and 120°f iats. since its only on the street its pretty safe, I wouldnt try to run texas mile with it like that.
no alky, just conservative timing, 11.5 afr and 120°f iats. since its only on the street its pretty safe, I wouldnt try to run texas mile with it like that.