Yet another fuel question...

[kwb]

Now I have read all that I can about fuel/octane/detonation that I can over the last couple days and now that I am a bit edjumacated (just enough to be dangerous) I have this question.

Boost is boost and with same combustion chamber a PSI is a PSI and should cause detonation in a consistent manner correct?

If this is the case and a turbo makes boost at say 12psi and then has a wastegate to regulate it to that level as R's go up and a S/C builds the pressure more linearly through the R's wouldn't detonation be more controllable by simply keeping your R's down where a turbo would not be able to get pressures down until much lower R's.

So is fuel criticality (octane requirements) more or less important with either a S/C or a Turbo given same boost levels?

Yes I am asking because I want to use less racegas and more pump with my S/C sled. It really isn't so much a money issue as a hassle issue of mixing/storing the fuel when I am on a week long trip that will eat up close to 100gallons over the week.

 

[Travis Moore]

Now I have read all that I can about fuel/octane/detonation that I can over the last couple days and now that I am a bit edjumacated (just enough to be dangerous) I have this question.

Boost is boost and with same combustion chamber a PSI is a PSI and should cause detonation in a consistent manner correct?

If this is the case and a turbo makes boost at say 12psi and then has a wastegate to regulate it to that level as R's go up and a S/C builds the pressure more linearly through the R's wouldn't detonation be more controllable by simply keeping your R's down where a turbo would not be able to get pressures down until much lower R's.

So is fuel criticality (octane requirements) more or less important with either a S/C or a Turbo given same boost levels?

Yes I am asking because I want to use less racegas and more pump with my S/C sled. It really isn't so much a money issue as a hassle issue of mixing/storing the fuel when I am on a week long trip that will eat up close to 100gallons over the week.

A big factor is also the charge temperatures. A smaller turbo/supercharger will typically produce a higher charge temp vs. a larger turbo/supercharger per psi of boost.

With that said, I'd try to keep over 100 motor octane if you are running 12 psi for extended periods (assuming stock compression ratio)

 

[kwb]

I am actually using an MPI stage one (10psi) with stock compression ratio so the charge is from the smaller supercharger (warmer charge).

I am not expecting anybody to tell me what to run but rather just trying to sort out the facts and make up my own mind as to how much risk I am willing to take.

My gut tells me that MPI's recommendation is fairly conservative 50/50 91/110 based on what I read others running for quite a while with no problems.

A semi-local station sells 114 so I can skip on needing to get a barrel at home but the road trips to Idaho and BC are where I struggle and am leaning towards taking a few jugs to mix about 20-30% 114 with premium from the local stations. The elevations in BC and Idaho tend to be a bit higher than where I ride when at home to add to the factor of safety.

 

[Travis Moore]

I am actually using an MPI stage one (10psi) with stock compression ratio so the charge is from the smaller supercharger (warmer charge).

I am not expecting anybody to tell me what to run but rather just trying to sort out the facts and make up my own mind as to how much risk I am willing to take.

My gut tells me that MPI's recommendation is fairly conservative 50/50 91/110 based on what I read others running for quite a while with no problems.

A semi-local station sells 114 so I can skip on needing to get a barrel at home but the road trips to Idaho and BC are where I struggle and am leaning towards taking a few jugs to mix about 20-30% 114 with premium from the local stations. The elevations in BC and Idaho tend to be a bit higher than where I ride when at home to add to the factor of safety.

I'd stick pretty close to MPI's recommendations.

 

[TurboJamie]

I run 10 psi on pump fuel and its on the EDGE forsure on a stage 1. Wouldn't run it for longer then 2000' distance on the bar.

 

[Ted Jannetty]

Factors that play in to detonation

There are many other factors that play in to detonation.
Water Temps- affects combustion chamber temps
Charge air Temps- same
Clutching- affects load on engine
Rider weight- same
Snow conditions- same
Outside air temp- affects oxygen content or density
Humidity level- same
Altitude- affects inlet pressure which in turn affects boost pressure
spark plug heat range- in rare cases can glow causing detonation
oil tempurature- affects piston tempuratures
Air Fuel Ratio- affects combustion tempuratures and burn rate
timing- needs to be reduced for more cylinder pressure.

These are basics but accurate we can ellaborate on each more if necessary.

The fuel is the Horsepower limiter no matter what you do.

If you want to run on pump gas you have to make some changes to the combination to be able to run safely at wide open throttle.

My first suggestion would be to retard the timing about 4-5 degrees because that is the easiest, you can do this by slotting you pick up coil and moving it.

The second would be to add a head gasket.

The third and least desirable would be to reduce the boost.

Now I hear what your saying about clutching it to run lower RPM to keep boost down but that could be worse here is why.

Peak cylinder pressure occurs at peak torque , somewhere around 8800 if my memeory serves me, and if you run the motor at peak torque , at full throttle it will be less tolerant to pump gas and will expire.

Cylinder pressure falls as you go past peak torque even though boost pressure continues to climb and the motor will live longer running at or just above peak HP.

If you can resist full throttle you can run around on 87 octane and it won't matter a bit.

Either way Have fun.