I read that a lot of superchargers just run race fuel and don't do the head shim like some of the pump gas turbos. Why? seems like you could get away with much more boost on pump fuel than the 5 to 7 pounds. Or is that just not an option with a supercharger?
Head shim on supercharger ?
- Thread starter adrenaline junkey
- Start date
I would say 9 psi on 91 pump would be OK, 100% 100ll av gas should probably let you go 12-14 lbs or so given thats its 98 true octane.
Heck boost is boost, the engine does not know how the pressure in made.
I can see a roots type blower heating the air a bunch more than a turbo but the Rotrex is 1/2 a turbo anyway. IMHO
Heck boost is boost, the engine does not know how the pressure in made.
I can see a roots type blower heating the air a bunch more than a turbo but the Rotrex is 1/2 a turbo anyway. IMHO
M
modsledr
Well-known member
Statement about 100ll octane being "true 98 octane" isn't actually true.
Avgas is rated differently than automotive fuel, and is more related to the Motor Octane rating of auto gas. So 100 octane aviation fuel is more accurately comparable to 102 motor octane auto fuel.
That's what i was thinking, just seemed like there would be much more potential for the stage one or two On lower octane if a head shim was used. stage1 mpi with a head shim and 220 on pump gas looks a lot better then the 5 pounds of boost that they recommend
M
modsledr
Well-known member
I'm running a stage II at 12-14 lbs on straight 100ll for over 1000 miles with no issues. Remember, with the lower compression, you'll lose some of that low end snap.
THe other thing to remember about avgas is that its specifically formulated to prevent detonation for safety. IF its good enough for boosted airplane engines, its more than good enough for boosted snowmobiles.
What about the ave gas and oxygen sensor? I can get the low lead for 3.39 a gallon So I wouldn't be opposed to that.
M
modsledr
Well-known member
I've got almost 1000 miles on my current sensor.
You can get them from Amazon.com for $45-$50.
Cool thanks that helps a lot
You know thats really good news,I have always treated 100ll as 98 or so to be way safe, but if it is 102 rated as pump gas is, (and you are right,it is) more boost. I have run tons of 100/130 (green) av gas and the best, 115/145 (purple) in the past, and the purple was as good or better than c16 as far as boost goes. (in boats) we ran 10-1 static with 24 psi on purple with zero issues.
running 14 psi with 100% would be really nice,and a ton cheaper than 11.50 a gallon C12.....
With a headshim you will need to run about 2 more psi to get the same hp numbers that you would get with out one. We do not run any head shims on any of our machines here at the shop. If you have anymore questions please call me here at MPI 888-649-4609 ext 121, Thanks Skyler
Is that something you would advise against or is it that you just try to keep it to a just bolt on and go?
I do not reccomend it. You will have no problems with out a head shim with running a good race fuel, Thanks Skyler 888-649-4609 ext 121
