how much boost out of an mpi super charger on av gas ?

[pylon]

im looking at building an mpi boosted sled this winter . why does the mpi site recomend 110 octane over 14 psi ? Ive ran my turbo nytro with a small shim in it now for 4 seasons at 17 pounds on 100LL with no problems . Is it thier fuel devliery system that they are worried about ?

 

[motojunkie101]

Are you leaving the headshim in, or is this a different sled? When you talk about running the correct octane for your boost level, the concern is detonation. Detonation will destroy your engine in very short order, costing you big $$.

There have been some discussions on octane/boost/altitude/compression in the past, I swear some of these guys have a PHD in chemistry and physics with how well they can explain it.

 

[sepeterson]

8-9lbs all year from 3-6000 50/50 av and super on my supercharger no problems!

 

[pylon]

i would be building a whole new sled . so i would have to put in a head shim . ive just always heard of super chargers running wayyyyy more octane to the same amount as boost as a turbo . a few guys ive met in revy have been running c112 or c110 to run big boost . i ride lots so theres no way i can afford to run that To me boost is boost ? i did really notice the lack of top end on the super charger compaired to a turbo . it rocked on the bottom end but seemed to be on par with a mcx 180 kit for top end pull

 

[motojunkie101]

As far as I know, boost is boost. Your engine isn't going to care what forces the air in. (although the SC runs off the crank which is going to "rob" a little power) I imagine that MPI recommends high octane as a safe way to "CYA" with their customers. If they told you it would run on 91, and it blows up - then they would be on the hook for your engine.

IMO a SC is a good option for boost, but they do seem to fall flat on top like you mentioned. IMO, its all about where you want the power, From the bottom to the midrange or from the midrange thru the top end.

 

[irondave86]

MPI kits don't come with a head shim, that's why they tell you to run more octane. What size head shim are you going to run? If you run the same head shim as in your turbo sled your fuel requirement should be the same. BUT if your gonna try to run 17lbs of boost at elevation (8000 ft+) your gonna have to really spin that blower which will probably create some extra heat, and warmer are charges require higher octane, so keep that in mind when choosing your blower.

On a side note Its gonna take 3-4 more pounds of boost to run with the turbo 4 strokes. So keep that in mind too.

 

[pylon]

great info ! thanks. i cant wait to get started on this build . i got a great deal on a supercharger so i wanna have a boosted back up sled instead of my xp i bought last fall . now i just have to convince my self not to put a 174 under this one too