Boosted fuel issues

[KC Boost]

I run straight VP C-12 in my nytro. Running 14 #'s boost no head shim or aftermarket pistons.

I have had this happen twice. The first time I was in mountains and was low on fuel. I borrowed some premium fuel from a buddy and put it in with my C-12. The mix would have been about 1/2- 1/2. The sled seemed to run better but we where dropping in altitude and couldn't really crank on it. So I thought it was just altitude.

Last night rode to a buddies place and got low on fuel so topped it off with premium again and the sled just rocked. On the way there I was running 8650 rpm on top end and air fuel was 13- 13.5. After I added the premium I picked up 500 rpm. Bounce off the rev limiter sometimes. A/F dropped a point and the sled just rocked.

The only change was fuel.

Anybody have any answers???

 

[Ultralord]

the fuel mixture would be hotter so it would have better combustion I suppose this could aslo raise engine rpm thats a tough one though I would wonder if maybe you dont have to much race fuel in it Do you have a knock detector?

 

[modsledr]

The difference in how it ran makes sense to me, but the drop in A/F is opposite of what I would expect.

Are you running the MPI controller, or a different one? Did you make any changes when you added the fuel?

I'm running the same setup, so maybe on my next ride I'll bring a gallon of 92 to add when I get low and see what happens. If I do, I'll let you know the results.

modsledr

 

[Ultralord]

what kit are you running without a head shim I would love to run a turbo on my sled with no head shim and 12 lb of boost everybody says I need a shim what gives?????

 

[modsledr]

These are MPI Stage II S/C's, not turbo's.

 

[moffatt]

boost

I run 14 lbs of boost at 6-8000 ft with c12-c14 with whatever i can get my hands i have a stage 2 super charger on and no head shim and I've heard of a guy running c18 with no headshim and no troubles love the 4 cyclinders they take a beating and keep on rocking not sure about the 3 cyclinders yet maybe try it next year

 

[KC Boost]

the fuel mixture would be hotter so it would have better combustion I suppose this could aslo raise engine rpm thats a tough one though I would wonder if maybe you dont have to much race fuel in it Do you have a knock detector?

I don't have a knock box yet.

Not sure where to get one at.

I didn't think that there would better performance from the 91 fuel vs 110

 

[KC Boost]

The difference in how it ran makes sense to me, but the drop in A/F is opposite of what I would expect.

Are you running the MPI controller, or a different one? Did you make any changes when you added the fuel?

I'm running the same setup, so maybe on my next ride I'll bring a gallon of 92 to add when I get low and see what happens. If I do, I'll let you know the results.

modsledr

That is what has me confused is the lower A/F #'s. and way more power and rpm's. It was all of 1 point if not 1.5 on the A/F. I had to stay out of the throttle on top end when I was on straight 110 because of the A/F. This is the first chance to ride it on the flatland.

We stopped at my buddies for about 2 hours and the temp dropped about 2 degrees. Added the 91 and away we went. I never made any changes to my MPI fuel contoller.

There was huge difference in power. It was the same as the first time but just didn't run it very long the first time to be sure of the difference.

It was 50 km to his place and 50 back. We rode the same fields home so it was a good test. Even my cousin on his M1000 said there was a differnece when we would crank them open

 

[modsledr]

The power, and subsequently the rpm's, are not necessarily surprising. My guess is MPI recomends we run straight race to cover their a$$es. The only thing higher octane really does is prevent detonation, and you want to run the lowest octane you can get away with, without incurring detonation. Higher octane fuel has a lower flash point, so it actually burns cooler. If you run too high octane for your compression and/or boost, you'll loose power (and rpm's).

I would call Parker Motorsports and get one of his knock boxes. You may be able to run less race gas, or switch to 100LL AvGas. He is on the leading edge of turbo development, and will probably be able to better answer why the A/F readings are doing what they are doing.

http://www.parkermotorsports.com/

Are you actually seeing 14lbs of boost at your elevation where you ride? Here in WA, we climb 3-4000 feet from parking lot to riding area, and I see a 2-4 lb drop from bottom to top.


modsledr

 

[KC Boost]

Thanks modsledr,

I notice a 1-2 lb drop in boost from 2000ft-7000ft.

I have 25/31 pulleys on now. When I had my 23/33 pulleys I would hit 18 lbs boost at 3000ft. I geared it down because of no head shim or low comp pistons.

Going to install pistons and rods this summer and go up to 18 lbs. Need to talk to somebody about changing my fuel pump to get enough fuel.