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thumper4life

VP Red

11 posts in this topic

VP claims their "red" leaded brand of fuel is good for motocross and other apps and is good up to 12.5:1 compression ratio, the 426 is 12.5:1. The octane is 105 and the manual says it needs pump gas. Anyone have any disagreements with the fuel being bad for the engine life? I'm going to run just motocross this year and would like a leaded fuel, this one seems right to me. Anyone wanna' help?

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VP Red is not a good choice for the 426. While it would be adequate for the 12:5 compression ratio, it lacks the distillation curve for our high-revving engine. In the VP fuels, C-18 would probably be the best overall choice if you ignore the cost factor. I've tried both C-12 and MR2 and find that the MR2 gives me the better throttle response across the RPM range once jetted properly. As with any "race" fuel, it's not a matter of dumping it into the tank and ride. If you aren't willing to jet crisp, you will be sorely disappointed.

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I use VPC12 with a 50/50 mix with 91 pump gas. we jetted the bike and I am running a FMF powercore with he FMF SX powerbomb head pipe. All I can say is this bike rips. However running full race gas the bike runs good but not as good as the 50/50 mix. Maybe its just my setup but its what works for me..

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For those of you who run race gas, where do you usually purchase it? Is it for sale locally, or do you have to order it through the mail?

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I have to drive about 30 miles to get fuel. MR2 is just under $10 a gallon and C-12 is just over $5 a gallon.

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I run the c12 straight and it runs great. Im at sea level, run a 168 main 45 pilot and 2 1/2 turns on the screw. My bike starts first kick everytime, revs like a prostocker and eats sprockets and tires like they were free. It is easy to end up with too much octane for a particular application, but that isnt the case with 12:5 and C-12. The motor octane of c-12 is advertised at 108 I believe. Motor Octane is the one that is crucial in a high RPM application. Your 91 pump gas is an averaged number of the motor octane and reasearch octane. Problem is they dont give you the numbers for the average. You could be in a situation like this, your motor octane is only 86, but the research octane is 96. That would be okay for something with 8.5-1 that only spins 3500 rpm. Its also what we call "bad gas". One other thing, 426 doesnt need lead, Ive seen tests that show that all things being equal, you'll end up making more horsepower with out it. Circle Track magazine did a test on this about 5 years ago running 15 different fuels. They ended up making the most horsepower with Sunoco unleaded 110 octane in a small block chevy with 12.5-1. just my $.11. (cuz this got long)

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I run Unocal 76 110. It is the official fuel of nascar too!! It specs out very similar to VP C-12 in all critical areas.

Don't forget, if you change to race gas you'll more likely than not have to jet leaner.

Ernie

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While my son was trying to qualify for Steel City, I was over at the Yamaha Semi and I asked the Yamaha guys about fuel requirements and the 12.5 to 1 compression ratio. I was told point blank to run pump gas unless it was highly modified. I asked about detonation. They said Yamaha had poured alot of R&D into an efficiant combustion chamber. They laughed & said you'd never get away with it on a small block chevy, but the 426 chamber was designed with pump gas in mind. That was straight from the horses mouth. Just thought I would share that.

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Compression ratio is not the only factor in this equation. The cylinder head and combustion chamber of the 426 is a top notch design but that doesn't mean that pump gas is the optimum choice. As the RPM's climb, there is less and less time for combustion and the average premium pump gas struggles to meet efficent combustion at higher revs. The CORRECT fuel accomplishes this with the added benefit of a built-in safety net against preignition via the higher octane. Again, choosing the proper fuel and jetting crisp provides the highest return for this engine design. I've experimented with C-12 and MR2 and on the advice of Rich Rohrich, I've found MR2 to be an excellent choice. In the future, I plan on trying C-14 and C-18. That's my 2 cents.

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