this is on http://www.rc51.org/
We've pretty much done the homework for you when it comes to testing various grades & brands of race fuels in the RC51 (or any other motorcycle for that part)
In hours & hours of dyno testing & Powercommander map building several key points were discovered some we intentionally set out to test others just came about on their own:
1. Standard Race Fuel (VP C12, C14, Sunoco 104, 100LL AvGas even high octane pump gas 96 or 100) ran straight on a stock RC51 motor will actually lose horsepower.
This is argued by many because the throttle response becomes crisper & is often mistaken for more performance when in truth the bike is making less power on the dyno sometimes by as much a 4-6hp. Many race fuels are designed for higher compression engines >13.0:1 & simply do not perform well in low compression motors like our RC51 (10.8:1). As has been noted many times on just about every sportbike forum on the net more octane does not mean more power! It simply means more resistance to detonation. If a higher octane fuel happens to make more power in a motor it is because of the additives in the fuel having the potential for more energy not just because it is higher octane.
What can be beneficial, but not always so is a blend of about 25/75 of race fuel & pump gas (1 gallon of race fuel added to 3 gallons of premium pump gas) which has been shown to consistently yield a horsepower or two. However I strongly urge you to stay away from the race fuels on a street bike if for no other reason than the extra contaminants it will leave in your motor. For me the cost of premature wear on the motor is not worth the negligible horsepower gains.
2. Oxygenated Race Fuels (Nutec #4, VP MR1 etc) can add 3-5hp without any fuel or mapping changes at all & 5-10hp sometimes even more on a stock motor with proper mapping & lots of playing around with the ignition timing. Some oxygenated fuels benefit from retarding the ignition while others benefit from advancing it.
The catch is that A. the stuff is really expensive usually about $15-$20 a gallon & B. it is highly corrosive & must be drained from your tank after each race weekend to keep it from eating parts of your fuel system. There are also horror stories of racers getting a bad batch of the stuff & ruining a set of carbs or throttle bodies due to a varnish that settles onto the components that is basically impossible to remove. I have actually witnessed this myself once & could not believe how bad it actually was.
There are some newer oxygenated fuels out now such as VP MR9 & Ultimate 4 which is claimed to be much less caustic to fuel system components (o-rings, gaskets etc..). I have sampled the MR9 & was very impressed with the performance & the Ultimate 4 is just plain awesome even in a stock motor plus at about $8 a gallon it's a pretty damn good deal. I've been mixing it about 50/50 on my stock engines & running it straight on my more built engines with excellent results. Not as powerful as the MR9, but nowhere near as expensive either.
3. In testing various grades of pump gas I consistently found that 87 octane fuel makes 1-2 more horsepower than those exact same bikes ran on Premium 93 octane. We tested five liter class motorcycles (97 CBR900RR, 02 Honda 919, 2000 RC51, 2000 GSXR750 & an 02 R1) & only the R1 seemed unaffected by the octane of the fuel. Now I am certainly not going to tell you to run less than the recommended octane (92) in your RC51 as the specific needs of the motor dictate that a higher octane fuel is needed, but the results are blatant in that more octane does not mean more power.
It is only fair that I note that when testing the pump gas on some of the 600's (Yamaha R6 & the GSXR600) the inverse was true in that they did lose a little horsepower on the 87 octane vs the 93 octane. Most likely because of the higher compression ratios of the smaller motors, however the CBR600F4i gained a little horsepower.
Additional notes (not tested on the dyno): Never add any type of octane boosters or fuel system cleaners to your motorcycle tank. Additives sold in auto stores are designed to treat anywhere from 16-22 gallons of fuel from one small bottle of concentrate & more often than not those chemicals are very hazardous to your motorcycles fuel system especially if the mix ratio is not absolutely perfect. I cannot tell you how many carb jobs I have done over the years because some yahoo dumped half a bottle (or more) of octane booster into his fuel tank. The bike runs great for awhile but within a day or two a varnish starts to set up on the fuel system components & it just gets worse from there. Run quality fuels & stay away from the additives period.