WHAT IS IT?
U4.4 is VP’s latest version of their extremely popular Ultimate 4. It is a leaded fuel with an increased oxygen content.
WHAT’S IT COST?
$15.60 per gallon; $78.90 in 5-gallon containers.
www.vpracingfuels.com or (951) 696-5100.
WHAT’S IT DO?
With the advent of the four-stroke era, VP Racing Fuels’ U4 became an instant hit. Originally called Ultimate 4, U4 didn’t depend on a massive octane increase, but instead pumped up the oxygen content from the then-AMA-mandated 2.8 percent to around 6 percent. If you remember anything from your Smoky the Bear fire safety seminars, you know that oxygen is an integral part of the fire triangle (heat, fuel and oxygen).
Not content with U4, VP developed U4.1 to address some of U4’s shortcomings. Unfortunately, U4.1 was a jetting nightmare on production bikes, and U4.2 was quickly developed to replace it. Which brings us to VP Racing U4.4 (no word on what happened to U4.3).
WHAT STANDS OUT?
Here’s a list of things that stand out with VP’s U4.4 fuel.
Is it legal? Yes and no. Because its oxygen content exceeds the mandated limit of AMA Pro Racing (which is currently 4 percent) and it has lead, U4.4 is not legal in AMA Supercross or AMA Nationals. But, it is legal at AMA amateur events and all local races. If you are an AMA Pro racer, you should consider using MR-PRO4.1. It is an unleaded fuel formulated to meet AMA Pro Racing standards.
Designed as a pour-in replacement for premium pump gas, U4.4 does not require any jetting changes on fuel-injected bikes (the electronic sensors can compensate). And while VP suggests going up on the main on a carbureted bike, MXA had no issues with the stock jetting on our 2010 YZ250F. When we went richer, we noticed some extra residue on the valve faces and seats, though, so jet carefully to avoid going too rich.
U4 would gum up the carburetor if it sat unused for any extended period. U4.4 did not leave a sticky residue. Better yet, it didn’t give off the sickly odor that permeated your garage with the original U4.
Thanks to its oxygen content, U4.4 did produce more power for our 2010 Yamaha YZ250F. It gained 0.66 horsepower at 8000 rpm, 0.20 horsepower at 9000 rpm, 0.30 horsepower at 10,000 rpm, 0.24 horsepower at 11,0000 rpm, 0.77 horsepower at 12,000 rpm and 0.76 horsepower at 13,000 rpm. Peak horse-power jumped from 37.5 horsepower to 38.0 horsepower. On a 450, the horsepower gains were exactly double that of our 250 four-stroke.
If you are a tech weenie, you will appreciate that U4.4 has a motor octane rating of 103, research octane rating of 114, and R+M/2 octane number of 108.5. The specific gravity is 0.763, and it has an oxygenate rating of almost double the current 4-percent AMA limit.
WHAT’S THE SQUAWK?
Unlike a one-time purchase like an exhaust pipe, high-compression piston or ported head, U4.4 requires you to keep paying (or the horsepower will vanish).
You have to want the power increase more than the money.
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