should i run race fuel?

[xander1027]

i have a yfz450 with a sparks pipe on it with the cam one tooth forward and i want to know should i run race fuel?

[wilkin250r]

No

[rooster300ex]

race fuel is for high compression pistons.

yes^^

[chevy19]

will it hurt with stock compression or will it screw it up cause my friend filled his tank with race fuel on a sportsman 500.

hopefully ittl grenade and then he can buy a honda:cool:

[wilkin250r]

It won't hurt anything, but it won't help anything either.

[bwamos]

Originally posted by chevy19
will it hurt with stock compression or will it screw it up cause my friend filled his tank with race fuel on a sportsman 500.

THe general rule of thumb.. is that you want to use the lowest octane possible that doesn't pre-detonate (pinging/knocking).

Octane is not equal to power. Quite the opposite. It is a detonation inhibitor. It will actually lower your horsepower/torque if yo go too high. High Octane is required in race engines because of the 13:1 => 16.5:1 compression. Higher compressions will cause normal pump fuel to detonate before the sparkplug fires off. Thus they use the detonation inhibitors (Octane rating) to help keep the fuel stable so it won't detonate until the spark plug fires.

On a 2nd note: why did you move your timing a tooth away from stock? There's no reason to advance your timing w/ standard compression and an aftermarket pipe. I dont own a YFZ but I'd think you'd loose power by doing that.


So in summary:
Use Pump Gas (Premium for a YFZ, regular for a 450r)
Put your timing back to it;s stock setting.
Replace Air Filter w/ a K&N or a 2 stage foam.
Open up air box if you dont ride in the mud. Leave it on if you do.
Rejet your Carb

That should give you the most bang for the buck power increase.

Anything else you'll have to sink some decent money in to get an optimum power increase. Generally you go High Comp piston, Hone Sleeve (bore if you go oversized), Cam, Port/Polish, Valve Springs, Clutch Springs, CDI upgrade, etc.. all at the same time in order for the system to work together. Probably have to replace the rod in it as well if you go High Comp/Big Bore.

[wilkin250r]

Originally posted by bwamos
On a 2nd note: why did you move your timing a tooth away from stock? There's no reason to advance your timing w/ standard compression and an aftermarket pipe. I dont own a YFZ but I'd think you'd loose power by doing that.

The YZ motocross and the more mild offroad WR dirtbikes have essentially the same engine. The main differences are that the WR has a lighting coil to run headlight, and the exhaust camshaft is retarded one tooth for a slightly smoother power delivery.

The YFZ450 engine, as you can guess, is based of the YZ and WR motor. However, like the WR, the exhaust camshaft is retarded one tooth. Advancing it will shift power up, giving a harder hit and more top-end power, but a more narrow powerband.

[bwamos]

Gotcha.. so the YFZ in the stock form is actually off-timed for a flatter power curve. Makes sense.

[Airik79mx]

Originally posted by xander1027
i have a yfz450 with a sparks pipe on it with the cam one tooth forward and i want to know should i run race fuel?

If you want more power from face fuel use an oxygenated fuel that's lower octane. Like VP U4