Race Gas

[pantherpit218]

I have a 11:1 piston stage 2 cam and port and polish and the guy before me always ran race fuel, should i do the same or can i run the highest octane and be fine???

[GPracer2500]

Do a compression test. That info will tell you a lot about the engine's required octane rating.

And/or go find conditions that favor detonation. Run premium pump and if it detos then you've got your answer.

[Groves187]

I think there is more to running race gas then just the compression, If the motor's timing system isn't set right your not gaining anything at all by running the race gas except a cooler burn, So if the motor is set up for it i'd say run it. If i am wrong plz correct me!...... Thanks Nick

[CDCHONDAS]

compression test isnt really going to tell you much other than how many psi of compression, you have to cc the combustion chamber, etc. to figure CR as long as nobody did some serious cutting on the head or cylinder for compression you should be just fine on 93, 11:1 isnt that much but it will last longer than something like a 12.5:1

[GPracer2500]

The actual cranking compression measured in PSI tells you much more than the static compression ratio.

Cranking compression will take into account the timing of valve events, gasket thicknesses, and even local air density. A compression ratio does not. You could have two engines with identical pistons yield different cranking compressions because of differences in cams, gaskets, etc. That's what makes a comp test more informative.

The stickler with comp tests on so many of today's ATV engines is the use of auto-decompression devices. Many of our engines have these devices and that screws with comp test readings. But on the 400EX, the auto-decomp mechanism is usually removed when an aftermarket cam is installed.



Groves187, ignition timing is a factor in an engine's required octane rating. The more ignition advance, the more octane rating required. Said another way, lots of ignition advance creates conditions that favor deto.

[eliasxr400]

If there is an airport near you you can run AV gas. It is 100 octane but only cost like .20 more a gallon than super in my area. I run this in all 6 af my bikes and quads. They seem to run cooler.

[300EXrider356]

Originally posted by GPracer2500
The actual cranking compression measured in PSI tells you much more than the static compression ratio.

Cranking compression will take into account the timing of valve events, gasket thicknesses, and even local air density. A compression ratio does not. You could have two engines with identical pistons yield different cranking compressions because of differences in cams, gaskets, etc. That's what makes a comp test more informative.

The stickler with comp tests on so many of today's ATV engines is the use of auto-decompression devices. Many of our engines have these devices and that screws with comp test readings. But on the 400EX, the auto-decomp mechanism is usually removed when an aftermarket cam is installed.



Groves187, ignition timing is a factor in an engine's required octane rating. The more ignition advance, the more octane rating required. Said another way, lots of ignition advance creates conditions that favor deto.
I seriously think you are the smartest person on this site!:macho

But i used to run premium in mine when I still had my 11:1 it ran fine. Any higher though and you'll have to run race gas mix or something.

[CDCHONDAS]

true on the static vs. dynamic but I myself will not let that be the determining factor on whether or not to run race gas

As for av gas its generally not the greatest stuff for a quad as its normally low in lubrication and used to be or still is rated for engines running less than 3500 rpm i believe.

[orangeEX]

11:1 comp, stage 2 hotcam,440cc bore, uni filter,white bros silencer w/no plates or spark arrestor. VP racing C-12 mixed with 93 octane. 50/50 elevation below 3000 ' runs strong enough to keep up with suzuki 450 off the gate.... running 93 alone at high rpm i overheat..hope this helps

[eliasxr400]

Originally posted by CDCHONDAS
As for av gas its generally not the greatest stuff for a quad as its normally low in lubrication and used to be or still is rated for engines running less than 3500 rpm i believe. [/B]
I did some research and you are correct. My quad does run better with AV than 93 octane, but I will try some race gas. I also read that AV gas uses a different scale for octane and 100ll is really like 95-97octane. Thanks for the correction.

[GPracer2500]

100LL = 99.5 MON (minimum)

93 [(R+M)/2] octane pump gas = ~88 MON