wat octane required?

[400exfan19]

which 1

[400exrider707]

What is it going in and what are the mods?

[GPracer2500]

It depends. For some folks 91 might be ok. For others, race fuel is required.

[Honda#4]

I run 93 octane with no motor mods except for a pipe and filter.

[Glenyzracer25]

i would recommend 93 but you probably wouldnt ever notice if you put 91 in it. i run 91 and 93 with a 12.5:1 and dont have any problems at all.

[rooster300ex]

I voted for 91 but if you can get 93 then use it. I've ran 89 with 11:1 and didn't get any det. noises.

[jeremy_283]

93 will be fine............ if you live at a low elevation you may wanna look into a higher octane.............. but it is prolly unneeded

[400exrider707]

Sorry just noticed the 400ex with 11:1. On a 400ex considering that the compression ratios are not even correct due to the piston sitting down .040 in the cylinder at TDC.... I ran 87 in mine and had absolutely no detonation issues.

[bwamos]

Aye.. if you run no base gasket (using liquid gasket) and a XR head gasket to get the compression to a true value, then you may be tight on the 11:1 with pump.. but with your normal gaskets, 91 or 93 should be perfectly fine.

[400exrider707]

Originally posted by bwamos
Aye.. if you run no base gasket (using liquid gasket) and a XR head gasket to get the compression to a true value, then you may be tight on the 11:1 with pump.. but with your normal gaskets, 91 or 93 should be perfectly fine.


Even set up like that it still doesn't compensate enough for the gap that honda left from the factory and is still below the 11:1 IIRC

[GPracer2500]

My JE 10.8:1 with a HC stg 2 (old version) that pumped 180psi cold at 1300ft knocked pretty bad on Phoenix area 91. Running 91 in the dunes was not possible. Running 91 up in the mountains was possible as long as I rode easy.

Even my old 10.5:1 JE would just barely knock on a warm day at the end of a long sand hill climb. It was ok with 91 in the dunes but WOULD knock if I pushed the engine hard enough.

When possible, forget about static compression figures and use dynamic compression (as messured with a compression gauge, in PSI) to estimate an engine's octane requirement.

[honda250xrider]

93 i think should be alright, depending if you have a cam also can make a huge difference.

[400exrider707]

Originally posted by GPracer2500
My JE 10.8:1 with a HC stg 2 (old version) that pumped 180psi cold at 1300ft knocked pretty bad on Phoenix area 91. Running 91 in the dunes was not possible. Running 91 up in the mountains was possible as long as I rode easy.

Even my old 10.5:1 JE would just barely knock on a warm day at the end of a long sand hill climb. It was ok with 91 in the dunes but WOULD knock if I pushed the engine hard enough.

When possible, forget about static compression figures and use dynamic compression (as messured with a compression gauge, in PSI) to estimate an engine's octane requirement.

I more than likely live at a higher elevation too.