What octane

[zach0199]

Hi, new here just picked up an 01 400ex and it has a 85.5mm piston with 10:1 compression top end has around an hour on it what do you guys recomend I run into it i firgured 93 but read on some other sight too much octane robs hp. Forgot to ask the owner what he ran in it. Thanks for the help

[a4guy]

93 should be fine. If it runs hot go to a higher octane. Either way you should be good with at least 93.

[smelly$cat]

You should be totally safe with 91 or 93 with a 10:1 piston. You could probably go lower, but, I'd stick with 91-93 to be safe. Not worth the tiny bit of more power to go lower and risk issues.

[slightlybent47]

Yes you’ll be fine with that; 10:1 is good for any pump gas 87-93. that’s only a deference of 6 octane so any one will do fine.

[JOHNDOE83]

Really from 87 octane to 93, there is barely a difference, 10:1 is probally better with 87, 93 will not help or do anything.

Try running it on 87, when the tanks empty, go to sunoco and buy ther 110 oct gas and run that, you will see barley any difference. possibly even ran better on 87.

if your not high compression, high octane is useless, stick with 87 or 93, what ever you would rather use.

I myself have a 10:1, ive wasted money on sunoco gas, you would need 110 for 12:1 or higher, 11:1 run 93, 10:1 any pump gas is fine.

[TRXRacer1]

I could make my 10:1 ping on 87 all day long. It depends on how hard you beat it. I'd ride it like it was my last ride in the deep woods and she'd get hot enough to strait up need at least 93.

[honda400ex2003]

I run 91 but wish i had 93 lol. i have to go into town to get that so it gets 91 non ethanol from the closest station. never an issue with it. lol. steve

[400exrider36]

id agree with 87 - 93

i ran 91 in my yfz which had 11.9:1 and never had any issues... regardless its a different quad... :rolleyes:

[09RappySe]

Run the lowest octane fuel you can without predetonation (pinging) any higher than that is a waste of money and less power.

[TRXRacer1]

Originally posted by 400exrider36
i ran 91 in my yfz which had 11.9:1 and never had any issues... regardless its a different quad... :rolleyes: It's liquid cooled, shouldn't be anywhere near an air cooled octane question.


Originally posted by 09RappySe
Run the lowest octane fuel you can without predetonation (pinging) any higher than that is a waste of money and less power. True but you'll never notice having a little too much unlike not having enough.

[09RappySe]

Originally posted by TRXRacer1


True but you'll never notice having a little too much unlike not having enough.

I agree, but anything over premium is way overkill.

[TRXRacer1]

Originally posted by 09RappySe
I agree, but anything over premium is way overkill. I have personally disproved that. 93 was not enough for what I do. Plus 98% of riders out there have no idea when they are getting in the early stages of detonation.

[09RappySe]

Originally posted by TRXRacer1
I have personally disproved that.

How so?

[flyboy1294]

Originally posted by TRXRacer1
I have personally disproved that. 93 was not enough for what I do. Plus 98% of riders out there have no idea when they are getting in the early stages of detonation.

When you say what you do, I assume you mean the builds you run?

Also, aren't there other factors besides Static compression ratio to determine what octane you need? Dynamic compression is the deciding factor, I think. The main thing I can think of to affect the Dynamic ratio is the cam. (Sure, headgasket thickness and other thinks might play a small roll, but nothing as drastic.) For instance, with a Stage 1 Hotcam you have less valve over lap and a shorter duration than the Stage 3; thus creating a high dynamic compression ratio and needing higher octane, correct?

[TRXRacer1]

It's all about heat boys and yes higher compression will absolutely contribute. Flyboy I speak of the adventures I take on. Rappy I know when I can beat a perfectly jetted 10:1 416 with a stg 1 to the point of pinging that's all the proof I need. All these octane questions are answered with perfect scenarios and misconceptions. The truth is we all come from different backgrounds and corners of the world. Our riding styles aren't going to be the same neither will our conditions. The playing field would be a lot closer if these were liquid machines but being air all the OP can do is take an average and try to figure out where he fits in. Consider me the high side of this argument, worst case if you will.

[f4iracer]

I run half pump gas and half 110 and it runs great!

I just get straight up 89 octane and mix it with my sunoco 110.

so i guess i'm running 100 octane.

[440ex. ehhh!!]

i have read a few threads and from what i can tell, this is useless.
in my 440 i usually just ran lowest pump gas, but after last weeks racing with it screwing up and all, i ran some 91 octane in it, ran a lot better so i think i will stick with that. but a buddy of mine who is in charge at the track and rides speedway said he wil bring me 113 octane race fuel on saturday for the championships. Is it a waste? like would i be better off just running 91?

and also, i replaced the plug but i couldn't get my hands on one the same as stock, so i compared them and i got a NGK plug number DPR7EA and under it has the number 9. stock plug is DPR8Z can anyone tell me the difference or if i picked up a cold plug or something. i ran it for a good hour and a half with the 91 octane and it seemed to be fine.

Thanks
Josh

[Wheelie]

I couldn't run 87 in my EX when it was brand new, it would ping once it got warm, I always ran premium.

Personally I think recommending 87 for a 10:1 machine is bad advise. You're asking for a blown head gasket, overheating or meltdown.

When it comes to fuel, err on the side of too much octane rather than run on the ragged edge. This way, no matter what situation comes up, you know that detonation/pre-ignition won't be an issue.

[f4iracer]

yeah even the owners manual says 93 min. doesn't it?

The things ping, i run my 50% 87 and 50% 110 and it runs a heck of alot quieter and cooler.