what octane fuel

[GAZ-V-21]

What octane fuel is best to run in an all stock 2007 400ex? i want to use whatever is best for the engine i normaly use 93 octane

[CJM]

If its totally stock you can use 87 if you wish, me no matter what it is I use 93 or better-usually contains less ethanol (least I believe it does).

[400exrider707]

Anything other than 87 is a waste of money IMO, unless you have detonation or pre-ignition going on, which has got to be nearly impossible on a stock 400EX. I used to run 87 in my higher compression EX motor (11:1). If you're worried about ethanol, run additive.

[dxcody]

Originally posted by 400exrider707
Anything other than 87 is a waste of money IMO, unless you have detonation or pre-ignition going on, which has got to be nearly impossible on a stock 400EX. I used to run 87 in my higher compression EX motor (11:1). If you're worried about ethanol, run additive.

If you run 87 in an 11:1 it really is not good for your motor from what i hear. Causes premature motor problems.

11:1 reccomended octane is 105 on every piston i have ever seen advertisment for, but 93 is the absolute minimum i would run.. maybe 92, (i dont really think there is a difference.
but since this thread isnt about that... back to the topic.

since you said you run a all stock 400ex, 87 will do fine. You may get better gas milage with 89-93 tho. Just depends. Up to you.

[rockbrook]

I was wondering this same question cause i just got a 03 400ex not too long ago, i used to run 93 in my Scrambler just because........

[05DodgeDakota]

Onwers manual recommends 91 or above. I run 93 w/ some additive

[CJM]

Additive will not cure ethanol issues. Might help but it only helps so much.

Everyone I know runs 93 pump or higher and has no problems.

FWIW every single place I know that sells equipment has signs that state to only run 89 or higher due to ethanol problems-specially in 2 strokes.

[400exrip]

I would just run 93 octne pump gas you should be fine, also if you have a shell gas station near you go their cause their fuel is nitrogen inriched and helps clean up intake valves.

[400exrider707]

Originally posted by dxcody
If you run 87 in an 11:1 it really is not good for your motor from what i hear. Causes premature motor problems.

11:1 reccomended octane is 105 on every piston i have ever seen advertisment for, but 93 is the absolute minimum i would run.. maybe 92, (i dont really think there is a difference.
but since this thread isnt about that... back to the topic.

since you said you run a all stock 400ex, 87 will do fine. You may get better gas milage with 89-93 tho. Just depends. Up to you.

What problems does it cause? Can't wait to hear this.

Talking strictly octane, there is NO benefit to running a higher octane if a lower octane rating works without issues (pre-ignition or detonation).

If you want to run 91 or 93 go ahead, it's your money you're wasting.

I'm talking strictly on octane ratings, as for the amount of ethanol, I find it hard to believe one has more than the other, but I really don't know on that.

Running 105 on an 11:1 is a huge waste of money, UNLESS it needs it. I haven't seen an EX need it yet. There are stock dirtbikes that come with over 12:1, some even closer to 13:1 and they get by on premium (91-93 octane).

There is more to it than just a piston's advertised compression ratio. You need to look at the dynamic compression. The camshaft plays a role in this too.

It's amazing how many people feel the need to give recommendations when they clearly know nothing about the subject at hand.

[dxcody]

I kinda think your going a little overboard with

"It's amazing how many people feel the need to give recommendations when they clearly know nothing about the subject at hand."

i stated no reccomendation that was out of the ordinary to the OP.

What you stated "I used to run 87 in my higher compression EX motor (11:1)."
I shouldnt have said anything since that has nothing to do with the thread and you dont even have it anymore. but at the same time i personally do not feel i am wrong here.

I understand running 105 in a 11:1 would be stupid, but thats why i said you can get by with running 92 or 93. I was just stating reccomendations from where i bought my piston from.

I ran 11:1 in my old 416 and when i ran anything lower then 92 it ran really rich and sputtered when it got hot. and the local quad shop said it can cause premature motor wear. Just stating what they said.


Like i said i am not trying to argue here, or "burn my bridges" as so to speak, and i am not sucking up to you either by saying this but i respect you, as i do all the other guys on this forum because everyone has helped me alot. Including you. but it seems we deff have a disagreement here.

If you can get by with running 87 in an 11:1 more power to ya, the more money you save the better.

[powerbomb400]

Octane rating determine's when it will detonate. The higher the octane rating will prevent it from pre-detonation. I run 110 leaded mixed with 93 octane with no ethanol. I got a 1949 8n Ford tractor that loves the 110. Up till the 70's all fuel was leaded. When we run 93 unleaded in our quads I can tell a big difference vs running 110 leaded. I find though mixing 3 gallons 110 leaded to 2gallon 93 unleaded gives us the best preformance.

[400exrider707]

Originally posted by dxcody
I kinda think your going a little overboard with

"It's amazing how many people feel the need to give recommendations when they clearly know nothing about the subject at hand."

i stated no reccomendation that was out of the ordinary to the OP.

What you stated "I used to run 87 in my higher compression EX motor (11:1)."
I shouldnt have said anything since that has nothing to do with the thread and you dont even have it anymore. but at the same time i personally do not feel i am wrong here.

I understand running 105 in a 11:1 would be stupid, but thats why i said you can get by with running 92 or 93. I was just stating reccomendations from where i bought my piston from.

I ran 11:1 in my old 416 and when i ran anything lower then 92 it ran really rich and sputtered when it got hot. and the local quad shop said it can cause premature motor wear. Just stating what they said.


Like i said i am not trying to argue here, or "burn my bridges" as so to speak, and i am not sucking up to you either by saying this but i respect you, as i do all the other guys on this forum because everyone has helped me alot. Including you. but it seems we deff have a disagreement here.

If you can get by with running 87 in an 11:1 more power to ya, the more money you save the better.

You originally said running 87 would hurt the motor. It will not, if it's not detonating, then you changed it in your second post to say that. I guess your first post just wasn't as clear, but I don't disagree with what you're saying now.

Again, it all depends on the application and what other parts are being used, do you agree?

The cam will play a big role in what you can use for octane too, just things some people overlook. Each motor is different for sure. A stone stock EX? As long as jetting is close there is no reason not to run 87. Obviously if issues arise such as detonation, then well maybe 89 or 91 should be used, I just can't believe that would ever be the case.

My EX had an 11:1 Wiseco (if anyone knows anything about advertised compression ratios for a 400EX, they're typically all way off, it's probably closer to 10:1), and the thinnest head gasket Cometic made as well, always ran 87. Used a stage 1 hotcam. Always stayed on top of my jetting too though, which helps.

I can respect your opinions as well, didn't mean to start an "argument" even though reading back now I can see how one would think that, so, my bad.