What octane gas?

[waycott_259]

ok i have a 2001 400 ex punched out to a 416.. im not sure what type of pistion is in it but on a 416 ex should I use.. regular or supreme gas?

[GPracer2500]

Don't use regular no matter what. If your piston is 11:1 or lower you are probably ok with 93 octane pump. 11:1 is borderline depending on other factors. Anything over 11:1 is going to want straight race gas or a race/pump mix.

Listen for "knocking" or "pinging" coming from the engine under high engine load conditions. On a 400EX it kinda sounds like a loose exhaust heat shield or something. It's a somewhat irregular clatter that (if it's mild) will dissappear when you back off the throttle and reduce the engine load.

If you experience anything like that then you need higher octane fuel than whatever you were running.

[waycott_259]

ok thanks alot..so is 93 supreme?

[GPracer2500]

Originally posted by waycott_259
ok thanks alot..so is 93 supreme?

Don't worry about "supreme", "super", or whatever. Different gas companies use different nomenclature. Just pay attention to the number. 93 (or even 94, sometimes) is the highest octane pump gas you're likely to find. Some regions only get 91 as the top-dog at the fuel pump.

[waycott_259]

alright it isnt that i was really worried about it 2 much justthat here in New Brunswick it doesnt say the octane at l;east where i live it doesnt, it only says names..so i should run the best i can buy from the pump then? thanks thats good to know

[GPracer2500]

I've never heard of such a thing. I thought is was the law that octane rating ((RON+MON)/2 is the rating system used in the US) must be displayed on all pumps [shrug]. How else are you suppose to know the precise octane rating of the fuel?

[waycott_259]

I live in New Brunswick canada lol

[MarkyNark]

waycott_259,

Its pretty important to know exactly what your piston compression is. I think that if you dont know, you should find out. Call your mechanic that put your 416 kit in and find out exactly what the piston compression is.

Marky

[GPracer2500]

Originally posted by waycott_259
I live in New Brunswick canada lol

Ahhh. Maybe it's different up there. Still, the gas station should be able to tell you precisely what octane (and ocatane rating type--there are different kinds: MON, RON, and an average of the two) the fuel is. I wouldn't trust a fuel that just said "supreme" or "high-octane" or whatever on the pump.

[waycott_259]

which do i need? MON or RON?

[GPracer2500]

Originally posted by waycott_259
which do i need? MON or RON?

MON is a better measure of octane rating than RON. And RON is always going to be higher than MON for the same fuel. If all you know is MON or RON, than I'm not sure what numbers are going to be appropriate.

However, I'd bet that Canada uses the same (MON + RON)/2 system that the US uses for pump gas.

[waycott_259]

alright//i cant call because it already had a 416 kit in it when i boguht it..i guess im just gonna have to use the highest i can find around here.. or maybe start mixing with a bit of race fuel just to be safe..does it hurt my motor to use to low of an octane?

[GPracer2500]

Originally posted by waycott_259
alright//i cant call because it already had a 416 kit in it when i boguht it..i guess im just gonna have to use the highest i can find around here.. or maybe start mixing with a bit of race fuel just to be safe..does it hurt my motor to use to low of an octane?

What hurts your engine is the abnormal combustion phenomenon known as detonation. Detonation is prevented by using fuel with a high enough octane rating. So, yes it does hurt your engine to use too low of an octane. Octane ratings are nothing more than a way to measure a fuel's resistance to detonation.

[MarkyNark]

Originally posted by waycott_259
alright//i cant call because it already had a 416 kit in it when i boguht it..i guess im just gonna have to use the highest i can find around here.. or maybe start mixing with a bit of race fuel just to be safe..does it hurt my motor to use to low of an octane?

I suggest that you call the guy you purchased it from, find out the mechanics name, and call him to find out what compression it is. Its probably 11.5:1 or less. But I think its worth a little effort to know exactly what it is. Otherwise, you are simply shooting in the dark about the requirements of your engine when it comes to octane.

[250r4life]

hey gpracer, not that i run pump gas, but the highest octance rating i see around in the valley is 91... who sells 93?

[GPracer2500]

Originally posted by 250r4life
hey gpracer, not that i run pump gas, but the highest octance rating i see around in the valley is 91... who sells 93?

No one. If I implied 93 was available around here, I didn't mean to. I believe there is a station over in Ahwatukee that sells Sunoco high octane out of the pump (98 I think?). Pretty sure it's at 48th and Elliot or Ray--something like that.

Come to think of it, I need to check that out cause I'd like to find a reasonably priced and convienent source for some run-of-the-mill high octane.

[250r4life]

whata you normally run in your bikes?

[GPracer2500]

91 in my CR, XR, and until recently EX. My EX was freshly built just before my last dune trip and started knocking with 91 so I gotta find something better for it. I haven't ridden it since that trip.

My ski is a whole different story. It's blown right now cause I was borderline with 91 and didn't know it--can't hear the knock under the cowling. I ran one bad batch of gas through it and smoked the pistons. It's still apart and I haven't decided what to do about its compression. I have a stock head, but I hate to give up any performance. It's such a gas hog though I really want to stay with 91. Now, if I could find something in the 100 octane range that was reasonably priced and easy to get....I'm sure something is out there, I just haven't looked yet.

What do you run?

[250r4life]

ive always ran av gas, and its been good to me and many other people in my group... we've got people that run them in 2 strokes, 4 strokes, rails, etc...

its a higher octane and another thing i like is it doesnt go bad quickly like pump gas... we buy it out at falcon field... i think it is just under $4 a gallon right now...

[GPracer2500]

I might give Avgas a go.

[250r4life]

like i said its been good to me, and i know several other people who have been running it for years...

let me know if you need directions on where exactly to pick it up at falcon... although i would bet somewhere closer to you sells it as well...