What octane gas to run

[2813308004]

I have my 400ex bored to 440. it has an 11:1 compression ratio. the guy i bought it from used 98 octane and i wanna know if i can use 91 if i need to

[darkstar]

run 93 octane

[400exrider707]

You can use the 91. I've run 87 in mine once or twice with no detonation problems.

[underpowered]

you only need to run 93.

[ommkevin]

i run mine 87 since i got it

[400exrider707]

Originally posted by ommkevin
i run mine 87 since i got it

Yeah but your "bone stock" EX is only running about 9.2:1 compression stock. He's asking about an 11:1

[F-16Guy]

For that engine with that bore size, 11:1 is on the verge depending on location and riding style. I would try the highest octane pump gas you can find, and if it pings or knocks, you'll probably have to go 50/50 with race fuel. Ideally, you want to run fuel with the lowest octane rating possible that will not pre-detonate.

[400exrider707]

Originally posted by F-16Guy
For that engine with that bore size, 11:1 is on the verge depending on location and riding style. I would try the highest octane pump gas you can find, and if it pings or knocks, you'll probably have to go 50/50 with race fuel. Ideally, you want to run fuel with the lowest octane rating possible that will not pre-detonate.

Like I said I ran 87 on my 11:1 a few times without any hint of pre-det. I normally run 93 though. There shouldn't be any need for 50/50 at all. 12:1 is starting to get into race gas territory. Plus if its a wiseco piston its not really 11:1 anyways. Just think most bikes come stock w/ over 11:1 and you can run them on pump without problems.

[400exridernow]

Yeah you can run 91 through it my friend does he has a 440ex with a 11.1 so yeah just the stuff at the gastation works the most expenscive stuff at the gastation cya Mitch

[2813308004]

i live in northern minnesota and the highest pump gas is 91...there i a gas station just out of town that sells 98 out of the pump for $3.40 i think

[F-16Guy]

Originally posted by 400exrider707
Like I said I ran 87 on my 11:1 a few times without any hint of pre-det. I normally run 93 though. There shouldn't be any need for 50/50 at all. 12:1 is starting to get into race gas territory. Plus if its a wiseco piston its not really 11:1 anyways. Just think most bikes come stock w/ over 11:1 and you can run them on pump without problems.
If you can run 87, then you probably aren't at 11:1. It sounds like you have one of the 440 "kits" that came with the flat top Wiseco piston. You would need to have the cylinder decked and probably the head milled a little to get a true 11:1 CR. If you want to find out, you could take it somewhere and have the combustion chamber CC'd; then you'd know for sure exactly what CR you have. If what I'm guessing is right, you shouldn't have any problems running pump gas.
If you were really at 11:1, you would probably have to run at least 50/50. Other bikes can run on pump gas at higher CRs, but that has a lot to do with water cooling, combustion chamber design, piston shape, etc. With a larger bore like a 440, 11:1 is getting to the limit of pump fuel with this particular engine.

[2813308004]

the heads are milled... thanx for all the help

[400exrider707]

Originally posted by F-16Guy
If you can run 87, then you probably aren't at 11:1. It sounds like you have one of the 440 "kits" that came with the flat top Wiseco piston. You would need to have the cylinder decked and probably the head milled a little to get a true 11:1 CR. If you want to find out, you could take it somewhere and have the combustion chamber CC'd; then you'd know for sure exactly what CR you have. If what I'm guessing is right, you shouldn't have any problems running pump gas.
If you were really at 11:1, you would probably have to run at least 50/50. Other bikes can run on pump gas at higher CRs, but that has a lot to do with water cooling, combustion chamber design, piston shape, etc. With a larger bore like a 440, 11:1 is getting to the limit of pump fuel with this particular engine.

Yeah I know its not true 11:1. Also mine is a standard bore as well. I know how to get the CR with the syringe but never really cared to do it. Im just making him aware that he could probably do the same cause no wiseco 11:1 is actually that high.

[F-16Guy]

Originally posted by 400exrider707
Yeah I know its not true 11:1. Also mine is a standard bore as well. I know how to get the CR with the syringe but never really cared to do it. Im just making him aware that he could probably do the same cause no wiseco 11:1 is actually that high.
That's crazy.... I just realized that I was talking to the wrong guy; I totally thought you started this thread. Anyway, when I put my 416 together, I did the calculations as closely as I could (using compressed gasket thicknesses, etc.), and my CR came out to just a hair under 11:1. I think as long as you use the thinner gaskets, the domed Wisecos don't have that problem. I wish someone would come out with a piston with a lower pin height so that the squish band problem would be corrected.

[IRONMIKE113]

f-16 how does the baffle system work is the baffles the less backpressure or vise versa :confused: