Wiseco Piston Question

[2004exrider]

A while back i bought a Wiseco 416 11:1 piston and an XR head and base gasket. I got the 11:1 because i was told it would be perfectly fine for 93 octane, but now i'm getting mixed responses that i'll have to run a higher octane or do a 50/50 mix. Now my question is do you think it would be at all possible to mill a little off of the piston itself to bring it down to 10.5:1 or even 10:1 or something? I'm not sure if there's even a way to know how much to take off, but if i knew how much it wouldn't be hard for me to get it done. If anyone knows any kind of information that could help me out it would be greatly appreciated!

Jimmy

[bubba's400ex]

hey sorry to enterupt but do you have to have a ring compressor to get your piston back in to the cylinder?
thanks

[02440exkid]

nope just put the piston at the bottom of the jug and push the rings together and it should go in fine.

[GPracer2500]

Machining the piston to reduce compression sounds dubious. It's not like they build them with a bunch of extra material on there.

I think you'd be better off mitigating compression with cam and gasket choices or just choosing a different piston altogether. Maybe double up on the base gasket? I've never done that so I'm unclear on potential problems of doing so. I suspect it could be done with little consequence (other than reduced compression). Or maybe have a base gasket cut out of a thicker gasket material.

I'd just use the thickest gaskets you can find (not the XRs) and take your chances.

FWIW, my JE 10.8:1 416cc with thin gaskets and a HC stg 2 (old version) won't tolerate the crappy 91 available around me. It's ok for light trail riding but riding that builds max heat and cylinder pressures (dunes!) creates pretty heavy deto. That holds even at 6000ft which really suprized me. I can ride around it--I just have to back out of the throttle when it starts to knock. I choose to run a race/pump mix to avoid those situations. Could I squeek by on 93? I dunno--maybe, but I doubt it.

Unfortunately, there's no set in stone rules when it comes to an engine's required octane. Plus, I suspect there are plenty of folks who get a touch of deto with their 11:1 pistons and don't even realize it. When you're pushing the edge of what pump gas will handle then all sorts of little things can push you one way or the other. Elevation, regional differences in fuel, gasket thicknesses (that's a big one), cam choice (that's significant too), manufacturing tolerances of the cam, head, case, crank, rod, etc can all add up to one thing or another. I only brought up my experiences above to illustrate that determining an engine's octane requirement is tricky buisness. You may not end up with what you were expecting--one way or the other.


I know fuel is expensive, but you can't have your cake and eat it too. Good luck.

[2004exrider]

Im not really to concerned about fuel prices, just having to go out of my way to buy some (none to close to where i live). But i guess i could always just sell this piston and buy a different one if wiseco even makes a lower compression one. Thanks again for your help!

Jimmy

[Aceman]

I'd run 2 base gaskets and a regular fiber head gasket.

[F-16Guy]

Do you have problems with detonation, pinging, knocking, etc. under a moderate to heavy load? I have an 11:1 piston in my quad, and I can run 91 (highest pump gas in Phoenix) with no problems unless I go to the dunes. If you have problems, either mix your fuel 50/50, or double up the base gasket (cheap fix). You could also buy another piston, but I would listen to you quad. If it isn't knocking or pinging under a load, then you're probably okay.

[400exmkt]

I run a 11:1 426 wiesco on 93 and it works just fine.

But there are alot of ??s elevation and other differences that will effect your quad.

[400exrider707]

The wiseco pistons for the 400ex motors are not even correct anyways. The advertised compression is higher than the actual compression. The 400ex pistons are actually just XR pistons. I ran an 11:1 wiseco in my 400 with a cometic thin head gasket (even thinner than the XR gasket) and I ran 93 all the time. For testing purposes I even ran full tanks of 87 in my EX with that piston and a stage 1 hotcam and never had deto. You will be completely fine running 93 in your machine. Just make sure your jetted correctly and you'll be fine.

[rooster300ex]

I know somebody that runs 87 in his 06 450r. Tried to tell him not too. But all he said was ahh it goes fast enough. lol I didn't feel like explaining why he should run something alil better. Liquid cooled motors are different though.

[Toadz400]

Ditch those XR gaskets and go back to 400ex gaskets. What's your elevation? Depending on that and how you jet your machine you should be able to pull it off on 93 octane. Around here at 1000ft above sea level, a friend of mine had no problem running his 416EX 11:1, Stage 2 HotCam, FCR39mm carb, porting and full exhaust to the max all day long with no detonation. That was on 92 octane.

[cals400ex]

i would run it as well. we run 11:1 with a thin head gasket and no base gasket all on 93 octane. yes, the ratings on the piston are for the XR's anyways. so the rated 11:1 is when using the thin gaskets. however, i know the wiseco ratings were off a few years ago. i was thinking the 11:1 440 with a thin head gasket and no base gasket was only around a true 10:1-10.5:1. there is no way i would double up the gaskets. the farther you move the piston away from the head the lower compression you have and the more inefficient the burn across the top of the piston is. i think you should be fine running a stock base gasket and the thin head gasket if you have a cam and your jetting is good.

[2004exrider]

Im not sure about my elevation, i think its somewhere around 800? About 90% of my riding is trail riding where i barely ever get out of second gear so i know its gotta be running pretty warm that's where my biggest fear is of getting detonation is coming from. Out of curiousity, the XR400 engine has a 9.3:1 comp ratio and the 400ex engine has a 9.1:1 comp ratio. Isnt the only difference the head gasket? So even if I put the XR head gasket on it still wont be a true 11:1 ratio? Is there something else different about the piston. im starting to feel a little more comfortable about using it from what a lot of you guys have said. I already have a stage 1 cam in there right now, so its not a stock one.

Jimmy

[cals400ex]

i am not 100% sure if the basegaskets are the same or not.....the head gaskets are different though. if you want a little less compression then run the stock head gasket. also, running the xr gasket for a stock bore bike will raise your compression a little bit too. i would get one for a 416 bore if it was me. a stock bore gasket will have a smaller hole. this means there will be a little less space in the combustion chamber making it a little more compression. a stock bore gasket for the trx or xr will work though. i don't know if wiseco's compression ratios are correct now or not. i remember the 440's at least used to be way off. its a hard choice i know...

[F-16Guy]

Originally posted by cals400ex
i am not 100% sure if the basegaskets are the same or not.....the head gaskets are different though. if you want a little less compression then run the stock head gasket. also, running the xr gasket for a stock bore bike will raise your compression a little bit too. i would get one for a 416 bore if it was me. a stock bore gasket will have a smaller hole. this means there will be a little less space in the combustion chamber making it a little more compression. a stock bore gasket for the trx or xr will work though. i don't know if wiseco's compression ratios are correct now or not. i remember the 440's at least used to be way off. its a hard choice i know...
It was the flat-top 440 piston that people were having issues with. They should make the "Have you decked the cylinder" thread sticky. There is so much good information in there about how to properly set up a 400ex top end if you are willing to read it.

[Iliketogofast]

Originally posted by Aceman
I'd run 2 base gaskets and a regular fiber head gasket.

Exactly.... instead of milling the piston down, which is stupid and will probably result in power loss, use a thicker gasket.

[2004exrider]

Originally posted by Iliketogofast
Exactly.... instead of milling the piston down, which is stupid and will probably result in power loss, use a thicker gasket.

Well it was just a question. I really wouldn't trust doubling up gaskets anyways. I think there'd be less power loss milling off a matter of a few thousandths than using two gaskets. Oh well i think i just might end up putting it all together and see what happens. :macho

Jimmy