10.5:1?

[WFO400]

Will a 10.5:1 compression JE piston give me any noticable power gain? My ex will have a stock bore, stage 2 HC, HMF slip on, uni air filter, jetted, HD timing chain, and modified/ no air box lid. anyone ever run a similar setup with a stock bore? Is the extra compression worth it, or should I just wait until I decide to bore? Will I need HD studs with this piston?

[GPracer2500]

I ran a similar setup for several years. I had a JE 10.6:1 406cc with a WB Track cam, modded air box w/ K&N filter, WB E-Series slip-on, and a WB rev box. I bought it that way.

I liked it. It was definitely faster in a sand drag than your average "piped and filtered" 400ex. It had stock head studs. I did eventually blow a head gasket. It took several dune seasons though. I couldn't say 100% that the blown head gasket was a stud problem. Seems likely that it was though.

After that I went to a JE 10.8:1 416cc with a first generation HC stg 2. I also changed over to a UNI filter. Everything else was the same. It seemed a little bit faster (obviously I couldn't run a back-to-back test to see how much faster). But I wouldn't call it a night and day difference.

Not sure if that gives you any insight to your question, but that was my experience.

[BlasterEaten250]

I just put a 10.0:1 wiseco piston in mine with the stock bore, and it has a noticeable gain in torque. It has more of a solid hit when you pin it.

[WFO400]

bumb

[Brehmmotorsport]

another aspect to ask cause I am in this same boat. You guys that went to the 10.5.1 with stock bore did you stay with pump gas on the stock head studs.

[espergre]

I installed a wiseco 11:1 piston and a stage 1 hotcam. When correctly jetted I blow away my friends 400ex w/ hmf slipon that use to be even with me. On a 200 yard drag I beat him by 7 bike lengths at least now. Runs great on 93 octane. No need for race gas. I also have an hmf setup but it is a complete system. Air box off and UNI filter w/outerwear. Iv paid the price from using a K&N on past quads.

[gcart2]

Originally posted by espergre
I installed a wiseco 11:1 piston and a stage 1 hotcam. When correctly jetted I blow away my friends 400ex w/ hmf slipon that use to be even with me. On a 200 yard drag I beat him by 7 bike lengths at least now. Runs great on 93 octane. No need for race gas. I also have an hmf setup but it is a complete system. Air box off and UNI filter w/outerwear. Iv paid the price from using a K&N on past quads.

I HAVE A SIM. setup. if you read my sig you will see. and it was built by a guy who raced on team honda and kawi back in the day. it was built right. all the ppl i race tell me its a stroker cuz its so fast.in conclusion, its the way you build it that makes the difference. yes i run 93 pump but keep 5 gallons of 110 around for when a 450 comes by =)

[WFO400]

Thanks for all the responses guys! The more the merrier. Has anyone ever had any head stud problems with this setup? I don't want to pay for HD studs right now. Is it worth the risk? I think it should be ok, shouldn't it?

[espergre]

I do not have heavy duty studs and have had no problems. I have only had mine for 3 months but I have ragged on it hard and no issues. I have dragged for hours on end and it never wears out.

[WFO400]

Well I'm getting a JE std. bore 10.5:1 piston, a stage 2 hotcam, a crf450r timing chain, a dynojet jet kit (so I can have an adjustable needle). I hope this combo works out well. I already have an HMF slip on and a uni air filter and that just isn't enough power.

On another note, I currently run synthetic oil. I've always heard that it is best to break in engines with regular oil. I've also heard that you should not switch back to regular from synthetic. I don't know what I should do, any ideas?

[speedjunkie13]

Don't break in the engine using synthetic oil, use conventional oil.

I wouldn't be too worried about switching oils, just drain the old oil as completely as you can and refill with conventional oil.

[mitchamus]

Originally posted by WFO400
Well I'm getting a JE std. bore 10.5:1 piston, a stage 2 hotcam, a crf450r timing chain, a dynojet jet kit (so I can have an adjustable needle). I hope this combo works out well. I already have an HMF slip on and a uni air filter and that just isn't enough power.


Keep us updated on this i have ben thinking about doing almost the same exact thing.
JE piston 85mm 10.5:1
Stage 1 cam
Convert slip on HMF to Full system.
Does anybody with this setup Recommend anything else for reliablitly issues?

[espergre]

If you put a high compression piston and cam with a full system, youll need to decide how you want to manage your air box. You are going to need more air flow so lid off if you are in dry conditions. If wet riding buy a lid with built in filter or buy a pack or two of uni air box vents and install them. The worst thing you can do for any engine is not keep your airbox/air filter clean, it really doesnt take much dirt in an engine to screw something up

[mitchamus]

Well i run HMF slip on, Uni Filter with outerwears cover and i run the GT thunder velocity Stack air box lid. will that be enough or should i go to a EHS lid.

[espergre]

most tuners recommend a 2.5" hole or equivant area to be cut from an air box lid to not restrict a stock carburetor for modified/piped 400. If you air box has air holes other than the snorkel then you'll be ok, otherwise when you blip the throttle, it wont be able to quickly suck in enough air and bog the motor a little

[gcart2]

Originally posted by espergre
most tuners recommend a 2.5" hole or equivant area to be cut from an air box lid to not restrict a stock carburetor for modified/piped 400. If you air box has air holes other than the snorkel then you'll be ok, otherwise when you blip the throttle, it wont be able to quickly suck in enough air and bog the motor a little

hey can you give a link to your secondary oil cooler plz. hows it work?

[espergre]

http://www.fourstroketech.net/
look under engine, they sell kit for $110

It is not a bolt on kit, it requires that you drill into your clutch cover and valve cover to create a bypass oil loop. It does lower temps but im not sure its worth it unless you are having heat problems.

[Flip_SideEX]

I pretty much have the same set up. I used to have a sparks x-6 exhaust when i first installed the kit and noticed a substantial difference. Then i decided i didnt want to piss anyone off so i went back to stock exhaust. the power is still there, and im sure if i tuned my machine perfectly, it would cruise. But i just dont have the funds/time at the moment to put into my machine.
But i thought it was definitely worth it because my 400 went 6 years without a rebuild and when i took that stock piston out, it looked very nice. Its good to rebuild the engine, and while your at it, why not just spend a little more cash and give it some more giddy up. I still run 93 octane, i dont see a point to run race gas, unless you really want to rip it up. For the head gasket and studs, i havent had a problem except for the fact that i forgot to tighten the head/jug all the way down before i took it out for a ride. Finally noticed when my oil was going down fast and there was some sputtering coming between the two, plus the power was way down. But once i fixed that problem, she ripped like no other. stage 2 hotcam/crf 450 cam chain are my only engine mods i guess you could say. I havent put any wholes into the air box and am currently running a uni foam filter with k & n jets.

And while i think about it, for some reason my gas consumption went way down after i did the rebuild. I found myself using less gas, quite amazing i have to say, though i have no idea how this was possible.