11:1 JE 426, Is it actually 11:1 compression?

[toby400ex]

My 426 kit will be here friday, and i need to get it together to ride saturday. To have it a true 11:1 or very close will i need to not use the base gasket and only one layer of the head gasket with high temp spray paint on it? JE says its 11:1, but it is for the xr400 and 400ex, and i know alot of pistons for the 400ex arent the actual compression number listed.

[toby400ex]

Anyone know?

[toby400ex]

any body?

[sandspanker]

:) PRETTY SURE THAT THE JE PISTONS ARE WHAT THEY SAY THEY ARE.CALL COLBY AT C&D HE CAN TELL YOU FOR SURE.

[montyjcm]

Toby, are you going to be running pump gas?

[cals400ex]

i don't think the pistons are what they say they are. i do believe even the ross and je pistons are made with the xr400 and 400ex in mind. since the deck height differences, the pistons can't be the same ratio in an ex and a xr. if you have a piston cut to your desired ratio for the ex, then yes the ratio will be what ever you prefer it to be. i do believe you can get close to the listed compression ratio when using no base gasket and one layer of the head gasket.

however, a 11:1 piston will be cutting it close when using 93 anyways even if the listed 11:1 is only 10.6:1 or so. driving conditions and temp will probably play a factor. i think usually around a true 10.5:1 is about the highest you want to go for pump gas.

[Dunlap]

EX and XRs are the same, only the head gasket it thiner on the xr. I cc out a 12:1 JE piston in a 440 kit and it was a 11:1 , so if you want to be close and safe don't use a base gasket and use a .027 thick head gasket and it will run good.

[pnut420]

I ran a JE 11:1 in my 426 and it was awesome, until I missed a shift and blew the rod. Not sure if it has base gasket only or the whole gasket. If you havent ordered one yet, order a Wiseco from Micky D and it will be the exact deck height and you can run a normal gasket. Im getting ready to order one in the next week myself.

[cals400ex]

Originally posted by pnut420
I ran a JE 11:1 in my 426 and it was awesome, until I missed a shift and blew the rod. Not sure if it has base gasket only or the whole gasket. If you havent ordered one yet, order a Wiseco from Micky D and it will be the exact deck height and you can run a normal gasket. Im getting ready to order one in the next week myself.

what else did you have on your bike. i think i heard you say you pulled on a stock yfz???? the more i think about it, i don't think i would even have a prayer against a stock yfz. if your running with one, i need some secrets. :eek:

[toby400ex]

Originally posted by Mickey Dunlap
EX and XRs are the same, only the head gasket it thiner on the xr. I cc out a 12:1 JE piston in a 440 kit and it was a 11:1 , so if you want to be close and safe don't use a base gasket and use a .027 thick head gasket and it will run good. When u say.027 thick head gasket do you mean 1 layer of the head gasket? Im really hoping to run pump gas.

[markeg192]

Toby just leave the gaskets out and wrap it in saran wrap.:blah:

[toby400ex]

Good idea mark, how bout you wrap your head in saran wrap.;)

Originally posted by toby400ex
Im really hoping to run pump gas.

Then why did you go with that compression???

[SnellCRP]

Originally posted by Mickey Dunlap
EX and XRs are the same, only the head gasket it thiner on the xr. I cc out a 12:1 JE piston in a 440 kit and it was a 11:1 , so if you want to be close and safe don't use a base gasket and use a .027 thick head gasket and it will run good.

With the thin gaskets setup how thick is your squish band? Do you feel comfortable running a .030" squish on a motor without stock rev limiter? I know you will get some rod stretch at high RPM and am just curious where you run your squish and if you have ever had piston to head contact in a overrevved or missed shift situation with .030 or closer squish band?

[Dunlap]

11:1 will run pump gas just fine with a .040 squish. To get a .030 squish you would have to run no gaskets at all. That is why some people run one layer to give it .040. I told everyone to run the .027 head gasket to be safe yet keep the compression good for pump gas.

[SnellCRP]

Thanks. I was just wondering I have had .030 taken off the bottom of the jug and with a Cometic base and head gasket my squish was .036 with an 11:1 Ross 89mm piston. Thanks again.

[toby400ex]

Who makes a .027 gasket, can I just use an xr400 gasket. Ill be calling around after school today to find one.

[pnut420]

Originally posted by cals400ex
what else did you have on your bike. i think i heard you say you pulled on a stock yfz???? the more i think about it, i don't think i would even have a prayer against a stock yfz. if your running with one, i need some secrets. :eek:

Haha, Im selling the EX motor and getting a CRF450 and Arens frame now. But yeah I had between a mild and race port job, FCR39MM, Sparks Exhaust, stage 2 cam and I swear by it me and 2 other YFZ's would start from a 4th gear dig and I just kept on pulling, I know I only weigh 125, but I pulled by alot, they got me in the sand drags but a little off the line cause I had MXR tires, not sand tires, but as soon as I hooked up and I would strart to catch up, once I hot 3rd it just flew from there, it would pull through all the gears awesome and had good bottom end, mid and top end. I also raced a YFZ450 on the MX track and he didn win, because I hit my kill switch, but when going up the uphill straight I was trying to pass him, then on the downhill I toasted him. The YFZ at the MX track Im pretty sure was stock, but the ones at the dunes had exhaust mod, K&N and all the little power ups. Off the line mine rips, some say the FCR looses bottom end, but I only see that when the accelerator pump arm is set to advanced and dumping to much gas in to fast, mine is adhusted clse and does not have that low end bog FCR's are common for, Ive booged it low and get in the mid to top with the crack of the throotle, not to sound like it is a beast or anything, but it was damn fast for what it had, Im keeping the motor for my brother and selling his stock motror, so Ill see how bad my CRF450 motor punishes him.

I have a FCR39mm for sale, as well as Sparks exhaust fro sale if intersted.