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pman03
09-06-2005, 04:25 PM
What is the highest comperssion piston I can get for my 400ex and still run 91 octane pump gas? I have been told that it was 10.8:1 or would it be fine to run a wiesco 11:1?
400exrider707
09-06-2005, 04:33 PM
wiseco 11:1 will be fine considering that it probably has a lower measured compression than the JE since it was designed for an XR. Match the wiseco or the JE with thinner head gasket and your in business. I have an 11:1 standard bore wiseco for sale if interested and an 11:1 416 JE.

http://www.exriders.com/vbb/showthread.php?s=&postid=1791809#post1791809
pman03
09-06-2005, 05:04 PM
Originally posted by 400exrider707
wiseco 11:1 will be fine considering that it probably has a lower measured compression than the JE since it was designed for an XR. Match the wiseco or the JE with thinner head gasket and your in business. I have an 11:1 standard bore wiseco for sale if interested and an 11:1 416 JE.

http://www.exriders.com/vbb/showthread.php?s=&postid=1791809#post1791809

I am going to stick to standard bore. What would a thinner head gasket be? I already have a set of stock gaskets that I picked up today. What would the compression be with a stock head gasket and a 10:1 or 11:1 wiseco? Has anyone else that has a wiseco 11:1 had any problems with detonation (sp?) when running pump gas?
400exrider707
09-06-2005, 06:21 PM
Originally posted by pman03
I am going to stick to standard bore. What would a thinner head gasket be? I already have a set of stock gaskets that I picked up today. What would the compression be with a stock head gasket and a 10:1 or 11:1 wiseco?

I have a standard bore as well......... Its hard to say without actually measuring it. The cometic thin gasket is probably the best to get or you can just get an XR 400 head gasket. The thinner gasket allows it to raise the compression a little more. A stock gasket and an 11:1 is actually closer to the 10:1 I believe. It might actually be even lower but Im not sure. Either way its more than stock and will help with power. A stage1 cam to go with it will help also. The combo does wonders for an EX.
pman03
09-06-2005, 06:28 PM
I agree, a friend of mine has a 400 w/ a JE 10.8:1 and hot cam stage 2 with a full Curtis Sparks system and it goes pretty good. I don't think i have $150 to spend right now, school is starting tomorrow and I have a lot of other stuff to pay for. Another fiend also ported my head for me so that should help give it some more power.