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steed2

Engine rebuild

4 posts in this topic

Well i have decided to rebuild my 2004 xr650r...

Im going to use the xr'sonly bigbore kit and i want to install 3mm larger intake valves and 1mm larger exhaust valves, i already have a hotcams stage 2 cam (loved the results) and an fmf powercore 4 muffler. I will also be getting the fmf header and want to know if anyone have done an engine similar to this and does it yield healthy results? (hp) Also I was thinking about shaving the head and having a port and polish done ?? i have heard of people having bad expeirience with this ?

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I believe the reason why people do not get results from porting the head is because they usually do not upgrade the carb. if the carb can only flow x amount and the head is causing no restriction the no matter what you do to the head isn't going to help the carb and intake flow better. I believe you can get great results with your plan but you will need much more air and fuel, at least a 43mm in My opinion. Now people may argue and talk about velocit being lost but with the huge cc's of the pigs motor I do not think lost velocity should be a problem.

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You should look into BWB63 posts... if i recall correctly, he went 3mm over on the intake and 1mm over on the exhaust. .. i kinda remember him saying that he felt 3mm over was too big and made things too tight in there. You can do it, but it wasnt recommended... I'm just pulling this from memory, so shoot that dude a PM before taking my word on this :applause:

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Well i have decided to rebuild my 2004 xr650r...

Im going to use the xr'sonly bigbore kit and i want to install 3mm larger intake valves and 1mm larger exhaust valves, i already have a hotcams stage 2 cam (loved the results) and an fmf powercore 4 muffler. I will also be getting the fmf header and want to know if anyone have done an engine similar to this and does it yield healthy results? (hp) Also I was thinking about shaving the head and having a port and polish done ?? i have heard of people having bad expeirience with this ?

I have to go to bed but, I have tons to say here......

In short....

If it is for the dirt, NO porting! The head flows more then enough. Both the 3mm oversived intake and 1mm oversized exhaust WILL NOT work together. You will have to machine the piston for the larger valves, clay testing is a must. 3mm oversized intake valves will soften the bottom end but, hold on for the top end. Smooths the whole power curve a lot. 1mm intake is the best for the most bottom end-mid power, a little crazy but, fun. Do not steel sleave! Go Nikasil! Lukes Racing. I stop by in a few days to see how this is going.

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