Is it worth the $ to port the 400 or 426 motors? How much does i trun and who can do it?

I've never found the need, but b4 you slap down some cash you may want to read motoman's ideas on porting . I ran my bike in his way and it certainly hauls ass so maybe he knows a thing or two about porting. Also from motocross action mag 2005 YAMAHA YZ450F *

*Intake ports are 9 percent smaller for increased fuel velocity

I'll have to agree with the articals that mx_crash has posted, having built drag racing engines I have found that size is not as important as shape and contour. All that I have done to mine was blend the valve pocket (seat to bowl area) and remove any bumps or casting flash from the ports and left the intake side with a simi rough finish for better atomization, and it did make a very noyiceable differance through the entire rpm range. :cry:

I asked Eric Gorr from Forward Motion and was told it was a waste of time. He said a big bore kit was the way to go. The stock head is very good and not all that much can be done with it for the average rider.


Interesting, and here was me thinking dragracing was the possibly the only place where porting may help due to it being WOT racing. One day I'll get the guts to fill the ports on my road bike ,a ktm640sm and see how it goes.

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