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radish150

400 Head porting?

7 posts in this topic

So, with a 400, free mods, YZ pipe, YZ timing, exhaust hotcam, is there much to be gained by a head massage? Light port smoothing and matching, does anyone have any experience that would enable them to offer a bit of a tutorial? I dont to just kill my low end for a bit more high end or anything useless like that, but I'd love any reasonable gains that could be had without screwing up the useability characteristics of the bike.

thanks

Mark Sheldon :ride:

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Mark,

I have a WR426 and had some head work done by Kenz cycle tech in AZ. The proting coupled with the hotcams gave the motor much more mid range and top end and didn't change the bottom end power. I also put in a 97mm piston.

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How many HP does porting alone give you? anyone know? is it worth spending the money? I am also interested in possible doing this?

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Quote: I have a WR426 and had some head work done by Kenz cycle tech in AZ. The proting coupled with the hotcams gave the motor much more mid range and top end and didn't change the bottom end power. I also put in a 97mm piston.

MMm, 97mm piston... thats a little like saying that I bought new socks and I ran faster, but I also took vitamins and bought new shoes. :ride:

mark...

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I remember once when we were kids me and a friend each had RM 125's, 83 and his was like an 85. We both heard about head porting and each tore the top end down and took a die grinder to our heads. I somehow had sense enough to just to a mild job on it, he ported the hell out of it. My bike gained quite a noticeable bit of power in the upper .5, I dont know why but his ran like crap ever after, ran like a tractor, seemed to loose all it's top end?... mine walked away from him till re-re-did his motor. I guess if you make the ports to big you might loose velocity of the gas exchange???

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Do a search for posts from a guy named "Hammish" who used to post here all the time. He had some really significant reshaping done to his ports (major epoxy build up on the floor of the intakes) and was very happy with the results.

I had mine cleaned up and smoothed out by Eric Gorr. It cost about a buck and a half, I think. There was a noticable, thpough not tremendous boost in performance all the way thru the powerband, buty I can't compare to stock as the bike already had hot cams in it. As you may expect, the port and cam geometry go hand in hand to determine powerband. Overall, the combination of 13.5:1 compression, big bore (444 cc), hot cams and mild port job makes a powerband that just rocks. Lots more than stock everywhere, harder hit than stock WR, but not as hard as YZ in the mid, and bounces off the rev limiter at will! A great combination, even if I do have to run VP!

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MMm, 97mm piston... thats a little like saying that I bought new socks and I ran faster, but I also took vitamins and bought new shoes. :ride:

mark...

Huh.... You could say that, I don't really know what did what but I know that I'm really happy with my motor. I know that with all the mods I did to my motor I didn't lose any bottom end and gained a ton in the middle and up top. I think the hot cams and the right jetting will give you the best bang for your buck.

Most decent shop that you give your head to will also check out and replace any valve stuff that doesn't look good. Kenz was a bit pricy but they did a great job and totally checked to make sure my head was in good shape.

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