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Old 08-15-2008, 04:26 PM   #91
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Originally Posted by floss View Post
could you explain the relationship between timing and duration, i thought timing was more to do with plug selection.
I believe the timing is related to your ports. Higher ports will have less compression stroke timing and more intake and exhaust timing. How low the opening will affect the amount of flow through the port. Most will contour the lower edge leading into the port opening. Cutting the top of the port will alter the timing making changes to the powerband of the engine. Some will actually not touch the upper port opening, but shim the sleeve up. You must also readjust the head clearance though when this is done.

The duration is the amount of time the crank throat is open in the carb port area. If you cut the crank port clockwise or counterclockwise to rotation making the crank opening wider, you will widen the duration timing. Front to back will not change it, only alter maybe the amount of flow through the crank opening.

As with any engine, bigger is not always better. Too big and you lose air velocity and flow.
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Last edited by ezveedub; 08-16-2008 at 09:48 AM.
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Old 08-15-2008, 07:14 PM   #92
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good job dub
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Old 05-01-2009, 11:41 AM   #93
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I bought a 2008 version of the 367. Breaking it in went well, but when I went to begin tuning and track running it it has NO power compared to my old V-Spec and Ninja. I took the motor appart and found two significant design flaws that kill the power. The top of piston travels quite a ways below the bottom of the exhaust port (probably .050") and the window in the crank comes about .080" from the front of the opening in the case. I pulled out the dremel, opened the bottom of the exhaust port to match the top of the piston at BDC, ground the crank to match the case, and epoxy ramped the crank. I didn't want to start changing the port durations, just see what the engine was originally designed to do.
After a Minnesota state nitro series race weekend now I have to say I was never out run by any motor and was getting more than 10 mins of runtime with the 8mm insert. I'm VERY happy now.
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