spokexx.DeleteThis@gmail.com wrote:
>Howdy, i have an 83 XT 550 and love it but id like to squeeze more
>power out of it. According to bikez.com (maybe not that reliable) it
>makes 38hp at 8.5:1 compression. So i was thinking of bumping up the
>compression and changing the cams. Any thoughts on this or other
>ideas?? Where can i get parts?
Blindly bumping up the compression without knowing what you are doing can
result in an engine that
pulls like a tractor at low speed but won't rev up to redline. The engine
with too much compression actually has LESS horsepower than the stock engine.
Don't ask how i know that.
Experienced tuners increase the compression ratio only enough to work with
the cam timing and give the hot rodded engine enough power to get the
motorbike moving without slipping the clutch and using a bazillion RPM.
The engine only has one camshaft.
In order to get more horsepower out of an engine you need to make it turn
faster.
It's very possible to get 55 horsepower out of a 550 cc engine, if it can
stand the extra RPM. You'd have to turn the engine 30% faster, assuming you
didn't install a big bore kit to give it more cc's.
But that would make the engine peaky and harder to ride, you'd have to keep
it "on the boil" to get the power you want out of it.
You can find out if you would enjoy riding a motorcycle with such a peaky
engine by degreeing the camshaft to close the intake valve 3 or 4 crankshaft
degrees later.
Google for information about degreeing cams using the "lobe center" method.
If you're going to eventually install a re-ground cam, or an aftermarket
billet cam, you're going to have to learn to degree cams sooner or later.
http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=653868
Item #3 is one of a pair of bolts that fastens the camshaft sprocket to the
camshaft.
In degreeing a camshaft, the sprocket is removed and the holes are filed oval.
Then the camshaft and sprocket are reinstalled with the bolts almost tight.
The camshaft is repositioned so it closes the intake valve later and the
bolts are installed with Loctite to keep the sprocket from shifting.
The exhaust valve will open later by the same number of degrees and the
exhaust system will be able to extract a little more horsepower from the
acoustic effects in the hot exhaust system.
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http://www.motorcyclekb.com/Uwe/Forums.aspx/yamaha/200706/1 >> Stay informed about: Want more power from my XT 550 
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