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over sized piston

chevyCowboy

chevyCowboy

I might be crazy but i ain't dumb
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Location
Springfield Nebraska
i have my 91 trx 250x tore down right now on a hunt for a nock that it had. i found the cause of the nock and have thought about going to a 76mm bore piston over the 74mm that is stock

making it a true 250 insted of a 246 will this net me anymore power
any one every try this
 
You will not get any real noticable gains with 4cc's. I would go up as little as possible on the bore size. If you have it apart go with a cam and rebuild the head. You will notice the cam way more than the extra 4cc's.
 
i decided not to go oversized but i am thinking about raiseing the compression to 12:1 it is 9:1 stock, what should i do to the head new valves and springs? one rocker arm needs replaced. the valves seem to be seated pretty good. i was thinking about a cam got any sugestions
 
If you bump the compression up, you will need to run race gas. If you haven't priced it lately it is big bucks, like $8 a gallon. On the head I would do a valve job and springs, since it is apart. I would maybe do a little clean up porting too. As far as the cam goes, I don't have rec's on one. You will have to get ahold of a bike shop and see what they reccmd. What are your goals for this bike? You have to remember when its all said and done, its still going to be a 250. You may want to pick up something bigger instead.
 
I'd say you'll Feel more Torque going up a few Sizes right off the Bat, rather than just Boring by the .25 or however it goes for your Motor.
 
Would you expect to run 12:1 in your car/truck and use pump gas? You may get away with 92, but I doubt it. You don't gain a whole lot by bumping up the compression anyways. There are benefts to it though. You generally bump the compression up when you add a cam with alot of overlap. I think you should aim for a little more comp. like 10:1 and run a mild cam with some 92 octane gas. Add a good exhaust and you will probably have about 10 more HP. You probably have about 13 hp stock
 
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