Time for a new piston, please help! Motor is completely bone stock except for a filter.

I am going +.020 on the cylinder.

What type of piston should I go with?

What's the highest compression I can run on 92 octane?

How much larger should the cylinder be versus piston size)? .005", .003"???

Any other modifications I should do to the motor while it is down?
i.e., cylinder head, are reeds worth it, carb?

What would be the best torque pipe and silincer?

Thanks for the help!

 

have it ported, for the type of riding that you do!!! that will really increase the "zip" of the motor...also have the cases port-matched!

 

Wiseco or Pro-x are good pistons
with a Wiseco you want to leave a little more clearance, say 3 thousandths...the spec on them is 3-5 thousandths.
with a Pro-x piston you can run them a bit tighter, I just had mine bored to a 2 thousandths clearance.

as far as compression goes, I would stick to 180 lbs of compression (with a a stock motor and head) with pump gas, any more and you're somewhat pushing it, even tho some will argue this.

as far as your pipe questions, I would try an LRD Team B, they are a nice pipe for just about anything other than drag racing.

if you want to do other mods, they will take time and money..for a carb buy a Keihin 38MM AS, reeds/cage buy a Delta VForce, and porting, well there are many opinions on porting, but porting is something that will take awhile (a month or more) so you may want to bypass that until winter. run an ATC 250R head gasket for a mild bump in compression while not requiring the use of race gas..guess thats all I can think of, good luck

 

Dill is correct with all his accessments. My R is maxed out for use with pump gas(read my spec sheet). I WOULD recommend the cast Pro-X piston as it is more forgiving about clearances and warm up times than the forged Wiseco(I've used both). As for porting, the closer to stock that the porting remains--the more reliable it will be.

 

165 psi is pretty safe for 92-93octane.FMF fatty pipe is a good pipe that will work with your stock motor and will work with a port job later on.I like the factory honda(art) pistons the best, then pro-x. Wiseco are probably stronger but are more prone to seize when you don't poperly warm them up.They are more out of round when cold than cast pistons. But if you warm the engine up like you are suppose to before you ride hard, you won't have any problems. The factory piston should have .0025 clearence, at .005 you should bore over to the next size. A rad valve or v-force with a 38 flatside would give a great midrange boost. Remove the lid on the airbox if you don't ride in the mud,also a outwear cover over your filter would help if you ride in sandy conditions.Remember your motor is a air pump the more air you get through it the more power it will make.You can also add a Hinson adjustable timeing tab, if you add a couple of degrees of timeing to the motor it will have more low end power but loose a little rpm's on top.Be careful of too much timing with more than 165psi of compression with only 92 octane gas. The 88-89 cdi box has the best timing curve from the factory. Western Honda sold me a new one for $80.Rick at MacDizzy can reshape your factory cylinder head for a resonable fee and he does very good work. good luck

 

I have a 86 trx250r with a wiseco .020 piston boyesen reeds,FMF fatty gold series pipe,power core 2 silencer, and it is ported by a local shop called performance machine service.I can beat a banshee in a 100 yard drag.This on a mx track going to the first corner.I also beat a ct330r.I know some of U guys won't beleive me but oh well.

 

As long as you don't get too wild with the port width, porting an engine will have no effect on reliabilty. If you widen the windows out to gain the maximum port time area, then yes, you lose vital support for the piston to ride across and the piston will wear faster. Most "cookie-cutter" port jobs tend not to go that extreme.

Go with a cast piston. Have it coated. A dry film lubricant on the skirts and a heat reflective coating on the crown. The dry film works, I've had problems in the past with accelerated piston wear from exactly what I spoke about above(I knew going into the project), and the piston lasted about another 10 hours of hard drag racing. The crown coating is a safety margin, to me not meant to be there to push it right to the edge, but rather if you encounter leaner conditions (from any number of problems), you may not hole a piston. I don't think that either will help in all situations, but for the $35 or so additional cost, I'd go for it.

 

concerns the piston i have friend who races dirt bikes he was using weisco but when they get hot they expand causing them to burn up he said he reather run stock untill he found a piston called vortec has a coating over it that keeps it cool as for your pipe fmf phatty and power core silencer the only way to go. as for porting there right i would wait untill winter it does take a while.

 

Hey guys, THANKS FOR THE INFO.

- I am going with a +.010 Wiseco and will bore the cylinder .003" over piston size.
- A CR head gasket, and an FMF Fatty and silencer. I will wait on the porting job for now.

Thank you very much for the help on clearences and part suggestions.