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Discussion Starter #1
What compressin do you run on your mx r's ?
Right now i have a 295 resleave, shortrod motor, with a pro desien head thats puting out around 230 psi. I ask because i am kinda of worried about head gasket and crank shaft reliabilty. Man this thing has some rip just off idle though!

On another topic i have a 265 dri pv that i ran for 20 minutes and broke a ring. when i have the cyl re-plated do they have to re-port it or do i just have to get a new piston and rings?
 

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I'm running right around 230 psi, and have had no problems that I can tell. And yeah, that low-end rip is sure nice to have on the track! I do have to run straight 110 fuel though, but it's cleaner anyway, and the extra grunt is worth it! ;)
 

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Discussion Starter #3
i dont know if it is that i have the carb just rite or what but i had this cyl on a long rod all last seaon and it never had this kind of power. the only thing i did diff is went to a 50 pilot from a 52 and put it on a NOS 86 bottom end.the comp seams to be the same as last season. hell i cant keep the tires on the ground or just spininge !!!! i almost kind of worried that it might be to much power!!!! welllllllllllll maybe not!!!!!! it will be nice to have some low end to pull those 4 pokers out of the hole!!!!!
 

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if all was fine otherwise ...& if only a broke ring could have been more related the bore job & radius's at the ports more than compression or perhaps poor break in methods
& BTW what was the piston to cyl . wall clearance on it ?
 

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Discussion Starter #5
the cyl that i broke a ring with did not have high comp, maybe 185-190. i purchased the cyl used and that may have something to do with why i broke a ring. i am going to send it to duncan to have redone and checked out. the 295 cyl i have i rechecked comp with a better gauge and have 240-250 psi! i just called esr to get a diff sized dome. i am hopeing to lower it to around 220-230. i had a 23cc dome in it and orderd a 21cc. i thought the lower the cc number the higher the comp? any ideas?
 

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i just realized you were in Kansas City. I am in Grain Valley, what part of the city are you in?
 

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If your running a 23cc dome right now, if you get a 21cc it will have even higher compression.

Could be in the cylinder how the porting is, your trapping more from the exhaust port roof up & might need to adjust the dome say to around a 26cc or bigger.
230 compression on a MX engines sounds right, long as you dont try to rev it to the moon.
High compression & high RPM fight each other.
Ol 250Rs just seam to run better if you set them up a grunt engine.
Neil
 

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Discussion Starter #10
well the guy i talked to at esr is a dumb ass then, i gave him the part number off of my old dome and he said it was 23cc and it was a "race gas" dome, so i told him that i wanted to lower the comp he said to go with a 20 or 21cc dome!!! any body know where i can get a 26cc dome for a cool head for a 295 cyl? (stock cyl resleaved) i think this head is diff than a reg sleave cyl but i dont think it is the same as one for a pro-x style either. any ideas?
 
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