How much does either cost? and do they make the 250r unreliable?

 

check out ctracing.com and other websites or get a dirtwheels mag and check out the ads

 

I have one for sale attached to my '87R. I shattered my wrist and have to sell all of my toys because I am going to be out of work for the next couple of months. You can check it out at
My 87 310R

It has never let me down.

 

most builders require you to machne your cases to fit the 330 kit .. however ESR makes a completely bolt on kit and no machining is required. the big bore kits are not modifications on your existing cylinder but rather an aftermarket cylinder from Pro-X. hence there are no issues with unreliability since the cylinder wall has not lost any integrity