No replacement for displacement. Big bores will produce low end torque, allowing you to short shift and use lower rpm range. Perfect for the woods. Porting and pipe are key. 310 kits performed very well in the hay day of the trx250r in the GNCCs.
Obviously a big bore that is setup incorrectly would be a nightmare in the woods. Riding a real pipey motor is difficult to keep traction and will wear you out.
My old 330 non PV Prox cylinder was absolutely incredible. In sand trails, I could leave it a gear high coming out of a corner, roll the gas and would power out super smooth. No clutch, but all smiles
In the big picture of performance, the cost difference between modifying a stock cylinder vs buying an aftermarket is minimal. After market cylinders offer further bore options.
if you need to replace your crankshaft go +4.if you don't stick with the oem crank.if you don't have a cylinder under 68mm or cant find one then go with a 310.but porting will cost the same esr or oem and will cost $350-$500 for either one.if you just buy a stock ported 310 you wont be happy.it wont really make anymore power than an oem cylinder.
Thanks for the input American opel , not sure about the sprocket bolts that’s what was on it when I got it just making lite of my situation I’m know my engine isn’t that powerful, I think I’ve made up my mind to buy an esr cylinder and 4 mil crank and have it ported . By the time I buy a used cylinder, get it bored and buy a piston and rings I’ll have $400 in an oem cylinder and Esr sells a new one for $700 , 310 or 330 is the next question? I have the 38mm carb and an ESR atc Pipe already so I don’t want to buy a bigger pipe if I have to go 330 . Speak about the atc esr pipe I have been very pleased with it , a lot of people complained about the chrome coming off of theirs but I ride mine in mud all the time and my chrome is fine