KTM 520exc top end

I am planning to put a new piston in my 2003 ktm 520exc (yes I know they supposedly didn't make an 03 520 but that is what my vin says). I was thinking about upping the compression...what is the highest compression ratio that you can still run pump gas?

Is there anything else (within a $400 budget) that I should do while I have the cylinder off??? Port and polish? Over bore and run a larger displacement?

I know your question is about performance improvements but you might need to spend some of the budget on updates and maintenance. Your first priority should be to be sure the later motor updates have been done (cam sprocket, screen, etc.). Not expensive but should be done while apart.

Next the intake valves are very soft on the RFS and likely will need to be replaced.

Only then if you have $$ left should you even consider performance upgrades.


Edited by BDM

I don't think you can bore your cyl without getting it renicle and thats more of a pain in the a** than just buying a big bore kit . but I agree with BMD worry about the must dues before the want too's ride hard and fast

I have a 2003 525 and just did a 12.5/1 wossner piston and had djh put in oversize kibblewhite valves and unshroud the valves. Bike runs great on 91 pump gas. If you need to have the cylinder redone, you might as well do a 540 kit. My cylinder was fine so I stayed with the stock bore.

Ok, so it looks like i need a new cam sprocket, and possibly intake valves? Is there any way to tell if the valves need to be replaced? Also, what is the screen you referred to? Sounds like I should run a stock sized piston (95mm) and not run any higher higher than 12.5:1 compression. Anything else I should do while i'm in there?

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