How much compression is in a stock 400 scram I have 110 psi cold. the reason i ask is my wife didn,t see the temp light was on last weekend riding the light is bad not here fault. i don,t know how long it was run like that she did not run it hard or for long i do know that. But now i here a rattle now at idel sounds like piston slap. should i be concerned with it, it still runs fine and starts fine or is it time for a topend rebuild?

 

Stock compression should be around 125psi. I think it is time for a top end. I would also shave the head .20 to raise the compression to 135psi. You can run up to 145psi on 92 octane.

 

Well i will look at the exhust port today see what i can find. atleast it should be warrented .