Anyone know what the proper stock compression should be for 86 TRX250R (to decide wether or not I should do the top end), and how much I would need to shave the head, using the stock gasket, to get 160 and 185 psi? I haven't decided which yet, I will probably try around 160 first.

Thanks in advance,
Rod

 

Off the top of the head stock compression should between 160 and 170 PSI. There is an easy and non-permanent way to up the compression. The stock TRX head gasket is around .052" thick, whereas a '89 CR250 head gasket is about .012" thick. With this gasket it sets your squish clearance down, which will make more power than higher compression alone. I have ran these gaskets on several motors. Jetted properly, 92 octane has been sufficient, but I highly reccomend trying it out listening VERY carefully for any sounds of pinging(pre-ignition) or knocking from detonation. Jet slightly fatter, 2 or 3 sizes on the main, and up one position on the needle clip, or a fatter needle, like a DDJ.

 

Thanks Backcountry, that answers question #1 (I have 120 psi). I have heard people saying things about those CR250 gaskets, like they have a tendancy to blow out, has this actually happened to anyone? I suppose I will break it in stock for starters anyway. It sounds like that thin head gasket is optimum for 92 octane gas, and I don't want to start mixing race gas, so that seems to be the way to go.

Rod