I am trying to find out what the compression should be on my bike. I have a 78 RD400 but can only find the compression ratio, does anyone know about what the PSI should be? Thanks
find Lyn Garland he's on here, Vintage Specialties, I believe is his thing. He knows something about RDs and he's in your neck'o da [email protected] is his email, hope he doesn't mind me giving it ...?
Your compression depends on the state of tune of your engine, the duty cycle of the track your are running, the fuel available, and your ignition timing. Having said all that, for most RDs running Talladega 2.0mm BTDC timing and track 110 octane fuel 7.0:1 compression is fine. (This is cylinder capacity calculated from exhaust port closing to top dead center divided by combustion chamber capacity, not from full stroke like four strokes do it.) That is too high for high speed, long duration full throttle tracks like Roebling Road and Road Atlanta where 6.5:1 is preferable at 1.7mm BTDC timing. If you want more info you can call me at (770) 775-3249 or visit me. I live in Jenkinsburg, GA, about 40 miles south of the downtown Varsity. Lyn Garland
Lyn he may be asking for PSI on a pressure gauge... Again this depends on the state of tune of the bike, if you have pipes etc.. the best way to check is to measure the motor and calculate the static compression ratio as Lyn has suggested. I would say you should see no less than 115 psi and not over 145 psi... this would indicate depending on the state of tune/port timing that the rings are working well and you have decent compression. If it is below 125 psi I would suggest that you might consider a good checkout of the motor and its specs...
good info, thanks guys. I may have to get some help once i am ready to tear the motor apart! Thanks again.
