i got a b16a in a 89 crx si and when i drive it hard like or rev it up my check engine light comes on

 

what code are you getting ?

 

havent checked yet because everytime i shut the engine off it the light isnt on anymore

 

does that only happen when u go past a certain speed ? for a certain amount of time ?

 

Just because the check engine light is not on doesn't mean that the ecu is still not blinking the code. Check the code on the ecu and then post it so we can help you. The only way to clear the code is to reset the ecu, so if it came on then the ecu is still blinking. I'm almost centain it's the O2 sensor code.