Compression discrepancy

[Clats97]

Quick question... I have a Skyhawk Gt5a, and I shaved the head for. Higher compression. .. I am being told by 2 different people 2 entirely different "normal" readings for a stock engine.

One guy says 80-90psi stock

Other guy says they come 130-140 stock.

Pretty big difference here.

Any thoughts?

What's your compression ratio and is it stock or modified?

 

[Greg58]

Some where around 100 is considered normal, I shaved the head on one of mine and get 130. Be sure to open the throttle to get a more accurate reading.

 

[Greg58]

Don't trust the gauge with the rubber end you have to hold in place, use the type that screws into the head and records maximum compression.

 

[Clats97]

Don't trust the gauge with the rubber end you have to hold in place, use the type that screws into the head and records maximum compression.

Yeah the screw on one was only 5 bucks more that's what I got. I didn't k o about the full throttle tho

 

[lewdog7431]

My self with the tall hi compression head I've got a reading of like between 145-150 don't know really if it's not good enough or whatever .....but that's what i got

 

[Jimmy Bloodmaker]

90-110 psi is good for stock. under 80 and you have some serious problems. shouldn't take your compression over 150 psi if you want long life or high rpms. if you have a jackshaft non-hd freewheel, best to leave it below 125psi or you might burn out the freewheel fast. for an all around machine, shoot for 135psi. good longevity, and nice power. at 150 psi on a single speed, you'll get a few season out of it with hard running. at 135 psi with some good beatings now and then, but ran cruising mostly, it's will last for a decade.