502 Leakdown NumbersWha

[Bucketlist]

My stock 1998 Mercrusier 502 EFI 415 hp was completely rebuilt last year using my stock heads, better quality valves, springs, upgraded pistons, rings with stock compression, etc with the goal of being as close to stock hp with increased reliability.

I currently have leakdown numbers of +/- 140 psi right now. What leakdown numbers should a factory fresh 502 415 hp have?

I'm not an engine guy so sorry if I have left out some pertinent facts and lingo.

Thanks

 

[Outdrive1]

That’s a compression test number not a leak down. You’re not concentrating on the actual number so much as differences between the highest reading and lowest reading cylinder. 5 to 10 percent difference between the lowest and highest number is ok. Anything more and I would do a leak down test which is completely different. Gauges seem to read different plus the test can be done differently. Normally you do a warm engine with the throttle wide open.

 

[Bucketlist]

That’s a compression test number not a leak down. You’re not concentrating on the actual number so much as differences between the highest reading and lowest reading cylinder. 5 to 10 percent difference between the lowest and highest number is ok. Anything more and I would do a leak down test which is completely different. Gauges seem to read different plus the test can be done differently. Normally you do a warm engine with the throttle wide open.

 

[Bucketlist]

Thanks for your reply. After reading the above im now embarrassed i asked this stupid question. I should have known this. I will get more info from my mechanic and post again.

 

[obnoxious001]

I currently have leakdown numbers of +/- 140 psi right now. s

If all 8 are very close to 140, you should be good to go.

Are you chasing a problem or just checking? Paul's information is correct, if there were one or more bad cylinders a leak down would help determine where the air leak was without tearing down the complete engine, whether it was the rings, or intake or exhaust valves.

 

[BDMar]

All the info from Paul and Barry is dead on. The one thing that stands out to me is your builder saying he upgraded pistons, valves, etc. The stock pistons are JE. The exhaust valves are inconel and intakes are severe duty. JE makes replacement pistons in std. and .030 over with the exact dome that came on the original pistons to keep the compression the same as stock. You're not really going to upgrade the original parts. Mercury is famous for overbuilding their engines from the factory. Just some info you might be interested to know. Always makes me wonder what the builder is actually using for parts.