ftf396

I decided to check my compression while I replaced plugs. Numbers are
# 1- 135. # 2- 137
# 3- 138. # 4- 142
# 5- 150. # 6- 150
# 7- 138. # 8- 140
This was a dry test engine cranked 4-6 times each.
Are these normal numbers?
Thanks

Tim Ware

Did you hold the carburetor open when you turned over the engine ? Closed carb reduces air flow.

ftf396

Yep.

zwede

Readings are a bit low, even with the low compression in '71. What's your altitude?

7T1vette

Numbers are all within reasonable range of each other. I'm assuming that the engine has significant miles on it. If you don't have any blow-by after start-up or when you punch it, keep it maintained well and 'keep on cruising'.

ftf396

Altitude is 381 ft. Macon Georgia.
Mileage is over 100k. Motor has been rebuilt by previous owner but appears to have been run hard. It does smoke some.

ftf396

Thanks all for the info. What would be the compression on a newly rebuild 454?

zwede

Going from fuzzy memory here, but I'd expect about 160 PSI with 8.5:1 CR & stock cam.

7T1vette

160psi is the 'factory new' baseline number for the 365hp 454; 150psi for the 425hp 454.

For an engine with 100K miles on it, cylinders that make 85% of 'factory new' expectation (135psi) is not all that bad. Piston rings wear; bores wear out-of-round; valves have burnt/distorted areas where they originally sealed well.

I'm still of the opinion that if the OP is OK with engine function and performance, there is no immediate reason to rebuild that engine.