Compression Test Numbers

Hi all,

What are good compression test numbers for a 1973 motor home block 440? Also, what would be considered bad numbers? I would like a rough range to see where I fall when I get around to doing my test. Also, how would a wet test change the numbers from a dry test?

Thanks!

nuteguy said:

Hi all,

What are good compression test numbers for a 1973 motor home block 440? Also, what would be considered bad numbers? I would like a rough range to see where I fall when I get around to doing my test. Also, how would a wet test change the numbers from a dry test?

Thanks!

Click to expand...

My estimate is 102-110 dependent upon condition of cylinder

There are a few factors that dictate the numbers you get. A High static compression ratio with a very mild cam can register numbers in the 190+ range. That same engine with a more rowdy and lopey cam will have much lower numbers. I was showing 190 when I had almost 11.0 compression and a Mopar 509 cam.
The motorhome, truck and van engines were often in the 7.5 to 8.0 compression range. Pistons were often .150 in the hole and they had open chamber heads. The cams were not very big. I'd be surprised to see anything over 130.
The real issue is consistency. You want to see less than 10% variance from the highest number to the lowest. This is assuming that you intend to just cram the engine right into another vehicle.
You can still make decent power with low compression but you'll need some good cylinder heads and a decent cam.