Compression Test???

AKS Racing · 10-20-2002, 05:14 PM

Had a few moments the other day, so I ran a compression test. I feel like the car has been down on power for some time, but have been attributing to the tuning.

Ran the test and they ranged from 138 - 165 psi. One was at 165, one at 138, all others were from 145-155. I run a very large 240° duration at 0.050" solid roller. Center line is 114°.

Thoughts on if the cam is why the cranking compression is so low?

Aaron

SPD DMN · 10-21-2002, 03:53 PM

Wow, that is pretty low, especially with a 114 seperation. What compression is the motor?

AKS Racing · 10-21-2002, 10:56 PM

Motor is 9.2:1. Car still makes plenty of power, test values just seemed a bit low.

Aaron

black bart · 10-28-2002, 05:09 PM

Aaron check the open & closing on your cam card I think you will find that you have about 15 degrees of overlap that would kill the cranking compression. :seeya

johndezman · 12-11-2002, 04:02 PM

awful lot of variation from high to low

BAdAzZV8 · 12-11-2002, 08:25 PM

mine were:

203
200
205
190

190
205
195
190

is this about right.

0ski_dwn_it · 12-12-2002, 05:06 PM

I don't trust compression testing anymore. I just pulled my 350 apart and I tested it SEVERAL time via compression tests. Each time the results were the same, ~155psi +/-2psi across all pistons. Did a leakdown test, and then had a reputable shop verify my finding. All the cylinders were leaking at LEAST 20%, #7 was up to 50%. Pulled the engine for a new 406, and I took the pistons out. In every cylinder, the top ring was broke in two, and #7 the top ring was in about 15 pieces!

Never did the car burn oil. But I knew something was up when we did the leakdown. So I guess what I am saying is if you want to get to the bottom of it, do a leakdown test. Otherwise you might as well be guessing. I know in certain instances the compression test will work, but in all those cases, the leakdown will tell you the same+some.