Compression Test Result with PI Headswap and Comp Cams262

[97GTSTANG]

Test was just completed on PI headswap with stage 2 port and polish and comp cams 262.
Test was done on a very warm engine.

All cylinders came out at 195-200 except for cylinder 1 which came at 185. Is that a problem?

The tech said the car pulls very strong and he said maybe when it was being ported the valves did not seat properly yet. No idea what that means but overall he said the car has very strong compression and very healthy.

Any suggestions?

 

[fullrearview]

From what I remember in auto shop (Now this was on a pushrod v8 not a Mod motor) if they are all with 10% of eachother, you are doing really well. I take it this is the stock bottom end?

If so, don't worry about and have fun!

 

[2002BLGT]

has to be more than 25 percent to be out of spec

 

[trinity_gt]

Test was just completed on PI headswap with stage 2 port and polish and comp cams 262.
Test was done on a very warm engine.

All cylinders came out at 195-200 except for cylinder 1 which came at 185. Is that a problem?

The tech said the car pulls very strong and he said maybe when it was being ported the valves did not seat properly yet. No idea what that means but overall he said the car has very strong compression and very healthy.

Any suggestions?

The difference between highest (200) and lowest (185) is 15 pounds which is ~7.5%. That's not that bad.

Spray a tea-spoon of oil in the cylinder and re-run the test to see what happens to the number. If it comes up you've got rings leaking.

If you're still curious you might want to bring the piston on that cylinder to TDC on compression and apply air pressure (say 15-20 psi) through the plug hole and listen for sources of air leakage. Out the exhaust or intake suggests a valve sealing issue and out the oil filler cap says rings.

But a 7.5% difference high-to-low is nothing over which to lose sleep.

 

[bhuff30]

Were the cams degreed in? Cam timing does affect compression numbers, and can give seeming random numbers.

I have never heard of it taking time for the valves to seat. The materials are very hard and should be cut to seat correctly. If the valves are in fact leaking as evident from a leakdown test, then you should have them re-cut.

 

[BurningRubber]

Those are strong numbers.

Could be a number of things causing that small difference, but don't sweat it as stated already.

 

[97GTSTANG]

The cams were not degreed. Also the throttle was not set to WOT and the injectors were not disconnected. Dies that make a difference?

 

[97GTSTANG]

is it a problem that he did not disconnect the fuel injectors to run the test? Also when i read that the WOT should be set, are you talking about engaging it in the engine or getting it to WOT while cranking the engine inside the car?

 

[trinity_gt]

is it a problem that he did not disconnect the fuel injectors to run the test? Also when i read that the WOT should be set, are you talking about engaging it in the engine or getting it to WOT while cranking the engine inside the car?

If you go to WOT you do two things:

1) The fuel injectors are cut-off by the PCM (i.e. they don't inject fuel to produce a clear-flood mode) so there's no need to disconnect the injectors.

2) You open the intake tract to the atmosphere allowing the maximum amount of air into the engine during the compression test.

Connect the compression tester. Sit in the driver's seat. Hold the throttle wide open and crank the engine for 4 or 5 cycles. Go and see what the reading is...

If the throttle was not at WOT during cranking the values will be low but the effect will apply across all cylinders. The fuel injected during cranking won't otherwise affect the readings.

 

[97GTSTANG]

Thanks for explaining, I know he cranked each cylinder 4 to 5 times, I am sure he was at WOT or else reading won't be at 185+. The only thing I was sure he didn't do was disconnect injectors. Which as u said won't affect reading. So overall nothing to worry about that one cylinder at 185. He also didn't degree the cams. Maybe that's why that one cylinder is low. Is that possible?

 

[BurningRubber]

Not degreeing the cams will affect each bank of cylinders, not just a single cylinder.

 

[97GTSTANG]

Well I know he did not degree the cams. So I guess he just lined them up very well then. lol