Compression Test Numbers
07-24-2009, 01:56 AM
#1
Compression Test Numbers
There sure are a lot of low compression tests out there. Lots of 155# cylinders.
I check mine every year and write the results on the bottom side of the spark plug cover. I'm still at between 250# and 255# on all 4.
I wonder what the difference would be in hp between a motor with 255 and one with 155#.
Anyone know? How much does low compression on a stock motor affect it's output even if the cylinder pressures are somewhat equal?
fltsfshr
I check mine every year and write the results on the bottom side of the spark plug cover. I'm still at between 250# and 255# on all 4.
I wonder what the difference would be in hp between a motor with 255 and one with 155#.
Anyone know? How much does low compression on a stock motor affect it's output even if the cylinder pressures are somewhat equal?
fltsfshr
07-24-2009, 07:16 AM
#2
So nobody knows what a decrease in compression cost in hp?
There's a lot of cars on here that report 180# to 190#.
fltsfshr
There's a lot of cars on here that report 180# to 190#.
fltsfshr
07-24-2009, 10:17 AM
#3
Registered User
If a F20C shows compression numbers of 155 across the board, then the difference between their results and yours is probably caused by the test equipment and test procedures, rather than any real and significant difference between the engines. If you use the same technique and tester that they use, in the same conditions, then you'll likely get approximately the same results.
07-24-2009, 11:56 AM
#4
Originally Posted by mxt_77,Jul 24 2009, 02:17 PM
If a F20C shows compression numbers of 155 across the board, then the difference between their results and yours is probably caused by the test equipment and test procedures, rather than any real and significant difference between the engines. If you use the same technique and tester that they use, in the same conditions, then you'll likely get approximately the same results.
07-25-2009, 03:24 AM
#6
Registered User
As mentioned by mxt 77, there is a lot of variation in test equipment and test conditions. If your battery is not strong, resultant compression numbers will be low comapred to measurements on the same car with a fresh battery. Compression testers vary widely as well, with some reading higher than others.
In my experience leak-down is a better indicator of engine performance than compression. As an example, I had good compression in my 1.6 liter Miata engine (around 170-180psi), but terrible leakdown (10%,15%,25% and 38%). The engine was about 15% down on power as a result.
In my experience leak-down is a better indicator of engine performance than compression. As an example, I had good compression in my 1.6 liter Miata engine (around 170-180psi), but terrible leakdown (10%,15%,25% and 38%). The engine was about 15% down on power as a result.
07-26-2009, 10:23 AM
#7
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Originally Posted by directportjuicedS2k,Jul 24 2009, 12:00 PM
Isn't perfect compression 240? I check mine every month, prob over kill but its like a disease, feeling the need to check it often.
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07-26-2009, 04:40 PM
#8
Isn't checking compression a PITA??? I looked at my helms and it seems like some stuff needs reset afterwards and connected to a special tool while doing the compression test??? My K20 was simple, just disconect the injectors and that is it.
07-27-2009, 12:38 AM
#10
Registered User
Originally Posted by Fast Jack,Jul 26 2009, 10:23 AM
Do believe it is 250/ap2 210/ap1.
the number change depends on the method you used to do the test, the temperture of the engine, the brand and condition of the gauge.
compression test is only meant to be used as a first step in testing the overall "health" of the motor. on a used car 8-10 percent variation is "accepted" on a new and rebuilt motor is around 5 percent.
i did a compression test on a recently broken in ap2 and it's 210-215 across the board, ZOMG it's a lemon because it's not 250
