Compression numbers for AP2 looks too good... seems fishy
12-11-2014, 04:49 PM
#1
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Compression numbers for AP2 looks too good... seems fishy
I'm about to buy a used car, and I had the seller bring the his car to a reputable shop in Arizona (scienceofspeed), and the 4 numbers came out to exactly 235 for each cylinder. I've read that over 200 is good, and brand new should be outputting 240.
I'm not exactly sure how they did the test (whether car was warm or WOT), but is this normal to have the numbers to be exact like that?
By the way, what causes numbers to drop over time? How do you maintain the car to keep good compression?
I'm not exactly sure how they did the test (whether car was warm or WOT), but is this normal to have the numbers to be exact like that?
By the way, what causes numbers to drop over time? How do you maintain the car to keep good compression?
12-11-2014, 05:23 PM
#4
This makes no sense....a cold motor compression test will generally read LOWER. The reason you are supposed to do the test while warm is so that the pistons have had a chance to expand in the cylinders giving a more accurate reading.
To the OP- I see no issues with those numbers. A properly taken care of engine will keep and maintain good compression numbers. Timely oil changes, air filter changes, valve adjustments, etc. will keep the engine healthy for many miles.
12-11-2014, 05:47 PM
#5
Originally Posted by jst2878' timestamp='1418350358' post='23434686
Could've done the test on a cold motor. Take it to your guy if u want to do another test
This makes no sense....a cold motor compression test will generally read LOWER. The reason you are supposed to do the test while warm is so that the pistons have had a chance to expand in the cylinders giving a more accurate reading.
To the OP- I see no issues with those numbers. A properly taken care of engine will keep and maintain good compression numbers. Timely oil changes, air filter changes, valve adjustments, etc. will keep the engine healthy for many miles.
12-12-2014, 04:34 AM
#7
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The guys at SoS know what they are doing. And the numbers seem fine! I did mine last year at ~100k miles and I got 235 across the board as well; and my leakdown was less than 5% across the cylinders.
Sounds like the care was well taken care! Get a valve adjustment done and a leakdown test after you buy it and if that comes out ok, peace of mind is at hand (at least engine wise).
Sounds like the care was well taken care! Get a valve adjustment done and a leakdown test after you buy it and if that comes out ok, peace of mind is at hand (at least engine wise).
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12-12-2014, 06:33 AM
#8
After jordan rebuilt my head mine tested at 240 on my '05 with 75k, and that was with a verified calibrated gauge. (edit: correction, I had another rebuilt heap swapped on for mine - didn't actually rebuild mine).
Sometimes gauges are off (sometimes by quite a bit) but a lot of times shops won't care, because what you're typically looking for is even distribution which won't matter if the gauge calibration is off since it's still apples to apples on each cylinder.
Sometimes gauges are off (sometimes by quite a bit) but a lot of times shops won't care, because what you're typically looking for is even distribution which won't matter if the gauge calibration is off since it's still apples to apples on each cylinder.
12-12-2014, 06:39 AM
#9
I'm not an expert, but to answer your question on compression dropping over time there's tons of things that can wear over time and cause it to drop. Essentially, every seal in the engine that is in direct contact with the combustion chamber. The things I know can be poor valve timing/adjustment allowing the valves to not seat correctly, intake/exhaust valves (seats themselves, or being bent/burnt), worn/scored/scuffed cylinder walls, piston rings, head gasket or bridging between cylinders. There may be others but like I said I'm not an expert on this sort of stuff.