I don't think there s problem, but I am doing this prior to a tranny swap from auto to 4 speed just to be sure the motor is strong.
Need to know what compression PSi numbers I should expect from a 2.8 with 80k miles on it. All my books show that if its below 100PSI theres a problem, but they don't say if 125 to 140 is good or great whatever.
So far I'm getting between mostly 125 - 130 psi consistinly in all cyl. with an at least one or two reading at 135-140 PSI out of each cyl. Seems if I crank the engine 4 to 5 rev it get slightly higher readings.I think that nornmal. Does that make the PSI go higher?
Recording 6 readings on each cyl and getting rid of the first one is the way I am doing it.
Please let me know if this sound good for its age . What were the 2.8 PSI NEW???
I try the oil test in a couple of cyl. but I didnot see that much differenace at all so I don't think I have a ring problem.
Should I do them all with oil. The back one are tough to get at with the oil.
Thanks in advance

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jerryglasstoys

1987 Fiero GT

ok, nominal air pressure at sea level is 14.7 psi. if your compresssion ratio is 9.0:1(like my duke), then you should expect readings of 132.3 psi, more or less. i seem to recall reading that the 2.8 has a lower compression ratio, 8.?. maybe i'll go check with mr. chilton or mr. haynes.

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'84 2m4 se, a work in progress http://www.mtsu.edu/~mkr2c/fiero.htm

luker
I sent you and email but the 1987 2.8 compression ration from Mr. Chilton is
8.9:1 not 8.3.:1 as I put in my email

How do I calculate the PSI per cyl. that I should be getting on the test??

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jerryglasstoys

1987 Fiero GT

Jerry,
I recently did a compression test on all cylinders of my 88 Formula. I had just bought the car and it had 246,000 miles on it. I do not know if the engine had ever been rebuilt or replaced. I got #145 to #150 on every cylinder except #6 which was about #130. Afetr a valve job on both heads, compression was in the #145 to #150 range. I have a screw in type comresion tester. I have noticed that readings tend to come out lower using the type you hold in the hole. I got my measurements by cranking the engine until the needle did not go any higher.
There is NO direct relationship between compression ratio and your readings on the compression tester. The major reason is valve timing. Two (otherwise) identical engines with differing amounts of valve overlap will show different readings on the compression tester. More valve overlap = less cylinder pressure. Incidentally, this is why long curation cams REQUIRE higher compression ratios.
I hope this helps.

SD iconoclast
Thanks for you info.I heard from another source that from the factory it normally would be 140PSI. But like you said, the timing of the engine could have the number ranges look different. As with mine, numbers are close together but in a different range.
I am using the screw in type also.
What were the problem that you were have that made you have the heads redone?? And how is the enginee now?

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jerryglasstoys

1987 Fiero GT

quote Originally posted by sd_iconoclast: I do not know if the engine had ever been rebuilt or replaced. I got #145 to #150 on every cylinder except #6 which was about #130. I got my measurements by cranking the engine until the needle did not go any higher.

I second almost everything that sd_iconoclast said.

My 90k mile (at the time) '88 GT had compression readings about 145 - 150 across the board. I, too, cranked until the needle stopped moving, while holding the throttle wide open.

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Doug Chase
Chase Race
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