Good Compression??

Lex · Apr 20, 2004

Whats a good compression check I should get out of each cylinder?
Thanks

bhuff30 · Apr 20, 2004

Ford spec is with in 25% or eachother. For example, if you get a high of 100, and a low of 76, they are in spec.
I would like to see the numbers be a bit closer though. I think 10-15% is the minimum before I started to wonder what was wrong.

Slugstang · Apr 21, 2004

bhuff30 said:
Ford spec is with in 25% or eachother. For example, if you get a high of 100, and a low of 76, they are in spec.
I would like to see the numbers be a bit closer though. I think 10-15% is the minimum before I started to wonder what was wrong.

Is that correct only 100 is good compression for a turbo 2.3? I did a compression check on mine because I started blowing the dip stick out at anything over 12psi of boost and I had 100 in all four. I thought 150 was good for compression, is it lower in the turbo 2.3 because the compression ratio is so low?

Lex · Apr 21, 2004

Are we talking Turbo here? Mines just a N/A ? Just curious.
Thanks

Stinger · Apr 21, 2004

The gauges will vary greatly, one gauge might show 150 and another will show 100 on the same car. That's why they say if they are within a % of each other then it is fine.

Stinger

Slugstang · Apr 27, 2004

Stinger said:
The gauges will vary greatly, one gauge might show 150 and another will show 100 on the same car. That's why they say if they are within a % of each other then it is fine.

Stinger

Tested my pressure gauge on three different cars. A Dodge Stealth Twin Turbo, My 2.3 Turbo Mustang and a Chevy 350 V8 VAN. The dodge was at 180psi with a few pounds differeance between each cylinder and the chevy van at 150psi with a few pounds differeance between each cylinder. My mustang shows 100psi with a few pounds differeance between each cylinder. So are you saying my motors compression is good? I don't totally agree with your statement. There should still be a high and low limit for the compression. I think 100 is low but I have not see any documentation on my motors expected compression reading so I can't say for sure if it's low or high. Does any one know what it should be at? I know they should all be realativly close to each other but shouldn't it be higher. I'm using a high end gauge so it should be fairly acurate. I am going to try another gauge tonight to see what it shows on these same cars.

bhuff30 · Apr 27, 2004

seriously, if they are close to eachother, it doesn't really matter. Have you ever blow the dipstick tube out? if not, you probably don't have much blowby (or the PCV is toast). Do you ever see blue smoke on acceleration?
Compression is altered by a lot of things, one being the volume inside your tested. If you are using a tester with a long hose and leads to a guage, it is naturally going to read low because you effectivly changed the compression ratio by adding more area. If you are just using one of those gauges that you just push into the spark plug hole, then the volume of the gauge is smaller, and will tend to read higher.
Your cam grind can also effect the comrpression ratio. On my NA engine, I used to get ~190psi. Then, I rebuilt it, raising the compression from 9:1 to 9.7:1 and installed a performance cam. The compression dropped to ~180. This is normal, the cam isn't as effective at filling the cylinders at low rpms (500rpm is probably what you are cranking at).
My point is, you can't compare compression readings between cars, testers, or even the same test on a slightly different combo. You can only truely compare the results relative to each cylinder.
If you don't have any problems with smoking on acceleration, or blowing the dipstick tube out, then don't worry about it.

Lex · Apr 27, 2004

Well did a compression check and it was

cylinder 1 150
cylinder 2 180
cylinder 3 180
cylinder 4 200

Does this seem normal? cylinder 1 seems a bit off

legomaniac32 · Apr 27, 2004

make sure the engine is at operating temp before you do compression check.
rotate engine about 7 compression strokes to get reading.
according to my book, compression says 101psi..not sure about that.
in the chart it says the highest number..yours being 200..should have a min compression of 150, which you do.
so according to this chart..its ok.
but if you want to check,
1.low compression on the first stroke and gradually increasing could be worn rings
2.low compression on the first stroke which doesnt build up could be leaking valves or blown head gasket. (or cracked head)

add about 3 squirts of oil to the cylinder that is low, and if it goes up, the rings are worn.

are you just checking? or did you notice a problem to make you want to check?

if you want to know for sure for leaks you can do a leak down test at a garage and it will pinpoint where any leak is.

hope that helps.

bhuff30 · Apr 27, 2004

also, ensure that the throttle body is open when you are cranking it. If you leave the TB closed, it takes longer to get the compression up because you can't suck enough air throught the TB.

legomaniac32 · Apr 27, 2004

wouldnt you only do that on a carbed engine?
didnt think you had to do that on a fuel injected one?

just a question

³à³ · Apr 27, 2004

Also remove ALL the plugs b4 doing the test.

Slugstang · Apr 28, 2004

bhuff30 said:
Have you ever blow the dipstick tube out? if not, you probably don't have much blowby (or the PCV is toast). Do you ever see blue smoke on acceleration?
If you don't have any problems with smoking on acceleration, or blowing the dipstick tube out, then don't worry about it.

I am blowing my dipstick out constantly that's why I have been running compression checks. I have a one way valve in the PCV line and the correct PCV valve and it's new not blown. I even plugged the PCV and still it blows the dipstick out. I have no visible smoke out the tail pipe and it runs great just blows the dipstick out. I do get smoke once the dipstick blows out as oil goes everywhere but none from the tail pipe. This only happens at anything over 12psi. If I keep it under 12psi it does not blow it out. I'm thinking it's rings.....

I think I understand the compression testing theory now. I'm going to try a few things descibed in some of these posts but even though my readings are real close to one another I still feel my rings are toast and my compression is crap. Would an almost blown head gasket cause this problem... maybe under high boost it's forcing air into an oil passage? Motor has 85,00 miles and still has the stock factory head gasket.

Thanks guys.

legomaniac32 · Apr 28, 2004

one other cause could be too much oil in it..make sure its not too full. also maybe try changing the oil filler cap. if its clogged could be the problem as well. could just borrow one from a friend to test it. when you pull the PCV, with the engine running there is sucking air right? if not there could be a block in the line somewhere. if so its ok.
what is the condition of the oil on the dipstick? does it look frothy or discolored?

the oil cap would be the easiest and cheapest first test

Slugstang · Apr 28, 2004

legomaniac32 said:
one other cause could be too much oil in it..make sure its not too full. also maybe try changing the oil filler cap. if its clogged could be the problem as well. could just borrow one from a friend to test it. when you pull the PCV, with the engine running there is sucking air right? if not there could be a block in the line somewhere. if so its ok.
what is the condition of the oil on the dipstick? does it look frothy or discolored?

the oil cap would be the easiest and cheapest first test

Oil level is correct and I just changed it. Yes the PCV system is sucking and operational. Oil does not look frothy or discolored. Still looks like it came out of the bottle. I have a spare oil cap I can try. Why would the oil cap cause this problem? Please explain...

legomaniac32 · Apr 28, 2004

there should be a small pressure relief hole in the cap.
if its plugged it will cause excess pressure as well.

its a possiblitity.

bhuff30 · Apr 28, 2004

next step, do a wet test. squirt a little oil down the cylinder, and check the compression again. If all the cylinders are miraculously close to eachother, then you know that the piston/rings are to blame. It sounds like that is your problem though.

Lex · Apr 28, 2004

Ya I had all plugs out when I did the test. I did squirt oil in cylinder one to see if I could get higher then 150. No change. I guess I'm pretty impressed with the car ever since I gutted the cat. So I'm just doing fine tunings now. I do have a knocking sound which I believe is lifters and that could be the compression issue. Anyways thanks for the advise and tips. This all really helps.

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