Engine Compression Query

joetrainer31 · May 6, 2013

Hello Stangnet,

I'm looking for some input from you brainiac types concerning a compression question.

Since I am the new 2nd owner of a 95 GT I decided to run a few tests on it including a compression test. The car only has 64k on the odometer, but it is 18 years old. Here are the particulars:

1. Engine cold test.
2. Could only get line finger tight on the cylinders.
3. Cranked the engine over the same amount of times for each cylinder.
4. All spark plugs were removed prior to test.
5. TB wide open via gas pedal.
6. Y303 heads, or at least GT40 heads.
7. No additional oil was put into cylinders.
8. All plugs had a little bit of oil them, but were all white on the electrodes. (Maybe wrong heat range?)

The results:

C1 120
C2. 115
C3. 115
C4. 115
C5. 115
C6. 116
C7. 115
C8. 115

What say you all? Considering the test conditions do I have cause for concern or am I good to go?

ratio411 · May 6, 2013

That looks excellent to me. ???
Maybe someone else can divine more from it, but so long as your readings are all close, like that, everything's cool.
If you still have concerns, then a wet test might be in order.
I know a wet test tells you different things than a dry test.
Someone might chime in with why you should or should not do a wet test on top of your dry test.

joetrainer31 · May 6, 2013

ratio411 said:
That looks excellent to me. ???
Maybe someone else can divine more from it, but so long as your readings are all close, like that, everything's cool.
If you still have concerns, then a wet test might be in order.
I know a wet test tells you different things than a dry test.
Someone might chime in with why you should or should not do a wet test on top of your dry test.

Ratio411,

Thank you. I really value any input from you all. I'm planning on replacing the lifters. Would u go ahead and do head gaskets if already down to the lifters considering that they might be 18 years old, or are these numbers good enough?

ratio411 · May 6, 2013

When it comes to a well balanced long block, if it ain't broke, don't fix it... that's just my opinion though.
The only times to tend to break that rule is oil pump, if I have the pan off for some reason, timing set if I happen to have the timing cover off, or the stock valve springs/seals if I get a chance. Beyond those parts though, I like to keep it simple if everything is working well.

Give it time... it will give you reason to fix something soon enough!

ratio411 · May 6, 2013

I realize now why you might do a wet test....
It will tell you if you are having oil control issues in cylinder #1.
That little spike over the others is within tolerance, but what if it is wet from a problem?
Then it might actually be very low compared to the others when they are wet.
I'd do a wet test just to feel warm and fuzzy.

joetrainer31 · May 6, 2013

ratio411 said:
When it comes to a well balanced long block, if it ain't broke, don't fix it... that's just my opinion though.
The only times to tend to break that rule is oil pump, if I have the pan off for some reason, timing set if I happen to have the timing cover off, or the stock valve springs/seals if I get a chance. Beyond those parts though, I like to keep it simple if everything is working well.

Give it time... it will give you reason to fix something soon enough!

That's helpful. Anyone else want to chime in?

revhead347 · May 7, 2013

The compression is excellent. Leave it alone. With compression like that, the rings are fine, so the oil is not coming up that way. It might be the valve stem seals, but not likely. More than likely the PCV valve is old, and sucking in a little too much oil. change the breather element, and the PCV valve, and see if that fixes the oil problem. That will run you about $6.

Kurt

joetrainer31 · May 8, 2013

revhead347 said:
The compression is excellent. Leave it alone. With compression like that, the rings are fine, so the oil is not coming up that way. It might be the valve stem seals, but not likely. More than likely the PCV valve is old, and sucking in a little too much oil. change the breather element, and the PCV valve, and see if that fixes the oil problem. That will run you about $6.

Kurt

Thank you, Kurt.

The pcv & element are new. I just pulled the upper off today & the gasket literally fell apart. There was also a vacuume leak from a brittle line under the upper. I'm pulling the lower tomorrow along with the valve covers to fix what seems to be a lifter tick.

Your info on the compression was most helpful, thank you.

revhead347 · May 8, 2013

Sounds like you are going through things logically. Stick with it.

Kurt

joetrainer31 · May 8, 2013

revhead347 said:
Sounds like you are going through things logically. Stick with it.

Kurt

Thank you for the encouragement, Kurt.

joetrainer31 · May 8, 2013

lifter bath.
dirty boy intake had a gasket that was so brittle it fell apart. The lower intake bolts were little more than hand tight. Its a wonder the car even ran!

joetrainer31 · May 9, 2013

clean lower intake. heads read for light sanding/vacuum, then an ascetone wipe down. how are these for factory rocket arms. These come standard with the SVO GT40 dealer option.

ratio411 · May 21, 2013

Those roller rockers came on Cobra engines, from Detroit, not the dealer.

joetrainer31 · May 21, 2013

ratio411 said:
Those roller rockers came on Cobra engines, from Detroit, not the dealer.

Hi ratio,

Yes, those came on cobras of the same year from Detroit. They also came on GTs as a dealer SVO GT40 upgrade package along with several other componants for an additional $3k. As soon as my parts all arrive I'll be finishing up the job. I'll have before/after pics and plenty of step by step pics. I hope that they will be helpful to others who may want to do a lifter replace & restoration as they dig into the engine as I am. Thank you for your input once again.

revhead347 · May 22, 2013

I hope you got more than a Cobra engine for $3K.

Kurt

joetrainer31 · May 22, 2013

revhead347 said:
I hope you got more than a Cobra engine for $3K.

Kurt

Hi Kurt,

The package consisted of an SVO intake manifold, revised strut tower brace, GT40 Heads, 1.7 RRs, Motorsport shorty headers, Aluminum underdrive pullies, and a rear end ratio of 355s or 373s. Mine has the 373s. I'm pretty sure that the idea back in that day was to offer a performance upgrade option (under warranty) that would allow the Mustang to compete with the Z28 & Firebird of that time period.

I am the 2nd owner of the car so I did not need to absorb the initial cost. The previous owner was also kind enough to install a cat-back upgrade, subframe connectors, and a K-member x-brace. For me, those modifications are enough. I'm just replacing noisey lifters and anything else that looks suspect on the way in/out (e.g., MSD cap, rotor, wires, coil, and various other parts).

revhead347 · May 23, 2013

That's a Cobra engine and strut tower brace. It's a lot of money for just a few things, but that's what dealer upgrades cost I guess.

Kurt

joetrainer31 · May 23, 2013

revhead347 said:
That's a Cobra engine and strut tower brace. It's a lot of money for just a few things, but that's what dealer upgrades cost I guess.

Kurt

I guess so. I assume that they would have charged that amount because the customer would have those upgrades while still being under warranty. Also, they were 50 state legal (a big deal here in CA).

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