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Discussion Starter #1
I ran a few tests on my 289 C-code motor today and would like for someone who knows about motors to help me understand the results.

Oil Pressure:
At idle (~600RPM), my oil pressure is 40psi when the motor is cold. It drops to 20psi after the engine is fully warmed up. I held it at 2000RPM in neutral and the oil pressure was 40psi.

Vacuum:
My engine vacuum is 17 at idle (~600RPM). It stays about that amount from 8 to 16 degrees advance (based on 40 year old harmonic balancer markings.

Engine Compression:
Let me first explain how I tested compression. I warmed the engine, blocked the fuel line, disconnected the coil, held the thottle wide open, and then had my wife crank the motor over.

The psi continually rose with each crank so I was not sure when to have her stop. I measured it at what looked to be the 6th compression stroke and on the 8th compression stroke. I stopped on the 6th cause it seemed to be enough cranking (in my mind) and at 8 because that was about the max for each.

The results are:
1 - 143 @ 6 / 152 @ 8
2 - 150 @ 6 / 160 @ 8
3 - 145 @ 6 / 150 @ 8
4 - 150 @ 6 / 155 @ 8
5 - 150 @ 6 / 160 @ 8
6 - 150 @ 6 / 160 @ 8
7 - 148 @ 6 / 160 @ 8
8 - 142 @ 6 / 152 @ 8

The shop manual states compression should be between 130 and 170 for a 289. My engine is the lowest compression engine (c-code) and still has the stock heads.

Read Spark Plugs? (@600 miles)
1 & 2
3 & 4

5 & 6
7 & 8

A little background is I purchased the car 1.5 years ago and have put 1000 miles on it. I've not had any trouble but I've occassionally seen a hint of blue smoke if I start it and then rev it a little before it is completely warm.

When I purchased it, I was told by the 25 year old owner that it was rebuilt before he purchased it from his girlfriends dad. He said the motor was rebuilt 8 years prior. When I asked for mileage since rebuild, he said 160,000. However, he told me he drove the car on weekends only, it had not been inspected in a year, and the odometer read 70,000.

I'm skeptical on the history of the motor but would like to make sure it is ok to work with it as is. I don't have much money but would like to add a 4 barrel intake and a few other parts to make the car a little more fun. If the motor is not up to the task, I'll save the money and just have the motor rebuilt in a year or two.

Thanks for reading all this and for any advice/help you can provide.
 

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Because the compression tester is not a calibrated/precision instrument, and altitude matters to some extent, what you are most concerned with is no cylinder-to-cylinder variations. (FTR, you should have also removed all the spark plugs first; ambiguous whether you did that or not.)

The compression numbers look fine in terms of variation.

The plugs don't look bad (in that they aren't oil fouled or anything), but it's hard to do a plug check from a car that's been idling for a long time and have it be meaningful in terms of mixture setting, etc. Your oil pressure is also fine.

I don't see anything to worry about. Modify away...
 

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Compression certainly seems good, well within spec for variation. So does the oil pressure and vacuum, and the plugs look to be at least good, if not excellent (been a while since I've tried to really "read" a set carefully).

To have put 160k on an engine in 8 years, he would have to have been averaging 20k per year, which seems a bit impossible if he was just tooling around town in the thing. :shrug: I mean, I live in the middle of nowhere and I can't imagine piling on that many miles per year in a car like that, even if I took it on extended road trips every year or something.

:wtf:

Sounds like the "puff" of oil smoke is probably worn valve seals, and a recently rebuilt motor shouldn't have those issues. Not that I'd be too unsettled by it, but it's no fresh out of the machine shop beauty. I'd also expect slightly better hot oil pressure from a fresh engine, but it's still more than OK. I'd say you seem to have a solid engine that you can confidently upgrade, though I don't know how hard or how often I'd beat on it, since you don't know its' entire pedigree. :D

On that tack, it makes me think that a leakdown test might help you to to get a more solid feel for exactly how sound the engine is? I would certainly be tempted to test it, more for the sake of just because than anything else. :D
 

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Looks good to me. About the only thing I would change is the oil pressure sending unit to be as sure as you can be about the oil pressure without using a wet gauge. However, if your lifters aren't clacking you likely have adequate pressure. I'd say you can modify away with confidence.
 

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Discussion Starter #5
Thanks for the responses.

I did remove all the spark plugs before starting the test but forgot to mention it.

I don't understand the how he could put 160,000 miles on an engine in 8 years either. The Mustang was not in the type condition that you would go driving it 20,000 miles a year.
 

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160,000/8years=20,000 miles/year. That is very easily do able for a daily driver, even if it is a 40 year old Stang.

I see no problem doing any of your mods, use it till it needs a rebuild.

As to the puff of blue, I agree that it is probably the valve stem seals. You could R&R them on the car...not worth all the trouble, but cheap.

Or, if it were me, I'd pull the heads for a Cyl Head rebuild job...OR look for a decent set of late model GT40 type heads (which if you look you could probably find for the same $ or even a little less than the cost of a valve job) and put it back together with your mods.
 

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Discussion Starter #9
I was thinking the compression and oil pressure looked good from the little I know. I was not sure about the vacuum or the plugs.

Does compression slowly degrade or just one day something fails and a cylinder drops?

Anyone see a problem with the numbers I posted?
 
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