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Discussion Starter #1
Hi All
Looking at buying a 1972 Mustang fastback. I had the pre-purchase motor vehicle inspection compression test done on the 429 engine (unknown origin - Engine No. 1J227610) in it. The average psi over all the cylinders was 125psi. Is that low? I’ve been told it is and that the heads might be worn or the head/inlet gaskets might be compromised. There was also a lot of brown sludge in the radiator reservoir. It wasn’t oily but I can’t explain its origins?

Any help you can give me on my enquirers would be truly appreciated👍
Cheers
Carl
 

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What is your altitude?
Cylinder head casting number below valve cover rail between 2 and 3rd exhaust port?


At sea level a low compression 460 with stock cam and straight up cam timing will typically crank at about 135 to 145 psi. With a mild cam I've seen them down at 125#


SJ
used 2b RHP
 

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I would say that the fact that they were all the same is more important (good) than them being 125 psi. More would be better for off idle torque and low rpm fuel economy, but much of that (especially if it's due to a larger-than-stock cam being installed) can be corrected for with a proper timing curve, which is to say lots of advance at idle while still not having excessive timing at higher rpm.
 

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Discussion Starter #4
Thank you all for your support and replies to my questions which I truly appreciate:)

Taking on board the consensus of what has been said I’ve done the following Compression tests:-
Hot Engine - Compression Test Results (PSI)

Cylinder 1

Dry - 135

Wet - 150

Cylinder 2

Dry - 150

Wet - 155

Cylinder 3

Dry - 150

Wet - 150

Cylinder 4

Dry - 150

Wet - 150

Cylinder 5

Dry - 150

Wet - 150

Cylinder 6

Dry - 150

Wet - 165

Cylinder 7

Dry - 150

Wet - 165

Cylinder 8

Dry - 150

Wet - 150

Cold Engine Compression Test Results (PSI)

Cylinder 1
Dry - 125

Cylinder 2
Dry - 120

Cylinder 3
Dry - 120

Cylinder 4
Dry - 135

Cylinder 5
Dry - 135

Cylinder 6
Dry - 117

Cylinder 7
Dry - 135

Cylinder 8
Dry - 135

Are these hot engine compression test results good for a 1971 - 429 Engine or are there some signs of the head gasket being compromised and/or valve problems - worn heads. In other words should I dump and burn and forget about buying this Mustang and try to find one with a healthier and stronger Engine or is this one good enough within the acceptable compression ratio limits for this big block Engine.
Any further feedback upon reviewing these results would be great!

Cheers

Carl👍
 

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The Ford truck and car shop manuals say "...compression pressures are considered normal if the lowest reading cylinder is within 75% of the highest". When I did my 460 with 60K miles on it I got 4 cylinders @ 150, 1 cylinder @ 145, two cylinders @ 125, and one cylinder @ 118. The engine was at normal operating temperature. No oil was added. The engine you are looking at doesn't seem to have any serious problems from a compression standpoint.
 

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Which cylinder heads are on your engine???


SJ
used 2b RHP
 

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Discussion Starter #7
The Ford truck and car shop manuals say "...compression pressures are considered normal if the lowest reading cylinder is within 75% of the highest". When I did my 460 with 60K miles on it I got 4 cylinders @ 150, 1 cylinder @ 145, two cylinders @ 125, and one cylinder @ 118. The engine was at normal operating temperature. No oil was added. The engine you are looking at doesn't seem to have any serious problems from a compression standpoint.
Thanks for your reply👌
Cheers
Carl
 

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Discussion Starter #8
Which cylinder heads are on your engine???


SJ
used 2b RHP
The mechanic who inspected the vehicle didn’t get those all important stamps for the heads. There is the cast number “34” next to spark plug 1 and the engine no. Is 1J227610. That’s all I have at this stage. The mechanic is having another look on Saturday. What do you think about the hot engine dry and wet results?
Thanks Mad Porter for all your help😎
Cheers
Carl
 

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The mechanic who inspected the vehicle didn’t get those all important stamps for the heads. There is the cast number “34” next to spark plug 1 and the engine no. Is 1J227610. That’s all I have at this stage. The mechanic is having another look on Saturday. What do you think about the hot engine dry and wet results?
Thanks Mad Porter for all your help😎
Cheers
Carl

The psi readings are fairly consistent and indicate that larger chamber heads might have been installed.
Original 1971 engines in good condition with a stock cam typical crank at 180+

If there are no casting numbers at the location I specified then the heads are later large chamber.

Have you lifted the valve covers? What style rocker arms?


SJ
used 2b RHP


.
 

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Discussion Starter #10
The psi readings are fairly consistent and indicate that larger chamber heads might have been installed.
Original 1971 engines in good condition with a stock cam typical crank at 180+

If there are no casting numbers at the location I specified then the heads are later large chamber.

Have you lifted the valve covers? What style rocker arms?


SJ
used 2b RHP


.
Hi Mad Porter

Thanks for your ongoing support in your responses to my questions. You’re Right! As you suspected. I had the inspection mechanic look around the locations as you specified where the head casting stamp might be and there was nothing. He also looked all around below the valve covers around the entirety of the heads and still nothing:/ If larger chamber heads have been thrown on is that necessarily a bad thing to the performance and longevity of the 429 Engine? And would they be just heads from another 429 they’ve slapped on. I can’t understand if they are heads from another 429 why those heads wouldn’t have some sort of stamping on them? The engine no. Being 1J226170, thanks to PISG for deciding it for me, is a 1971 block from Los Angeles could they still put on heads from a later year or would they have to be from the same year?

Any further help on this would be greatly appreciated!
Cheers
Carl
 

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Early small chamber castings utilize the 18 mm plugs with a 13/16" hex.
Later heads utilize the 14mm plugs with taper seat and 5/8" hex. That will answer your question as to chamber size.

Not necessarily a bad thing excepting the loss in static c/r and torque.

Definitely a regular fuel engine.


SJ
used 2b RHP


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Discussion Starter #12
Hi All
Looking at buying a 1972 Mustang fastback. I had the pre-purchase motor vehicle inspection compression test done on the 429 engine (unknown origin - Engine No. 1J227610) in it. The average psi over all the cylinders was 125psi. Is that low? I’ve been told it is and that the heads might be worn or the head/inlet gaskets might be compromised. There was also a lot of brown sludge in the radiator reservoir. It wasn’t oily but I can’t explain its origins?

Any help you can give me on my enquirers would be truly appreciated👍
Cheers
Carl
Carl
 

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Registered
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Discussion Starter #13
Early small chamber castings utilize the 18 mm plugs with a 13/16" hex.
Later heads utilize the 14mm plugs with taper seat and 5/8" hex. That will answer your question as to chamber size.

Not necessarily a bad thing excepting the loss in static c/r and torque.

Definitely a regular fuel engine.


SJ
used 2b RHP


.
Hi All
Looking at buying a 1972 Mustang fastback. I had the pre-purchase motor vehicle inspection compression test done on the 429 engine (unknown origin - Engine No. 1J227610) in it. The average psi over all the cylinders was 125psi. Is that low? I’ve been told it is and that the heads might be worn or the head/inlet gaskets might be compromised. There was also a lot of brown sludge in the radiator reservoir. It wasn’t oily but I can’t explain its origins?

Any help you can give me on my enquirers would be truly appreciated👍
Cheers
Carl
Carl
 

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Discussion Starter #14
Ok I’ll check the spark plug sizes with the mechanic. Also noticed weld marks on the sump and made enquirers about this. Just been told that the sump may have had to be modified to fit into the 72 Mustang fastback because the 429 engine might have come out of a truck. The deck is also taller so the bonnet has to be modified.
Is there any significant differences between 429 truck and 429 sedan engines in terms of quality, longevity and performance?
Thsnks
Cheers
Carl
 

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The vin stamp you posted is passenger car.

SJ
used 2b RHP
 
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