Rebuild or not?

Booboo

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I have a set of completely rebuilt PI heads with +1mm Stainless valves, BTR springs, MMR guides and seals, and XE262AH cams. I was planning on putting them on a fresh bottom end but am now thiking my existing NPI bottom end might be in good enough condition to use. It's a 1997 Mustang GT with about 120k miles. I just did a compression and leak down test.

Compression test results are.

1 - 155
2 - 140
3 - 155
4 - 152
5 - 145
6 - 145
7 - 165
8 - 152

Leak down test has all cylinders at about 7% loss with the exception of cylinder #2 that was closer to 10%. There was some loss in the spark plug holes from the adapter I had made to reach the deep spark plug treads on the NPI heads so loss is probably closer to 5% ???. I had some issues with cylinder #2 and had a hard time getting it to seal up and give me a consistant reading. I had to move the crankshaft arround to get it to seal up, so I don't really trust the results. The cooling system pressurized on most of the cylinders when testing. No water in the oil, no smoke out the exhaust. Could it be the intake manifold? Or is it a head gasket?
 

96blak54

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Im a little confused. The intake manifold question has me thrown off, but yes i agree with baddass98svt your equipment and components must be repeatable to be confident in the results.

Anyhow, take the lowest reading cylinders piston to the bottom and squirt(squirt is key word, you want oil on the cylinder walls) some oil into the cylinder, rotate the crank a few times to cycle the piston and then do a compression test. If the psi comes up strong, its the rings/bore relationship. If the reading remains relatively the same its the valves leaking. Could be a combination of both also. Its not uncommon for modular valves not to seal up when seated especially pi heads. Its theorized that the valve seats spin a few times before actually taking a seat, therefore reducing sealing valve to seat. Most modular heads that ive torn down show this alot on the exhaust seats.
 

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