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On Sunday I took my 74 Pantera out for the day with OC Panteras and put about 100 miles on it with a lot of starts, stops, and a few spirited runs. While it worked well overall, I learned that the car outputs some grey smoke primarily during deceleration. I could not see smoke in the mirrors except one time when I accidentally lugged the car.

The engine has .030 over pistons, a hydraulic roller cam, adjustable roller rockers, big pushrods, and stainless valves.  The cylinder heads are open chamber and probably original to the car.  I purchased the car with the cylinders heads off due to a blown head gasket.  There is no lip at the top of cylinder walls indicating that it does not have high miles since the engine work was done.  I took the heads to a shop and they did a complete valve job including new seals prior to reinstalling them.

I am trying to figure out the source of oil that is being burned. Typical sources are worn piston rings, worn valve guides and/or seals, and malfunctioning PCV valve. The inside of the intake manifold is clean which tends to rule out PCV.

Someone suggested a compression test and the results are below.  The test was done with the engine warm, all spark plugs removed, throttle wide open, and ignition off.

I appreciate any suggestions from you guys.

08F8596B-D406-4A1C-BE13-A5D5E45BA485

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Last edited by stevebuchanan
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The valve job was done with Viton clip-on seals.

Grey smoke was coming from both sides and that made me suspect a bad seal from the intake manifold gaskets.  I re-torqued the intake manifold and upon startup it still smoked but that could be residual oil.

I will be mounting a camera that records exhaust output in an effort to better understand this issue.

I am guessing the engine has more than 10,000 miles on it and the rings are seated (maybe even a little worn based the compression test).

I don't think the engine was smoking at startup prior to the Sunday outing.

As John suggested, I will pull the intake manifold and inspect and replace the gaskets.

Again, smoke is coming from both sides.  Here is a picture of spark plugs.

C366F530-6430-4856-AED1-A4E6C0039511

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The problem might be fixed.

I reinstalled the spark plugs and fired the engine prior to pulling the intake manifold.  To my surprise, there was no smoke!  As I mentioned earlier, I re-torqued the intake manifold bolts.  When doing so, I found the four 5/16 bolts were not very tight while all of the 3/8 bolts were already snug.  Tom Monroe's book for the 351C says torque for the 5/16 bolts is 21-25.  I have been using 25 pounds and have always thought it was a little light.  This time for the re-torque I simply muscled them down until they felt snug.

Spinning the motor for the compression test may have purged excess oil that had been hanging around prior to re-torque of the manifold.

Last Sunday's outing was the most demanding the car has done since the cylinder heads were reinstalled and may have revealed the problem with the under torqued bolts.

This Saturday our club has another event at Hillbanks Motorsports in Irvine and I will be taking the car there.  It should be a good test.

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