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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.

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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.

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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.

Grey smoke continued to be an issue and I pulled the intake manifold today.  It looks like the bottom of some the intake ports are not sealing correctly.  The gaskets are FelPro 1228.  The intake is Edelbrock Torker.  Cylinder heads are the original 351C 4V.  I am trying to figure out how to avoid this again.  Earlier I found that the four 5/16" bolts were not tight enough even though the got 25 lbs torque at installation.  I appreciate your suggestions.

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The connection to the carb needs to be higher then the connection at the valve cover otherwise you will siphon oil into the intake manifold.

This is a common issue with Fords and their PCV system.

You also need a proper operating PCV valve in order to apply negative pressure (vacuum) to seal the piston rings.



The oil filler cap also needs to be vented as the fresh air source into the PCV system. If it isn't, for sure you are siphoning oil from the valve cover. Depending on the cam profile as far as how much idle vacuum it gives you, it is possible that you may need to restrict the fresh air intake.

I had to do that with my Weber set up. Webers aren't often run with a "closed" PCV. In order to maintain a decent idle vacuum, the air intake needed to be restricted.


As I said previously, it sounds like your rings are not completely seated and it may be related to a non-functioning system.


Put a clean white t-shirt over one of the exhaust tips while the engine is idling. See if there is oil residue on it.

You can get exhaust smoke from the carburetor as well. Usually the accelerator pump but it could also be that the float level is set just a little bit too high.


With a Holley carb and E85 fuel, you need to set the fuel level in the bowls about 1/8" lower then the edge of the site plug hole.

With the current E85 fuel, the Holley fuel level setting instructions ARE WRONG. You will be set too high if you follow them.

Last edited by panteradoug

The Edelbrock Torker intake is single plane and is some what of a tall manifold.  Once the Holley 750 mechanical secondary carb is in place it looks like the PCV intake port is well above the altitude of the PCV valve's location on the valve cover.

The PCV valve is new and seems to be working correctly.  However, it is difficult to ensure that the valve I purchased is correct and optimal valve for this engine.

The breather cap on the opposite valve cover is vented and self filtering.  I do not know the specs on this cam but it seems to produce good vacuum at idle.  When disassembling the intake I noticed that the brake booster tube was not tensioned properly and could have been a vacuum leak.  Perhaps my brakes will work better after this.

It looks like the floats on my carb are adjusted too high.  I have been suspecting such.  This Holley carb has built in sight windows.  I will lower the floats as you suggest.

I am letting the silicon sealant on the manifold dry overnight and will test this in the morning.  Testing is a little tricky because it involves watching the the rear view mirror (looking for smoke) and scrutinizing the dip stick for oil consumption.  I am hoping the new gaskets, increased tension on the intake manifold bolts, and lowered carb floats solve the problem.

Also, it is better to take off the deck lid when doing this type of work.  It is only the removal of a couple of bolts and hinge pins, and assistance from a helper to remove it.  Doing so makes reinstallation of the intake manifold easier and more precise.

The Edelbrock Torker intake is single plane and is some what of a tall manifold.  Once the Holley 750 mechanical secondary carb is in place it looks like the PCV intake port is well above the altitude of the PCV valve's location on the valve cover.

The PCV valve is new and seems to be working correctly.  However, it is difficult to ensure that the valve I purchased is correct and optimal valve for this engine.

The breather cap on the opposite valve cover is vented and self filtering.  I do not know the specs on this cam but it seems to produce good vacuum at idle.  When disassembling the intake I noticed that the brake booster tube was not tensioned properly and could have been a vacuum leak.  Perhaps my brakes will work better after this.

It looks like the floats on my carb are adjusted too high.  I have been suspecting such.  This Holley carb has built in sight windows.  I will lower the floats as you suggest.

I am letting the silicon sealant on the manifold dry overnight and will test this in the morning.  Testing is a little tricky because it involves watching the the rear view mirror (looking for smoke) and scrutinizing the dip stick for oil consumption.  I am hoping the new gaskets, increased tension on the intake manifold bolts, and lowered carb floats solve the problem.

Also, it is better to take off the deck lid when doing this type of work.  It is only the removal of a couple of bolts and hinge pins, and assistance from a helper to remove it.  Doing so makes reinstallation of the intake manifold easier and more precise.

It just seems SO unlikely that the intake and gaskets are leaking anything.

DO NOT over tighten the intake bolts. 20 lb-ft is PLENTY.  The end bolts have been known to snap off the ears of the intake manifold itstelf. Particularly the driver's side, left rear.

I'd recommend the M.E.Wagner set up. It isn't just for the adjustability but it is the only PCV that comes close to closing 100% at idle.

Unfortunately the "replacement" PCV's that are obtainable supposedly as original replacement are totally and completely trash.

In a situation like you are in, they just complicate matters.



IF you haven't already tried to eliminate the PCV from the car for testing, you should however there are other sources of oil getting into the intake system that are possible and one of those is valve guides.

NONE of the valve guide systems are 100% tight and in reality they shouldn't be because the stems do need lubrication.



In the past I have been in a similar situation as you are now and sometimes just putting up with the smoke for now and driving it clears up the issue.



Best that I can do for you at this point is wish you good luck and hope that this is all caused by something silly that was overlooked and an easy fix.

You wanna' see exhaust smoke? Watch one of these bonsai starts with a Weber set up. The exhaust throws absolutely everything out but bolts.

Thanks Doug.

I will likely get the ME Wanger adjustable PCV.

Also, I should have mentioned that three of the intake port walls in the cylinder heads were tacky with oil while the others were dry and clean.  The three ports were the ones with oil on the gasket face.  And the entire intake manifold was clean on the inside with no signs of oil.  Thus, it is kind of pointing to the gaskets at this time.

Steve, the only thing I can imagine which hasn't been covered is the possibility that the block, heads, or intake manifold were not machined correctly.  Your OP stated you got the car with the heads off, so you may not know exactly what work was done previously.  Your photo of the intake valley leads me to believe that the head and intake surfaces are not parallel.  Now you would think that would also be a big vacuum leak, but with a closed PCV system, it might not be enough to notice.  Just a thought.

I was wondering the same.  The Felpro gaskets are very thick and perhaps they are intended to help compensate for this type of issue.  The thickness of the gaskets may have worked against me.  During the current reassembly I noticed that I used thin washers on the the 5/16 bolts and they had deformed.  Perhaps this was from heavy torquing later.  In any case the gaskets and washers may have added to the problem by relaxing when everything got up to temperature and then shrunk after cooling.  It is now reassembled with new gaskets, clean surfaces, and thick washers.  So far, so good,  During this I found a likely vacuum leak in the brake booster hose connection.  And Doug has identified a likely carb float level issue and possible improvements in the PCV system.  When the car fired up today it sounded better and I could not detect grey smoke.  I drove it a fair amount without issues.  My fingers are crossed.

I have good news and bad news.   We ran the car today and it looked good at first and there was no smoke.  Then I ran it in first gear to red line and released the throttle in an effort to produce maximum vacuum in the engine.  The engine released grey smoke on left side only.  This is actually a step forward because the smoke had been coming from both sides.  Maybe the intake gasket slipped when installed.  I will pull the intake again and try to find the root cause.

Last edited by stevebuchanan

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