351C smoking under wide open throttle

rdorman · #1 (**permalink**) 06-26-2002, 12:17 PM

During the dyno run on Sunday (the 'other' cleveland owner!) I noticed black smoke coming from the pipes. The amount of smoke grew as the RPMs grew with a nice big puff from the drivers side pipe at about 6000. The drivers side shows less smoke across the entire RPM band.

The car is running great and posted some pretty respectful numbers concidering the mild parts (324HP, 354 torque). The engine has 6000 miles on it and does not generally use oil. The consumption driving the car back from Arizona was high but I attributed that to a newer engine at the time (3000 miles when the trip began). Now I am begining to wonder if it was what I saw on the dyno. The engine ran at about 3900 RPM for 2000 straight miles.

I thought about the car running rich. But the dyno showed that the engine was actually lean throughout the whole run, 14.0 to 1 or more. With one spot at about 2600 RPM as lean as 17.0 to 1(any ideas on this one, holley 1850s out of the box).

Then I thought about oil build up in the valve covers being pulled into intake runner by the valve seals. The car does run a lot of vacuum, 16 at idle 22 at cruise.

Then I thought about it sucking oil into the intake from the lifter gallery. It does have Dexcool in it (but not for long) and I have read the posts about Dexcool and Felpro gaskets.

I thought about rings but I am doubting that very much since the engine is fresh, but I will be running a leak down test on the engine.

The crankcase is ventilated to the atmosphere on both valve covers.

Looking for ideas and similar experience!
Thanks

Mr.Fixit · #2 (**permalink**) 06-26-2002, 12:40 PM

That motor will eat itself for lunch with such a lean fuel ratio. Fix that now then worry about the smoke.

CobraEd · #3 (**permalink**) 06-26-2002, 12:45 PM

Black smoke is ALWAYS fuel (or burning rubber???) Bluish grey is oil, and white is coolant.

Ed

Jim Colman · #4 (**permalink**) 06-26-2002, 12:57 PM

rdorman,
How do you know for sure what your A/F ratio was? How does the dyno operator measure it? If he places a "sniffer" into your exhaust it could be fooled if you have any sort of exhaust leak. I know on my 351C, I had a leak where the headers joined the side pipes. I would think that the only true way to measure A/F ratio is to install an O2 sensor in the header itself.

Anyway, I agree with CobraEd. It sounds like you're running too rich if you have black smoke. BTW, did you know that brake fluid will produce white smoke? (don't ask how I know)

Cheers
Jim

rdorman · #5 (**permalink**) 06-26-2002, 01:03 PM

The dyno guy called it blueish grey. I must have been thinking about the puff at 6000, it was black. I am going to be working on the carb in the very near future. What confused me most was the big jump in lean at about 2600. It went from 14.0 to 1 at 2200 to 17.0 to 1 at 2750 and didn't return to 14.0 to 1 until about 3400.

At full throttle and those RPMs I would have thought we would be into the mains and I would imagine the power valve would be open. Sooo, how to correct the lean condition in the RPM band. Perhaps the secondaries are opening to slow? Or there simply is not enough fuel from the transition curcuits.

Hoping you all can help!

rdorman · #6 (**permalink**) 06-26-2002, 01:14 PM

Jim and Ed. While the dyno person said it looked blueish grey, it looked more like black to me. Jim your point about the sniffer could be valid. If I had an exhaust leak where the headers join the side pipes I doubt I would hear it! I do remember when the GT-40 was on the dyno the kept saying it was lean. Each time they richened up a bit. By the last run it sounded as though the car was going to barely run. Maybe he was getting a false reading.

Hmmmmmm, now where is my plug socket and magnifying glass?

Jim Colman · #7 (**permalink**) 06-27-2002, 01:13 PM

rdorman,
I think looking at your plugs is going to give you the best indication of whether or not you're too rich or lean. All that black smoke sounds like gas to me. You did say that you were using oil, but you could be losing it through valve seals, like you said.

My Cleveland was built in AZ and, due to the fact that it sat for a while in the dry air, I had to replace every valve seal. I was going through a quart of oil every hundred miles or so until I replaced the seals.

Cheers
Jim

Mr.Fixit · #8 (**permalink**) 06-27-2002, 01:13 PM

Look at your sparkplugs, then you'll know if ou are as lean as the sniffer says. I doubt it though, it wouldn't run very well at that A:F Secondaries opening does not affect the ratio, that is determined by orafice sizing. If the motor was that lean it would be "popping" if it's way rich you'll smell it. Your headers would be glowing cherry red as well at 17:1

rdorman · #9 (**permalink**) 06-27-2002, 01:26 PM

Jim, was your cleveland built by Duffee?

Jim Colman · #10 (**permalink**) 06-27-2002, 02:29 PM

Rick,
You've got mail

dscott · #11 (**permalink**) 06-28-2002, 11:23 AM

I just finished a Boss 302 which is close to a 351C. The problem was smoking at idle, under power and oil consumption. The 351C will draw oil into the intake ports if the intake gasket is bad. This is what our problem turned out to be. This was a fresh motor but the gasket started leaking right away. If you think there is any blue smoke I would check the intake gasket. If the problem is carburation you shouldn't be using any oil. The way rings seat now days you shouldn't ever have an oil consumption problem beyond normal, especially on a new engine.
Don

rdorman · #12 (**permalink**) 06-28-2002, 12:52 PM

What caused your intake problem? Dexcool? Shaved heads but not shaving the manifold? Unknown? Sort of leaning in the intake direction but I will be checking all possibilities.
Thanks

Mr.Fixit · #13 (**permalink**) 06-28-2002, 01:02 PM

You should also replace the intake end seals with just a bead of silicone instead of the seals included with the gasket set. After decking, the intake wants to sit down lower, but the end seals are too thick and can push the intake off the gaskets which seal the runners, allowing oil to get drawn into the runners from the lifter valley.

dscott · #14 (**permalink**) 06-28-2002, 02:24 PM

It wasn't a coolant problem. I used the Fel-Pro gaskets with the small bead of silicone around each port. It looked like when I torqued the intake the gasket split at the base of the port around the silicone. The small crack was allowing oil into the intake port. Don't know why, the 2nd gasket was the same and it's been just fine. I suppose it could have been an old gasket or maybe just bad.
Don

PS. Mr. Fixit makes a good point. I never use the end gaskets, always just a good bead of silicone.

rdorman · #15 (**permalink**) 07-08-2002, 09:06 AM

I pulled the intake yesterday and the gasket being used was the stock Ford pan. There where oil trails on the pan from the bottom of the ports into the top of the pan. About an ounce of oil in the top of the intake pan. The intake was as clean as the day it was made but downstream in the head the ports where oily and some build up of oil on the back of the valves. Even the intake manifold bolts where oily.

So, the oil problem was the intake gasket. I have not refired the engine yet but the problem seems pretty obvious.

I cut the sides off the stock pan so that I could still use it to keep the oil off the bottom of the intake and installed with a good set of Felpro gaskets. I did not use the end rails, only red RTV. Made a few 'laps' around the intake going back and forth from the middle out to ends until all bolts stayed at 30 foot pounds.

I can't wait to see how it runs with out the vacuum leak and oil being sucked into the combustion chambers! The two had to kill a few horsepower and I was already pleased with the Dyno run at the fling (still knowing that there is more power to be found). 323 HP, 354 torque.

This may also explain why the engine was a bit lean don't you think?

Thanks for your help!

Rick