Until recently when I reworked the 700r4 tranny governor, I could never get the car past 4,000 rpms or so. Now, full throttle will provide up to 5,600 or so rpm blasts! :D :D
Problem is, when I get upwards of about 5,000 rpms or so, huge clouds of smoke start coming from tailpipes! Obviously, not good! So my question is, what could this be? The car shows no signs of exhaust smoke under any other driving conditions. I'm pretty certain it is oil as the smoke looks bluish-grey from the rear-view mirror. I'm leaning towards either a PCV valve problem (ie. bad... tho fairly new, or possibly the wrong one) , or sucking oil in from under the intake. But would it not suck oil from under the intake at other times as well??

Thanks for any suggestions,
Bill C.

Bill,if your intake gaskets,pcv,rings check out ok then you could have a defective modulator on your trany allowing atf to be sucked into your intacke via a vacuume port which i have seen a few times over the yrs.

Scott

Ain't no modulator on a 700R4. Your theory would be fine with a TH350.

Does it do this in any gear at higher RPM's? In neutral or park?

well, Chad, since I don't have a local race track, this is only from street driving and pretty much only get to those RPMs in first gear! By the time I'm half-way thru second gear, I'm hitting about 65 mph, so time to let off! I haven't tried it in park yet... sure don't like revving the motor that high in park! Guess I could try tho?

Scott, do you have any suggestions on how to test the intake gaskets? I would think they would leak all the time, not just at high rpms if that were the case, but short of pulling the intake, how could I test? Also, is there any way of testing the PCV valve?

thanks,
Bill C.

Make sure there is a baffle where the aircleaner side of the PCV system hooks up. At higher RPM there is a lot more oil splashing around and more vacuum draw at the aircleaner, It can definately cause your problem if there isn't some sort of a baffle to keep the oil in the valve cover.

Bill,ooopps on forgetting the 700r4's dont have a modulator,sorry about that.

Back to your intake gasket question,if in fact your gaskets are leaking they will do so all the time but may not be leaking enough to adversly affect your engine performance at this time.
What brand/type of intake gaskets did you use?

You wont always see a lot of smoke because the oil can pool up somehwhat at times and when you wind it up to the higher rpms this will cause the oil to be sucked out of the intake directly into your motor and out the exauhst.

I had this very thing happen to my 396 with the felpro perf intake gaskets 1212,they are made of a hard/slick material that does not crush/seal well and are leaking.

I forgot if you have a bb or smb but felpro makes the same perf gaskets for both and tha same applies. I have read other posts with this same problem in the recent past too but keep in mind this is not the only place where oil burning problems can come from.

Unless you have a bad enough intake leak to affect your engine perf they can be hard to detect. You could try(with the motor warmed up) to spray some carb cleaner into your breather holes in your valve covers one at a time with the other one blocked when you do this and see if the idle increases slightly for a few seconds which would indicate an intake leak.

Again other things like pcv,ring seal,very bad valve guides/seals can cause this much oil smoke like describe. Another suggestion would be to take the carb off and look for oil,if resent then clean out the oil as best you can and re-install your carb,if oil is not present at all then the intake is less likely your oil source but could still have a very small leak that escapes you but still not likely at this point.

Now if you did see oil in the intake and cleaned it out then after the carb is re-installed you could unhook your pcv from your carb/intake vacuume source and run the motor on the street for a while if car is on the road and see if the motor still smokes after giving it enough time to suck up more oil into your intake. If no smoke its your pcv sucking up the oil and go from there,if it still smokes and you find more oil in the intake again(use a mirror over carb with throttle plates wide open and a flaslight to do this) then its time to remove it and check for flatness on the gasket surface & cracks,were the block/heads machined not allowing the intake to seat proprerly,ring seal (leak down check),guides/seals,etc.

let us know how you make out.

Scott

At WOT there is no vacuum at the PCV valve so the valve itself isn't the problem.

What carb are you running? If a vaccuum, maybe your secondaries are too rich and not opening at lower RPM (only a guess).

Ignition could be cutting out at high RPM and not firing all cylinders (also only a guess). Would probably show a power drop off.

what about oil pooling at the back of the heads and pouring through the rear valve seals.

Would the oil drain back issue allow enough oil at the top of the heads be enough to have it suck through the guides and seals?

IS your PVC hooked to the air cleaner or to the back of the carb?

Which is the right place for it to be hooked up?

Back of carb vacuume port or to the air cleaner.

what color smoke,blue or black

Bill, have you confirmed what the engine timing is at 4000+ rpm?? ( careful, isnt real healty to rev a freewheeling motor up quickly.)

Heya' Bill,

My version of basic troubleshooting on this one:
You said that there is no smoke at any rpm below 5000. If you had bad valve guides and/or seals, you would see smoke at any rpm and moderate-to-heavy throttle opening, and, at start-up following a hot-soak period. If the piston rings were not controlling the oil as normal, the oil smoke would gradually worsen in any low rpm to high rpm situation and would be progressively thicker with increased load. I tend to doubt that it might be the intake gaskets because you say that "huge" clouds of smoke come from the exhaust. An intake gasket that would allow that much oil to be leaked into any port would most likely show at least some oil smoke at idle and most certainly at any high vacuum situation.
I think that your valve guides, seals, rings, and gaskets are all OK.
My opinion is that there is oil accumulating in the passenger side valve cover and, more specifically, in the rear half of the cover. My logic being that the only two common things that coincide with the smoke are 5000-and-up rpm and the rearward force of acceleration.
The PCV system does close (effectively) at zero vacuum but CAN open again if the engine begins to pull vacuum at higher rpm. The closed position of the PCV valve would tend to force any positive pressure in the crankcase OUT the fresh air tube which is (should be) attached to the air cleaner housing. This situation would also tend to move any oil/oil-vapor through the fresh air tube and into the carburetor venturiis.
IF, this is the case here, the elevation of oil in the passenger side valve cover due to excessive volume (high rpm and predictible/repeatable results) and the rearward force of acceleration are causing the smoke problem.
Try cleaning the air cleaner housing to remove any oil film present and duplicate the high-rpm w/smoke situation. Examine the inside of the air cleaner housing immediately. If you find a fresh/wet film of oil around the fresh air tube opening, you have verified the source of the oil.

If not, then, as usual, I am clueless.

Good luck,

Louie

At WOT there is a fair amount of vacuum at the aircleaner portion of the PCV system. Like Louie said there also is a lot of oil in the valve cover. We had a lot of problems with a pan-u-vac system until I figured out the oil was comming directly out of the valve covers and put baffeled breathers on it. No more trouble.

Ok, guys, Sorry I haven't been around for the last day or two... been busy installing a new wood floor in the kitchen! I'll try to answer some questions.

First, the carb is a Holley 600 Vac sec, 80457. The PCV valve is hooked directly to the carb as I am running a round, open element air cleaner. When I pull the line off the carb, the inlet looks a little wet with oil and also, there looks to be oil seepage from around the PCV valve grommet...

The valve covers are the GM chrome ones, and they do have baffles in them. I'm not sure of what brand the gaskets are, they came in a kit from the machine shop. FYI, the engine is a 355 SBC.

As far a being rich, it is only a little rich as I monitor engine O2 levels with a guage and have it pretty dialed in. I do not notice any loss of power when this happens. Again, the smoke is blue-grey, so I'm pretty sure it's oil.

Louie,
Long time no hear, hope all is well!
I can't guarantee there is no smoke at lower rpms, but sure nothing noticable like this! It's like someone flips a switch or something and just pours oil in the motor... it just suddenly starts and it is a LOT of smoke! Then you let off and it goes away almost as fast! The oil pooling under the cover sounds like a possibility, is there any way to fix that? How much oil could actually be pooling? The PCV valve is actually located in the rear hole of the passenger side valve cover... could that cause a problem? The carb hookup is on the bottom of the passenger side of the carb, so the distance is much shorter.

Also, I realize there is no vacuum at WOT, but could the pressure be building up inside enough to cause the oil or oil mist to be forced out the PCV valve? My suspicion is that's where it is coming from, but keep the ideas coming!

If it doesn't snow tonight/tomorrow, then I'll try to unplug the PCV valve and try it without it.

Bill C.

Things here are just fine, thank you for asking Bill. You have your PCV valve installed opposite of the factory location which is usually the front end of the driver's side cover. I would put it there because it is much less likely to be flooded/surrounded by oil in the situation of hard acceleration and high rpm.
You haven't really made it clear as to whether or not you have a fresh air tube in the other valve cover, or, at least a breather open to atmosphere. You have to have some type of inlet for air into the crankcase if you are using a PCV valve system.
The quick fix would be to swap the valve covers side-for-side. You could easily fabricate a nice looking metal line using 3/8" brake line tubing to route the PCV vacuum to the rear of the carb. I usually do this to eliminate long stretches of ugly black 3/8" vacuum hose. Just use short pieces of rubber line to connect the hard tubing to the carb and to the PCV valve. Spray the line with high-heat Krylon silver and it won't turn to dull metal brake line grey.
Since you mentioned that your PCV valve is at the back of the passenger cover it pretty much nails the cause of the smoke.

Good luck,

Louie

Also, you might try and use a different PCV.( try one for a 1969 435 HP Corvette app) But Louie seems to have nailed it.

Thanks again Louis and Gene... I'll try the new PCV valve (you don't have a part number do you Gene?) and moving it to the drivers side front. FYI, sorry I left out the other detail, but yes, I do have a breather element on the other valve cover...

Bill C.

SO having the PVC going into the back of the carb is OK or best in the air cleaner? My big block smokes but at about all speeds. I think it is rings but they have less than 2000 miles on a full rebuild,new pistons, rings, guides, seals, etc. But it has great oil pressure and I'm wondering if it could be sucking it in through the PVC especially at the rear of the carb instead of being hooked to the Air cleaner.

Any comments?

Just try taking pvc off and plugging the carb and give it a test run to see if it smokes. Then this will tell you if it is pcv or not. Gary

Thanks guys, I'll try it as soon as the snow stops and it's safe to drive again! One thing that sucks about owning fast cars... they don't do well in the snow! It has been snowing for about 2 days now and supposed to continue thru tomorrow! Got aver 12" so far and still going, but we need it because of the drought!

I'll let you know when I get the car tested...

Bill C.