Hi guys,

Engine has 250 miles on it since being rebuilt.  I am working through issues with my tranny/govenor/modulator valve which, while taking a test drive last night, made me discover something about the engine.  I would it out to about 4500 RPM in first gear, then maintained that speed and RPM for a few seconds.  This caused a HUGE smoke screen behind my car.  I have never noticed any smoke at any other times, but I'll have to start paying more attention at all times and see if there are any other scenarios that cause it to smoke. Anyway, I am wondering if the high vacuum produced by the engine being at high RPM but at very low load is causing oil to be sucked somewhere that it shouldn't, or what.  Just in case it is related, when I re-installed the rebuilt motor (the Vette is an '81), I did not reinstall ANY emissions stuff, plus I went with a non-computer controlled carb and distributor.  So, it's a very basic, simple engine configuration.  The one thing I wonder about is that I did not install any form of PCV valve.  I simply installed a breather in each valve cover.

Any ideas on the cause of the smoke?

John,

I just had my engine rebuilt & the builder used chrome moly piston rings.  He told me that I should expect smoke until they break in & seat themselves.  I never asked how much smoke to expect or when.  Unfortunately my engine has 0 miles on it & it is still not in my car.

I would suspect that if oil was getting through the PCV, there should be some evidence of it in the valve or the hose.

Wish I could be more helpful..........Good luck,

Anthony

Hi guys,

Engine has 250 miles on it since being rebuilt.  I am working through issues with my tranny/govenor/modulator valve which, while taking a test drive last night, made me discover something about the engine.  I would it out to about 4500 RPM in first gear, then maintained that speed and RPM for a few seconds.  This caused a HUGE smoke screen behind my car.  I have never noticed any smoke at any other times, but I'll have to start paying more attention at all times and see if there are any other scenarios that cause it to smoke. Anyway, I am wondering if the high vacuum produced by the engine being at high RPM but at very low load is causing oil to be sucked somewhere that it shouldn't, or what.  Just in case it is related, when I re-installed the rebuilt motor (the Vette is an '81), I did not reinstall ANY emissions stuff, plus I went with a non-computer controlled carb and distributor.  So, it's a very basic, simple engine configuration.  The one thing I wonder about is that I did not install any form of PCV valve.  I simply installed a breather in each valve cover.

Any ideas on the cause of the smoke?

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first are you sure it is oil and not unburnt fuel ?

second..  you need to use a PCV...  you cannot use two breathers..  this does NOTHING at all.

the PCV sucks "smoky" fumes through the engine to burn them.  Also you should have the pcv on opposite sides and ends of the engine for the best results.  ie if the breather is on the passenger rear...  put the pcv on the drivers front.

I'm with Ben on the pcv valve, definitely needs to be there and configured in the way he stated. I noticed that you referred to tranny problems and mentioned your modulator. I would check to see if it's diaphragm is bad. There will be tranny fluid in the rubber hose connecting the hard line to the mod. This will be sucked in and burnt by the engine resulting in smoke. Check the plugs to see if they are rich to determin if oil or fuel is the problem.

Dave

Thanks for the input.  Can you help me understand the need for the PCV valve?  I was assuming that the breathers would allow any crankcase vapors to escape and keep pressure from building up in the crankcase.  If I run a line from one valve cover to a PCV valve and then to the under side of the air cleaner, I don't see the difference, other than the vapors being drawn into the engine to possibly be burnt.  Will the PCV setup create enough vacuum in the crankcase that it will help the rings seal better? (I've seen add-on vacuum pumps to do this.)  If that is the intent, I'm wondering if my setup would really provide much vacuum, as I don't run the standard air cleaner.  I am using an Edelbrock "Pro Flow" (or something like that) triangular shaped foam filter that is supposed to be such high flow, that I doubt there is much vacuum in the air cleaner itself.  Thoughts?

Thanks for the input.  Can you help me understand the need for the PCV valve?  I was assuming that the breathers would allow any crankcase vapors to escape and keep pressure from building up in the crankcase.  If I run a line from one valve cover to a PCV valve and then to the under side of the air cleaner, I don't see the difference, other than the vapors being drawn into the engine to possibly be burnt.  Will the PCV setup create enough vacuum in the crankcase that it will help the rings seal better? (I've seen add-on vacuum pumps to do this.)  If that is the intent, I'm wondering if my setup would really provide much vacuum, as I don't run the standard air cleaner.  I am using an Edelbrock "Pro Flow" (or something like that) triangular shaped foam filter that is supposed to be such high flow, that I doubt there is much vacuum in the air cleaner itself.  Thoughts?

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the PCV is required to create the air flow.  think of the PCV like running an attic fan in a home.  you have to open a window as far away from the fan as possible to get the air to flow through the whole house.  The PCV is a controlled vacuum leak.  Its intent is to pull clean air into the crankcase and pull the oily air into the carb to be burnt.

the two breathers are like having open windows..  air can get out..  but without a breeze..  nothing moves.  Especially since the oily air would be heavier than the ambient air and would have no incentive to rise out the breathers.

Ches, Summit and various others make filtered valve cover breathers to eliminate the line to the carb. I have a set up like that and the oil fill in the valve cover serves as the breather. No hose to the air cleaner is required, just a vac line to the carb for the pcv valve in the opposite side.

Dave

Ya know, I just had a wierd theory come to my head. So, I tried this today, I took mine up to over 55k, and noticed some smoke out the pipes. I haven't had it up that high in a long time, but was curious about this. Now, I replaced the valve seals a while back, and the cylinders didn't leak down very much, so I have faith in the rings. BUT, now the theory. I don't have baffeled valve covers, so the PCV valve sits right there in the mits of a lot of oil being thrown around. Once the engine levels off at rpm and the vac comes back up, what't to say the FOG of oil in the valve cover isn't getting sucked in the system? Is it possible? I have some Summit bucks to spend and now with Hot August Nites in Reno, Summit has a lot of sale prices. Thinkin about a new set of baffeled valve covers. We'll see

Dave