I sporadically have smoke coming from my tail pipes and can't figure out where to start troubleshooting.

I have a built NA LS1 in an old Corvette that I autocross. The engine is from a 2001 Camaro and was fully rebuilt about 6 years ago: machined the block, new forged rotating assembly stroked to a 383, cam, heads, bearings, etc. It has maybe 7,000 miles on it during that time. It's strong but nothing crazy. The engine has the stock 4th gen Camaro oil pan with an Improved Racing baffle, IR crank scraper, 04+ LS6 PCV setup, and I run 6 quarts of Amsoil 10w-30.

About a year ago, somebody came up to me at an event and told me that smoke was coming from the car at a few places on the course. Two more people have said the same thing since then at different events. It was never enough for me to be able to see from inside and the car feels completely normal power-wise. I finally got it on video and sometimes it looks like oil smoke (white/blue) under hard acceleration while other times it looks like it's maybe running rich, also under hard acceleration (darker smoke). I think I smelled oil a couple of times at a spot where the track crossed back over itself but don't put too much stock in that.

The worst spots were taking off from the start and after a long sweeper spent at minimal throttle, otherwise I couldn't really see anything out of the ordinary in the video. After a run, the next time I start it up it'll smoke for a few seconds then clear up. The smoke comes from both tail pipes which means it's coming from both cylinder banks since the car doesn't have a crossover pipe.

I can't replicate the smoke at all on the road, even with relatively aggressive driving (for a public road) and WOT acceleration runs. Zero smoke of any color at any time, which gives me hope that it's not rings. Same goes for other parking lot venues. It's only when I race at this specific airport venue that's high speed and high grip.

There are no traces of wet oil in the tail pipes but there is a ton of dry carbon. Enough that it'll leave black patches on the ground from idling in one place after just a couple of minutes. It only does this for maybe 2-3 starts after an event then it stops leaving black on the ground. I assume it's just clearing out residual in the pipes at that point.

Maybe valve seals but it's weird that it doesn't do it on the road at all. Could oil sloshing do this, even with the baffle? Sticking injector(s)? Anything else I should consider?


Lighter smoke near start line:


Darker smoke near end of lap (hard to see):


Smoke at start up (not a cold start):

 

GM was known for not being able to put round bores in LS engines. Could just be blowby or it could be a bad seal.

 

I would do leak down and compression tests. Sounds a lot like a valve stem seal with the motor in a high vacuum state in decel and hard corners ?
Only out one side, so I guess it has true duals ? Makes it a fuzz easier checking only one side.

 

To add to the above, these plastic intakes get heavily oil soaked on the inside from the PCV setup….even with a catch can sometimes. Pop your air intake tube off the front of the throttle body. Open the throttle body fully and look through it with a good flashlight. If it’s bad, you can see oil puddled in the intake floor. I’ve pulled intakes off of good running performance engines, and had oil running in the shop floor from the intake. Worth a look for a starting place.

 

No argument there, but the block was machined when I rebuilt it so I assume they're as round as they can be.

Yeah those tests are in my near future. Your theory makes sense with high vacuum scenarios.

Also yes to true duals. The smoke is most often coming from both but it's not always even between the two.

Can confirm. When I removed the original PCV system the intake runners were completely coated in oil. That was a big reason why I switched to the LS6 PCV system. PCV was my first thought as well, but when I pulled the PCV line going into the intake it was bone dry on the inside. I'll take a more thorough look inside the intake though.

 

Never assume any machining operation is correct. If you really want to know, you must check it. In this case, it would be a good thing to have the shop show you how round the bores are. They may have a readout of what the bores measured. They also may balk at inspecting them with the torque plates in place, because that would entail extra time retorquing them in place. Hopefully the machinist wrote down, or digitally entered, the data for each cylinder......

 

In the 20 minutes of spare time I had last night I pulled the plugs and intake. All 8 plugs had oil on the threads and the throttle body had a small amount of oil pooled there too. Looks like the next part going on the car will be a catch can.

 

I'd get a Mighty Mouse or Motion Raceworks can. The mighty Mouse has a check valve and operates as a pcv valve. Also get the updated Dorman 264-969 drivers side valve cover. It's got improved baffling and a fixed orifice.

 

So is the PCV in the stock ls6 configuration then with the same small line to the intake tube? You will want more ventilation on a stroker, short piston deal than stock that's for sure. In some cases you might be expelling oil out the blowby tube/s under load which would make it's way to the front of the TB.

 

Thanks for the recommendations, I'll look into those. I hadn't heard of the new valve cover it sounds like a worthwhile investment.

Yes the PCV is in the stock LS6 configuration. Valley cover -> intake, passenger valve cover -> throttle body, driver valve cover capped. How would I go about increasing the ventilation on this setup?

 

.
. BEST, Effective way to avoid engine oil contaminants, blow by contamination, and pressurized crankcase is ATMOSPHERIC VENTING of crankcase gasses. Omit the PCV valve, remove the fixed orifice(if equipped) , and stuff a 3/4 inch inside diameter hose in the drivers side breather port- DRILL if necessary.

About 5 feet of hose from rear rocker cover port will route up and OVER the brake master cylinder, back down the left side frame rail, and secure the hose END about an inch and a half below frame rail IN THE FREE AIR slipstream.

Remove right side rocker cover hose hose and CAP the throttle body breather port. Run a short length of 3/8" ID hose from passenger valve cover port to a cheap 3/8" push in hose mount breather filter- $12 dollar chinese special from ebay will work just right.

At any road speed above 35 mph you will be pulling VACUUM on the new Road Draft Hose under drivers side frame rail, at higher speeds the SUCTION, and net flow through ventilation will be two to 3 times what ANY stock PCV system was capable of, and further, as the engine ages, or you start pushing more power, or MANIFOLD Pressure- your free air crankcase VENTING system will still keep up, not build crankcase pressure, and at highway speeds will PULL VACUUM on your crankcase.

Oil consumption can approach zero, even on VERY high mileage engines, and you will NOT ingest blow by oil into your engine.
Less sludge, less smoke, cleaner oil, and no catch cans nor check valves required.

the Tried and True, old school Road Draft Tube: cheap, simple, effective, and NO down side.

 

I don't disagree with what you're saying but that's not the direction I want to go. If I had smoke at WOT regardless of the situation or oil in the clean air tube of the PCV system then that would be an indication of insufficient venting flow and I would be more inclined to go that route. But that's not what's happening.

Based on the symptoms, the most likely explanation is that high vacuum scenarios (high rpm at very light throttle) are drawing oil through the PCV system into the intake where it's pooling up. When I go to accelerate again that oil gets sucked into the cylinders and burned. The smoke at start up is just burning more of this oil that was drawn in by vacuum. There's no smoke during street driving, even WOT, because the oil has been cleared from the intake at this point and I'm not hanging the engine at high rpm/low throttle like on the course to draw more in.

I'm going to start with a catch can and go from there. Thanks for everybody's input!

 

I too believe you're pulling in too much blowby into the intake manifold. A sealed catch can will intercept some of the oil which will help. Venting to atmosphere I second.

 

I've been doing some research on new catch cans and they're pretty cool. The ones from Mighty Mouse or Motion offer the best of both worlds: they act like a sealed can 95% of the time and will catch oil before the air is drawn back into the intake. Then if crank case pressure exceeds intake pressure like it can during WOT, instead of allowing that pressure to feed into the intake, a valve will close and the can will to vent to atmosphere (I assume while still separating any oil). Sounds like exactly what I need.

 

About 10 years ago, I had to pull my stock LS7 intake. I then tilted it 90° to the floor, to carry it. Considering the amount of oil that came out of my intake, I was shocked to see the price of oil didn't drop!! Seriously, I decided right then to vent to atmosphere, into a bottle, repurposed for the task. Virtually every 4 cycle engine ever made before the mid 1960s had no PCV. Anyway, 60,000 miles later, and motor is still working fine. I remember some of my old Honda motorcycle engines that revved to 10,000+ rpm vented to atmosphere. On PAPER, there may be advantages to a GOOD PCV setup. But like many things, they don't make much difference in the real world. I'd say vent to atmosphere!!

 

You remove the factory PCV valve with those cans. Maybe someone can comment about whether you cap off the LS6 valley nipple (if you have one) or if you run a hose from it.

 

I'm planning to get the updated driver side valve cover and plumb that as the inlet to the catch can, no PCV valve involved. Then catch can to intake manifold. Fresh air source for the crank will still be the passenger side valve cover to throttle body with a 3/8" hose. I'll either cap the valley cover or put my old LS1 one back on.

 

What I have seen with my old 383 (Mahle powerpack pistons) that I built back in day, was an increase in blowby, the only oiling difference were the lifters used vs stock bottom end LS6 and clearances were probably larger by a bit. The oil in the valve covers needs to compete for space with the blowby in the crankcase under load, the valley cover PCV line is closed since the intake is at atmosphere or close so it needs to vent through the fresh air tube on the passenger side valve cover. With a lot of oil in the valve covers, high g force side loading and more blowby/windage with the 4" stroke I've found it carries oil out the fresh air tube with blowby which is why larger lines help reduce the velocity of gases and let thing settle out also. I could probably empty 1/2 a qt of oil out of my breather can after road racing and running the engine to 7000 often for 10-20 minutes. On the next run I experimented and if I lowered the rpm by short shifting I would get very little oil in the breather can, there was just not enough drain back happening.

Now before anyone pokes fun at the engine back then it was 2007-2008 ish and the same unchanged short block I used on my turbo deal with larger -10 breather tubes (speed density) 10+ years later. so it did a fine job. I'm personally not big on 4" stroke stuff anymore, but you really need to dial in the piston to wall and use the best pistons and rings to keep things tighter on the short pistons and prevent piston rock at bdc on stock sleeves. Obviously I'd do a few things differently 20 years later, but I was working with the knowledge I had at the time.