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#1 ·
I am interested in getting some input on next steps in diagnosing oil consumption of my engine.

I rebuilt my lt1 the winter of 2019/2020. Last year I put 4k miles on it. This year I have put 1k miles on. Engine started out as an LT1 with ~140k. I had been collecting parts to do LE2 HCI with a 227/235 LE cam. I ended up also doing a forged 383 (see signature) with a deck height of 9.015 and rings gapped for nitrous. Engine runs great, has nice drivability, and pulls hard to 7k, and so far has done 12.65@115 with a 2.09 60ft on street tires.

Here is a list of things I have done to diagnose and try to solve my oil consumption:

  1. Initially noticed some oil consumption and blue cloud on startup. Checked for external leaks. Even today, the engine has no external leaks. Found oil in throttle body, intake, and cylinder intake ports, and spark plugs. Observed big blue smoke cloud on start up after around 2-250 miles on the engine. This got progressively worse for 100 miles before plateauing.
  2. Compression test, dry, warm engine (psi): #1 [210] #2 [209] #3 [217] #4 [205] #5 [218] #6 [215] #7 [214] #8 [220]
  3. Installed a new valve cover baffle elbow between the passenger valve cover and the throttle body. No measurable improvement - oil still found in throttle body and intake, blue cloud on start up still exists.
  4. Installed a Mike Norris PCV catch can set up between the PCV valve (fixed orifice design) and the intake. The catch can only caught perhaps 2/5 cup of oil in 3k miles. no measurable improvement.
  5. Drove car for a bit, noticed spark plugs have oil on threads and carbon buildup. Engine consumes 1 quart of oil every ~200 miles.
  6. Inspected and replaced the valve seals fall of 2020. The valve seals I removed looked fine, but installed new ones anyway. Valve stems had a bit more play in the valve guide than when the heads were off during initial motor assembly - valve stems/guides were very tight and I did lubricate the stems and guides prior to installing the springs. No measurable improvement, still have plugs getting coated in oil and blue smoke on startup.
  7. Removed intake and replaced intake gaskets. Observed that intake valley was likely bottoming out on block before intake ports could compress against cylinder heads fully. Removed material from intake valley and enlarged intake-to-cylinder head holes slightly to enable easier assembly. Its possible that the intake still requires milling of the intake port face to match the geometry of the heads. Some improvement (maybe?): engine seems to consume oil at a slightly slower pace (1 quart every ~300 miles) and blue smoke cloud on startup is less noticeable.
  8. Engine runs smoother after cleaning/replacing spark plugs, which makes sense since the spark plugs are still coming out oil on threads, some buildup of carbon. When I changed the plugs I also did a quick compression test, cold engine. dry, #1 [230] wet (WD-40 spray), #1 [230].

The potential causes and fixes I see are:

  1. Valve guides are worn/burnt up --> pull heads and have the valve guides replaced.
  2. Intake doesn't fit heads/block well --> pull intake and have the intake machined to match the heads and block better.
  3. Longer stroke has resulted in additional oil mist in engine --> install second catch can between passenger valve cover and throttle body.
 
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#2 · (Edited by Moderator)
Were the heads milled? Was the block decked? What is the static compression ratio?

Did you reinstall the stock windage tray? Are you sure the oil dipstick is correct and installed correctly?

Have you done a leakdown test? Wet rings can contribute to high compression test numbers.

Catch can are band-aids to cover up the problem.

Did you have to modify the valve covers to clear aftermarket rocker arms? Is the baffle still in place below the PCV vent elbow in the passenger side cover?
 
#3 ·
LE2 heads were milled I believe, volume is 52 cc. Block was decked to 9.015" height. Static compression ratio is 11.237:1.

No, I am not using the stock pan or the stock windage tray. I am running a Moroso 7 qt pan (p/n 20206) that has uni-directional windage screen, crank scraper, and trap door baffle. I will attach some pictures of the inside of the pan. I am using the original dipstick. It is installed correctly. I originally added 8 quarts of oil (7 for the pan, 1 for the filter) but found I had loss of oil pressure under hard acceleration due to aeration. I stepped down to 7 quarts and didn't have any loss of oil pressure under hard acceleration. I also tried 6 quarts, again with no loss of oil pressure under hard acceleration. so now I keep the oil in the 6-7 range. I find that if I slightly overfill by half a quart I will see oil aeration and loss of oil pressure under hard acceleration. Loss of pressure under hard acceleration looks like seeing the needle go from 60-70 psi to 40 psi. cruising around the engine has 55 psi. Fully warm on a hot day at idle I see 30-40 psi. Oil pump is a Mellings 10554ST fitted with a Morosso 24360 pickup for 8.25" pan depth. The oil pump is standard volume, standard pressure, and has the helical gear design for smoother oil pressure delivery. I track oil volume and loss based on where the oil level is on the dipstick after I run the engine after an oil change. I park in the same spot to take measurements using the dipstick.

I have not done a leakdown test yet. Is that worthwhile?

Do you suggest that I shouldn't need a catch can? Or perhaps I shouldn't need a catch can if everything is operating correctly?

I did modify the stock steel valve covers to clear the aftermarket rocker arms. I trimmed some of the webbing out, but the baffle was retained.

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#4 ·
I can't comment on that pan/tray design because I've never used it. My setup is stock pan, stock tray on stock length extended main cap bolts, blueprinted stock pump with high pressure spring. No oiling problems. No oil on the plugs, Engines has a 7,200 or 7,400 RPM redline, depending on where we set nitrous cutoff. I have an aftermarket mechanical oil pressure gauge in one of the A/C vents. The only time I ever noticed any oil consumption was in the first few hundred miles after the build. After that, nothing noticeable, but oil changes are frequent. I run a 25W-50 racing oil when spraying nitrous, and switch to a 10W-30 oil designed for turbo applications for cooler weather. Your oil pressure seems excessively sensitive to oil level.

The "rings gapped for nitrous" are looser and can pass more oil, but mine are set for a 300-shot. Are your ring packs near the top of the piston, or have they been dropped further down on the piston to get them away from the intense heat of the nitrous?

I also run a totally stock PCV system, with no catch cans and no oil in the vent line or the throttle body. Yes, in your case the catch cans will help limit oil contamination of air entering the combustion chamber. That is important because oil effectively reduces octane of the fuel. As a temporary "fix" it makes sense if you are going to continue driving it. But there shouldn't be a significant amount of oil in the PCV system.

Do you still have the stock sheet metal baffle/pan on the bottom of the intake manifold? That keeps the intake manifold cooler, and also limits oil entrainment at the slots in the bottom of the manifold that feed the passages to the PCV valve

There should seldom be oil in the vent line from the throttle body to the valve cover. That line is supposed to be flowing air from the throttle body to the valve cover. It should only reverse flow when the engine is at very high load/RPM, and there isn't enough manifold vacuum to clear the crankcase of blowby gasses.

I also think the intake manifold to head sealing may still be off. But that's just a guess. If enlarging the bolt holes was required it may still not be mating correctly to the head.

Normal sequence of events is to do a "wet" compression test (adding oil to the cylinders) if the dry test produces lower than acceptable pressure readings. Higher pressure results in the "wet" test would tend to confirm ring problems. But in your case I'm thinking you may have already, in effect, done the "wet" test, and perhaps a leakdown test would allow the pressure to clear the rings of oil. Just a thought, may not prove anything.
 
#5 ·
Your oil pressure seems excessively sensitive to oil level.
I never would have discovered that sensitivity if I hadn't filled the engine up with 8 quarts initially. Perhaps even running 7 quarts is excessive. I have read of others with this style pan running as little as 4.5 quarts at the drag strip to save on hp. I have personally run as little as 5-5.5 quarts with this pan with no issues on the street.

I had the machine shop (JB's Auto Machine - they were fantastic to work with BTW, ) assemble the bottom end for me. I asked them to gap the rings for 150-shot. The pistons are 4032 Mahle PowerPak pistons (p/n SBC125030I16) and have the rings near the top. The ring gap is 0.024" top and 0.020" second.

I do still have the stock sheet metal baffle on the bottom of the intake manifold.

I wonder if I get oil in the vent line from the throttle body to the valve cover because I do a lot of engine braking. I mostly cruise around 2k, but shift near 3k when driving easy or have a cold engine. When I am playing in corners the rpms are above 4k the whole time. On the street hammering it, I shift around 6500 rpm. I shift as close to redline as I can at the drag strip, so usually 6800-6900 rpm.

I was able to get the intake bolted down the first time without enlarging the holes, but it was a tight fit and done on an engine stand with easy access. I enlarged the holes on the second go around to make installation a bit easier since I was doing the gasket replacement with the engine in the car. How does a machine shop know how to machine an intake - do I have to take specific measurements of the engine?

I wonder how the throttle body and intake would get so much oil if the oil was coming in from the intake gaskets or getting consumed via rings...

I will look into doing a leakdown test.
 
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