Generation IV Internal Engine - LS3 - good compression, but bad leak down results.. what's going on in there?

This is a stock LS3 engine w/ a D1SC making ~630whp @ 10psi.

I have been noticing some oil consumption the past few months, so I removed my ECS breather oil cap and returned my pcv system back to the exact setup from the procharger instructions (stock oil cap, line from valley plate T'd to line from valve cover, then that line run to air filter). I did an oil change and noted that the oil level was just over the middle dot. I drove the car hard for 450 miles... lots of highway rolls, ect. At the ~450 mile mark since the oil change the 'check oil level' light came on, so I checked it and had to add 1 and 1/3 quarts of oil to reach my original fill point of the middle dot.

1 and 1/3 quarts of oil in 450 miles seems excessive, even given the driving style. It seems like the consumption really picked up around March of '12 after TX2k12 and my addition of the ECS breather cap to the mix... before this I never remember having to add oil unless I'd done a few road course track sessions pre-blower.

The car still pulls hard...people mention seeing some smoke out the tail pipes on occassion, but other than that everything seems fine. I even did a compression check to verify the motor was healthy and came back with the results below with what looks like normal burn on the spark plugs.

(I didn't have the cylinder order handy, so D = driver side, P = passenger side, and 1-4 is the order from front (bumper) to rear (firewall))

http://img42.imageshack.us/img42/5312/imag0743g.jpg

http://img24.imageshack.us/img24/3809/imag0746s.jpg

http://img217.imageshack.us/img217/9100/imag0747x.jpg


Since the compresssion test looked good, I went ahead and did a leak down test too:

Here are the numbers from the leakdown test. Car was cold and had been sitting about a week. Also, the 'baseline' for the gauge at 100psi was ~3%, so I guess subtract 3% from each of the numbers below. On the higher leak % cylinders, I could hear the air blowing out my PCV line into the air filter.

http://img213.imageshack.us/img213/4685/numbersa.jpg

baseline
http://img688.imageshack.us/img688/9924/baseline.jpg

cyl 1
http://img696.imageshack.us/img696/9072/cyl1z.jpg

cyl 2
http://img220.imageshack.us/img220/7513/cyl2v.jpg

cyl 3
http://img502.imageshack.us/img502/3055/cyl3.jpg

cyl 4
http://img12.imageshack.us/img12/3222/cyl4.jpg

cyl 5
http://img840.imageshack.us/img840/1156/cyl5.jpg

cyl 6
http://img703.imageshack.us/img703/3836/cyl6.jpg

cyl 7
http://img69.imageshack.us/img69/3165/cyl7.jpg

cyl 8
http://img685.imageshack.us/img685/2630/cyl8.jpg


What's going on with this motor? Is there something I need to address right now, or can I run this motor for a while longer before building it? It seems odd that compression would be great, but leak down would be not so great.

Is the shortblock stock?

Is the shortblock stock?

yup, 100% stock motor, no cam, w/ 13k miles

Is the air in the pcv a lot or just a small hiss. I cannot see your pics from work but if it's a lot of air then the rings are bad. There is also the possibility of a cracked/broken ringland, especally if it's a stock short block. You may have burnt up the stock rings so a steel top ring is in order.

How many times did you turn the engine over for the compression test? 190psi is close to 13:1 compression ratio. You should only need 3-4 cranks. On a stock motor it should be around 150psi.

When you are doing a leakdown, is the engine warm or cold? It should be warm.

I checked the pics on my phone. 3 looks suspect. 1 and 6 definately have issues.

Is the air in the pcv a lot or just a small hiss. I cannot see your pics from work but if it's a lot of air then the rings are bad. There is also the possibility of a cracked/broken ringland, especally if it's a stock short block. Either way the rings should probably be replaced. After you verify the results you'll have to pull the heads to get a better look.

When you are doing a leakdown, is the engine warm or cold? It should be warm.

I checked the pics on my phone. 1 and 3 look suspect. 6 definately has issues.

It was a pretty small hiss, but still noticable... part of the reason I could hear it well is because the aluminum inlet pipe was removed and it worked like a horn to amplify the air being blown into the filter.

I did the test on a cold engine... first leak down tester didn't have enough psi, then it took me a long time to get the engine rotated just right and work through the test, so it hadn't run in over a week.

I'm going to put it back together and start it up and test cylinder 6 again while warm to see how much it improves.

How many times did you turn the engine over for the compression test? 190psi is close to 13:1 compression ratio. You should only need 3-4 cranks. On a stock motor it should be around 150psi.



I turned it over 8 times, that was the number where the needle stopped moving from what I could see from the driver's seat. I also did it on a cold motor too.

Sounds like a plan! I'd take a look at 1 as well.

I did that the first time I used my compression tester and got 210. WAY too high. Try 3 or 4 turns.

I updated my PCV setup and took the car out to heat it up for the 2nd leak down. I connected the valley plate nipple to the valve cover nipple to loop them, then added the breather oil cap. While driving I noticed quite a bit of oil smoke under boost/wot and heavy decel. After running it pretty hard for a while, I came back and checked the oil and saw it had dropped a bit and the oil was no longer above the 2nd hole in the dipstick. After seeing how much oil it was still going through, I skipped the warm leak down since there is something going on and not just a high number from a cold motor.

I borrowed a bore scope from a friend to see if anything was obviously wrong, but I'm not really sure what to look for, and it's hard to see the whole piston because of the angle into the cylinder.

Here's cylinder 6 (19%):

It seemed to have more deposits on the piston top
http://img835.imageshack.us/img835/1379/cyl6piston.jpg

I also saw these marks on the cylinder wall, but I'm not sure if these are actually scratches, or just spots where the camera wiped away carbon deposits while I tried to twist and position it
http://img696.imageshack.us/img696/8748/cyl6wall.jpg

Here's cylinder 1 (13%):

The deposits seemed lighter and I could even read some kind of part #
http://img194.imageshack.us/img194/130/cyl1piston.jpg

Here's cylinder 3 (9%):

The deposits seemed lighter here too and I could see the same part #
http://img708.imageshack.us/img708/5/cyl3piston.jpg