OK guys, once again I've come to you for your advice. I have a new LT4 engine that runs real strong but I seem to have high crankcase pressure. Here's what's happening. After the engine oil reaches operating temps when I exceed 4K RPM on decelleration I start blowing oil out of the dipstick tube. At first I had the LT1 tube and stick that doesn't have a seal so the oil would flow out of the top, run down the tube across the passenger side of the pan and onto the header collector on the passenger side. This would burn off and produce smoke. I ran it this way, keeping the RPM under 4K so I could get some miles on the engine and it didn't blow oil. At my last track event I changed to the LT4 dipstick tube with the sealed dipstick (O ring type) and it blew the dipstick out about a half inch and sprayed the engine with oil. Again if I ran under 4K RPM I had no problem. I had my mechanic do a static leakdown test and it passed without any problems, all cylinders leaking down less than 18%. It's a new GM Goodwrench LT4 engine with LT4 Hot Cam, long-tube headers, TPIS 52mm throttle body, and 30# injectors and Canton road racing pan. I removed all the EGR stuff. The engine has 2000 miles on it. Any suggestions on cause and fix? I've talked to Canton and to a chevy engine builder. Canton suggested using a breathered catchcan but the engine builder suggested that I'd forfeit vacuum if I did that and suggested that I check the vacuum at the passenger side valve cover where the hose goes to the throttle body to make sure it's adequate for the PVC valve to work properly. I removed the old PVC valve which seemed to be fine (rattled when I shook it) but replaced it with a new one to be sure. I'll check the vacuum this weekend. Sorry for the long post, but I wanted you to have the relevant facts. Thanks.

 

Anybody have an idea on this??

 

I just noticed LouisvilleLT4 has the same problem. I'm reading the responses there as well. Thanks.

 

Good luck man, let me know if you find a way to evacuate the crankcase better... I just ended up putting silicone on the dipstick so it holds a little tighter...

 

Leaking 18% sounds like a lot to me. Its been several years since I did one but it seems like anything over 10% is not good.

 

are the rings moly? sometimes the rings have to have longer to break in because they are HP. I run mobile one, but to break the motor in properly you need to use regular mineral oil. what kind of oil are you running?

 

I may be all wet, and from reading LouisvilleLT4's thread I am beginning to think I am. I admit I am not familiar with the LTx cylinder sealing situation, but back in the old days when an engine had 18% cylinder leakage and it blew the dipstick out and oil all around the engine compartment, it was time for ring and/or cylinder work. In THIS case, with a new engine, maybe the rings have yet to seat, but it's getting close to time, that they had.

Leakdown of 18% is PASS??? What does it take to fail???

RACE ON!!!

 

On a NEW motor, depending on the rings, 18% my not be that bad.

When my current motor was built,(This is my third) I used Stainless steel rings.
Took forever to seat and seal.
HUGE blow by at that point.

my two cents.

Matt383

 

I'll buy that on a NEW engine. I haven't checked many engines when they were new and fresh, but it seems to me they were under 10% and got better pretty quickly. I have no experience with stainless steel rings, but I can only imagine they would take quite a while breaking in. If I had a seasoned engine as saw 18% leakage in it, I'd start making plans.

RACE ON!!!

 

Rings now have a lapped finish and are designed to seal instantly. They really don't require a break in period anymore. 18% is too high, there's something wrong somewhere. Is this a recently rebuilt LT-4?

 

For a new engine, everything I've read says that anything higher than 5% on an engine built for racing and 8% to 10% on a everyday driver is too much.

For a used engine when attempting to determine if it is time to rebuild, I'm under the impression that about 15% or higher is time to think about it.

Also, it is my understanding, that a leak-down test should be done on a warm engine that has some lubricant in the bore to be valid.


On another note, I've seen many LT1 engines that had bore scores from the platinum pucks falling off the original Delco double platinum plugs -- that can't be good for blowby or leak-down tests.
I've seen engines with 6 out of 8 original plugs that had one or both platinum pucks missing.
I think these missing platinum pucks that cause the plug gaps as high as .090" that stressed the high voltage have been the cause of an early demise for many Opti-Sparks -- the wider the plug gap, the higher the voltage has to go to jump the gap and that higher voltage is seen by everything on the secondary side including the cap and rotor in the Opti-Spark.

All that being said, I wonder what kind of outcome the positive twist rings of the LT4 have on static leak down tests -- these positive twist rings are designed to "flatten" out against the cylinder wall at high rpm when combustion pressure forces them to.
It does make me wonder if they won't seal completely for a static leak down test.

Tom Piper

 

Thanks for all the input!!! I apologize for not getting back to you all but I was gone for the weekend. To answer a few questions:

1) It's a new GM Goodwrench LT4 Long Block
2) It currently has 1400 miles on it.
3) I broke it in on the track running no greater than 4500 rpm with dino oil. I switched to Mobile one at 750 miles and ran it on track up to 5000 RPM.
4) I'm not using platinum plugs because I was aware of the pucks falling off.
5) I'm checking with my mechanic again to see how he determined that the leak down percentage was acceptable. I'll let you all know what he says.
6) We did find a crack in the Canton Oil pan that I'm having welded.
7) It does not appear that I'm burning oil. No smoke from the exhausts.

 

Well here's the conclusion concerning the crankcase pressure on my LT4 with 1400 miles: The engine was pulled and torn down and all parts were inspected/measured. Two pistons had broken compression rings and all the pistons had compression rings that were ridged on the thrust side. No indication of engine overheating or over-revving was identified (I never took it over 5K rpm after breakin) and my break-in procedures were validated as appropriate. According to the engine builder who's doing the rebuild (Leggett Engine Research, in Maryland), it appears the cylinders were improperly honed at the factory (new GM Goodwrench LT4 long block) and had an hour glass shape. All the pistons were scapping the cylinder walls at mid-stroke. Other things were found (like a very slack timing chain) but weren't contributors to the crankcase pressure. The bad news is that GM won't warranty the engine because it was a '96 LT4 in a '93 Vette as well as not being installed by a GM dealer, and that I use it on the track. The good news is that the block is sound and is now bored .02 over with new pistons/rings. All the other potential problems were also corrected and I should be good to go for the upcoming events. The rebuild is covered by a strong warranty and included new main bearings, polished crank, 3-angle valve grind and new Cloyes timing chain, etc.

Bottom line is that you guys that said from the start, "Sounds like ring blowby' were absolutely right! See you all at the track!

 

Just a head-up on leakdown. Anything more then 4% is not good.

 

Actually, I had 3 leak down tests. The first leakdown test was done at a dealership and the gauge only gave ratings (good, bad etc) and the mechanic just guessed at the leakdown rate. That's why it was weird (10-15% and good??!). The final two leak down test were done last month and were with recently calibrated SnapOn gauges and they both showed less than 5% for all cylinders. The compression test, however, actually showed an average of 185 psi on the right bank and an average of 170 on the right with No 5 cylinder at 150 psi. That's why we tore it down. It never showed up on the leakdown test because it was done at TDC.

 

Do you have the ECM re-tuned for that Hot Cam??

The broke compression rings could very well be from detonation. Those little 1.5mm LTX rings and Hyper pistons don't stand up to much abuse. I have many LTX out and apart for a re build, all with severe blow by caused by... you guessed it broke rings. Cars all had a few things in common.
1. Young owners.
2. Modified, without a new tune.
3. Ran hard.

Will

 

That is a great point, and I wouldn't have though of that. That one is going into the memory bank.

 

The problem with the GM blocks and engines they don't torque plate hone at the factory and when your building better cylinder pressure with performance cams ETC. it kind of magnafies the blow by problems.

18% leak down is a lot as your only leaking down with only 100 pounds of pressure and when combustion takes place there is alot pressure building in the base.

Here is a link I did on plate honing a few years ago if the pics don't show right click and click on show picture.
http://www.camaros.net/forums/showthread.php?t=58964

 

Yes, the ECM was programmed by PCMforLess for all the modifications, hot cam, LT Headers, 30# injectors, etc. and there was no detonation. Purely and simply a bad hone job at the factory.

 

Great link, thanks!! BTW, my last two leakdown tests both came back with less than 5% leakdown. It was the compression test that showed the problem since that is a dynamic test while the leakdown test is static at TOC. Thanks again for the information!