I have a carbureted 383ci LT4 with a problem. The engine runs great, but burns oil and the spark plugs always have a good coating of oil in them when I pull them out. I have done a compression check and all 8 are almost identical. The stock PCV system is gone with a breather/catch can system in it's place. I pulled the valve covers and everything looks like the day it was new. I have a pancake type adapter on the filter that feeds an oil cooler and a 3qt Moroso sump. I can't really think of much else that could contribute to it...

Do any of you engine gurus have any ideas of what could be causing this?

Thanks in advance

 

For years I had an oiling problem with a 383 I was running. When I did the conversion, I modified a dipstick to fit a 70's style block. I ended up running with an oil level too high. The incorrect marking along with the added stroke of the crank caused the crank to throw up too much oil overpowering the oil rings. Went through a couple engines until I figured this out. Try running a half quart less oil.

 

A cyliner leak down test, it deals with how well the cylinder is sealing and nothing else. The readings are not affected by carbon deposits, cam timing, or even engine cranking speed. This is what I would do next. It is not uncommon for a typical 383 to use oil though.

 

Never thought about the extra stroke throwing more oil. Especially with the sump in there... a half quart low shouldn't hurt anything at all, especially with the accusump. Thanks for the advice! That is the new number 1 on the list of possibilities.

I was considering that already, but with all 8 being equal it seems odd that it would be something specific to 1 cylinder or valve. That is on the list of things to do this winter if I haven't figured it out by then.

 

If you're using low tension oil rings you'll use a lot of oil.

 

Low tension oil rings are used by many race engine builders and they will burn oil. You can help the situation by using a vacuum pump, it can make low tension oil rings seal better.

 

I wonder who started this fantasy about it making the rings seal better.. It de airates the oil and reducing foaming and oil splash by lowering the pressure in the crankcase the air bubbles in return oil and that beat by windage will separate out. A 4 psi change is dramatic for that purpose but in percentage to the pressure on top of the rings during compression or firing part of the cycle is microscopic in effect.

 

I agree,low tension rings, just went through this on my 396LT1, now I went from 500-750 a quart to about 1500 miles a quart.

 

Got a good windage tray?

 

My own personnal experience started this fantasy. I had low tension rings in my 355 Firebird and it burned a quart every 400 to 500 miles. I installed a vacuum pump that ran at 6" of vacuum and the oil usage dropped to about a quart every 1000 miles. Eventually I decided to make changes to the engine and I rebuilt it and changed out the low tension rings for standard rings.

 

If the engine is using oil something is not right with the ring package or in how the rings fit the pistons. It is also possible you have bore distortion in the upper cylinder region due to a discrepancy between torque plate loading when the block was honed and your final cylinder head torque. Differences in head gaskets used for honing and final assembly affect cylinder bore distortion quite a bit also. Low tension Oil rings should be combined with a Napier style 2nd ring. The best low tension oil ring is the U-Flex one-piece segmented 1.5MM or 2MM oil ring from Mahle. The main purpose of a vacuum pump is to reduce crankcase pressure below atmospheric pressure which frees up some horsepower which would otherwise be consumed by pumping loss from piston movement pumping air around inside. Good competition engines require very efficient ring sealing to restrict blowby which permits running a very high crankcase vacuum. Staying with a proven standard piston/ piston ring set-up and working on the cylinder heads and manifold is by far where the most gains for the money will be found rather than investing in the latest trick deal. Someone once said tricks are for kids.

 

 

I was finally able to get in touch with the engine builder and what I got was this. They are pretty sure that it was built with no exhaust valve seals. I've done some looking around on different websites and it seems like a lot of "race" engines are built this way and it is often responsible for smoke at startup (which I have) as well as some oil consumption at high r.p.m. (which I certainly turn).

They weren't 100% sure after the amount of time since they built it so I'm planning on pulling the valve covers again and giving a look to verify that it really doesn't have them.

He was also pretty sure that it was built with low tension JE rings but wasn't 100% on that either. The combination of the 2 could add up to a decent amount of oil being burned. I don't think I mentioned before that I am generally going through about a quart every 2 hours or so of track time.

Any thoughts/comments on this one. Engine building isn't my specialty and I would love to keep learning more.

 

Do you really think a car that runs the 24 hours of Daytona goes through 3 gallons of oil? Measure the blowby and you will find the problem. At WOT there is no vacuum to pull oil down the guides but cylinder pressure is high so if it is rings it will get real bad there. Do all 8 plugs come up oil fouled might be a first test. Second if the engine is into mild detonation it will rattle the rings and will burn oil, is TDC marked correctly and timing set at a sensible value? What do you have for a crankcase breather system is there one in the pan as well as the covers if wet sump? Is the pan overfilled if so you are screwed. What is the oil temp if to the moon you will not be able to pour it in fast enough. The crankcase vacuum pump is at the right side of the decimal point in the end and not the fix all if everything else is right. I have run a 410 with 18 degree heads at Daytona and other tracks it makes about 770 hp in one config and 740 in the second engine for shorter tracks it does no burn oil at all and wins and has no vacuum pump either. It is all about cylinder wall prep ring package and proper scavenge of oil they are both dry sumped and a big plus. If I was a betting man though not would put my money on a poorly fitted ring package too much piston to wall clearance or poorly fininshed cylinder walls if all 8 plgs dirty if just some might bet on intake gaskets or valve seals.

 

No, I don't think a 24 hours car burns 3 gallons. I know that it is burning too much, which was why I asked in the first place. It might be burning less than I said as it's tough to tell. I loose a lot into the breather/catch can system as well (that is getting fixed over the winter). I work my butt off to afford what I already have so at this point I'm doing what I can now to keep it in one piece.

I am all but certain that it is not a cylinder wall/build issue or something of that nature. The shop that built the engine is as good as they come and I find it highly unlikely that it would be something like that coming from them. The more that I research, the more I am thinking that it could be something as simple as being too full. I usually start with it right at the top of the full line with an external cooler and an accusump to boot. The stroker crank isn't helping in this regard. It does run hot ~260 degrees even with the cooler, water temps ~220 (not that it matters) although from what I can tell that isn't TOO hot. All 8 plugs look identical and compression is ~2% in all cylinders. I haven't done a leak down test yet, so that will help tell a little more...

At this point I'm hoping that it could be something as simple as the low tension rings mixed with keeping it a little too full, or possibly valve seals which I can fix with the engine where it is right now.

On a related note, I have a question with the accusump. With the 3qt accusump in the loop, how does that affect the situation if it is a quart or so low in the pan? Does it add some security in that situation?

 

A compression test or a leakdown test are OK for looking for bent valves from not enough piston to valve clearance or something but they will not be sensitive enough to point to the cause for high oil consumption in an engine that has not had time to have excessive wear yet.

You cannot blow that much oil through the valve guides unless the shop knurled the guides and they wore excessively which always happens with knurling.

With all due respects to your shop there is a high likelyhood there is something wrong with the rings. You don't install low tension oil rings unless you are on top of your game and you know you have oil control. Otherwise why wouldn't the OEM install them? Every hand would go up for more HP and better fuel economy.