Slightly O.T. leakdown test question?, for you knowledgeable engine builder types... Options

[wbergtho]

I have had a few problems with oil blowing out of my dip stick and oil filler cap on my LS6 motor. I always felt that it was a breathing problem due to crankcase pressure. I went on the big track a few days ago and my 1 qt. Moroso oil catch can/breather filled almost immediately and started bubbling oil through the K & N filter, which is mounted on top of the catch can. Oil then dripped onto my headers and caused a smoke screen down the track.

I went home and performed a leakdown test on all cylinders while the engine was cold. The values read were all between 6-8%. I understand a cold reading will improve to a lesser % reading when the engine is tested warm.

HERE'S MY QUESTION: Do I need to do another leakdown test with the engine warm? Or is a cold test good enough???

Thanks,

Bill

[Brad Roberts]

We do them warm.

I wouldnt worry about the leakdown.. I would fix the breather issue. Our 6cyl cars do the same thing if you dont vent them properly.

I can run 13ft of breather line on a 8k RPM 3.2 and it will still have oil in it 10ft into the equation (going to the front mounted dry sump tank)

Show me your breather setup/box.

I even have to get creative on semi pumped up 3.0's in 9146's. I put the breather into the trunk so it doesnt haze the engine with a fine oil spray. It is easier to clean the trunk after each event than it is to clean the engine compartment.


B

[andys]

I would think it's easier and more effective to evacuate the crankcase breather(s) via the exhaust headers with check (anti-backfire) valves. Racers do this all the time.

Andy1

[Brad Roberts]

Bingo.

They sell bung kits for the headers.

Watch a Top Fuel car sometime. The valve cover vents lay limp until they make the pass, then stand up running back to the catch box under full power.


B

[Aaron Cox]

use the exhaust as a vaccum and burn the oil?

[Brad Roberts]

Drag cars do this.. well because they are only making 6-7 seconds passes..LOL

The place a tube just in front of the collector on the header and run breather lines through a small adapter that acts like a muffler.

The engines are dry sumped. They help things along with valve cover vents to the headers.

B

[byndbad914]

I would think it's easier and more effective to evacuate the crankcase breather(s) via the exhaust headers with check (anti-backfire) valves. Racers do this all the time.

Andy1

Andy and Bill - you DON'T want to do this with a street or especially road race car. That is pretty much a drag-only mod. Even with baffled valve covers, at high rpm you will suck oil out of the engine like a mofo. If it is unbaffled you will have an exhaust full of oil. You may just need to fix the evacuation setup that engine should already have on it. If the check valve is plugged/stuck that could be causing it. Unless you removed it altogether with hotrod goodies (which is what it sounds like since you have a catchcan to begin with) - then your probably better to add it back in.

I am amazed how much my 930 trans wanted to puke fluid and had to get creative with the breather hose routing to get it to stop filling my overflow and running over as well. Another story...