Carbureted LSX forum - please validate my PCV hookup for a carbureted motor!

Or correct me if needed. I've found a lot of very interesting discussion for EFI but nothing for carbureted motors. I have an LS3 crate motor (LS376/515) sitting in a 69 Corvette chassis right now and I am working out all the plumbing differences, fuel, power steering and PCV. By analogy with the EFI systems and with my old SBC , I think this is the way crankcase ventilation should go.

http://i1220.photobucket.com/albums/dd452/cliffkancler/ls1tech/carburettedLS3PCV.jpg

There is something mysterious under the valley pan that is supposed to function like a PCV valve so I don't actually need another. That port (dirty air in red) routes to the vacuum inlet on the manifold through a catch can.

One of the things that bothers me is that I bought a Holley Ultra and it has no vacuum port in the base equivalent to the old small block setup. So the alternative would seem to be to plumb it through the manifold. That manifold inlet also has to power the headlights and wiper door by pulling a vacuum on the cannister.

For venting, clean filtered air (blue) would be plumbed through a hole in the air filter base and would go to the valve covers.

I haven't done any of this yet and am wide open to comments! This car will mainly be an autocrosser. I had a lot of problems on hard turns with oil carryover back into the intake with the old motor and don't want to repeat that.

The catch can is a good idea. I keep meaning to put one on mine. I only get a little oil residue in the vent lines so hasn't been a major priority.

I have the suction going to the (I think) 5/16 port on the carb base plate that also feeds the brake booster. No issues. If I were you I would probably just drill and tap the manifold to get a hook up. I did put a PCV valve on the outlet of the valley cover. Not sure if it is needed by I have one.

Instead of plumbing the vents back into the air cleaner I simply used a small paper fuel filter and hooked it to the passenger side vent with a piece of tubing. A lot cleaner looking than routing vents to the air cleaner.

http://www.arkansas-ope.com/GPS_0F0106_FUEL_FILTER.jpg

You can see the PCV valve and filter in this pic from my album

http://ls1tech.com/forums/picture.php?albumid=16828&pictureid=55421

I'm running two open element Metco breathers, one on the passenger side and one on the driver's side

Hey z28/2002 do your Metco breathers in place I have just one on the drivers side and its not very tight in place.


I'm running two open element Metco breathers, one on the passenger side and one on the driver's side

I'm running two passenger side valve covers with the fill tube removed. I have yet to have any issues with them being loose

I bought a grommet @ a local hardware store and just ran a pcv to the vacuum port at the rear of my carb, with a breather on the other side.

Or correct me if needed. I've found a lot of very interesting discussion for EFI but nothing for carbureted motors. I have an LS3 crate motor (LS376/515) sitting in a 69 Corvette chassis right now and I am working out all the plumbing differences, fuel, power steering and PCV. By analogy with the EFI systems and with my old SBC , I think this is the way crankcase ventilation should go.

http://i1220.photobucket.com/albums/dd452/cliffkancler/ls1tech/carburettedLS3PCV.jpg

There is something mysterious under the valley pan that is supposed to function like a PCV valve so I don't actually need another. That port (dirty air in red) routes to the vacuum inlet on the manifold through a catch can.

One of the things that bothers me is that I bought a Holley Ultra and it has no vacuum port in the base equivalent to the old small block setup. So the alternative would seem to be to plumb it through the manifold. That manifold inlet also has to power the headlights and wiper door by pulling a vacuum on the cannister.

For venting, clean filtered air (blue) would be plumbed through a hole in the air filter base and would go to the valve covers.

I haven't done any of this yet and am wide open to comments! This car will mainly be an autocrosser. I had a lot of problems on hard turns with oil carryover back into the intake with the old motor and don't want to repeat that.

Looks perfect.

Help me understand why you need a catch can. At low RPMs there is crankcase vacuum and you can feed filtered air from the base of the air cleaner (higher pressure). At high RPMs there is crankcase pressure and this can be alleviated by a feed from the base of the carb or manifold (low pressure).

My driver's rear valve cover port (using the stock PCV valve) connects to the base of my air filter assembly and the little pipe on the front of my pass valve cover runs to the base of the carb.

I have read that there is a slight power advantage when a crankcase runs under vacuum (less air for the crank and rods to push through). Consequently I do not run an "open" PCV system as some examples above.

Help me understand why you need a catch can. At low RPMs there is crankcase vacuum and you can feed filtered air from the base of the air cleaner (higher pressure). At high RPMs there is crankcase pressure and this can be alleviated by a feed from the base of the carb or manifold (low pressure).

My driver's rear valve cover port (using the stock PCV valve) connects to the base of my air filter assembly and the little pipe on the front of my pass valve cover runs to the base of the carb.

The way you have it hooked up you are probably sucking oil into your carb base. This effectively lowers the octane of the gas risking detonation.

The early LS motors had issues with venting the crankcase. GM did a pretty extensive redesign of the blocks for LS2's and beyond to fix some of the issues with the early blocks. This includes moving the PCV vent from the valve covers to the valley cover with the LS6 and beyond. They added a fair amount of baffling in the valley cover to try and trap the oil. You have bypassed all of that by essentially hooking the PCV system up backwards from the way the early LS motors were set up.

This site is full of people talking about the intake oil contamination issue and what they have done to stop it. Amazingly for cars that are really driven hard you need two catch cans for both the vacuum source intake and the vent going to the throttle body. The guy said when he is really reving it he catches oil blowing out of both places.

I'm sorry to hijack this guys thread, but let me elucidate and clarify. Oftentimes when TWO catch cans are necessary the real culprit is excessive blow-by or worn valve guides/seals.

(The PCV setup on my vehicle works flawlessly, it was well thought out and well-designed - thank you very much.)

A catch can is a band-aid type remedy and doesn't address the real issue which is too much velocity in the system which is often accompanied by too little volume. Simply put, the air is moving so quickly the oil cannot be easily trapped.

A PCV system open to the atmosphere is not the best design.