Thread: Catch Can on 4.6 GEMS V8

The right hand (manifold vacuum) one operates mainly at low throttle, the left hand one mainly at high throttle. At low throttle clean air is drawn into the engine from the throttle body (inlet) side by the vacuum side. So by choice the oil separator would be best on the manifold vacuum side as this always delivers fumes.

Originally Posted by bee utey

The right hand (manifold vacuum) one operates mainly at low throttle, the left hand one mainly at high throttle. At low throttle clean air is drawn into the engine from the throttle body (inlet) side by the vacuum side. So by choice the oil separator would be best on the manifold vacuum side as this always delivers fumes.

Thanks mate, perhaps it would be best to add a T-Piece and join both inlets to the catch can inlet

Originally Posted by TheTree

Thanks mate, perhaps it would be best to add a T-Piece and join both inlets to the catch can inlet

Allowing fresh air into the engine helps keep it cleaner, clears condensation, reduces varnish build up. I wouldn't consider this mod to be particularly worthwhile. Perhaps consider two catch cans if you must have them. Are your rings excessively worn?

Originally Posted by bee utey

Allowing fresh air into the engine helps keep it cleaner, clears condensation, reduces varnish build up. I wouldn't consider this mod to be particularly worthwhile. Perhaps consider two catch cans if you must have them. Are your rings excessively worn?

My rings are fine but my valve stem oil seals were shot ... guy installed commodore ones instead of k-line and they were crap. Just replaced them with k-line seals

Maybe i should wait and see how oily things get now with the new seals and if I do go the catch can route, only put it on the right side in place of the oil separator "tree"

Thanks for your input

Steve

Originally Posted by bee utey

The right hand (manifold vacuum) one operates mainly at low throttle, the left hand one mainly at high throttle. At low throttle clean air is drawn into the engine from the throttle body (inlet) side by the vacuum side. So by choice the oil separator would be best on the manifold vacuum side as this always delivers fumes.

A slight diversion from topic - thanks for that information I did not previously understand the subtle differences related to the passenger side. I though that as the intake was before the throttle body that it was simply the point for taking filtered air into the crankcase via the passenger head then sucked into the engine by engine vacuum on the drivers side into the inlet manifold.

Now the topic diversion - at least for a while I am still going to have my old venturi gas system (from my old carb 3.5) on the car so when on gas there will be a LPG/Air mixture in the inlet system before the throttle body. So I guess this LPG/air mixture can get sucked into the crankcase (boom ) and then sucked into the inlet manifold via the drivers side rocker. An issue?

If yes I was thinking of not having the passenger side inlet in the rocker not connected to the throttle body just before throttle but have its own small filter to filter the air or plumb it to the air filter before the gas mixer.

Thoughts?

After I have this engine up and running on dual fuel with its new petrol ECU I will then look at converting the old LPG system to a more modern injection system.

Garry

Originally Posted by garrycol

A slight diversion from topic - thanks for that information I did not previously understand the subtle differences related to the passenger side. I though that as the intake was before the throttle body that it was simply the point for taking filtered air into the crankcase via the passenger head then sucked into the engine by engine vacuum on the drivers side into the inlet manifold.

Now the topic diversion - at least for a while I am still going to have my old venturi gas system (from my old carb 3.5) on the car so when on gas there will be a LPG/Air mixture in the inlet system before the throttle body. So I guess this LPG/air mixture can get sucked into the crankcase (boom ) and then sucked into the inlet manifold via the drivers side rocker. An issue?

If yes I was thinking of not having the passenger side inlet in the rocker not connected to the throttle body just before throttle but have its own small filter to filter the air or plumb it to the air filter before the gas mixer.

Thoughts?

After I have this engine up and running on dual fuel with its new petrol ECU I will then look at converting the old LPG system to a more modern injection system.

Garry

Hi mate,

Yes the one on the right operates mainly at idle because the inlet manifold has a high vacuum at idle, however at higher revs the manifold vacuum is low so the right one would not suck very much; however the left one would suck due to the venturi effect of the air being drawn past it.

I doubt any significant amount LPG/Air mixture would get sucked into the crankcase, if you are worried about that a PCV type non return valve in the left tube would stop any flow from the throttle body back into the crankcase.

Not sure about the effect of feeding only fresh air into the throttle body, this kinda defeats the purpose of the PCV system which is to get the crankcase fumes/blowby and put it back into the combustion process so it is burnt rather than being vented to the atmosphere.

I have decided to leave the left side alone for now and I am monitoring the oil build up on the right to see whether it warrants fitting a catch can.

Steve

Originally Posted by garrycol

A slight diversion from topic - thanks for that information I did not previously understand the subtle differences related to the passenger side. I though that as the intake was before the throttle body that it was simply the point for taking filtered air into the crankcase via the passenger head then sucked into the engine by engine vacuum on the drivers side into the inlet manifold.

Now the topic diversion - at least for a while I am still going to have my old venturi gas system (from my old carb 3.5) on the car so when on gas there will be a LPG/Air mixture in the inlet system before the throttle body. So I guess this LPG/air mixture can get sucked into the crankcase (boom ) and then sucked into the inlet manifold via the drivers side rocker. An issue?

If yes I was thinking of not having the passenger side inlet in the rocker not connected to the throttle body just before throttle but have its own small filter to filter the air or plumb it to the air filter before the gas mixer.

Thoughts?

After I have this engine up and running on dual fuel with its new petrol ECU I will then look at converting the old LPG system to a more modern injection system.

Garry

Having the fresh air connection upstream of the LPG mixer is standard practice, many mixers have a connection point for this purpose. The trouble with this is that the original fume vent prevents oily goo from entering the IAC valve as the connection is usually on the opposite side of the throttle body. Running the fumes through the LPG mixer means that the IAC may gunk up after a lot of high load driving. So do it whatever way you need it for now, and hook it back up to its original connection when you get LPG injection. Allowing the sump to fill with combustible LPG/air mixture is unwise. I've seen a couple of engines that have ignited this mixture, the results were "interesting".

Thanks to you both - I will just leave it open to the atmosphere with a cheap in line fuel on the end of a bit of pipe so that any air that is sucked into the engine is filtered. Then change it back to original when I inject the LPG. The only reason I have the old LPG on is that the engine can run on it while I sort the electronics out for the petrol side out of things.

I have heard what you both have said about the passenger side rocker cover inlet allowing air into the crankcase at low revs but sucking it out at higher revs but I have to say I am not convinced. The Oil Separator Breather Pipe Insert only goes on the drivers side and catches the misty oil so it flows back into the engine.

If the passenger side also sucked out the oily mist at higher revs then surely a Oil Separator Breather Pipe Insert should also be fitted to the passenger side but I believe it is not.

Inseret.jpg

Cheers

Garry