Crankcase Ventilation

[garrycol]

I have a 4.6 with older 3.5 manifold and 175CD carbs. I need to set up a crankcase ventilation system. Note the vehicle also has LPG so input air cannot be taken from between the LPG carb and the engine die to LPG fuel air mix being sucked into the crankcase with the resulting explosion risk in the engine.

The old 3.5 has a hole at the rear of the block with a air filter on it that allows fresh air to be sucked into the crankcase. At the top of each rocker cover is a pipe with a flame resistor that goes the base of each carb where the crankcase fumes are sucked into the engine.

Now the 4.6 does not have the hole in the rear of the block so I have to rig up an alternate crankcase ventilation system. I am thinking of simply putting a filter on the passenger side rocker cover pipe (or running an intake pipe from the airfilter upstream of the LPG system) and sucking the air and fumes out the drivers side rocker cover pipe through a flame arrestor to a branched pipe to the relevant port on each carb. This will mean that fresh air is sucked in via the passenger rocker cover, down into the crankcase, up into the drivers rocker cover and into the carbs, so achieving crankcase ventilation - this is similar to what happens in a Thor system.

Can I have your thoughts on this or maybe better suggestions though not interested in making modifications to the engine etc.

Thanks

Garry

[paul c]

I drilled the back of my 4.6 block the same as the 3.5 block so it will vent the same. Having trouble getting the correct hoses for the SUs on mine and one of the hoses I did find new is actually hard, so going to have to find some alternative hoses. I was trying to make it look all original.

[ChrisJC]

I think you are right - setting something up similar to Thor / GEMS is your only option. I guess it goes into the inlet before the throttle butterflies.

Chris.

[garrycol]

Thanks to you for both your replies.

Paul I did think about drilling the back of the block but as the 4.6 casting is different to the 3.5 casting I was worried I might drill into something I shouldn't do

Yes Chris I know all about the Thor system so I thought I would model this on that system.

Cheers

Garry

[Pistonsquirter]

I’m going to joint both carbs with an old tin 3-port flame trap then pipe to one of the rocker cover ports, then the other rocker cover port I’ll pipe to the airbox.
Will need a restrictor in that airbox side pipe so the carbs draw a slight vacuum on crankcase.
Mine is a 4.6 GEMS with twin HIF6 and MJLJr going in an 80” landy.


HH

[ChrisJC]

Should make the 80" sit up nicely...!

Chris.