Crankcase ventilation with blow through supercharger

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dart_68

dart_68

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I'm contemplating putting a blow through supercharger on my 360LA and in the process of thinking about the details of actually making it run a question came to mind (one of several, btw). What do you use as a crankcase evacuation system? Right now my normally aspirated engine is using a standard PCV valve plumbed to the base port of my carb. Doesn't a blow through supercharger negate any manifold vacuum?

Thanks in advance.
 
What is your air filter setup? AKA piping from the filter proper to the inlet of the blower is going to generate SOME negative pressure. This will increase with throttle/ RPM. Blowby is not much at idle, so if you can put the fitting as close to the blower inlet as possible it will give you at least "some" vacuum, not much. You may have to play with valving, or use none at all, AKA open hose from rocker cover to inlet
 
Run a catch can attached to both valve covers with the largest hose, fittings, and filter you can find. Motion race works makes a nice one. That’s all you need.
 
My first inclination would be to ditch the PCV setup and run a set of open valve cover breathers, like these:
1700631104288.png

But after digging around to see how Mr. Norm handled it when he put Paxtons on the GSS, all I could find was current Paxton/Novi installations, which look like they retain the PCV valve, although no mention is given as to how they plumb it.
1700631388174.png

An inquiry to a Paxton dealer would quickly answer your question- you could try these guys:
Mopar Small Block 340 Carbureted Paxton Supercharger NOVI 1200 System 1201851 - TREperformance.com
 
I agree with either the open valve cover breathers, OR you could use a header evacuation kit. Although they don't offer "much" evacuation at lower RPMS. Still better than nothing.
 
They say that header evacuation requires open headers. Do not remember where I read that.
 
Professor Fate said:
My first inclination would be to ditch the PCV setup and run a set of open valve cover breathers, like these:
View attachment 1716169345
But after digging around to see how Mr. Norm handled it when he put Paxtons on the GSS, all I could find was current Paxton/Novi installations, which look like they retain the PCV valve, although no mention is given as to how they plumb it.
View attachment 1716169346
An inquiry to a Paxton dealer would quickly answer your question- you could try these guys:
Mopar Small Block 340 Carbureted Paxton Supercharger NOVI 1200 System 1201851 - TREperformance.com
Click to expand...
I bet the kickdown linkage gets really interesting with that Paxton hat. I think I can see it kinda layin down along side the intake. Those kits typically had one way check valves installed pre pcv and brake booster.
 
pan evac does not work with mufflers, creates back pressure to engine. made for open headers only. i've seen this before, guy blew dip stick out, with pan evac, and mufflers, .just food for thought
 
On my race cars I simply welded a 1” stub into the valve cover and put 2-3 foot piece of 1” heater hose on it running down towards the ground. I put it wherever it fit the headers and chassis at the time. Since they were circle track motors they were always left front of the valve cover, pass side had no hoses or breather, no pcv valve at all. Did that for close to 20 years.
 
perfacar said:
pan evac does not work with mufflers, creates back pressure to engine. made for open headers only. i've seen this before, guy blew dip stick out, with pan evac, and mufflers, .just food for thought
Click to expand...

You put the pan evac after the muffler.
 
:DAdmittedly out of my league on this, but i'd thought i throw in $0.02.

When i was racing Pontiacs, a fella i knew (naturally aspirated) stuffed a little electric vacume pump under the fender and plumbed it to somewhere to do something.

I know, i know, super vague, and i probably sound stoned, but I'm not, and it might lead you down a path to enlightenment.
 
As soon as manifold pressure went positive of crankcase, the PCV valve would close, as it would with a backfire, thus not exploding the crankcase.
 
Last edited:
inertia said:
As soon as manifold pressure went positive of crankcase, the PCV valve would close, as it would with a backfire, thus not exploding the crankcase.
Click to expand...
Correct, but two of my own observations;
1. Most normal pcv valves don’t seal for **** under positive pressure so it still pressurizes the crankcase somewhat.
2. The breather that normally flows into the crankcase is now trying to evacuate pressure that gets past the rings and is normally too small to do that efficiently.

Like I said vent both valve covers to a catch can with big hoses and a big filter. This is THE best way to get it done. Ask me how I know.
 
perfacar said:
pan evac does not work with mufflers, creates back pressure to engine. made for open headers only. i've seen this before, guy blew dip stick out, with pan evac, and mufflers, .just food for thought
Click to expand...
But some modern mufflers flow more than an open pipe.
 
TT5.9mag said:
Correct, but two of my own observations;
1. Most normal pcv valves don’t seal for **** under positive pressure so it still pressurizes the crankcase somewhat.
2. The breather that normally flows into the crankcase is now trying to evacuate
Click to expand...

My answer was to the pcv only, as the hoses would blow off with any great pressure. As to pcv leak, I use pcvs for fuel tank vent joker valve in case of rollover, the ones I use hold fuel back without leaking.

And yes, put in lotsa vents for excess crankcase pressure, I didn't mean to touch on that as you had it covered, as do others, lol.
 
I'll clear up what I can based on 25 years of ownership of a Procharged 408.

I run a crankcase evac kit from Speedway. I use Flowmaster and run the evac tubes right after the collector. The collector gets the best signal but I had just had my headers coated so I went a couple inches further down.

Evac kits will work with the Delta shape in the Flowmaster and similar. DO NOT USE EVAC KITS with fiberglass (or any kind) of muffler packing. Otherwise you're good.

That car is due up for it's 2nd resto mod now that Arthur's Duster is done. I will do the Motion or similar quality catch can in line with the same evac kit. Do not run oil gasses back through the engine or piping with this. I do not recommend using a PVC anywhere in this style setup. It's not good for the engine to ever send it back through the engine but it's been the solution for years to keep oil off the roads. With a catch can you keep the oil gasses from running back through keep the engine cleaner at the same time.

I'm not really worried about low rpm vac signal because when I am in low RPM im probably just warning the car up so the engine isn't running warm so there are less gasses. Otherwise, idling at temp still produces gasses but if you get the biggest hose and fittings you can get like @TT5.9mag said, the catch can will still be viable at the low signal.

If you want to see a really cool PCV for other engines check this adjustable PCV out.
 
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