G'day all, I am building a 401 Nailhead to run in my A40 Austin gasser and have a question about venting the crank case. I have read that they had a habit of building up pressure in the crank case. Now I picked up 4 of the small Moon breathers to help combat this but don't think this will work alone for a street/strip motor....... The motor will be run on the street as well as raced pretty hard. Here are the rough specs, 30 thou over bore, Gessler level 4 heads, Toms roller rockers, TA413-401 cam, standard stroke, 12-1 compression ratio, Hilborn injection, schiefer aluminum flywheel and top loader Ford cog box (1971 XY GTHO). Now I believe I would be better off running a PCV system, though where to run it to? I was thinking the headers? There is nowhere to run one to the injectors! Now if that works what about the breathers? To be efficient with the PCV system the breathers need to be as far from the PCV so that it doesn't just draw air from the closest breather. The breathers are already in the valve covers (NOS Eelco). Would I be better off blocking off the rear two breathers so that more air is drawn from the crank rather than just from the top of the motor? Another soluion that has been suggested to me is to run breathers on the sump pan itself, I dont like that idea though. I am spending some serious money on this motor so I want it to be as strong as I can!! All help and advice much appreciated. Cheers, Doc.
I like your idea of running the PCV to the headers. I imagine you would weld in a bung that you can screw in a pipe thread inlet. As for hose, you would need something that can withstand 4-500*F. You would definitely see blue smoke from that side of the exhaust all the time too, especially under load. Just my .02:TU:
This is simple..... come off the tappet valley cover at the back of the engine.... with a grommet and a pc valve and then run a 3/8'' hose to the intake either just under the carb or thru the same fitting as the power brake usually goes to,,,,, it will take care of any normal engine vapors.... if you run it to the exhaust system without a ck valve in the system the exhaust can come into the crank case/ or a backfire could cause a crank case explosion... The factory set up pc system is hard to beat for keeping pressures down and the engine clean.....copy it as close as possible...
The full-race header collector evac setup won't function properly when the mufflers/exhaust is in place, in fact it might mean the end of the mufflers themselves due to oil residue. Devon
In reality the only real option you have is an external vacuum pump. The stock PCV valve is inoperative under WOT conditions as there is 0 vacuum, or should be. In most normal conditions the PCV valve works great if your rings are good. Once the rings start to wear crankcase pressure builds up & the PCV valve can't handle the amount of pressures associated with this. Just remember, wherever you install the breathers make sure there is some kind of baffling or stainless wading to keep the PCV from sucking up all the oil vapors, splash or over spray.
Yeah, being a street strip motor I didn't think of the full exhaust system, though would it really push that much oil into it? With the injection it is a single runner from the velocity tube/injector body into each cylinder. No provision for equalizing it across all 8 cylinders and it would lean out one cylinder seriously. Thats why I was asking bout running to the headers, no intake port provision for it. I guess I will have to look into an electric vacuum pump? Doc.
Going to the headers is fine. It's been done since the dawn of time. Just make sure your fitting is 45 degrees to the center of the collector. You won't need a pcv or anything. Exhaust gasses passing BY the 45 degree fitting will create a vacuum and draw out anything. Then again, 4 breathers on valve covers should be plenty of 'vent' for the 'case. Mike
hey i got a question for you guys my engine has the draft tube and i have no clue where to find a pvc valve. can i just run say breathers on each valve cover and would that work just as good as a pvc?
You could but, the reason it is below the engine is to place the tube in the air flow or "draft". This causes a negitive pressure in the tube and the valley.
No. A draft tube has to extend down below the engine, and point toward the rear of the car, for it to work properly. The "draft" is formed by the air under the car moving toward the back, while you are moving forward, pulling the air out of the tube. This pulls crankcase gases out. The fresh air goes in at the top (valve cover inlets). If the draft tube does not extend down into the rushing air, it will not draft. The blowby will come out under your hood, out of the fresh air inlets. If the inlets and outlets are all too restricted, this will cause crankcase pressure to build. If the draft tube is brought up under the hood, all those crankcase gasses (and oil vapor) will mess up the engine compartment. (They have to go somewhere.) Does that help?
What jim says is right dead on.... you can come off it with a tube to the intake but then you are right back to the factory pcv system..... so the best thing to do is that any way..... it keeps the engine a lot cleaner inside...
so a tube to the air intake is all i need to do i just want to clean it up under there on my newer cars ive done a seperate filter on the end of the pvc though really didnt cause an issue
