Yes the purpose on a race engine is about ring seal. After all, pistons go up AND down, so any pull would not really be helping. Besides how could a few inches of vacuum compare, at say 4% increase in performance, to the amount of pressure developed by combustion? Is there 4% less heat coming out the tailpipe or off the radiator or is this "free" energy from fantasy land?

I kind of doubt this will help at all with standard rings in a bore that is not carefully prepared, bored and honed with a torque plate. Front seals often draw in air and dirt even with a normal pcv system. I would take a good look at it.

On most street performance engines I have worked on, extra crank breathers or larger breathers have helped. definitely keep the pcv to keep the case clean. With a restricted system like the one being described, the engine will likely see POSITIVE PRESSURE in the crankcase under full throttle. Just letting it breath as much as possible and keeping the pressure as low as possible is more realistic and should be of more benefit.

It is a real working thing on a race car with a real system, but the scale is way off trying to just use the pcv valve to supply the vacuum. When you need it the most, there won't be any vacuum.

Remember that the crankcase ventilation will contain oil residue. Running that back through the intake may or may not be a problem. It could actually be helpful in raising the relative octane rating. But, depending on where and how you route it back into the intake tract, you may not want oil residue (read: anywhere BEFORE your intercooler)
That's the one place in the intake tract that will draw significant vacuum, and like the exhaust, it will INCREASE with increased throttle input. IOW, when you reach WOT, you will be seeing the highest vacuum levels. The downside here is the oil residue will no pass through your compressor and your intercooler. Now you can probably easily remove and clean your intercooler periodically. The same can not be said for removing your turbo for periodic cleaning.

The last turbo car I had, I had spent some $$ on the turbo, so I completely re-routed the stock PCV system so that it wouldn't get anywhere near my shiny snail!
Too much crankcase vacuum? Is there such a thing? hehe There were several people who talked about deploying such a system. How many actually did it? I have no idea. But I personally know of two cars that used the exhaust for crankcase ventilation. One was STRICTLY a drag race car the other was barely street legal (it was built for road racing). Both cars had complete rebuilds before the system was installed, so the engines were in extremely good shape.

Here's my take on this, PCV systems have some function or else the manufacturers wouldn't bother installing them. If you have some $$ in your bottom end, and also in your turbo, then I'd seriously consider using something other than the intake for crankcase ventilation.

6" of mercury will drop pressure in your crankcase ~ 1.25%. If you could get your engine REALLY tight, you may get down to 5% where you may see some improvements. You may actually benfit more from the hindered heat transfer than the reduced drag.

Crankcase oil in the intake tract effective lowers the octane rating of the fuel, rather than raising it.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

How about plumbing the oil breather into the pipe between the intercooler and the TB? That would not be hard at all. Would it foul the heat sensor there? It seems like there would not be much oil. Most would get sucked in by the PCV would it not?

Sam

_________________

Plumbing the breather hoses into the exhaust has been done for years on race cars. Moroso called it the "Vac-U-Pan" system. It was basically 2 Chrysler style breathers with a pair of EGR anti-backfire valve plumbed with heater hose. Simple yet very effective.

Vacuum above atmospheric pressure has been proven to starve the oil pump and kill bearings.

Moroso makes a shimmable check valve to mount in the valve cover and control vacuum.

_________________
Official Cookie and Mater Tormentor.

There will be boost pressure between the intercooler a TB.
Putting it in front of the turbo, like on a stock GN turbo inlet, will suck in all kinds of oil that will coat the intercooler and puddle in the bottom. I hated to plug mine in even for the smog checks. Removing that line and plugging the fitting at the turbo inlet is a standard thing to do on a GN.

Aside from the exhaust, I really see no source of vacuum that will have the capacity to really do anything.

A side note, PCV valves do not really seal very well to pressure. In fact they usually bleed pressure into the crankcase under boost with a turbo. Many people, including myself, put a check valve in the PCV line to prevent this on GNs.

Slantzilla says:

Vacuum is no atmospheric pressure. How do you translate vacuum into pressure? What inches of mercury is equal to one bar,or atmospheric pressure? From zero to one bar is from complete vacuum to 14.5 psi or so, or 0-1 on the KPA scale. Do you mean total vacuum will kill the bearings? Isn't that about 32 inches? Or is that inchs of water? My high school science is escaping me here. I can see how the oil pump would not be able to suck in the total absence of any atmospheric pressure, as suction is really only using atmospheric pressure to do the work of moving a liquid.

Sam

_________________

Vacuum is negative pressure. Remember, an oil pump does not "suck" oil into the pickup, it generates negative pressure so that atmospheric pressure pushes oil into it. No pressure in the pan, no oil in the pump.

The guys who had the most trouble were trying to run 20 inches of vacuum or more.

_________________
Official Cookie and Mater Tormentor.

Thanks for that explanation Anothersix. I should have realized that plumbing the breather tubing into the intercooler pipe would not work. The check valve would keep the pressure out of the crank case, but there would be no draw there . I thought the pcv valve is a check valve. Maybe you just are suggesting a stonger check valve for boosted applications. Do you have a part number or check valve for another application that would work? I assume you are running it in series with the PCV valve.

Sam

_________________

Technically, in the everyday world, there is no such thing as negative pressure. A vacuum is the absence of pressure.

Dennis is absolutely right about the oil pan pickup. The oil pump reduces atmospheric pressure on the oil pickup side of the pump, and the atmospheric pressure inside the oil pan pushes oil up the pickup tube. If you reduce the pressure inside the crankcase using a vacuum pump, then you will not get oil to the oil pump.

Lou

_________________
Home of Slant6-powered fun machines since 1988

A pcv valve is not really a check valve, the spring pushes the poppet open, not closed.

A part number for a check valve from Mcmaster-Carr is 7775k61 for a 1/8" npt male male, or 7775k51 for 1/8" npt female female. These have viton seats and are good for 400 degrees, you can get buna seats as well. They are about $12.00. You can check them out or order online. They have the same valves in larger sizes too. I ran mine quite awhile and never had to replace it.

If you do have any vacuum in the intake side before the turbo, I would do whatever you can to eliminate it. It makes a big difference to a turbo to have the greatest density possible feeding it. It can cut the turbo lag by a large amount too.

What would create a vacuum on the inlet side of the turbo? I have only the breather hose, but that has a check valve in it to prevent the vacuum from sucking in that direction. It can blow through to relieve crank case pressure, but no vacuum that I can figure. Thanks for the part numbers. McMaster Carr is amazing. You get your stuff the very next day.

Sam

_________________

When I was at the race car shop we would place an order before noon and have it the sdame day. You are correct, McMaster rocks.

_________________
Official Cookie and Mater Tormentor.