FUSE69

Rough sketch of my existing set-up...

The hose from the provent to the MAF boot is currently 1/2 inch, plan is to get this hose out to 3/4 inch...

On an N/A 32 (which mine is) I 'm not so sure that this is a problem... I would expect to see oil leaks or at least weeping around the cam cover plugs and gaskets if there was to much crankcase pressure... which at the moment I see no evidence of....
Picked up a boost/vac gauge today that I will hook up to the oil fill neck to get an idea of exactly what is happening at various rpm and load.

Leon Speed

What hose/connector did you use to plug into the MAF elbow?

ramcram

Ben, I agree with about the advantages of pulling cold air into the cam box and helping to return oil in vapour to the sump. I know this is done in competition engines with scavenging systems.
As I said initially, if I did this again sometime, I would put more emphesis on venting from the crankcase ports at the base of the filler neck because I don't like the idea of the crankcase gasses having to swim upstream against the cam oil returning to the sump.
As I'm not into competition and the car is extremly unlikely to be raced, the challenges for me are much less. Plus the engine is in very good condition and has never displayed any adverse signs with the driving my wife and I give it.
I believe that Porsche restricted and shielded the cam cover elbow that originally connected to the manifold in an effort to limit oil escaping that way.
I've doubled this path by using the standard 2 elbows on both covers and used the un-shielded ones for balance pipe.
One thought I had during this project was that on the transition to boost, the vacuum vent valve closes blocking the air path from the crankcase to the inlet manifold, which Porsche has positioned after the MAF. My boost vent path then feeds into the system ahead of the MAF, thus removing a flow of unmetered air and replacing is with metered air, effectively richening the mixture for boost.

ramcram

Ben, I agree with about the advantages of pulling cold air into the cam box and helping to return oil in vapour to the sump. I know this is done in competition engines with scavenging systems.
As I said initially, if I did this again sometime, I would put more emphesis on venting from the crankcase ports at the base of the filler neck because I don't like the idea of the crankcase gasses having to swim upstream against the cam oil returning to the sump.
As I'm not into competition and the car is extremly unlikely to be raced, the challenges for me are much less. Plus the engine is in very good condition and has never displayed any adverse signs with the driving my wife and I give it.
I believe that Porsche restricted and shielded the cam cover elbow that originally connected to the manifold in an effort to limit oil escaping that way.
I've doubled this path by using the standard 2 elbows on both covers and used the un-shielded ones for balance pipe.
One thought I had during this project was that on the transition to boost, the vacuum vent valve closes blocking the air path from the crankcase to the inlet manifold, which Porsche has positioned after the MAF. My boost vent path then feeds into the system ahead of the MAF, thus removing a flow of unmetered air and replacing is with metered air, effectively richening the mixture for boost.

FUSE69

That's fair enough... Have to say I like how you have implemented the vacuum vent valve and there are many that vent via the cam covers, so no doubt it works.
I am just a little concerned that, without some fresh air being introduced, at least at off throttle, you will be subjecting the crankcase to an unnessecary amount of vacuum...
But this is also why I asked if you have the provent with the vacuum limiting valve? As when I exposed mine to idle vacuum it shut totally... Which then meant that the crankcase was pressurising at 'off throttle'
I ended up safety wiring it in the open position...

FUSE69

At the moment it is the standard connector and using Earls 'superstock' 1/2" hose.

A 3/4" twist tite hose connector (or an-12) such as those that summit racing sell fits perfectly into the MAF boot opening... Issue then is that the fresh air needs to be drawn from somewhere else.
Either connecting to the air box or fitting a small filter would be the easiest, but then that air which is drawn in is no longer metered by the MAF... Which I guess will lead to idle issues and potentially leaner running conditions at part throttle, this I guess could be overcome by shark tuning, but I'm not sure that you could compensate for the extra unmetered air at idle...??
I will be converting to ST alpha, so it won't really be an issue for me...

Leon Speed

Thanks, the summit connector is a good tip. I don't follow the fresh air thing, since there's no fresh air getting in but throught the MAF (but then again I didn't follow the previous discussion )

FUSE69

That's the idea, that all air that shall be ingested by the engine is metered by the MAF...
The fresh air that I mention is drawn through the y-piece at the MAF boot into the rear cam cover elbow.
It will be difficult to replicate that fitting using a larger diameter hose... Which brings about the issue of where should filtered air now be taken from and allowed to flow into the cam cover...

Although quite difficult to read as its all one paragraph, this link on Louis Ott's page is a pretty good description of how the system functions...
http://www.performance928.com/cgi-bi...ss_parent=1128

(it's path 3 that we want to avoid if possible)

Leon Speed

Ok I get your 'fresh air" thing now. Don't have a solution. I did see on Louie's page it is mentioned that the Y has a check valve - never knew that. Mine doesn't have it anyway. They're just two straight through connectors.

Ed MD

In regards to "excess crankcase vacuum," that's not a problem. The "vacuum" increases the pressure differential across the ring package, producing an improved ring seal. The improved ring seal allows the use of a low-tension (reduced friction) ring package (as the new BMW M3 V8's have), yielding a power increase as well. Further, the reduced crankcase pressure dramatically reduces windage losses at high RPM.
Here are a few observations I found when trying to deal with the blow-by on the Supercharged 85 Euro. First of all, in most engines, the expected power gains will occur with 8 to 10 inches HG crankcase vacuum. Beyond that point, more vacuum does not generally produce any measurable power gain until (a) you get more than 20 inches HG of vacuum AND (b) you are operating in excess of approximately 8300 RPM. I tried to achieve crankcase vacuum with an exhaust extraction system from Moroso coupled with an electric scavenger pump, utilizing two oil/air separators, with the oil pump back into the crankcase but never was able to get more than 5 inches of vacuum.
This is more common than I had realised after scanning Corvette and Mustang forums. Good luck,
Ed M

FUSE69

Check valve is actually on the port of the oil filler base...

FUSE69

Agreed, on a system/engine designed for that much vacuum... On a 20+ yr old engine, without allowing fresh air Into the system, then at idle or off throttle you will be pulling more than 20 inches HG on the crankcase... All this will do is pull unfiltered air past cam cover, oil pan, main seal etc gaskets... As they are not designed to have a high vacuum pulled on them... The engine will sound like a whistle at idle as the air rushes past various gaskets...

Herman K

I kept all the original Porsche designed orifices in place allowing for fresh air in to the crank case per factory design-

I added an oil separator with check valve to stop oil and oil vapors from being returned to the TB when the flow in the fresh air line reverses at medium to WOT-

Last road trip I got 25+MPG when steady cruising at 75-80MPH and 17+MPG at 50/50% cruising to driving hard

ramcram

Great work Herman. Almost wish I had my GTS back!

Leon Speed

Ah ok.