Joe Dyer

Yea Jim, your right. With the SC and increased acceleration, I'm going into 4th (auto) at start/finish and maybe getting close to 140 down the straight. My car is not stripped, so it's heavy and corners are slower. I am on the throttle most of the time, so the drip into the valve cover never gets enough time to dump all the oil pushed out.

kraabel

test

Bill Ball

I suppose us open road racers would have an even greater problem with dripback systems. We are on the gas for 30-40 minutes straight, probably never seeing negative crankcase or cam cover area pressures.

Since all of my outflow appears to be from the oil filler breather, and the orifice is quite small, I've been working under the idea that widening that orifice and putting a baffle in front of it may suffice. But with positve pressure the entire race, no matter what I do, the oil thrown into the breather or in the vapor will probably never have a chance to drain back from the breather hose. Even using the pot scrubber to precipitate oil from the vapor will probably do no good as the airflow will still drive it out. Once in the breather oil is either thrown or condensed from vapor in the breather hose, it will inevitably get blown out by the expelled gas pressure. I could catch it in a can, but that's about it.

I'm going to modify the oil filler in a way similar to Tony's, but I'm now not too optimistic that you can stop the outflow under constant positive pressure.

123quattro

This is a pretty common problem on boosted applications. The crankcase gets pressurized and wants to push the air with small drops of oil in it out. Even brand new engines do this. The GXP Solstice sees up to 5 psi in the crankcase during long pulls, and that's a brand new engine. I think using a catch can (wit h period draining), or an oil separator with a check valve are the only two options, other than a dry sump.

C.F.

Joe
Is it a GTS block ? new GTS short block ? or a S4 block with GTS rods/pistons ?

John V

I'll second the larger vent tube approach but from a different angle (well very much inline with the air velocity theory).

I have twin turbo charged diesels in my boat that run well over 22 psi of boost and 17.5:1 compression... lets just say some blowby is to be expected and thats being kind. Myself and many other owners of similar engines struggled for years with this issue always looking towards a better seperator. After numerous home brew and even some factory attempts failed, the solution finally came simply from enlarging the entire venting system... at which point, even the crappiest seperators worked fine.

It appears that the real problem all along was that the vent system as a whole had just enough flow capacity to deal with "perfect" conditions. As desinged and in ideal conditions, the system worked but the venting air velocity was very high due to the systems small diameter. We believe that this "high veleocity venting" is more prone to carry oil mist/vapor, which coupled to the systems marginal flow capacity, eventually cuased bigger problems. Since perfect conditions don't last forever, the venting system eventually lost some flow capacity which leads to higher crank case pressures. As the CC pressure built, the air velocity increases and carries more vapor - which then starts to saturate the lines and seperators. As the seperators became saturated, venting is further restricted which in turn raises CC pressures which now must either push the oil through the seperator to vent or cc pressure continues to rise. Eventually, the seperators oil draining fails - due to high CC pressure backin up the drain and the seperator and/or vent failed all together. In many instances, there was enough CC pressure to pop the dip sticks and eject oil out of the dipstick tubes (gallons not quarts). By simply enlarging the vent path (in my engine it even meant drilling out an elbow in the valve cover which was a bottleneck), all my seperator problems were fixed... even the original factory seperator works fine and is what I'm using. I beleive it's the higher volume and lower velocity of venting gasses that work together to make it harder to build cc pressure in the first place and keeps the sepertor drain working.

Warren928

John V has a point. high velocity ar going thru a small passage will pickup more oil due to the smaller pipes of alot of systems out there.

A catch tank, one way valve coupled with larger diameter hoses or pipe throughout the system running back to the engine should get more oil back to the engine and not spilled all over. Porsche probably designed the breather system for a 1/3 of the capacity that an engine with a SC would be putting into the crankcase.
I would think 3-4 times larger volume capacity would be adequate, even if it means running dual hoses or lines.

AO

John-

That's some very useful information! Makes a lot of sense to me. So, how big is big enough?

hacker-pschorr

Is that a hint to post your hood picture again?

I agree John, that is some excellent info.

Bill Ball

I have been thinking along those lines as well. I am planning on enlarging my oil filler breather, but I think that is just not enough. Probably we should have more breather outlets in the cam covers so each sees reduced velocity and pressure.

PorKen

Couldn't you vent through the plug(s) on the rear of the S4- heads, with replacement bored aluminum plugs?

It looks as if the spark plug boots can go deeper - at least 1/4" or more. How about making a spacer between the head and the cover? It would make more breathing room under the cover, so the factory vents might work better, and/or you could vent through the spacer.

Darien

Link no worky...

Vilhuer

It seems in general GTS blocks have sylinders in thinner side of specs for some reason. Its probably not intentional and has more to do with casting mould wear or such changes.

One problem in stock head breather system is 90 degree angles mounted to valve covers. Factory version has very small hole inside compared to outside diameter. These could be improved a lot.

Porken, only one head has large plug at rear. On drivers side its at front. In any case it goes to water area of the head. Not to oil side.

Bill Ball

Hmmm.. It workied earlier. The whole site appears to be down at the moment.

SwayBar

I tried too, and it does look like the site is down.