964 RSR case mods.
 

A friend bought this for $100 !
Thought it could good to post some pictures for reference.

http://forums.pelicanparts.com/uploa...1276364897.jpg

http://forums.pelicanparts.com/uploa...1276364969.jpg

http://forums.pelicanparts.com/uploa...1276365012.jpg

From the inside:
http://forums.pelicanparts.com/uploa...1276365065.jpg


Unfortunately this explains the $100 :)

http://forums.pelicanparts.com/uploa...1276365255.jpg

http://forums.pelicanparts.com/uploa...1276365303.jpg

Will make a nice table stand thou. :)

where is the "from the inside" pic located in the case?

Funny they still do all that useless boat tail work ....I wonder why????

I thought some here say that it is useless work with no gains to be had. Was that factory work or a local machine shop?

PFM

Between the cylinders.

We guess its factory. Thats why he bought the case, to see if they had done anything special to it.

Windage mods do work, it is just that the gains are only noticeable in a racing engine which spins very fast for most of its life and spec (Carrera Cup) racing can make small horsepower differences more noticeable.

I have talked with a number of factory guys that have stated they have never seen a factory motor modded this way. The GT3 cups are a great example as there are no mods done to the case at all.

Most,if not all of the mods are done thru the independent shops running the cars.

The GT3 Cups do not use the windage mods because they use an excess-flow oil scavenge pump. They draw down the air pressure in the case to negligable levels. Since there is no air in there, there is no point in shaping things aerodynamically. :)

Aaron is correct.

The factory doesn't do those case modifications on cars delivered to customers. That was done by a professional engine builder.

For engines that live above 7K, it does make a measurable difference in power. :)

Do the 964 Cups use crankcase vacuum also?

No, they were normal.

They were not shuffle pinned either as far as I can tell. The case was simply "houred" out and replaced with a new case. You can see a great deal of fretting on the houred out cases.

We tried a GT3 negative pressure valve on the dyno with a GT3 oil pumped engine and found no HP difference. Thinking about it though, maybe we should have held the engine at high RPM for a while to generate crankcase vacuum and then we may have seen a difference. Oh well.

Perhaps the valve system needs the two extra scavenge pumps that the GT3 has on the exhaust cam boxes to make the crankcase vacuum system work?

The case is isolated from the cam boxes on the GT3 so the main oil pump just scavanges the case.
Were you able to verify you had case vac?

Did you use the special rear main seal? If not you will pull air thru the seals and not produce the required vac to see the HP increase. FYI you can simply install the stock rear main seal backwards and it should work fine.

The other vac specific parts are low tension rings.

You are exactly right on the cam boxes being separated from the crankcase on the GT3, thus camshaft oil never returns to the crankcase and the main scavenge pump is free to pump more air instead.

The engine was built on 2.0 alloy case, so had early, small main seal.

We didn't measure case vacuum.

If you atempt it again, please keep me posted. I've been wanting to do it for some time now.
Cheers!

How much vacuum is required for windage mods to not be necessary? I'm guessing the. motorsport cars have an electric vacuum pump of some sort? Any details on specs or part numbers?

There is no electric vacuum pump. Just a huge oil scavenge pump, in the GT3 with two pickupsv just for the case plus the afformentioned cam box pumps. http://forums.pelicanparts.com/911-engine-rebuilding-forum/548297-when-use-gt3-vs-930-pump.html#post5409097
Because there is so much extra scavenge flow (fixed displacement pump) the pump sucks some air out, too.

All oil scavenge pumps are actually sucking a mixture of oil and air. This "foam" varies in density due to rpms. That is the reason for the baffles in the oil tank- as an air/oil separator.

all dry sumps run a slight neg pressure in the cc. The GT3 just added a one way valve and larger scavenge section w/ special crankshaft seals to enhance it. In the hot rod world where thay run american push rod V8s w/o dry sump they sometimes add electric(or other pumps) to generate neg cc pressures

Jason Andreas posted these pics of the GT3 cc breather valve & seals

http://forums.pelicanparts.com/uploa...1276870249.jpg
http://forums.pelicanparts.com/uploa...1276870263.jpg
http://forums.pelicanparts.com/uploa...1276870279.jpg
http://forums.pelicanparts.com/uploa...1276870291.jpg

Pretty cool info. I didn't know a dry sump system could pull enough vacuum to make aero mods not necessary, at least for street engines.

Piston rings also seal better without positive crankcase pressure. This probably results in more net power gain than the mods for internal air flow, but for a max-power engine, every thing helps.

MHO,
Sherwood