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

The gt3 pump fits in an 3.0-3.2 care, right?

Does this special seal and valve fit also?

Anything else?

The case would need machining to fit. The pump is not a drop in.

The seal would fit and you would cut the vent hose and install inline. Not sure of a diameter difference between GT3 and air cooled.

So the breather valve" is basically a pressure regulator?

Anyone know what neg pressure it operates at?


I read something about something like this in the 80's. I think the guy's nams was Bob Norwood who builds Ferrari's and Porsche's. He was doing this on air cooled 911 race motors he was building and he noted a significant HP advantage from it. I have long been wondering about this. Cool if the factory is doing this.

I think its just a check valve.

Good thought. That makes some sense.

If the combustion blow by exceeded the scavenging pump's abilities one could end up with a lot of pressure in the case.

Wonder if there is a reason to add a regulator function so Vac dose not get to hight.

Blow by combustion gases in the crankcase are normally vented (rerouted) to the intake system via a positive crankcase ventilation (PCV) system or other, equivalent crankcase breathing system. If there's insufficient venting, excess pressure will find its way out (along with oil) via the weakest gasket, oil seal or other passage to atmosphere.

Not sure how a scavenge oil pump would reduce blow-by pressure unless the system produces excess foamy oil (not normal). Flieger. Can you confirm?

There should only be lube oil in the lube system. You don't want air in the lube system because air sucks as a lubricant.

Sherwood

According to a Racecar Engineering article on this subjct of reduced crankcase pressure, the oil in the case (at higher rpms used in the heat of battle) is a foam and gets sucked up by the oil pump. The baffles in the oil tank are very important to de-aerate the oil and allow the pressure pump to only push liquid oil.

The article mentioned that the Toyota F1 team had found a significant horsepower advantage with the crankcaase vacuum (ten, IIRC). They started blowing engines, though, when the vacuum got too strong. They had to add a tiny pinprick hole in the case to allow just enough airflow. There had to be a flow, not just a vacuum. The pressure was still much less than ambient and the motors lasted and were very strong.

I will review my archives and find the article.

I imagine that at least GT3 Cup motors should work similarly, if most street motors do not make foamy oil.

The point was that it was not a big deal for an oil scavenge pump to pump air and create vacuum.

Interesting stuf!

I wonder if at come point the vaccum starts to pull oil from the bearings and such.

I think the vacuum started to overcome the oil scavenge pump. No oil pumped out means no oil in tank to be pumped to bearings, = blown engine. http://forums.pelicanparts.com/suppo...ys/explode.gif It is like sucking a thick milkshake through a straw.

I remember several of those Toyota grenades. They were quite spectacular with huge clouds of smoke and some flames. That was in the V10 era.

The crankcase in an enclosed space with two positive displacement pumps acting on it, one pumping fluid IN and one pumping fluid OUT. Whether or not a vacuum is created depends on the relative capacity and efficiency of the pumps working against each other.

Normally the scavenge pump must be larger than the pressure pump because of its inefficiency in pumping due to the sloshing of oil in the sump (foaming) and aspiration of air instead of purely oil.

If the pump pumping fluid in (pressure pump) is greater in capacity than the one pumping fluid out, a positive pressure will be created in the crankcase.

If the pump pumping fluid out (scavenge pump) is greater in capacity than the one pumping it in, a negative pressure will be created.

So, one wants the largest scavenge relative to pressure pump size so as to create the greatest vacuum.

I suspect the Toyota failures were due to the engineers, in trying to achieve the greatest vacuum, made the pressure pump too small relative to the lubrication needs of the engine and therefore the engine starved for oil with consequent failure.

At hight rpm some of the oil on the pressure side may be bypassed back to the oil tank for more of a differental.

I suspect there is also a contribution to crank case pressure from combustion pressure escaping past the rings.

Apparently some of the alcohol dragsters run a detected vacuum pump driven off the fan belt.

This is the driving reason behind the vacuum system. Windage is just an added benefit. The majority of windage issues should be resolved when the case reaches 0 pressure or a slight negative...yet the Pro stock dragster engines continue to see HP increases as the Vac increases. The feedback I got was 25HP @15". Keep in mind that this is for an engine producing over 1000 hp so the % is minimal.....but it's "free" hp.


Engine damage:

Too much vac can indeed cause problems if the engine was not designed for it. The wristpins will fail in short order after 15" unless piston squirters or pressurized oil is implemented.

The HP gains we see on the dyno show most of the gains are in by 8 to 9" Hg. On a 300 plus HP VW engine with 15" Hg and low tension rings the gain is in the 15 HP range at 8000 plus RPM. Keep in mind this is a drag race application.

I would not go past 10" Hg for a road race deal without a lot of R&D time to keep an eye on the oiling system as a whole.

Without going to lower tension rings and doing all the minor tweaks like better engine seals the gains are not nearly so impressive.

Stay tuned,

PFM

Reliable sources at Porsche tell me the negative crankcase system in the GT3 is worth 6 - 8 horsepower.

CupCar,

Did your source share at what vacuum level?

PFM

Didn't say. I will try to check, will maybe take a few days.

CupCar,

Thanks, I would love to seal this thing up and get the pump to draw down 8" Hg at say 6000 RPM. If the pump was running at or near engine speed it would not be a problem. As it runs at 1/2 that (cam speed) it may not be possible even with a well sealed case and great crank seals.

Thanks for the info.

PFM

Why are low-tension rings necessary and how do they work?

It's a ring that generates a smaller amount of pressure against the cylinder wall. Vac then "loads" the ring. You can also run a thinner top ring without the ring sealing issues normally associated with them.

Agreed, seems to be a 2% gain wether it's a prostock drag engine or gt3.