964 RSR case mods.

[safe]

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

Does this special seal and valve fit also?

Anything else?

[BURN-BROS]

Originally Posted by safe

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.

[911st]

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.

[safe]

Originally Posted by 911st

So the breather valve" is basically a pressure regulator.

I think its just a check valve.

[911st]

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.

[911pcars]

Originally Posted by 911st

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

[Flieger]

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.

[911st]

Interesting stuf!

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

[Flieger]

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. 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.

[Cupcar]

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.

[911st]

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.

[BURN-BROS]

Originally Posted by 911st

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

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.

[PFM]

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

[Cupcar]

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

[PFM]

CupCar,

Did your source share at what vacuum level?

PFM

[Cupcar]

Originally Posted by PFM

CupCar,

Did your source share at what vacuum level?

PFM

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

[PFM]

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

[Flieger]

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

[BURN-BROS]

Originally Posted by Flieger

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.

[BURN-BROS]

Originally Posted by Cupcar

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

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