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The gt3 pump fits in an 3.0-3.2 care, right?
Does this special seal and valve fit also? Anything else?
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Magnus 911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI. 911T Coupe -69, 3.6, G50, "RSR", track day. 924 -79 Rat Rod EFI/Turbo 375whp@1.85bar. 931 -79 under total restoration. |
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Quote:
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.
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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. Last edited by 911st; 06-19-2010 at 01:10 PM.. |
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I think its just a check valve.
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Magnus 911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI. 911T Coupe -69, 3.6, G50, "RSR", track day. 924 -79 Rat Rod EFI/Turbo 375whp@1.85bar. 931 -79 under total restoration. |
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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. |
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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 |
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Max Sluiter
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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.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance Last edited by Flieger; 06-19-2010 at 03:45 PM.. |
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Interesting stuf!
I wonder if at come point the vaccum starts to pull oil from the bearings and such. |
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Max Sluiter
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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.
![]() 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.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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120 HP/Liter is all I ask
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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.
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"It all started when I began looking around and just could not find my dream car. So I decided to build it myself” - Ferry Porsche Last edited by Cupcar; 06-20-2010 at 08:02 AM.. |
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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. |
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Quote:
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.
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PFM
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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 |
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120 HP/Liter is all I ask
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Reliable sources at Porsche tell me the negative crankcase system in the GT3 is worth 6 - 8 horsepower.
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PFM
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CupCar,
Did your source share at what vacuum level? PFM |
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120 HP/Liter is all I ask
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Didn't say. I will try to check, will maybe take a few days.
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"It all started when I began looking around and just could not find my dream car. So I decided to build it myself” - Ferry Porsche |
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PFM
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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 |
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Max Sluiter
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Why are low-tension rings necessary and how do they work?
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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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.
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Agreed, seems to be a 2% gain wether it's a prostock drag engine or gt3.
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