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Niether, but I would say most comparable to AX. There are areas of the country that might as well be a track, but yeah not lap after lap after lap like a track.
With all the oil starvation issues and issues related to crankcase ventilation it is too bad there is not money to be made by developing a true dry sump system.
If it were $3k or under, I would buy it.
I have been happy with my pressure stability on track running 2QT deep sump, XP9 oil and street tires, PS4S and have only noticed drops below 3 bar under heavy cornering when the oil is hot. Like late 2nd or 3rd track session. That said, the switch to track specific tires is coming and I know this issue will never get better then it is right now. So again, I would certainly go dry sump for a number of reasons, even addition to the pressure stabilization of it were available.
Yes, a dry sump is the ultimate solution and I'm amazed that there is not one offered for the M96/M97 engine. You can get dry sump solutions for everything from 2.0 Pinto engines to LS's for Pete's sake!
I suspect that the cost would be high and not too many systems would be sold, integration would be difficult, and so on.
What do Spec 996 and Spec Boxsters use, Accumsump?
I have the same issue and I'm working on the solution since this drives me crazy. Don't take my word for it at all, I'm in the middle of the process and this is where I am right now.
The two main things I found is that the return swirl pots are too restrictive and too high oil pressure is causing aeration, both at high RPMs. These issues should be exaggerated when running thicker oils. Solution: get the 997 return pipes, updated pressure relief valve (its stronger and doesn't open as easy including the smoothed edges which helps for aeration) and don't run too thick oil. As long as oil return to the sump quick enough the original design should easily be able to sustain a 1g turn(check oil level according to the manual, hot and level). It should be able to do 1.4g very briefly if filled full, <2 seconds. I see no benefit from different baffles right now. Deeper sump have several benefits as long as flow is not restricted to the pick up, but maybe not needed.
I'm in the process with these modifications, as said, this is very preliminary.
Let me go back and restate my post #7. The left hand cylinder bank has a scavenger pump. When you go through a right hand sweeper the oil that goes to the cylinder head is pumped back to the sump by the scavenger pump.
The factory did not add a scavenger pump to the right hand cylinder bank. So, again, if you go through a left hand sweeper with enough g-force, the oil will continue to build in the right hand cylinder head as there is no scavenger pump to push it down to the pump. In other words, the right hand cylinder bank relies on gravity to return the oil.
The only thing I can think of is you have a bad component in the oil pressure reporting circuit. No idea where. Need to get it tested and certified as accurate to know if you do, in fact, have a pressure issue.
In 2011...They did not think that street / track tires like RA1 or NT01's could generate enough g's to cause this to happen.
I wonder if modern tire technology (improvements in grip) could be partially responsible for an increase in pressure losses in the turns for street tires over the last 10 years or so? I was able to get pressure loss in turn 9-10 (Carousel) at Road America with just Michelin All Seasons (AS3+)!
Last edited by Mike Murphy; 09-16-2020 at 06:04 PM.
In 2011 when I bought a '99 to use primarily as a DE car, I was asking all these questions too. Not happy with the answers I got on this forum, I went to the Racing and DE forum. 996 drivers there had been fighting oil starvation for a long time. A lot of knowledge had been gained since the intro of the car. It was the prevailing theory at that time that on the track, oil starvation would occur on long left hand sweepers when running true racing slicks. They did not think that street / track tires like RA1 or NT01's could generate enough g's to cause this to happen. I ran my car for 4+ years with an X51 oil pan and Bridgestone RE-11 tires. Over that time I got maybe a flicker or 2 from the oil pressure light or saw the needle drop to 10.
Since then, I have seen two things of interest on this topic. First, the original X51 package over came oil starvation by adding a second scavenging pump to the passenger side cylinder bank. The driver's side aready had a pump and is why you should not get an starvation on right hand sweepers. I am adding a diagram of the X51 oil circuit and a picture of the actual pump below.
If you have the full X51 package, which the 40th Anniversary cars do not have, you would see the pump and return oil lines easily when looking under the car.
The second point of interest is that I read that if you are running tires with more grip than "N" spec, then you may be able to generate the g's to pool the oil in the right bank. I think that was from Adrian Streather's 996 Essential Companion.
So the bottom line as I see it is that for "spirited runs around town" an oversized sump should keep you very safe. If you are going to the track, then an ACCUSUMP is the ticket.
Just to be clear, please correct me if I’m wrong:
The 996 original engine has one scavenging pump per cylinder bank, but another 1 or 2 pumps have been added over time (one on the X51 like you say) and then 2 more on the 9A1 engine, is that correct?
Mike, in my first full DE season, my instructor took me out in my car with all season tires in the PCA Red group. The car was a bone stock 911SC. The instructor was one of the better PCA racers. We were passing just about everything on the track expect dedicated track cars or stock GT3’s. This was 2008 and the 2006 tires didn’t squeal once.
My point is car balance is a major factor in going fast. If you are not smooth, you probably aren’t going fast for long.
Let me go back and restate my post #7. The left hand cylinder bank has a scavenger pump. When you go through a right hand sweeper the oil that goes to the cylinder head is pumped back to the sump by the scavenger pump.
The factory did not add a scavenger pump to the right hand cylinder bank. So, again, if you go through a left hand sweeper with enough g-force, the oil will continue to build in the right hand cylinder head as there is no scavenger pump to push it down to the pump. In other words, the right hand cylinder bank relies on gravity to return the oil.
The only thing I can think of is you have a bad component in the oil pressure reporting circuit. No idea where. Need to get it tested and certified as accurate to know if you do, in fact, have a pressure issue.
There is scavenge pumps in both heads, it's standard. What you might be thinking about is the dual scavenge pump on the X51 which I believe was a one head only fitment?
I am quoting info from the UK 911 site and the topic is the X51 package. They are calling the cylinder head pumps “scavenger “ pumps. And according to that site the X51 would not suffer from oil starvation as a result of oil pooling in the right hand cylinder head.
For my 2 years of ownership of my 40th Anniversary car, I have been looking for definitive info on this and this is as close as I can find. Would love to be corrected and pointed to more definitive info and sources.
I'm not really buying the idea that oil pools in the heads. There is oil residing in the head but if you measure oil level according to the manual(hot), this is canceled out. The heads are symmetrical(more or less comes from the same cast) and the scavenge pumps sits on opposite ends. What this means is if one head was pooling, the other would be in a off-pooling state....so flow to the sump would still be even. My theory (just a theory!) is that oil pools inside of the swirl pots and the cavity above at high RPM. Oil is pumped to the top of the pot but then it needs gravity to go down and out thru a small exit at the bottom. In a turn at high RPM oil would probably fill it, gush out the top and in to the cavity above instead of going in to the sump. No de-aeration and lower level in the sump as a result.
You are leaving out the factor that we are talking pooling happening under high g-force that is stronger than gravity to drain the oil back down. Plus we are talking about happening on a long sweeper, not a quick turn with plenty of oil in the sump to continue pumping.
Yes, a dry sump is the ultimate solution and I'm amazed that there is not one offered for the M96/M97 engine.
It does exist, and has around here for a long time.
That said, the main driving factor I've seen behind the oil control issues is oil temperature. If the oil is kept cool, the oil pressure fluctuations are limited, and very controllable. Couple this to an oil with a proper viscosity index, formulated to operate in a proper temperature window, while maintaining viscosity.
We learned this building these engines for Grand Am and etc back in the day. We could run a whole race, with perfect reliability, and never use a single bolt on additional sump, extra scavenge pumps, or etc.
The other key is internal specifications. In factory form these engines are too tight, and the induces shear, which leads to even higher oil temperatures, and reduced oil life.
Loose is fast.
Loose lives.
It does exist, and has around here for a long time.
That said, the main driving factor I've seen behind the oil control issues is oil temperature. If the oil is kept cool, the oil pressure fluctuations are limited, and very controllable. Couple this to an oil with a proper viscosity index, formulated to operate in a proper temperature window, while maintaining viscosity.
We learned this building these engines for Grand Am and etc back in the day. We could run a whole race, with perfect reliability, and never use a single bolt on additional sump, extra scavenge pumps, or etc.
The other key is internal specifications. In factory form these engines are too tight, and the induces shear, which leads to even higher oil temperatures, and reduced oil life.
Loose is fast.
Loose lives.
This makes a lot of sense.
Who manufactures the referenced dry sump system and is it currently available ?
Well, I must be mixed up. I understand standard 996 engines have a scavenge pump for each cylinder head. Because of the symmetry, one of these pumps is in the front of the head and the other is in the rear. I thought the front pump was in the driver side / LH head and was the reason fast (high G load) uphill right hand turns starved the engine of oil. The oil accumulates in that head where the scavenge pump can't reach it to return it to the sump. I think I have the situation correct, but perhaps I am wrong about which head has the pump in the front (of the car).
09-16-2020, 04:31 PM
