Boxster Dry Sump System
03-25-2017, 01:21 PM
#1
Boxster Dry Sump System
Gents,
I have developed and installed a functioning dry sump system for Boxster racecars.
First a few facts about the problem. Most of you have run into these already.
The stock oil system does not do a good job of keeping the oil pump pickup covered in oil under all conditions. This leads to interruptions in oil supply to the main and rod bearings, causing them to fail. If a main bearing fails, the rod bearing it feeds will fail soon after. Once the rod bearing fails, one of two things happens: the increased clearance allows the piston to contact the cylinder head, and the piston explodes. Or, the rod breaks and flies off the crankshaft. Either failure mode ruins the engine.
There really isn't anything else wrong with the oil system or with the basic design of the engine.
None of the aftermarket deep sumps I tested addressed this problem to my satisfaction. Some of them are worse than stock, and some give a good improvement.
I didn't test it completely, but the X51 sump seemed to perform MUCH WORSE than stock.
Accusumps don't address the problem at all, although they can be helpful in very extreme circumstances.
Dual scavenge pumps on the cylinder heads do nothing to address the problem.
The problem gets worse as oil/coolant temperature goes up.
The problem in 2.5 liter engines is less severe than in larger engines. A 2.7 is much worse than a 2.5, and I expect (but have not tested) that the 3.2 + engines are worse yet.
The severity of the problem is not very dependent on the speed of the car or driver. I have data showing that a driver going 5 seconds a lap slower than another driver in the same car, in the same race, with the same temperatures, does not significantly reduce the risk of bearing failure.
Driving style DOES play a role. Trail braking and correct corner entry speed make the problem worse, but not significantly.
The drops in oil pressure in a given corner are influenced by the track configuration before the corner.
Some tracks expose the problem very badly, and some do not. Watkins Glen is probably the kindest track I have data for. Thunderhill, COTA, and Road Atlanta are among the worst.
Thicker oil appears to help in that it sloshes around in the sump somewhat less. Also its higher baseline oil pressure tends to mask drops in pressure. I am not a believer in magic oil, but it is obvious that some oils have characteristics that make this situation better or worse.
The situation in a rear engine car is very different from the mid engine car. I theorize that rear engine M96 cars don't have the problem as severely, but I have not tested this.
I have VERY extensive data on Boxsters, 2.5 and 2.7, being run on many different tracks and many different conditions.
I made several generations of deep sumps with different types of attempts to keep the oil near the pickup. I spent a great deal of time and money on this and got absolutely nowhere. What became clear was that the deepest sump was the best, and none of the other variables were important. Ground clearance with a "standard" deep sump is already unacceptable, so I gave up on this in the fall of 2016, after making a really nice billet sump that did no good at all.
I started design work on the dry sump system in Dec 2016 and first tested it in Feb 2017. The test was successful and now I am outfitting a few other cars so the system can be tested thoroughly in the 2017 season. I plan to run my two cars for most of the WRL season, which will include about 170 hours of racing per car at around 10 different tracks.
The first race is at Road Atlanta on April 7 and 8. Two 7 hour races.
A few facts about the system:
Since my cars are used in endurance racing, I used all professional quality parts in the system. The manufacturer of the pump, for instance, builds pumps for many NASCAR and Le Mans teams.
The system can be installed without disassembling the engine completely. The engine does have to be removed from the car and there is some engine disassembly required.
The system is not compatible with A/C.
The installation is complicated and is exacting work.
My dyno tests so far so show that there is no improvement in power. I cannot conclusively prove this at this time.
So far it is been installed on 2.7 engines only. A 3.2 is exactly the same as a 2.7 externally, so no problem with those. A 2.5 is a little different but I expect that the unmodified 2.7 system will work.
The oil tank is quite large and is installed near the transmission. I designed the system around the Cayman S transmission. The 2.5/2.7 Boxster transmission is much smaller and won't pose any problem. The 986 Boxster S transmission has not been tested. I am working on a smaller oil tank but the supplier has not been able to make what I asked for.
Cayman systems will have some detail differences which I hope to work out later in 2017.
The design of the current system did not consider rear engine applications. The concept should work fine on 911s and most of the parts should fit without modifications, but none of this work has actually been done. I hope to design a rear engine system later in 2017.
Feel free to ask for any data that you think might pertain to your situation. If I have it, I will post it.
If you wish to challenge any of the facts I have presented above, please do so publicly and with data to support your argument.
Chris Cervelli
Cervelli Technical Service
I have developed and installed a functioning dry sump system for Boxster racecars.
First a few facts about the problem. Most of you have run into these already.
The stock oil system does not do a good job of keeping the oil pump pickup covered in oil under all conditions. This leads to interruptions in oil supply to the main and rod bearings, causing them to fail. If a main bearing fails, the rod bearing it feeds will fail soon after. Once the rod bearing fails, one of two things happens: the increased clearance allows the piston to contact the cylinder head, and the piston explodes. Or, the rod breaks and flies off the crankshaft. Either failure mode ruins the engine.
There really isn't anything else wrong with the oil system or with the basic design of the engine.
None of the aftermarket deep sumps I tested addressed this problem to my satisfaction. Some of them are worse than stock, and some give a good improvement.
I didn't test it completely, but the X51 sump seemed to perform MUCH WORSE than stock.
Accusumps don't address the problem at all, although they can be helpful in very extreme circumstances.
Dual scavenge pumps on the cylinder heads do nothing to address the problem.
The problem gets worse as oil/coolant temperature goes up.
The problem in 2.5 liter engines is less severe than in larger engines. A 2.7 is much worse than a 2.5, and I expect (but have not tested) that the 3.2 + engines are worse yet.
The severity of the problem is not very dependent on the speed of the car or driver. I have data showing that a driver going 5 seconds a lap slower than another driver in the same car, in the same race, with the same temperatures, does not significantly reduce the risk of bearing failure.
Driving style DOES play a role. Trail braking and correct corner entry speed make the problem worse, but not significantly.
The drops in oil pressure in a given corner are influenced by the track configuration before the corner.
Some tracks expose the problem very badly, and some do not. Watkins Glen is probably the kindest track I have data for. Thunderhill, COTA, and Road Atlanta are among the worst.
Thicker oil appears to help in that it sloshes around in the sump somewhat less. Also its higher baseline oil pressure tends to mask drops in pressure. I am not a believer in magic oil, but it is obvious that some oils have characteristics that make this situation better or worse.
The situation in a rear engine car is very different from the mid engine car. I theorize that rear engine M96 cars don't have the problem as severely, but I have not tested this.
I have VERY extensive data on Boxsters, 2.5 and 2.7, being run on many different tracks and many different conditions.
I made several generations of deep sumps with different types of attempts to keep the oil near the pickup. I spent a great deal of time and money on this and got absolutely nowhere. What became clear was that the deepest sump was the best, and none of the other variables were important. Ground clearance with a "standard" deep sump is already unacceptable, so I gave up on this in the fall of 2016, after making a really nice billet sump that did no good at all.
I started design work on the dry sump system in Dec 2016 and first tested it in Feb 2017. The test was successful and now I am outfitting a few other cars so the system can be tested thoroughly in the 2017 season. I plan to run my two cars for most of the WRL season, which will include about 170 hours of racing per car at around 10 different tracks.
The first race is at Road Atlanta on April 7 and 8. Two 7 hour races.
A few facts about the system:
Since my cars are used in endurance racing, I used all professional quality parts in the system. The manufacturer of the pump, for instance, builds pumps for many NASCAR and Le Mans teams.
The system can be installed without disassembling the engine completely. The engine does have to be removed from the car and there is some engine disassembly required.
The system is not compatible with A/C.
The installation is complicated and is exacting work.
My dyno tests so far so show that there is no improvement in power. I cannot conclusively prove this at this time.
So far it is been installed on 2.7 engines only. A 3.2 is exactly the same as a 2.7 externally, so no problem with those. A 2.5 is a little different but I expect that the unmodified 2.7 system will work.
The oil tank is quite large and is installed near the transmission. I designed the system around the Cayman S transmission. The 2.5/2.7 Boxster transmission is much smaller and won't pose any problem. The 986 Boxster S transmission has not been tested. I am working on a smaller oil tank but the supplier has not been able to make what I asked for.
Cayman systems will have some detail differences which I hope to work out later in 2017.
The design of the current system did not consider rear engine applications. The concept should work fine on 911s and most of the parts should fit without modifications, but none of this work has actually been done. I hope to design a rear engine system later in 2017.
Feel free to ask for any data that you think might pertain to your situation. If I have it, I will post it.
If you wish to challenge any of the facts I have presented above, please do so publicly and with data to support your argument.
Chris Cervelli
Cervelli Technical Service
03-25-2017, 05:19 PM
#2
I will be following, we have experienced oil pressure in our 2.5l at Cal speedway and Spring Mountain. When you have a consumer system ready I will be interested. Will you need to have this approved for Spec Boxster class?
03-25-2017, 05:53 PM
#3
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Join Date: Jan 2011
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Very impressed with your work. I will be the first in line when your system becomes avalable to buy. I myself have been trying to make my engine trackworthy. If you need a ginny pig for 986 S, I can install one in my car for you. I drive it hard on track ewery week on Hoosiers/Pirellis. It has a stand alone engine computer, with data logger were I among other things monitor oil pressure.
03-27-2017, 11:29 PM
#7
Drifting
This is important if the new dry sump really prevents engine damage. The risk/frequency of very expensive damage to well prepared (& therefore expensive) engines deters many of us from Tracking our cars.
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03-28-2017, 05:30 PM
#10
Rennlist Member
If it gets the SPB nod and the cost is modest I expect a lot of these to sell. And if neither of those things can happen it still sounds like a great product for endurance racers and other groups.
04-03-2017, 08:56 PM
#12
Rennlist Member
Chris thanks for doing the hard work on this. Really! I'm impressed with what you came up with, and look forward to learning more.
One question I hope you can answer from your research: which oil pickups did you find fared best? The 997 type or the 996 with more of a defoamer design?
One question I hope you can answer from your research: which oil pickups did you find fared best? The 997 type or the 996 with more of a defoamer design?
04-03-2017, 09:04 PM
#14
Rennlist Member
Subscribed. Already lost one Cayman motor. ��
04-04-2017, 09:21 AM
#15
I having been working like crazy to get the cars prepped for the Road Atlanta WRL race, so I have not updated this.
I will post more information here after the weekend.
Thanks,
Chris
I will post more information here after the weekend.
Thanks,
Chris