SPB for endurance
08-31-2016, 10:54 PM
#16
Addict
Rennlist Member
Rennlist Member
I am new to SPB so new I have bought my car and havent raced it yet alothough Ive been racing Caymans and 911's for 20 years. I have been hesitant to think about using the SPB for races like AER. You have given me the thinking of moving forward as I enjoy endurance racing so much more than sprints.
Thank you.
Thank you.
08-31-2016, 11:43 PM
#17
Burning Brakes
Thread Starter
I am new to SPB so new I have bought my car and havent raced it yet alothough Ive been racing Caymans and 911's for 20 years. I have been hesitant to think about using the SPB for races like AER. You have given me the thinking of moving forward as I enjoy endurance racing so much more than sprints. Thank you.
08-31-2016, 11:55 PM
#18
Chris
Are you running accusumps in your cars? My 2.7 doesn't have one and there seem to be mixed opinion amongst the spec boxster guys whether it's needed or not? I'd love to save the weight and the complexity, but also want a motor to last as long as possible. We are cutting the rev limiter back to 6800 on the 2.7 since we have so many different drives.
Are you running accusumps in your cars? My 2.7 doesn't have one and there seem to be mixed opinion amongst the spec boxster guys whether it's needed or not? I'd love to save the weight and the complexity, but also want a motor to last as long as possible. We are cutting the rev limiter back to 6800 on the 2.7 since we have so many different drives.
On a Boxster, the Accusump will be plumbed in at the oil filter or it will be plumbed into a remote mounted oil filter, usually in the trunk. In both cases the extra plumbing will cause the oil pressure to drop unnecessarily, although I doubt this drop is severe enough to cause a problem on its own. However, in some installations, an extremely small oil filter is used, and I expect the drop to be large in this case.
Anyway, the Accusump cannot solve the problem due to its reactive nature. In practice it works like this:
When the oil pressure is higher than the gas pressure in the Accusump, the oil system operates normally.
When the oil pressure at the Accusump's outlet falls, the Accusump discharges some oil into the system. The problem is that the oil pressure does not fall unless the oil pickup has sucked up some air (which it does surprisingly often) and the oil released by the Accusump simply follows that air through the oil system. That air has to go somewhere, and that somewhere is usually the main bearings. The Accusump cannot cause the air to disappear or become harmless, and therefore does not prevent the cumulative damage that I described above.
In cases where the oil pressure is lost for multiple seconds (such as when the oil pan has been removed by a curb, for instance) I can see the Accusump making a positive difference. I ran into an unusual circumstance at Indianapolis where the engine was losing oil pressure for over 5 seconds due to a series of corners preceded by a very long straight, and I think an Accusump may have helped there.
There is one other major potential problem with the Accusump: it can make setting the oil level very tricky. This alone disallows its use in customer cars in my opinion. The chance of the oil level being set incorrectly are way too high, although admittedly, if you think through the situation, this can be overcome. Also, the Accusump's discharging of oil can cause the oil level to become too high while racing, which can cause huge clouds of smoke or worse.
I think cutting the revs to 6800 will help longevity only very slightly and it will almost completely erase the engine's advantage over a 2.5. It would make much more sense to just use a 2.5. The revs alone won't hurt anything, but they do aggravate the already marginal oil situation.
Chris Cervelli
09-01-2016, 12:38 AM
#21
Chris
Thanks for the response. That has been the opinion of my mechanic as well, but he only does the SPB sprints and 60 minute enduros. I bought the car with a 2.7 in it, so that is what we will run in WRL. I see that I am leaving 400 rpm on the table by limiting at 6800, but was more worried about multiple drivers wringing the car out over 9 hours and was looking for a little insurance. Might move it back to 7200 if it doesn't matter anyway ( and when I say move it, I mean reprogram the AIM dash lights, because that is what we are using to signal). I am fairly certain it cuts at 7200 rpm currently with OEM flash.
Thanks for the response. That has been the opinion of my mechanic as well, but he only does the SPB sprints and 60 minute enduros. I bought the car with a 2.7 in it, so that is what we will run in WRL. I see that I am leaving 400 rpm on the table by limiting at 6800, but was more worried about multiple drivers wringing the car out over 9 hours and was looking for a little insurance. Might move it back to 7200 if it doesn't matter anyway ( and when I say move it, I mean reprogram the AIM dash lights, because that is what we are using to signal). I am fairly certain it cuts at 7200 rpm currently with OEM flash.
09-01-2016, 12:46 AM
#22
It actually gently closes the throttle at 7200 (assuming the setup is all stock 2.7 with drive by wire throttle) and then cuts at about 7350 if you manage to get it that high.
It is much smoother than the 2.5 rev limiter.
Chris Cervelli
It is much smoother than the 2.5 rev limiter.
Chris Cervelli
09-01-2016, 02:16 PM
#23
Burning Brakes
Thread Starter
Hard to win in a beater. Another factor is speed as a defense for contact. With WRL the Boxsters are among the fastest cars on track. You spend the entire race overtaking cars - rarely being overtaken. As such, less likely to get caught up with other cars.
09-02-2016, 07:09 PM
#24
Rennlist Member
I had a blast racing against Joe Bunton at Mid Ohio in 2014
Close racing with him at the end...
Close racing with him at the end...
Two Boxsters competed in the NASA 25 Hours of Thunderhill last December in class "ES".
Both Boxsters were entered by Cervelli Technical Service of Wheat Ridge, CO. There are some nice photos of the cars at the race here. The Boxster drivers were: Chris Cervelli, Chad ***, Steve Dunn, Joe Bunton, Glenn Conser, Chris Sarian, and Robert Ames.
NASA puts SPB in endurance class E1. Cervelli says they ran in ES not E1 so that they could refuel using NASCAR dump-cans, instead of 5-gallon jugs as required in E1. Since they didn't mention any other reasons for ES, I'm going to guess that the cars conformed to SPB rules.
Their fastest lap was 2:04.4 (with bypass). One didn't finish due to an engine bearing failure, and the other finished with 590 laps.
The overall winner, an Audi R8LMS, did 690 laps. The highest-placing 2016 Mazda MX-5 Cup (factory) car did 562 laps in class E0.
Finishing 590 implies no major failures. I'm kinda surprised that the 986 gearbox made it 25 hours!
According to their Facebook page, they rebuilt the engines of both cars before the event. I hadn't heard of crank bearing failures before in the 986 engine, so I was surprised. But apparently, they made some error in assembling one of the engines. The factory-assembled ones don't seem to have a problem with crank bearings (as far as I know).
Both Boxsters were entered by Cervelli Technical Service of Wheat Ridge, CO. There are some nice photos of the cars at the race here. The Boxster drivers were: Chris Cervelli, Chad ***, Steve Dunn, Joe Bunton, Glenn Conser, Chris Sarian, and Robert Ames.
NASA puts SPB in endurance class E1. Cervelli says they ran in ES not E1 so that they could refuel using NASCAR dump-cans, instead of 5-gallon jugs as required in E1. Since they didn't mention any other reasons for ES, I'm going to guess that the cars conformed to SPB rules.
Their fastest lap was 2:04.4 (with bypass). One didn't finish due to an engine bearing failure, and the other finished with 590 laps.
The overall winner, an Audi R8LMS, did 690 laps. The highest-placing 2016 Mazda MX-5 Cup (factory) car did 562 laps in class E0.
Finishing 590 implies no major failures. I'm kinda surprised that the 986 gearbox made it 25 hours!
According to their Facebook page, they rebuilt the engines of both cars before the event. I hadn't heard of crank bearing failures before in the 986 engine, so I was surprised. But apparently, they made some error in assembling one of the engines. The factory-assembled ones don't seem to have a problem with crank bearings (as far as I know).
09-04-2016, 09:23 PM
#27
Burning Brakes
Thread Starter
09-04-2016, 09:24 PM
#28
Burning Brakes
Thread Starter
09-04-2016, 11:20 PM
#29
Rennlist Member
My car has the accusump and I don't really understand it, but it's there. From what I'm told the deeper pan with a windage tray that I installed is a better solution for insurance. Got both now.
10-13-2016, 07:35 PM
#30
Drifting
The Accusump is a cool idea but it does not help the problem I have described above, except in unusual cases.
On a Boxster, the Accusump will be plumbed in at the oil filter or it will be plumbed into a remote mounted oil filter, usually in the trunk. In both cases the extra plumbing will cause the oil pressure to drop unnecessarily, although I doubt this drop is severe enough to cause a problem on its own. However, in some installations, an extremely small oil filter is used, and I expect the drop to be large in this case.
Anyway, the Accusump cannot solve the problem due to its reactive nature. In practice it works like this:
When the oil pressure is higher than the gas pressure in the Accusump, the oil system operates normally.
When the oil pressure at the Accusump's outlet falls, the Accusump discharges some oil into the system. The problem is that the oil pressure does not fall unless the oil pickup has sucked up some air (which it does surprisingly often) and the oil released by the Accusump simply follows that air through the oil system. That air has to go somewhere, and that somewhere is usually the main bearings. The Accusump cannot cause the air to disappear or become harmless, and therefore does not prevent the cumulative damage that I described above.
In cases where the oil pressure is lost for multiple seconds (such as when the oil pan has been removed by a curb, for instance) I can see the Accusump making a positive difference. I ran into an unusual circumstance at Indianapolis where the engine was losing oil pressure for over 5 seconds due to a series of corners preceded by a very long straight, and I think an Accusump may have helped there.
There is one other major potential problem with the Accusump: it can make setting the oil level very tricky. This alone disallows its use in customer cars in my opinion. The chance of the oil level being set incorrectly are way too high, although admittedly, if you think through the situation, this can be overcome. Also, the Accusump's discharging of oil can cause the oil level to become too high while racing, which can cause huge clouds of smoke or worse.
I think cutting the revs to 6800 will help longevity only very slightly and it will almost completely erase the engine's advantage over a 2.5. It would make much more sense to just use a 2.5. The revs alone won't hurt anything, but they do aggravate the already marginal oil situation.
Chris Cervelli
On a Boxster, the Accusump will be plumbed in at the oil filter or it will be plumbed into a remote mounted oil filter, usually in the trunk. In both cases the extra plumbing will cause the oil pressure to drop unnecessarily, although I doubt this drop is severe enough to cause a problem on its own. However, in some installations, an extremely small oil filter is used, and I expect the drop to be large in this case.
Anyway, the Accusump cannot solve the problem due to its reactive nature. In practice it works like this:
When the oil pressure is higher than the gas pressure in the Accusump, the oil system operates normally.
When the oil pressure at the Accusump's outlet falls, the Accusump discharges some oil into the system. The problem is that the oil pressure does not fall unless the oil pickup has sucked up some air (which it does surprisingly often) and the oil released by the Accusump simply follows that air through the oil system. That air has to go somewhere, and that somewhere is usually the main bearings. The Accusump cannot cause the air to disappear or become harmless, and therefore does not prevent the cumulative damage that I described above.
In cases where the oil pressure is lost for multiple seconds (such as when the oil pan has been removed by a curb, for instance) I can see the Accusump making a positive difference. I ran into an unusual circumstance at Indianapolis where the engine was losing oil pressure for over 5 seconds due to a series of corners preceded by a very long straight, and I think an Accusump may have helped there.
There is one other major potential problem with the Accusump: it can make setting the oil level very tricky. This alone disallows its use in customer cars in my opinion. The chance of the oil level being set incorrectly are way too high, although admittedly, if you think through the situation, this can be overcome. Also, the Accusump's discharging of oil can cause the oil level to become too high while racing, which can cause huge clouds of smoke or worse.
I think cutting the revs to 6800 will help longevity only very slightly and it will almost completely erase the engine's advantage over a 2.5. It would make much more sense to just use a 2.5. The revs alone won't hurt anything, but they do aggravate the already marginal oil situation.
Chris Cervelli
Do you think the starvation is due to the scavenger pumps or the pickup tube?
I added a baffle, 0.5qt to my 3.2L sump. If there's been a pressure issue on track -- i've been too busy to notice on my after market oil pressure gauge :-)
Mike