928 Estate decision time...5 speed conversion or stay auto?
11-08-2010 | 04:08 PM
#16
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I raced for years on gearboxes with "Porsche" style syncros and never had any issues. I actually prefer them, as does my son. They have a bunch more "feel" than the Borg Warner style boxes and the syncros actually cool and work better, since the friction surface is on the "outside" and not on the "inside". Keeping a Borg Warner style gearbox "alive" on the race track has always been a real challenge....even on the 964/993 vehicles.
Perhaps for pure street driving the less "nothcy" feeling of the Borg Warner style gearbox might be easier to drive, but keeping the syncros "alive" on the racetrack is tough.
At minimum, you will want to add a cooler, a pump, and modify the tranmission case to allow oil to spray onto all the gear/syncros, for both boxes....especially when adding a limited slip. The cooler they stay, the longer they last. Even with a cooler, the Borg Warner transmssions will "crunch" on tracks that put a lot of heat into the gearboxes.
The advantage of being able to install a "real" limited slip, into the early gearboxes, without a bunch of extra work makes it very attractive. My vote would be to find a limited slip, for that gearbox, add a cooler and spray system, and install it.
Perhaps for pure street driving the less "nothcy" feeling of the Borg Warner style gearbox might be easier to drive, but keeping the syncros "alive" on the racetrack is tough.
At minimum, you will want to add a cooler, a pump, and modify the tranmission case to allow oil to spray onto all the gear/syncros, for both boxes....especially when adding a limited slip. The cooler they stay, the longer they last. Even with a cooler, the Borg Warner transmssions will "crunch" on tracks that put a lot of heat into the gearboxes.
The advantage of being able to install a "real" limited slip, into the early gearboxes, without a bunch of extra work makes it very attractive. My vote would be to find a limited slip, for that gearbox, add a cooler and spray system, and install it.
11-08-2010 | 04:32 PM
#18
Nordschleife Master
Joined: Jun 2006
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From: ɹəpun uʍop 'ʎəupʎs
Can't you pickup a used 4-spd auto cheaply for now, and start keeping your eye out for a 5-spd track car for sale? (they seem to crop up semi-regularly)
There's enough people here watching 928 ads that a stripped out track car shouldn't take too long to hunt down.
Then you could lose the hideous estate mod that is a bad hangover from Lemons
There's enough people here watching 928 ads that a stripped out track car shouldn't take too long to hunt down.
Then you could lose the hideous estate mod that is a bad hangover from Lemons
11-08-2010 | 04:45 PM
#19
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Joined: Feb 2003
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From: saratoga, ca
yep, maybe we need to do a chassis swap at the next Sharktober fest!
actually, we are stuck with the estate. its pretty evolved now. its a LOT of work to make a race car, even just the gut and go 928. the estate has a nice cage in it and has all the bugs worked out. now, it just needs a 5 speed.
I say, start savings for one now. cut that big hole in the fenderwell to put in the mastercylinder, get the torque tube, transmission linkage, etc, and put it together. thats a HECK of a lot easier than gutting a new car and welding in a cage! dont you think. so, it looks "interesting" now. heck, if he can win or place high against the spec e30s, an other GTS 2s, that would be cool!
I can see the headlines now, "X lemons racer wins GTS2 championship".
mk
actually, we are stuck with the estate. its pretty evolved now. its a LOT of work to make a race car, even just the gut and go 928. the estate has a nice cage in it and has all the bugs worked out. now, it just needs a 5 speed.
I say, start savings for one now. cut that big hole in the fenderwell to put in the mastercylinder, get the torque tube, transmission linkage, etc, and put it together. thats a HECK of a lot easier than gutting a new car and welding in a cage! dont you think. so, it looks "interesting" now. heck, if he can win or place high against the spec e30s, an other GTS 2s, that would be cool!
I can see the headlines now, "X lemons racer wins GTS2 championship".
mk
Can't you pickup a used 4-spd auto cheaply for now, and start keeping your eye out for a 5-spd track car for sale? (they seem to crop up semi-regularly)
There's enough people here watching 928 ads that a stripped out track car shouldn't take too long to hunt down.
Then you could lose the hideous estate mod that is a bad hangover from Lemons
There's enough people here watching 928 ads that a stripped out track car shouldn't take too long to hunt down.
Then you could lose the hideous estate mod that is a bad hangover from Lemons
11-08-2010 | 04:51 PM
#20
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From: saratoga, ca
11-08-2010 | 06:03 PM
#22
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Joined: Oct 2006
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From: Orange, Cal
I see a false economy from buying an older 5 spd, after the cost of rebuilding, you might as well have started with a good 85+.
What sort of HP gains are possible if you "dry sump" the transmission?
What sort of HP gains are possible if you "dry sump" the transmission?
11-08-2010 | 06:12 PM
#23
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Joined: Feb 2003
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From: saratoga, ca
why? hp gains only? Ive measured the losses of the total drivetrain, in neutral, so not going through the gear box, but the diff was spinning along with drag due to bearings and tire friction, and the losses which are very significant, are 10hp at 70mph and 20hp at 150mph. with our cars, thats nearly half the totall losses. there is easily 7% more (for a total of 15% overall) in the gear box, which you might be able to save 1% if you were lucky, even running it dry. 
11-08-2010 | 06:18 PM
#24
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From: Seattle, WA, USA
My '85 auto had the bracket from the factory, I confirmed this myself.
I was very close to deciding to convert that car to a 5 sp, but in the end did not.
11-08-2010 | 06:18 PM
#25
Chronic Tool Dropper
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From: Bend, Oregon
Dry sump the trans? Doesn't buy anything, nd you'd want to figure out how to pressure lube the parts that are used to swimming on oil now. No crank throws whip up the oil, No combustion blowby gasses to manage and exhaust, no waiting for oil to drain back from the heads. Maybe a standard wet gearbox, with a large cooler, a cool oil reservoir, and a pump. No need to degas the oil since there are no gases added. Just deaerate and cool it.
11-08-2010 | 07:06 PM
#28
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Joined: Feb 2005
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From: Anaheim
you shift right and there is no "crunching" issues whatso ever. about 8 years ago, i did notice this, as the race went on , on a hot day, the gear box was harder and harder to shift. same gear box, 10 years later, no mods, no coolers nothing, it shifts like a dream. why, because after driving 928s for 15 years, i finally learned the secret of shifting the 928. its matching engine speeds, in racing, its hard blips of the throttle. (what a concept) both anderson and me are shifting MUCH better than when we were racing these things 10 years ago. Now, Ive REALLY raced both, and I can tell you, there is no comparison with the older gear boxes, even when the synchros are working well. there is NO reason to prefer the older gear boxes in a race application, except if you want the "real "LSD, which is debatable for most of the tracks we visit, along with the power we have. so, I guess I just dont run the gear box hard enough, huh!
Im running 1:36.1 at laguna seca on DOTs, and have been running 1:37s for 3 seasons now with the stroker and no mods to anything on the car.
watch the video, listen and judge for yourself.
http://www.youtube.com/v/Sih48Dby9d0
Mk
Im running 1:36.1 at laguna seca on DOTs, and have been running 1:37s for 3 seasons now with the stroker and no mods to anything on the car.
watch the video, listen and judge for yourself.
http://www.youtube.com/v/Sih48Dby9d0
Mk
Note that I was mentioning what I prefer. I would never speak for someone else.
Having been in charge of race cars with the Borg Warner syncro design at many, many events...let me assure you that one driver can completely kill one of these gearboxes in one "session". Been there, had it done to the cars I was in charge of...more than once. You get them hot and they are done working. Sometimes they get better, when they cool off and sometimes they need a new syncro/gear (since the hub is part of the gear). Tough to get a Porsche design syncro to overheat....and if "kujo" the killer driver damages it, you only need a syncro, not a whole gear.
"When you get drivers whose egos want them to be as fast as everyone else, the gearbox is always the first thing that gets abused"....that is always the case.
BTW...I treat virtually everything that happens with your car as the "exception", not the rule. If you were to try and find the 6-7 seconds per lap difference between your times and Anderson's times....you'd be singing a completely different song. Making up 6-7 seconds a lap is an eternity, on the race track.
11-08-2010 | 07:42 PM
#30
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Joined: Sep 2004
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From: Stockton, CA
UPDATE.....I scored an 1988 4 speed with LSD off ebay for $750!!! Its the same one that has been listed forever at $899....sent him an offer for $750 and he took it!! Its enroute now!! So I will be stating with the automatic...its just easier and "fits" the mold of cheap racing better than spending big bucks on a conversion.....
I will take it to a local Mercedes transmission expert to look it over and give it some new seals + a torque converter stall increase and in it goes!!!!
I will take it to a local Mercedes transmission expert to look it over and give it some new seals + a torque converter stall increase and in it goes!!!!