928 Estate decision time...5 speed conversion or stay auto?
11-07-2010, 05:16 PM
#1
Race Director
Thread Starter
928 Estate decision time...5 speed conversion or stay auto?
Okay with the recent discovery that the automatic has significant leaks from the main oil pump seal and needs to be dropped to repair it....it has me thinking about biting the bullet and doing the 5 speed conversion or installing an automatic with LSD.....
I have most of the parts for the 5 speed conversion...but the trans I have is a 1979 and will need new synchros, which is $$$ and doesn't have an LSD... The upside to a 5 speed is it allows me to race with any group....the automatic can only run in Lemons-Chumpcar and NASA....SCCA won't accept the auto
I can source an automatic with LSD for fairly cheap...but should at least refresh the seals in it too....
The cheapest option is to repair the automatic that's in the car....
Thoughts ideas.....opinion from people who have done the conversion before? I do like the automatic....since its been SO reliable....and makes the car super easy to drive.....
I have most of the parts for the 5 speed conversion...but the trans I have is a 1979 and will need new synchros, which is $$$ and doesn't have an LSD... The upside to a 5 speed is it allows me to race with any group....the automatic can only run in Lemons-Chumpcar and NASA....SCCA won't accept the auto
I can source an automatic with LSD for fairly cheap...but should at least refresh the seals in it too....
The cheapest option is to repair the automatic that's in the car....
Thoughts ideas.....opinion from people who have done the conversion before? I do like the automatic....since its been SO reliable....and makes the car super easy to drive.....
11-07-2010, 05:27 PM
#2
Three Wheelin'
FWIW, it's a lot more fun to drive my car since it was converted to a 5-sp. It might not be faster on a track, but I get the sense that a lot of this is about having fun and going on the journey...so I say, turn the page, and see what a new chapter brings.
11-08-2010, 10:33 AM
#5
Why does SCCA not accept autos? What if you make it so its shifted manually - which I believe you already had done?
I vote to just fix the one you have unless you are dying to race SCCA.
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11-08-2010, 12:33 PM
#8
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From someone who has done the conversion, its fairly straigthforward---two of us did my car in about 12 hrs on a lift. . In your particular case, it would open up some opportunities in SCCA, and, in my opinion, be more fun to drive. However, I don't think I would do it unless you put a LSD in with it. You can then enter into a huge debate with Mark K on the various benefits of gearing, but if it was me, with a stock 4.7, I would go with a 2:75 final drive and close-ratios....you shift more often, but keep the motor closer to its peak power, and you will still almost never get into 5th....
I would do it if I were you.... but I would also reverse the "estate" conversion if no more lemons races are in store...
Steve
I would do it if I were you.... but I would also reverse the "estate" conversion if no more lemons races are in store...
Steve
11-08-2010, 12:54 PM
#10
Rennlist Member
actually, Steve, there is really no noticable difference in gearing with the 2.75 vs the 2.2. the gears are not closer. Ive raced both at laguna in the exact same set ups many times. my time are almost identical. you give me a hp, and a reasonably same set up car, ill spin the same time. the only difference in gearing is not that the gears are closer, but the fact that the 2.75 puts you in a gear on one straight , turn 5-6,where you would need to shift, in an awkward point, and the other gear straights and turns, you shift exactly the same amount and get in to the exact same gears. We did a conversion to scots 2.75 4.5, then 4.7 and then 5L euro to a 2.2 after having the 2.7 in it for a long time. I drove and raced both. same times. 2.2 was much better for laguna, due ot the turn 5-6 straight. (kink). give it more power like the holbert or stroker, and the 2.2 becomes optimal. give it even more like anderson has and the 2.75 then becomes optimal again. all trade offs.
Now, not to diverge into a gearing discussion, but the stick is the way to go. it will make the car a little faster, and safer. remember, if the car dies you are coasting. when I lost my brakes at laguna (blown brake line) if i was in an automatic, it could have been a serious crash, vs not even an off track excursion due to downshifting and pitching the car. thats why they dont allow autos in SCCA or most other racing orgs. its not really that save if something goes wrong with the brakes.
Now, not to diverge into a gearing discussion, but the stick is the way to go. it will make the car a little faster, and safer. remember, if the car dies you are coasting. when I lost my brakes at laguna (blown brake line) if i was in an automatic, it could have been a serious crash, vs not even an off track excursion due to downshifting and pitching the car. thats why they dont allow autos in SCCA or most other racing orgs. its not really that save if something goes wrong with the brakes.
From someone who has done the conversion, its fairly straigthforward---two of us did my car in about 12 hrs on a lift. . In your particular case, it would open up some opportunities in SCCA, and, in my opinion, be more fun to drive. However, I don't think I would do it unless you put a LSD in with it. You can then enter into a huge debate with Mark K on the various benefits of gearing, but if it was me, with a stock 4.7, I would go with a 2:75 final drive and close-ratios....you shift more often, but keep the motor closer to its peak power, and you will still almost never get into 5th....
I would do it if I were you.... but I would also reverse the "estate" conversion if no more lemons races are in store...
Steve
I would do it if I were you.... but I would also reverse the "estate" conversion if no more lemons races are in store...
Steve
11-08-2010, 12:56 PM
#11
Rennlist Member
LSD is not a requirement, but thats an easy adder. with the little power you have it would be and is fine at most tracks. I raced with an open diff for few years when I was in the 240rwhp range. at 200rwhp, it wasnt much of an issue.
its a big job, and you have to think about it, if it is worth it will SCCA let you run with no rear windows?
its a big job, and you have to think about it, if it is worth it will SCCA let you run with no rear windows?
11-08-2010, 01:02 PM
#12
Nordschleife Master
Answered in you're own post, you don't have the budget for a good 5 spd with LSD. I wouldn't bother with less than an 85+ with good syncros and LSD, and those aren't cheap, or easy to find lately even at reasonable prices. Hunting down a good used AT shouldn't be that hard, maybe freshen up the seals before putting it back in.
When or if you find a good 5 spd, you can do the swap, pulling the existing tranny is just a fraction of the total job and you get to keep driving in the mean time.
When or if you find a good 5 spd, you can do the swap, pulling the existing tranny is just a fraction of the total job and you get to keep driving in the mean time.
11-08-2010, 02:00 PM
#13
Rennlist Member
I agree with Mike. A 5 speed will be only be an improvement of it is a later style in good condition. Otherwise you will have to shift slowly and carefully. So swap in the least expensive good used auto you can find for now and keep your eyes peeled for a good deal on a good late 5 speed for the future.
11-08-2010, 03:20 PM
#14
Former Sponsor
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, 04:01 PM
#15
Rennlist Member
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
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.