968 transmission in a 928?
#17
Race Car
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I'm surprised Mark would not approve of this swap... if you use the 968 box (and it doesn't blow up), you will have 5 useable gears instead of 4, so you will have more Kiborts!
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
![EEK!](https://rennlist.com/forums/images/smilies/eek.gif)
#18
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
the only swap I would approve is a cup car gear box 6 speed swap.
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
1, 0,..... read above.
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
#19
Race Car
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I remember from when I owned my 968 that the gears 3-4-5-6 were very close, which would be optimized for a very peaky HP curve. I'm not exactly sure if the extra HP would pay off with the higher number of shifts.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
![EEK!](https://rennlist.com/forums/images/smilies/eek.gif)
#20
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
just plot out the RPM range each gear was responsible to cover. plot it against the HP curve and see. you got to figure .2 seconds loss per shift, for not accelerating, but actually braking. (unless you have a sequential gear box) . just think about that for a second. (no pun in tended) 2 shifts is near .5 seconds. just think how much HP you need to gain to offset .5 seconds off a 1/4 mile time for example. sequential gear boxes with no lift shifting really add a lot of performance!
#21
Race Car
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
just plot out the RPM range each gear was responsible to cover. plot it against the HP curve and see. you got to figure .2 seconds loss per shift, for not accelerating, but actually braking. (unless you have a sequential gear box) . just think about that for a second. (no pun in tended) 2 shifts is near .5 seconds. just think how much HP you need to gain to offset .5 seconds off a 1/4 mile time for example. sequential gear boxes with no lift shifting really add a lot of performance!
Dan
'91 928GT S/C
![EEK!](https://rennlist.com/forums/images/smilies/eek.gif)
#22
Three Wheelin'
Join Date: Jun 2008
Location: Surprise, Arizona
Posts: 1,914
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
For the cost of a conversion to fit a four banger transaxle into the 928, (If I were to want to do such a thing) I'd look at other transaxles out there... I know the Corvette transaxle won't work without major modification (it's too freakin big and it's upside down), but for around 8K you could explore a Ford GT rebuilt.
Or from FFR they got the Slick 6 that looks small, but will handle big HP/TQ. It runs about 8500 BRAND NEW.
Lets face it. As 928 strokers continue to up the ante in HP, the stock transaxle is not going to cut it any more...
What happens to your racing class with a swap though?
Or from FFR they got the Slick 6 that looks small, but will handle big HP/TQ. It runs about 8500 BRAND NEW.
Lets face it. As 928 strokers continue to up the ante in HP, the stock transaxle is not going to cut it any more...
What happens to your racing class with a swap though?
#24
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
1st 12:1 unusable
2nd 7.6 kind of a tall, same as 928s first gear, actually a good tall 1st gear! (58mph)
3rd 5.3 very close to 928's 2nd, but taller (85mph)
4th 4.2 exactly to 928's 3rd. (118mph)
5th 3.4 shorter than 928's 4th 146mph
6th 3.0 Taller than 928's 4th 166mph
Doesnt lok like any gains in my book. same gears you would use on the race track, 2nd, 3rd, 4th with a 928 and 3rd, 4th and 5th for the 968 gear box on the track.
these ratios are very close to the M3s I race with . they use 3rd through 5th and I use 2nd through 4th. same same same!
2nd 7.6 kind of a tall, same as 928s first gear, actually a good tall 1st gear! (58mph)
3rd 5.3 very close to 928's 2nd, but taller (85mph)
4th 4.2 exactly to 928's 3rd. (118mph)
5th 3.4 shorter than 928's 4th 146mph
6th 3.0 Taller than 928's 4th 166mph
Doesnt lok like any gains in my book. same gears you would use on the race track, 2nd, 3rd, 4th with a 928 and 3rd, 4th and 5th for the 968 gear box on the track.
these ratios are very close to the M3s I race with . they use 3rd through 5th and I use 2nd through 4th. same same same!
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
Last edited by mark kibort; 09-23-2010 at 01:37 PM.
#25
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
1st 12:1 unusable
2nd 7.6 kind of a tall, same as 928s first gear, actually a good tall 1st gear! (58mph)
3rd 5.3 very close to 928's 2nd, but taller (85mph)
4th 4.2 very close to 928's 3rd. (115mph)
5th 3.4 shorter than 928's 4th 146mph
6th 3.0 Taller than 928's 4th 166mph
Doesnt lok like any gains in my book. same gears you would use on the race track, 2nd, 3rd, 4th with a 928 and 3rd, 4th and 5th for the 968 gear box on the track.
these ratios are very close to the M3s I race with . they use 3rd through 5th and I use 2nd through 4th. same same same!![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
2nd 7.6 kind of a tall, same as 928s first gear, actually a good tall 1st gear! (58mph)
3rd 5.3 very close to 928's 2nd, but taller (85mph)
4th 4.2 very close to 928's 3rd. (115mph)
5th 3.4 shorter than 928's 4th 146mph
6th 3.0 Taller than 928's 4th 166mph
Doesnt lok like any gains in my book. same gears you would use on the race track, 2nd, 3rd, 4th with a 928 and 3rd, 4th and 5th for the 968 gear box on the track.
these ratios are very close to the M3s I race with . they use 3rd through 5th and I use 2nd through 4th. same same same!
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
#26
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
You just said two different things here. I run the gear box I have because I cant change it (at least from the closer ratio persepctive) but, the gears I have are optimal for the tracks I visit and wouldnt change a thing. So, they are "Best" actually for racing. sequential gears? now that would be best! ![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
and by the way, the 968 gear box is not "a close ratio" one as shown by the ratios. close at the top 5-6th, but that is not a shift needed. actually, 1st to 2nd is unusually long!
Plus, there would be no need to, due to the flat HP curve. So your almost right. it wouldnt "mean much". It also means Im at the max potential to accelerate at any speed im at. it doesnt get better than that. Great example of that is the Audi R10. it only needed 5 gears to put down the 650hp that the 650 other high rever's did with 6. Flat HP curve!
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
and by the way, the 968 gear box is not "a close ratio" one as shown by the ratios. close at the top 5-6th, but that is not a shift needed. actually, 1st to 2nd is unusually long!
Plus, there would be no need to, due to the flat HP curve. So your almost right. it wouldnt "mean much". It also means Im at the max potential to accelerate at any speed im at. it doesnt get better than that. Great example of that is the Audi R10. it only needed 5 gears to put down the 650hp that the 650 other high rever's did with 6. Flat HP curve!
#27
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
."3rd 5.3 very close to 928's 2nd, but taller (85mph)
4th 4.2 very close to 928's 3rd. (115mph)
5th 3.4 shorter than 928's 4th 146mph " if second is taller and 4th is shorter the three gears you would use look to me to be closer ratios and less RPM drop.....
4th 4.2 very close to 928's 3rd. (115mph)
5th 3.4 shorter than 928's 4th 146mph " if second is taller and 4th is shorter the three gears you would use look to me to be closer ratios and less RPM drop.....
#28
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I didnt go through the numbers, but its all so close, considering that I dont use 4th but a couple of short times at the tracks we visit, and go deep in to 4th as is where it counts. on that same straight, 3.4 vs 3.2 is not that much of a diff, worthy of a change for that amount of time. taller 2nd would be an issue for getting off the turns. 3rd is the wild card. let me check..................
actally its identical. 4.2:1
so, there. 2nd is better at 5.9, 3rd is the same, and 4th is slightly shorter.
over all the gears are closer, but the trade off from 2nd for 4th advantages, cancel out, (hp-seconds) and you end up with not much being changed. SO, why bother. taller 2nd, same 3rd, shorter 4th as far as usable gears.
AND, with the broad HP curve of the 928, it becomes no- change event.
There you go! The HP curve alows you to determine this in a snap.
Mk
actally its identical. 4.2:1
so, there. 2nd is better at 5.9, 3rd is the same, and 4th is slightly shorter.
over all the gears are closer, but the trade off from 2nd for 4th advantages, cancel out, (hp-seconds) and you end up with not much being changed. SO, why bother. taller 2nd, same 3rd, shorter 4th as far as usable gears.
AND, with the broad HP curve of the 928, it becomes no- change event.
There you go! The HP curve alows you to determine this in a snap.
Mk
#29
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Here is the million dollar question. Anyone know why that the 3.4 vs 3.2 wont make any additional accelerative forces at the rear wheels with a flat HP curve in that area?
![Wink](https://rennlist.com/forums/images/smilies/wink.gif)
#30
Nordschleife Master
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
If there are 6 gears instead of 5 won't it be 20% faster?
People are on to the right path: if you're going to go with a different transaxle, go big. The 968 won't fit without lots of mods.