another ring & pinon ???
05-18-2010, 08:29 PM
#1
Race Director
Thread Starter
another ring & pinon ???
Okay the early automatics (3 speed) have a 2.75 rear end gear..... Will this ring-pinon work in later 4 speed automatics?
I just bought an early 8 plate LSD for the Estate..& figure its a perfect time to change the ring-pinon at the same time!
I just bought an early 8 plate LSD for the Estate..& figure its a perfect time to change the ring-pinon at the same time!
05-18-2010, 09:25 PM
#3
Race Director
Thread Starter
after researching WSM it appears the 2.54 would work no doubt and it also "looks" like the 2.75 mounts the same way as the later 4 speeds.....but I'm not 100% sure either....
2.75 would be about perfect.....it would give me 3 usable gears vs the two I have now....
2.75 would be about perfect.....it would give me 3 usable gears vs the two I have now....
05-19-2010, 11:19 AM
#5
Rennlist Member
did you not see the trade offs that you would see with the change? yes, you will get a lower gear, but you might have undesired trade offs in the other taller gears you spend most of your time in , especially at the tracks you visit. either way, it will be a rounding error change as far as lap times. why? because of trade offs. spend your time and energy getting the HP up to the 240rwhp range, as your one legger wont even be a factor to the downside until it becomes a factor to the downside. 
Just to go over the exercise again, what are the top speeds in the gears now?
Just to go over the exercise again, what are the top speeds in the gears now?
05-21-2010, 03:34 PM
#6
Rennlist Member
Here is the net net of the transmission game we have beat to death on so many occasions.
2.2 rear end 4 speed automatic
1st 8:1 60mph
2nd 5.3:1 90mph
3rd 3.1:1 150mph
to contrast to a stock S4, and redline in each gear (optimal gear box for laguna and 300 to 390rwhp)
1st 8.9 55mph
2nd 5.9 80mph
3rd 4.2 118mph
4th 3.2 155mph
If you put a 2.75 rear end on the 4speed auto, you get:
1st 10:1 unusable on a road course
2nd 6.6:1 72mph
3rd 3.9:1 127mph
If you remember all the "Acceleration = power/(mass x velocity)" discussions, you have to look a the time you will be spending in the HP ranges according to the speeds you would be at for most of a lap ( at a track near you).
one of the MAIN factors is your HP curve. if you notice on that 198hp 928 Estate, is that its peak hp is near 5000rpm and has peak torque near 4000rpm. (also near top HP values at peak torque, as 240ft-lbs of torque at 4000rpm, IS around 182rwhp. since in both cases, you would be using only 2 gears either way, and the 2.75 is obviously more optimized for the tracks you visit as far as TOP speed, BUT, if you look at the speeds you most frequent and for the longest times, you would see that tracks like thunderhill you might be better off with the gear box you have, certainly at Sears too.
Now, mainly because your hp curve only gives up 10hp at the lower rpm, it means that the gear box is much less of a factor, as HP determines the acceleration, not the gear ratios. in other words, if you had a flat HP curve from 3500rpm to 6500rpm, you could run around a track in 1 gear if you never had a speed slower than 64mph and faster than 120mph. (i.e. laguna, sears, thunderhill, etc for your car) . more gears would not add anything but shift time. in reality, you need a lower gear for those 2-3 times a lap that you need 45mph, and that would require only 1 more lower gear.
So, even if you could optimize the rear end for the speeds and engine performance you have, the gains for such a 2.75 change would be very minimal. again, spend time on lightening the car and getting larger wheels and it will pay MUCH better dividends for sure.
2.2 rear end 4 speed automatic
1st 8:1 60mph
2nd 5.3:1 90mph
3rd 3.1:1 150mph
to contrast to a stock S4, and redline in each gear (optimal gear box for laguna and 300 to 390rwhp)
1st 8.9 55mph
2nd 5.9 80mph
3rd 4.2 118mph
4th 3.2 155mph
If you put a 2.75 rear end on the 4speed auto, you get:
1st 10:1 unusable on a road course
2nd 6.6:1 72mph
3rd 3.9:1 127mph
If you remember all the "Acceleration = power/(mass x velocity)" discussions, you have to look a the time you will be spending in the HP ranges according to the speeds you would be at for most of a lap ( at a track near you).
one of the MAIN factors is your HP curve. if you notice on that 198hp 928 Estate, is that its peak hp is near 5000rpm and has peak torque near 4000rpm. (also near top HP values at peak torque, as 240ft-lbs of torque at 4000rpm, IS around 182rwhp. since in both cases, you would be using only 2 gears either way, and the 2.75 is obviously more optimized for the tracks you visit as far as TOP speed, BUT, if you look at the speeds you most frequent and for the longest times, you would see that tracks like thunderhill you might be better off with the gear box you have, certainly at Sears too.
Now, mainly because your hp curve only gives up 10hp at the lower rpm, it means that the gear box is much less of a factor, as HP determines the acceleration, not the gear ratios. in other words, if you had a flat HP curve from 3500rpm to 6500rpm, you could run around a track in 1 gear if you never had a speed slower than 64mph and faster than 120mph. (i.e. laguna, sears, thunderhill, etc for your car) . more gears would not add anything but shift time.
in reality, you need a lower gear for those 2-3 times a lap that you need 45mph, and that would require only 1 more lower gear. So, even if you could optimize the rear end for the speeds and engine performance you have, the gains for such a 2.75 change would be very minimal. again, spend time on lightening the car and getting larger wheels and it will pay MUCH better dividends for sure.