UKKid35

I'd always assumed that Auto boxes didn't have the equivalent of first gear in a manual box, but when I decided to check the charts I found I was completely wrong:

928 Transmission Info

MPH per 1000rpm (S4 Man vs S4 Auto)

Gear..........Man...........Auto
1.................7................7
2...............11...............11
3...............15
4...............20...............19
5...............27...............28

Auto boxes are missing the equivalent of 3rd gear - weird...

Brett928S2

Hi PAUL

My S2 Auto does....44 in first....77 in second....117 in third and 160+ in top

There is something weird about that table...but I cannot quite figure out what lol

All the best Brett

UKKid35

Hi Brett

Your figures approximately equate to the shift up points for a A28.02 box under kick down, which you will find on the same page on the link I posted.

MPH per 1000rpm on your on your box is roughly:
8.5
13
22
31

jpitman2

tHATS WHAT TC ARE FOR. MULTIPLY TORQUE WHEN NOT LOCKED UP.
JP

FlyingDog

Your rounding is a little off, and they're doing some funky math.

Brett928S2

Hi Paul

Mine is a 28.08 box (last of the S2s) which is interesting as it gives me 11 mph better than an S4 at top of third gear...(due to diff ratio)

I wonder why they lowered the ratio for S4s...and also raised the rev limit I think....I would assume they raised the rev limit to offset the diff ratio alteration.....but WHY alter the diff ratio in first place???

Any ideas anyone ??

All the best Brett

mark kibort

just give me the ratios and ill give you the speeds at 6500rpm

S4s with 2.2 manual is:

55mph
80mph
115mph 4.5:1
155mph 3.2:1
220mph 2.2 :1

MK

atb

My '88 S4 A/T shifts at 5500rpm in first, so no help there. 2nd is good to a documented 94.25mph while banging the rev limiter ('87 S4 A/T at the drag strip), and third is 145mph (according to the ever so accurate stock speedo). Never held it flat in 4th to top speed.

UKKid35

Yes, I did use a little poetic licence, but not much. I rounded 7.63 to 7, 11.63 to 11. I should have correctly rounded 19.53 to 20 which would have made my point stronger still, but I messed that up!

I'm still interested in how Auto boxes can cope without the equivalent of a manual's third gear.

danglerb

The TC covers a lot of ills, and the ratios could be what was handy in the MB parts bin.

IcemanG17

Paul
These are the about the same #'s I came up with, but yours are a touch low.....my auto will do over 50mph in 1st, 80ish in 2nd, 140 in third & ??? in 4th, but mine does shift at 6200rpm in every gear too...so if a 5 speed if driven without third gear it is the same as an auto (for 2.20 S4's)......once the 5 speeds and autos had different rear ends then things get different....

Brett928S2

Hi Mark

Ratios...

1st = 3.676
2nd = 2.412
3rd = 1.436
4th = 1.00

The rev limit is the bad point here...on my S2 the rev limit is set to 6375 revs (unalterable) on an S4 auto I think its 6500 ?

Under hard kickdown... my autobox changes up at 5900....with a final drive ratio of 2.357...

Under hard kickdown PLUS Nitrous....I can actually hit the rev limiter (not a good idea) because the engine is increasing revs so fast it sort of beats the change up mechanism....



All the best Brett