mark kibort

I have limited knowledge of the internal workings of our gear boxes, but when we are in 5th gear and its 1:1, is it 1:1 without a stage of reduction like 4th and the rest of the gears are. If so, then running a 3:09 rear end could have its advantages if we could show an efficiency gain buy using a 1:1 vs some greater reduction. if its just the difference of two gears of the same size (1:1) vs two gears of different size, then 1:1 wouldnt gain really any efficiency.
In the gear box world, for each stage of reduction you loose efficiency, even with multiple ranges of gear ratios within each stage of reduction.

this came up with a BMW racer buddy, who was touting his 1:1 5th gear (that is the same ratio as our 4th gear in our 2.2 S4s) as being more efficient and would put down more power to the wheels.

I do remember a dyno test i did with 3rd gear vs 4th gear, and i did see about a 7hp gain which may be the situation with 4th to 5th as well.

someone needs to do a 5th gear dyno run and compare it to 4th gear. (even if you dont take it to max rpm, just to get a few data points)


mk

Jim bailey - 928 International

When in 5 th the power comes in on the pinion shaft straight to ring gear the but all other gear use the layshaft. So power comes in on the inout (5th) then makes a 90 degree turn into the gear set then a 90 degree onto the lay shaft then jumps on the gear for 1,2,3,4 which transfers to the coresponding gear on the pinion. Everytime you turn directions with the power it has mechanical losses bearing loads and creates heat that heat energy is a direct loss of go fast energy....two gears when meshed and transfering power would just as soon jump apart from each other as turn.

Vilhuer

1 picture = 1000 words. Counter shaft will rotate when 5th is selected like it always does but it and Reverse gear are just along for the ride. So 5th is more efficient. I think 1:1 gear ratio is ever so slightly more efficient than 2:1 or 1:2 for example but this is very small gain compared to saving direct shaft provides over any gears.

Jim bailey - 928 International

Right you could throw away the layshaft and ALL the gears and still have a working 5 th gear !

dr bob

Hmmm. Those lines look more like a 6-legged 'W' than the double-H that shows on the top of the shifter. Must be that fancy ball-cup linkage that translates the motion. Cue is that 5th is on the top and left in this picture but down and right on the gear selector.





[pay no attention to the man behind the curtain... ]

hacker-pschorr

Now that would be a neat trick Mark - once you hit the straight, pull a lever to dump all of the gears you no longer need

IcemanG17

MK
It makes sense that a "direct drive" gear 1/1 would be slightly more efficient than a reduced or increased gear would be...but your major bummer is that if you try to dyno your car in 5th gear it will max out the top speed of most dyno jets.....so it will stop reading.....thats with the 2.2.....a 3.09 wouldn't have that problem.....but your speed in gears would drop something horrible.....

1st 38.7mph (6200rpm)
2nd 58.2mph (6200rpm)
3rd 81.6mph (6200rpm)
4th 108mph (6200rpm)
5th 157mph (6200rpm)

So 1st is basically useless....you could skip it altogether & start in 2nd which would be a touch higher than your 1st gear now, but a touch lower than an automatics 1st gear.....

mark kibort

thats why i was suggesting someone dyno in 5th, regardless if you couldnt make max hp numbers due to top speed limitation. any data point would be good enough along the way.

as i was talking about last year, the 3.09 basically just buys you an S4 gear box with a 4x4 1st gear (useless) and the rest of the gears are almost the same as the stock S4. However, that last gear, now 5th, (was 4th by numerical ratio) could have more efficiency as jim said and on a track like road america or Cal speedway, it could make a difference, especially since you stay in 4th for as long as you do in all the other gears combined! (actually longer!) if it was a 3% efficiency gain, that could be worth near 10hp and its effects would be even more due to the length of time spent in that 1:1 gear.

however, a major drawback would be gas mileage on the way home from the track!

Mk

IcemanG17

MK
You know you like your 221mph 5th gear....at least on the way home to save on gas you do!

mark kibort

Its pretty funny. i have to go 80 on the way home to get that 22mpg, otherwise, im in 4th on the way home!

It is pretty cool to drive 2.5hours home from thunderhill, with the engine barely above idle.

mk