Taller 6th gear..?

[tartan_rob]

I am not thinking of doing this but has anyone replaced the std 6th gear with anything really tall? I heard the Lotus Carlton does 1.7k rpm at 70mph. It would be nice to drops the revs off like that.

Anyone done that on any S/RS car?

Rob

[Jarv]

I think Hutch and Viperbl have both done this, though it was to get a higher top speed rather than lower revs at 70. Used a gear out of a tdi box IIRC.

[rikrose]

Indeed, the diesel 6th seems to be the current recommended solution to this, but the question arises - are you going to make back what you spend opening the box up and fitting a longer 6th gear compared to what you save in fuel on the lifetime of the vehicle? Also, is there enough torque to run the engine that slowly if the motorway goes from flat to slightly uphill? What about if you want to go from 65 to 70. Is there enough torque there to do that in a reasonable time?

The basic question is about what trade-off you make. Sure, you *can* lower the gearing more, but you'll end up losing on fuel economy if the engine has to work really hard against hills, or going from 65 to 70. On top of this, there's the cost of the gearbox surgery.

I agree that 6th is a weird gear, and doesn't drop the revs as far as any of the other gear changes do. I'd also like to have a longer 6th gear for all the same reasons, but I just don't think that the end will justify the cost, even though across my driving life, the car spends around 80 to 90% of its time in 6th gear. Maybe even into the 90s.

[derdle]

I've always been amazed at how short sixth gear is. I wonder if it is set this way in order to let the engine spin at a particular rpm at "maximum speed" of 155mph?

[Blue_Thunder]

Don't know about the RS4, but in the S4 doing 70-80 in 6th gear, you're at just the right revs to let the turbos kick in if you accelerate.

[tartan_rob]

Like I said, I wasn't going to do it, but I have done something similiar in the past and when the box is out, it is no big deal to play with the cogs.

Just wanted to know if it had been done much.

[Hutch]

I used a TDI 6th ratio (.60) Standard is (.68 )

@ 3500rpm I was doing 106mph. Standard gear = 93mph

@ 5000rpm = 151. Std gear = 132

@ 7600rpm = 229. Std gear = 201

It was a good gear to cruise in on the motorways although you have to really change down to 5th when you get stuck behind a car doing 60 or less.

Bit of a flat spot around 165-175mph then it started to take off again.

It's not an ideal solution as there is a big drop from 5th to 6th. You could try changing 5th aswell but you just move that drop down the box.

A .64 ratio gear would be good but Audi don't make one.

[s4woody]

A .64 ratio gear would be good but Audi don't make one.

i know a company that mite be able to..well they machine most other type of gear..

[philipwalker]

Great quote

Bit of a flat spot around 165-175mph then it started to take off again.

[Jarv]

@ 7600rpm = 229. Std gear = 201

Bit of a flat spot around 165-175mph then it started to take off again.

Hear you're getting your box sorted and will be trying to better your 191 on 9th. See you there