Good ratio for street and strip in heavy 245T...?

[HenrikGM]

Hmm...You know, when you have too many options, its getting hard to pick the right one...

I have this 245T 16V with GT3588 from a bus.
Its not really a drag car but more a very fast streetcar, wheighing in at maximum 245 wheight(Electric everything, 7seats, etc)

Last year i ran 12,32@196km/t, 2,09 60´ and 8@150 at best, picking up 46km/t the last 201m.

I use the E39 6speed getrag and 3,54 rear on Toyo R1R 255/40-17.

That gearbox is really nice, shifts like a machinegun, really sharp feel.

However....:
Being a 6speed there are a lot of gears to shift, in basically shifting all the time. Its vey easy to launch though, cause the car wont spin the tires in first gear due to the low 1st it basicaly runs the gear out without really loading the engine., it just flies off regardless if its on moist road, it does 2-2,1sek 60feet every time. It does on the other hand not really load the engine, so im halfway through 2.nd gear before boost goes past 1,5bar. This causes the car to run through 3gear faster than 2nd gear, which actually gives a feeling of sitting in a large rubberband that just keeps accelerating.

The speeds look like this now:
E39 6spd 3,54 7000
54,8
93,3
146,2
192,6
236,9
285,4


I could start it in 2nd gear, but the few times i tried it, it felt a lot like too high gear(or too much grip), and the 763 slips on the sinter disc, or the engine bogs down.

If i switched to 3,91 rear:
E39 6spd 3,91 7000
49,6(skip first)
84,4
132,4
174,3
214,4
258,4
Good 1:1 speed in 5th. 84 in 2nd might be a good start gear. Only 10km shorter than just starting in 2nd now.

or went to 3,15 rear:
E39 6spd 3,15
61,6
104,8
164,3
216,4
266,2
320,7
Good speed in 4th, but the gear is not 1:1, 2 top gears become very high. First probably still too low.

Or even ditched the nice getrag and went to a ZF GS6-53 from 530D:
GS6-53DZ 3,91 7000 skip 1st gear
42,2(skips first)
76,6
120,5
170,2
214,4
255,3
Maybe a really nice choise. Requires new GB and clutch disc. Concerned that the 1031 and 3,91 might not be a good choise?
Doubt about the actual gear ratios in the GS6-53DZ, have these data, can anyone confirm??
530D e60
5,08
2,8
1,78
1,26
1
0,84




Ideally, i would like a 1:1 top gear, freeway cruising speed(130+) at nice low rpm, not a too low first so i can launch a bit better, and save a shift on the quartermile. Yeah, want it all again...

What would the experienced audience suggest, giving a relatively strong B234 in a heavy 245T that needs to go fast on the strip, and be nice and driveable on the street?

Edit; Cleared up the omitted 1st gears for better understanding.

[The]

Something is wrong in the speeds?
3,91 is the lowest ratio still you have higher speeds in low gears then for 3,45\3,15?

[The]

The issue with "modern" gearboxes from diesels is that the stepping and ratios is way of for what you actually would want for a petrol engine.

With "normal" ratios in the axle you loose 1-2 gears since the ratios is made for high final gear ratios (and diesel engines rather short rpm register)

[HenrikGM]

Edited it for better understanding. I omitted the really low 1st, but can see it can get misunderstood. More clear now, i think.

[HenrikGM]

Anyone have a good shot at what a good gear ratio could look like?

Im thinking to try this config:

E39, use the first gear, 3,15 rear

It will then look like this:
E39 6spd 3,15 7000
61,6
104,8
164,3
216,4
266,2
320,7


The 1st may still be too low.

Another option is this:
gs6-53 4,11 7000 skip1
72,9
114,6
161,9
204,0
242,9




How fast can a 245 go in first gear considering the launch still needs to be reasonably easy? What are people using for first gear ratio?

In a few years im considering to buy a Gforce clutchless for drag, so it is nice to have a bit experience to start from.