Hi guys.What do you think about gearbox with shorter gear ratios like one from Alfa 156 2.5?I just bought Quaife diff and i have dilemma if i should install it in Alfas gearbox with little shorter gear ratios then original 6 speed Coupe gearbox.Honestly i do not need top speed i just want to make my car accelerate even better.My turbo is GTX3076 and its laggy as you all know,so maybe shorter gear ratios will help a little bit.

If it is possible and you are confident it won't negatively affect the gearbox then it makes sense to improve acceleration.

Alfa 156 2.5 diff is 3.9.....20VT is 3.1......for me the better option is Lancia Kappa 20VT GBox - 3.45....and it's direct fit.....

Yes but Kappa is 5 speed gearbox?

I don't think that shorter gears will make you faster if lag is your problem : big turbos usually need heavy loads to spin : the longer the load is, the faster the turbo will spin.
If you are just looking to have a better match between speed and rpm (for example going 4500rpm at 50mph instead of 3500rpm) then a shorter ratio will help with getting the jump faster. On a long run, the acceleration will still remain the same

bojke, can you post up your dyno graph?

I've got these ratios for the 156 V6 spd
3.937
3.500
2.235
1.520
1.156
0.971
0.816

Using your dyno plot, I'll show you a power to speed graph across all gears and calculate the performance before and after

As I always say though, simply fitting shorter gear ratios won't improve acceleration. You'd have to tailor every single ratio to suite the power curve to get any real benefit from it.

I do not have dyno plot unfortunatelly because i am currently abroad.
My plan was to increase a little rpms in lower speeds where the car is mostly used. I love to cruise on low rpm,but in real life i use the car around a city mostly.
I just do not need 200 mph top speed.

I remember when i had Tipo 16vt with Coupe engine that the car was much faster with tipo 16v gearbox. It was crazy.

Yes.....is your 20VT using 5 or 6 speed GB???
You can fit 6speed GB but with few mod's......

I already have 6 speed gearbox since my car is Turbo Plus model.I would only like it to be little shorter.

I decided it was easier (and more fun) to increase the power to the point that the gearing became too short. The car has been taken to about 6,750rpm in 6th gear - the needle was off the end of the 180mph speedo and there was still about 750rpm to go before the limiter (and it was still accelerating)

Acceleration is already "brisk" - with shorter gearing, I reckon it would get through the lower gears too quickly

Trappy - it would be interesting to see the effect on the stats of changing the gear ratios on my car (as you know, we've played around with my stats so that they are now VERY close to proven dragstrip figures)

I’ve already run the calculator over your car with 5spd, 6spd and Alfa 2.5 V6 gear ratios and, lo and behold, it’s makes next to no difference to acceleration. I’ve been saying this on here for years but it falls on deaf ears (much like the grip vs tyre width thing).

All that matters is the power available due to gearing at the particular speed. A better way of explaining the reasons for this might be to show a graph of (bhp@wheels-drag/tonne) against speed. I’ll send the spreadsheet over to you to have a look yourself and see what I mean. Gearing can be used to make this curve as smooth as possible and remove the dips between changes, but shorter gearing overall just shifts this effect around.

All this torque multiplying effect is irrelevant. If gearing could give you the perfect smooth curve (cars like a remapped Audi TTRS do this – have a look) then you have maximised the acceleration.

BTW does anyone has tightening torque specifications on gearbox. I will change diff so i need some info.