[MrRocky]

Just curiously thinking whilst pottering in the shed.
I have a clapped out 5spd box on the floor from a 1.3 sierra and also a maruti 4spd box in reasonable nick.
Now my experience swapping the 5spd into the 1ltr car is that rpm isnt greatly reduced with the 5spd. Does anyone know the rpm difference at say 100 with no other changes than the engine/gearbox swap ???

[Gwagensteve]

Circa 17% from memory.

[MrRocky]

Hmmm too much for me but maybe an option as gearing for stock wt ratio on hwy ?

[Gwagensteve]

I'm not really following. WT diff and transfer gears are taller than 1.0? Wouldn't you need shorter gearbox gearing (numerically higher) if you wanted to run WT diffs in a 1.0?

[MrRocky]

Sorry my car is 4.1 diffs and 6.5 gears i was hoping that the final drive ratio of the 4spd was a little closer to the 5spd as a bit more distance between the gears is desireable for my setup and terrain.
I meant putting the maruti 4spd into a stock wt may be some benifit on the hwy if it reduces final ratio by 17% seeing as though it doesnt suit my application.

[Gwagensteve]

No, it doesn't work like that.

Basically a 1.3 gearbox has a wider ratio spread (1st is lower and 4th is direct +17% overdrive 5th)
The 4'speeds have a taller first (3.0:1) and a direct 4th- that's narrower- i.e smaller gaps between the gears.

Are you trying to raise or lower your cruise revs? In 4th in both gearboxes road revs will be the same for a given speed, but in a 1.3 box you can go into 5th and lower cruise revs 17%

[MrRocky]

Ahhh i was hoping a wider spread of gears with the 4spd and a closer final drive ratio to the 5spd box in 5th but if all its going to do is essentially delete 5th and lower my final drive 17% then its not suitable for me to use

[Gwagensteve]

The 1.3 gearbox will only lower your final drive when it's in 5th. When it is in 4th the ratio is the same as the 1.0 box.

[henno]

So with that in mind, is there ever a circumstance (ease of fitment and/or existing equipment notwithstanding) where a 4speed would be more desirable than a 5 speed? If the 5speed gives you a lower 1st and an overdriven 5th while everything inbetween is virtually the same, then there really isn't any circumstance where it would be favourable, is there?

[MrRocky]

Certainly doesnt seem there is
Id driven alot of 5spd converted marutis and to be honest didnt think there was a huge amount of difference in top gear 5th vs top gear 4th but obviously 17% is a lot more than my seat of the pants comparison.

[Gwagensteve]

No- never a good reason to use a 4speed, especially as 1st is taller.

[Gwagensteve]

Just to put some actual data around this:

SJ410 transmission ratios
1st: 3.160
2nd: 1.947
3rd: 1.423
4th: 1.00

SJ413 transmission ratios
1st: 3.650
2nd: 1.947
3rd: 1.423
4th: 1.00
5th: 0186

So according to that, 2nd and 3rd and 4th are the same for both transmissions, and my numbers were slightly wrong, 5th is 14% taller than 4th.

[henno]

Well that confirms it. Unless you already have one installed or you can't be bothered with tunnel mods, the 4spd is virtually a waste of time.

[Gwagensteve]

Except that everyone thinks they can simultaneously put 30" tyres on their 1.0 litre and pull 14% less RPM on the highway, so 5 speeds are like totally awesome, right?