[SPEEDY]

And it's a doozy.

I got a 99 Jimny that's pretty much all kitted out, down side being above average death wobbles (being dealt with) and a top speed of 90kph at just over 4000 rpm.

I hate that 5th gear too, having to hold your foot down to maintain speed down a hill is bloody annoying.

I had planned to put a G16B into it anyway but I was just thinking about the box.
It was an auto conversation to manual, the thing about that is now it has a separate gearbox and transfer case, so I'm wondering if when I swap the engine out if I could just use a regular box from a baleno or similar to give it a bit more speed, with the crawler transfer case it's more then slowly enough in 4x4 and I'm not doing any heavy off road stuff anymore anyway.

So what would be my best option.

1) swap gearbox for more top end speed.
2) swap engine and leave gearbox alone.
3) swap out both as a unit.
4) swap out both and put in a 4 speed auto box again.

[monley]

What size tyres are you running?
What transfer case are you currently running?

[SPEEDY]

Sorry missed that it's a 6.5:1 and I'm running 235/75R15's
It also has ARB lockers front and rear.

[jdk81]

Gearbox from a balina?
Planning a long drive to Ballina, or are you talking about a holden commodore berlina, or a suzuki baleno. All of which options wont help you one bit.
However a holiday in Ballina is probably the best option of the three.

1) swap gearbox out for more speed - gearing wont magically produce more speed/power - look at the transfer's high range reduction if you don't like the rpm
2) swap in a g16b if you wish, the engine change wont fix your gearing, it will still be revving at 4000rpm at 90 km/h
3) only if putting in vitara aw4, otherwise leave it alone
4) swapping in a jimny auto wouldnt be worthwhile, id swap in a g16b and vit auto

The transfer case is offering a lot more range reduction than you really desire, so keep revving it higher until you get the speed you want.
At 100 km/h with 29" tyres, you are about 4200 rpm

Just keep using the jimny manual box in it.

Alternatively, if you want to auto it, fitting an aw4 (03-72LE) from a vitara would be my choice.
As its a great auto, and the OD ratio is 0.73, which would correct for the high range reduction in the transfer
However, with the auto torque converter slip etc you will have excessive reduction in a twin locked rig with glass drivelive.

Easiest and most sensible option would be to swap the transfer for something a little more desirable.

Other areas to look at

how are you measuring speed?

What is the engine compression like? If low on compression etc it would explain where the ponies went, so a g16b would be the desirable option (rebuilding a g13 is mostly a waste)

How old is the cat and muffler?
If the cat/muffler is dead and/or blocked it will really restrict the power and how it drives at speed etc

[Jezza86]

just do the extra RPM. mine is 4300 at 100kph.

[SPEEDY]

Speed is measured by GPS, engine was rebuilt about 35,000 ago, the muffler has a couple of loose baffles but was changed the same time as the motor, I plan on swapping it out anyway as I hate sports exhaust as the noise is Damn annoying after the first 3 hours of driving.
I would keep the rpm up but I don't like running and engine that high for 12 hours strait. I don't even like doing it for 2 hours strait.

But pardon any typos, work is extra busy atm an I've only had 5 hours sleep in the last 2 days and I still have to make it through this one.

[jdk81]

I agree, try a new quiet exhaust
4000 rpm isn't a lot for a small suzuki engine, its not under high load, I really wouldnt worry.
IMO trying to keep the rpm down by short shifting is super hard on many of the smaller suzuki engines.

Rebuilt engines don't seem to last long, so a compression test may be worth considering.

Based on info I can find, I get 3660 rpm for a stock g13bb jimny manual at 100 km/h

Assuming 235/75R15 = 29"
4.16 gears = 3930 rpm at 100 km/h
4.9 gears = 4050 rpm at 100 km/h
5.14 gears = 4150 rpm at 100 km/h
6.4 gears = 4100 rpm at 100 km/h
6.5 gears = 4200 rpm at 100 km/h

Now I I can look at the rpm, swapping transfer gears doesn't really offer much help.
The issue is with the jimny diff gears/your chosen tyre size.

Besides fitting a vit 4 speed auto, your other two options are to fit bigger tyres or just tolerate the rpm.