Thread: Which gearbox, & how to fix?

Yeah but what are the msa ratio's compared to the lt85?

Originally Posted by Vern

Yeah but what are the msa ratio's compared to the lt85?

Depends on your MSA. But first is way lower.
I had a MSA-5P fitted, now MSA-5G.

MSA5G,
5.788:1
2.998:1
1.594:1
1.000:1
0.776:1
5.798:1

MSA5P,
5.788:1
2.998:1
1.735:1
1.000:1
0.776:1
5.798:1

MSA5R,
4.987:1
2.998:1
1.594:1
1.000:1
0.728:1
4.774:1

Lt85 1st is .3.64, 2nd is 2.18. That's why you don't use first. We did the calcs on the lt85 with 1.22 transcase V's the lt95 with .966 transcase and the lt85 combo was 150rpm lower in top gear at 100k running the same size Tyre.

Originally Posted by rovercare

I only have the lt230r, yours if you want it

LT230R - that'd be needle bearings as opposed to roller bearings, yes? What problems would that potentially cause at the back of the 4BD1???

Up to late in 1988, the 4BD1T used in the Land Rover 6x6 produced peak torque at 1800 rpm. The later 4BD1T produced peak torque at 2200 rpm. See pic below comparing both versions.


For the later 4BD1T the torque is flat (+ or - 3 Nm) between 1800 and 2600 rpm.

Brake specific fuel consumption (BSFC) for the late 4BD1T is lowest at the same rpm as peak torque.

The only 4BD1 performance curves I have are for the late 88 on version. Peak torque is 255 Nm at 1900 rpm and the curve is flat (+ or - 3 Nm) from 1500 to 2400 rpm. BSFC is lowest at about 1400 rpm.

Since simple tuning adjustments (increase full load fuel rate and boost pressure) yield more torque from a 4BD1T, you should expect a similarly tuned 4BD1 to give similar performance.

The values above are for full load performance, we can only quess what might occur at cruise.

For what it's worth, I have geared my 86 trayback (1989 4BD1T with non-rover drive train and 33" tyres) for cruise between 1600 and 1800 rpm (100 to 110 km/h). My gearing is quite flexible and if I were cruising with a load on I can drop down a gear and cruise between 1800 and 2100 rpm (95 to 110 km/h) - see graph below for high range.

I have an LT85 and 1.21 LT230Q in mine, with 255/85-16 tyres.

I am happy with the 1.2 ratio. Even with standard size tyres, it would be a lot more comfortable on the highway than an LT95!!!!

Originally Posted by isuzurover

I have an LT85 and 1.21 LT230Q in mine, with 255/85-16 tyres.

I am happy with the 1.2 ratio. Even with standard size tyres, it would be a lot more comfortable on the highway than an LT95!!!!

How so. My calcs came up the same as Verns, hardly any difference in revs at 100km/h. Having swapped to an LT95, gearbox noise isn't noticably worse than my LT85, although I do have decent trans tunnel insulation. Engine noise still dictates.

Originally Posted by Bush65

Up to late in 1988, the 4BD1T used in the Land Rover 6x6 produced peak torque at 1800 rpm. The later 4BD1T produced peak torque at 2200 rpm. See pic below comparing both versions.

Another interesting thing John. Cheif managed to pull out the fuel pump calibration for the pump on my JDM 1986 4BD1T and it has a max injection volume about 10% higher than the one you have previously posted.

This gives some backing to the niggling memory I have of a claimed 330Nm/100kw rating for my engine. If we take that 6x6 4BD1T curve and crank it upwards about 10%, extend the power line out to 3,200rpm and the numbers seem to fit.
Injection quantities for calibration of 69-73 cc/1000 shots for the 88 onwards and 78-80cc/1000 shots for my pump.