Thread: LT95 T/F ratios Stg1/110/Isuzu

Originally Posted by powerband

I have a civilian 6x6, which runs 4 speed box. Has been fitted with 3.5 diffs, 31'' tyres. Using the GPS at 100ks it is doing 2,900 rpm & will pull quite well from 1,800 in top. I would not like 1st to be any higher. Hope this helps. Paul

If your numbers are accurate and tyre size is exactly 31" then you have 1.2:1 high range transfer gears.

Your first gear is 17.3:1 in high and 47.8:1 in low, vs 21.6: 1 and 63.5:1 of a perentie with 4.7s.

If Diana fitted a LR 5-speed and 1.2 t-case with 3.5s the 1st gear ratios would be ~ (H)14:1 and (L)39:1 - which would be miles too tall IMHO.

Ben

I get your point, but keep coming back to the same issue, if a 110 County 5speed uses the LT85+1:1003 LT230+3.54 diffs and 31" tyres standard, then I can not see why you're advising dropping 40% off the ratio in the LT230 just because it's got an extra diff, springs and 40" of chassis and will have a standard 110 tray.

I am adding a turbo and trialling a drop of 20% over the standard ratios. (We already have Justin C, suggesting the 6X6 perentie on 4.7 and 1.113 going 80KPH will be at the limit set by the fuel governor county-ratios-same-perentie)

Diana

Originally Posted by Lotz-A-Landies

Ben

I get your point, but I keep coming back to the same issue, if a 110 County 5speed uses the LT85+1:1003 LT230+3.54 diffs and 31" tyres standard, then I can not see why you're advising dropping 40% off the ratio in the LT230 just because it's got an extra diff, springs and 40" of chassis and will have a standard 110 tray.

I am adding a turbo and trialling a drop of 20% over the standard ratios. (We already have Justin C, suggesting the 6X6 perentie on 4.7 and 1.13 going 80KPH will be at the limit set by the fuel governor county-ratios-same-perentie)

Diana

Powerband has said above that he wouldn't want his gearing any taller in 1st. His vehicle is basically what you will have +/- a few hundred kg.

1.003 in an NA isuzu 110 is very tall. You need to be doing 100 km/h to change into 5th. While driving one through Wyoming (US) with DaveS into a very strong headwind (only load was 3 people, 3 backpacks and a roof rack with a tent and a few spares/tools), the fastest we could go was 80km/h in 3rd. We couldn't pull 4th or 5th.

If you were driving around unladen all the time I may agree with you. But don't you plan to put a camper on the tray AND tow with it???

Since you said you have soem 1.4 t-cases, it would make sense to build it with that and swap later if you think you can pull the taller gears.

EDIT - also don't forget that a hill start in an NA 4BD1 is the same as in a 4BD1T.

EDIT 2
For the purposes of comparison, both the current NLR200 and NPR200 have equivalent GVM and GCM to you
http://trucks.isuzu.com.au/media/164...00_ark0582.pdf
http://trucks.isuzu.com.au/media/482...75_ark0536.pdf
They run 3L or 5.2L TD engines. The 3L is about the same output as a 4BD1T.

Both have a first gear ratio of ~24:1

The NLR200 has 27.5" wheels and the NPR 29" wheels.

Originally Posted by Brian Hjelm

My 110 Australian supplement handbook gives the following-

3.9 Diesel LT95 0.996:1

LT85 1.003:1

V8 Petrol LT95 1.336:1
LT85 1.410:1

I have drawn a gear split chart for 3.9 diesels using either gearbox. I will see if they scan and post them.

OK, here are the split charts. Bear in minmd that the operating range of an automotive diesel engine is the revolutions band between governed rpm and maximum torque. There may well be excellent torque at revs below maximum but the law of diminishing returns applies. i.e. the lower the revs below max. torque the less power is available. The chart allows you to understand and select a gear that matches road speed to best power. In theory, full throttle, constant speed, at 1900 rpm is the best and most economical use of a 4BD1 or any other diesel engine. So you need to match your gear selection to this. Not generally possible but do your best.

If you are running a LT85 Diana, then I would use the 1.222:1 LT230. With a turbo fitted it will do as ben suggests, pull all the way to the fuel governor in top gear About 135kkph in 5th.

My rangie with LT95 at .996, and running 33" tyres I could see that speed flat maggot on a stretch of highway

JC.

Originally Posted by justinc

If you are running a LT85 Diana, then I would use the 1.222:1 LT230. With a turbo fitted it will do as ben suggests, pull all the way to the fuel governor in top gear About 135kkph in 5th.

My rangie with LT95 at .996, and running 33" tyres I could see that speed flat maggot on a stretch of highway

JC.

My box stock 110 County, 4BD1, LT85, tops out at 125-130 k's in high 5th. The engine does not have sufficient power to exceed this speed. Theoretical top speed @ 3200 in high 5th is 162 k's.

If anyone has a spare set of .996:1 tfr case gears I will take them off your hands.

Garry

Roverphiles,

I have been researching for a project and come back to this thread regularly.

I believe the Perentie vehicles all have the same transmission and transfer case gear ratios as follows:
4x4: HI 1.123:1, Diff ratio 3.54:1, and
6x6: HI 0.996:1, diff ratio 4.7:1.

The simple reasons were that ARMY did not want the 4x4 to be able to travel too fast, and for the 6x6 the gear ratio and top speed was linked more to start-up gradeability and overall maneuverability rather than highway speed: 95 Kph@3300 RPM. Some models had the fuel pump adjusted to give 105 KpH @ 3600 RPM.
Any spanners or greasers out there who can support or correct please?

MS