Interesting to read these old threads, then place them into context with personal experience.
Obviously hard to do without dyno graphs, and how many of us have easy access to those.Quote:
Originally Posted by shack
Seat of the pants experience still can count as proof tho.
Back in the day(30+ years ago), dad had an Isuzu truck, can't recall the exact model, all I remember it had the 3.9 4 banger.
Tons of low down torque, first gear(of 5) useless unless fully loaded to 4+ ton and uphill take off.
I do remember tho it did run out of steam at 2500RPM. That is, it'd rev beyond 2500, and 2700 was the 100k/h cruise revs, but it felt strained and losing a lot of it's initial torque that was so obvious from idle to about 2000ish RPM.
We used to do a weekly run to Ballarat(from Melb), and that meant doing the Pentand Hills climb. Not very steep, but just a fairly long climb, so getting momentum doesn't really help.
The Suzi, with about 3-ish ton load, would scream along at 2700 RPM at 100k/h, and then early on up the climb would drop down to about 70 at about 2000 RPM(maybe 1900, can't recall exactly), no need to drop a gear, as all that did was rev the motor with zero gain.
The other truck I used to regularly drive at that time too, was some (totally unknown model) Ford trader.
Similar style std 5 sp to the Suzi, I don't know engine size tho. That truck had to be moved off the line in 1st, loaded or not. Didn't have a rev counter so couldn't compare revs at 100 with the Suzi, but both trucks maxed 100 on a flat, Suzi just got there quicker too.
The other truck I had a lot of experience with was a very old International C1300. 280 ci six. No idea on revs, but faster(70MPH) on flats, but couldn't hold 4th up Pentlands, had to drop to 3rd, and max up the climb was never more than about 60k/m(or 40MPH).
Inter was far easier to stall than the Suzi, especially uphill. Had to use throttle on the Inter, where sometimes just letting clutch out and no throttle would see the Suzi creep uphill.
Inter motor finally died and dad had a 5.8Lt UD NA diesel fitted to it. What a monster that was! .. by comparison to the old 280 petrol donk.
5 speed came with the UD motor, but what the conversion really needed was a high speed diff ratio.
1st and 2nd were totally useless. Easily take off in 3rd uphill, and 4th take off on a flat was no problem. When I used to drive it, I always thought about the wasted effort in not having sped up the diffs to max out the ability.
Up Pentlands in this new setup always maintained 60MPH(5th), I remember about 2500-ish RPM and you had to feather throttle as well, unlike the petrol Inter or Suzi where you just held it hard to the floor.
I can't confirm Red's reply that the Isuzu motor compared to the Tdi has more power overall or not, and likely that the Isuzu truck motor was tuned/cammed for a more truck like environment(ie. all low down grunt with no thought to any higher than about 2500 RPMs), compared to what was best for a Landrover existence.
Or maybe, dads Isuzu was just badly tuned. But my experience with the Isuzu 3.9 was that it had nothing of value in terms of power/torque beyond about 2500RPM.
