Reflections on 4BD1T vs 300TDi

**C H T** · 6th December 2011, 05:37 PM

FWIW

I have been thinking, for sometime now, about providing an update on the 4BD1T conversion in my Defender - so here it is.

The vehicle is used extensively for remote area/long distance travel. It was originally fitted with a 300TDi which we replaced 4 and a bit years ago with a factory turbo Isuzu4BD1t. The 300TDi did a great job but was simply too small for the work asked of it, and after two head gasket failures in quick succession followed by a new head, and then the failure of the new head (a manufacturing fault - yes it was supplied by Landrover and repaired under warranty) and no the engine had not had any cooling issues, nor had it been overheated I decided that to pursue the 4BD1T. I chose a factory turbo engine because of the higher spec of the internals, piston oil squirters etc.

The vehicle covered 214000ks with the 300TDi and has now covered almost 176000ks with the Isuzu (I have owned the vehicle from new). The conversion has transformed the vehicle: excellent liftoff torque (no more looking for low range when turning round on heavily broken ground), effortless cruising at the legal limit, excellent performance off road and total reliability (eg three solo and one 2 vehicle Simpson Desert crossings in the last two years). The only negative has been an increase in fuel consumption when compared to the TDi - average consumption has ranged from 18-20mpg towing to 21-23 mpg on the highway fully loaded vs 21-22mpg towing to 23-25mpg on the highway when fitted with the TDi.

I used a late suffix R380 and 1.2 transfer case which combination suits the power characteristics of the engine very well both on and off road. The gearbox has stood up very well, and apart from the fact the first gearbox needed a rebuild at 300000+ks everything is standing up very well.

I looked at other engine options including the 2.8TGV but settled for the Isuzu because the engine was factory fitted to LRA manufactured vehicles here in Australia, it has an enviable reputation for reliability, and genuine parts are easy to come by and reasonably priced.

What about costs? The conversion cost about $17000.00 (it was professionally fitted) all in including new alternator and aircon compressor.

Was it worth it? in one word - yes -

Would I do it again? again yes - but only if I could source a late model (92 on) engine - they are much more refined than the earlier engines (mine is a lot quieter and smoother than a 300TDi). I would do the conversion myself next time round to save on labour costs.

I still think the 300TDi is a great engine - I have a RR classic with one fitted that has been totally reliable with getting on for 350000ks on the engine. The engine is much better suited to a RR Classic/90/SI Disco size vehicle, and works extremely well in that application. If I could not get another Isuzu 110 I would probably look seriously at a 300TDi 110, and simply accept that it will have its limitations in performance.

I trust that all of the above is of interest

C HT

**flagg** · 6th December 2011, 06:42 PM

Good it hear it's all still going well. I was thinking not long ago about your gearbox.. and how it was going.

Doing the Simpson solo would be something indeed.

**Bearman** · 6th December 2011, 07:50 PM

Well done Chris, Although I am not a fan of any of the 5 speed boxes behind the Isuzu (especially turbo) it appears that you have had a good run with yours. I am convinced that a lot has to do with operator techniques and the way you treat a gearbox (i.e knowing when to shift to the appropriate gear to prevent lugging and not doing lightning fast shifts). I am still convinced that the best box behind a 4BD1T is an LT95 (with a 0.996 ratio TRB of course). I have done a lot of K's with one of these with minimal maintenance (500,000 K's) behind my turboed Isuzu and just recently replaced it due to a little bearing chatter at low rpm. All the gears are still fine as is the T/case and TRB intermediate shaft, only the mainshaft/layshaft bearings need replacing. Synchros and everything else are still good. It will be an easy reco. The added advantage is that with the availability of s/h LT95's (especially from RR's) parts are readily available at a reasonable cost.

**C H T** · 6th December 2011, 08:27 PM

Bearman

I have given serious consideration to replacing the R380/LT230 with an LT95 for the robust strength of the LT95, but thus far it has not been warranted. I do however think that the best LR gearbox to use behind a 4BD1T is an LT 95 from a strength and durability point of view. But even then I am very confident about the strength and reliability of my set up - particulaly considering where my vehicle has been and the way that the drive train has stood up to very harsh conditions. As you rightly say gearbox life does have a lot to do with the operator - and I do try and exercise a degree of nmechanical sympathy. I think the secret is not to hold onto fifth for too long on the hills and not to labour away in too high a gear.

C H T

**Bearman** · 6th December 2011, 08:51 PM

Originally Posted by C H T

Bearman

I have given serious consideration to replacing the R380/LT230 with an LT95 for the robust strength of the LT95, but thus far it has not been warranted. I do however think that the best LR gearbox to use behind a 4BD1T is an LT 95 from a strength and durability point of view. But even then I am very confident about the strength and reliability of my set up - particulaly considering where my vehicle has been and the way that the drive train has stood up to very harsh conditions. As you rightly say gearbox life does have a lot to do with the operator - and I do try and exercise a degree of nmechanical sympathy. I think the secret is not to hold onto fifth for too long on the hills and not to labour away in too high a gear.

C H T

I agree whole heartledly and commend you on the the run you have had with the R380 - you are evidently a very knowledgeable and experienced operator who treats his vehicle with respect. In the hands of a "driver" it may not have lasted as long. Having been in the machinery game for most of my life I can identify between "drivers" and "operators". Some people just do not understand how a gearbox or machinery in general works and have unreal expectations of 5th gear. When you see the size of it and what it does it really is incredible how long some of them last. As you say the instant it starts lugging or slowing on a hill is the time to downshift.

**uninformed** · 7th December 2011, 03:42 PM

where were you when my 300tdi died and I went the 2.8tgv....

as a point, the 2.8tgv I did was brand new. All in all costs would have been $15000. Was your engine new? does it sit further forward or back of the stock 300tdi postion? How is your front axle case fairing?

**uninformed** · 7th December 2011, 03:44 PM

also if replcacing the gearbox, why take a backward step to a rover product when you could have an Isuzu 5 or even 6 speed that will outlast the rover by 3x

**C H T** · 7th December 2011, 05:24 PM

uninformed

In answer to both your posts - The Isuzu sits in exactly the same position as the 300TDi; the engine I used was secondhand; and the front diffhousing is a Maxi-Drive laminated housing which is now in its second vehicle, and is standing up very well. I didn't use an Isuzu box because there were no easy options as to fitting one, and I already had the late suffix R380. I have looked at the MYY6S because the ratios would work very well but cost is a factor, and I'm not sure whether TheGrubbs conversion kit would suit the late model box

FWIW

C H T

**rick130** · 7th December 2011, 06:24 PM

C H T, what radiator did you end up using ?

<edit> and is it intercooled ?

**C H T** · 7th December 2011, 07:30 PM

rick130

I used a Landrover factory Isuzu radiator with an army core fitted. I have not fitted an intercooler - yet!

C H T

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