Converting from a 6.2 to the best 6.5L Turbo Diesel for a Defender 90

[Madrugador]

I am a newbie to this forum and in need of a lot of help. I currently have a Land Rover Defender 90 with a GMC 6.2. It was installed not too long after I bought in 2005. For folks not to familiar with Land Rovers, their engines are inherently prone to problems. I have been super happy with this motor, but because of the gearing for the vehicle is for a high revving engine, at about 70mph it was at the maximum rpm output for the 6.2. So I added a overdrive and that helped the situation a bit better where I can go about 70mph and the engine doesn't sound like it is going to explode, but the RPMs at this speed is still a bit on the high side. Well the only thing left for me to do was to change the ring and pinion to a higher ratio and in doing so, the vehicle in general runs infinitely better, however the vehicle has trouble maintaining 5th gear with the overdrive engaged. The great thing is that the RPMs are in the optimum power range for the motor and best of all is the noise level is significantly reduced. In order to push through 5th gear with the overdrive engaged, I need more power.


I am new to the world of Diesels and the reason that I have a GMC 6.2 is that my mechanic thought that this engine would be a great match for this vehicle. It took him a little over a year and a half to install the engine in his spare time. Since it was a monster of a project for him and I would like to have quicker use of my vehicle upon installation, I am going to need a shop that can work on specialty projects or a shop that is familiar with the Defender 90. Now that a 6.2 is already installed, wouldn't a 6.5 or Cummins be easier to installed? There is alway the question of room? I am thinking that if a 6.5L can fit a Jeep then the 6.5L should fit a Defender, how can one know for sure? Are the new 6.5L motor like the P400 AM General more fuel efficient that 6.2 motor? Because there are counterfeit motors out there, I am going to need to know what reparable suppliers to purchase a motor from?

Any good tips would be greatly appreciated! Thank You for your time.
-Madrugador

[convert2diesel]

First of all, welcome to the board. No better place to learn about these engines.

Something does not add up. What RPM are you turning now @ 70MPH with everything locked up? For reference, I installed a 6.2 in a Buick Roadmaster with 3.23 gears and 235x15 tires (28.8 in diameter) and at 70 MPH the engine in 4th gear, locked up, was turning a little over 1,900 RPM. Never had a problem with not being able to keep it there on the level though partial grades would unlock the torgue convertor occasionally.

To put it into context, this was a 5,000 lb. car. Granted the aerodynamics were better than the Rover but the engine had more than enough umph to keep it at highway speeds. Ideally, these engines like 1,800 RPMs, and get their best torque and fuel economy at that speed. Thus I usually drove it at 60-65 MPH.

If I was in your shoes, I would be looking at the current powertrain before investing in another major engine swap. As I said, something doesn't add up.

Bill

[Edahall]

Never had a problem with my 82 Suburban staying in overdrive. In fact, the faster I would drive, the more power it had in overdrive. It has 3.08 gears, 700R4 transmission and 30x9.50 tires.

Does the engine develop any black smoke while trying to maintain 5th gear?

A Cummin 6bt would be neat in that Land Rover but it would break everything behind it.

[trbankii]

I agree with the others. The 6.2 came in fullsize pickups and Suburbans - so your Defender should be well within its capabilities.

If you do go for a switch, the 6.5 should pretty much bolt right into place of the 6.2 - with the exception of the turbo. The Cummins is quite a bit taller and longer and would be like starting from scratch for a swap.

[Madrugador]

Thanks for all of the responses. I will try to answer some of the questions.
The gearing in a Land Rover (I am assuming) is very different than that of GM.
The transfer case is the stock case for the vehicle, but there is a Global Roamer Overdrive that can be engaged by a level inside to lower the RPMs by 28%.
The standard differential ratio is 3.54:1 ;however, I changed the differentials to a ratio of 2.83:1, so that when I am in 5th gear with the overdrive engaged, it is a quite a pull for the motor, but there isn't any smoke in this gear. I may be able to get by by installing a turbo, because I don't think I may need much more power to pull that gear comfortably. It is nice to have all options on the table.

[trbankii]

If I may ask, why were the diff gears changed? That’s an awfully high ratio. Any chance to change them back?

[Madrugador]

Hi Trbankii,

I changed the diffs out because, with the stock diffs I would run the 5th gear out with the overdrive engaged. It is as if I needed another gear. The RPMs would race past 2,500 and the engine noise was deafening. Land Rover don't offer a lot of choices of Transfer cases, so changing the diffs was my only option. Believe me, the truck runs "infinitely" better, it is just getting enough power to comfortably pull 5th gear with the overdrive engaged. I don't think I would need to have a lot more power because depending on the wind conditions and the lay of the terrain it can hold it. Hopefully, this gives you some more insight into my problem. Thanks for the interest!

[AKMark]

Interesting. I have a 6.2 with 4.10 gears, and no overdrive and while it maxes out close to 72 mph, there's no reason my K-5 should ever go that fast.

I've driven several 6.2's with 4.10 gears and stock size tires with no overdrive and they use almost the same amount of fuel vs the ones with overdrive and 3.42 gears. Are they louder, yes, it's a product of owning a indirect injected Diesel.

I can say the non overdrive trucks lasted longer and worked better for me. The old 6.2's if not turbo'd love to run at near 3000 rpms. They'll do that all day long without issue.

I know guys with 6.2's with no overdrive and 4.56 gears that max out at 62 mph. Still works great, loud, but pulls a trailer better than just about any other 6.2 out there.

To each his own.

[trbankii]

What size tires are you running? Something just isn’t adding up here.