I'm interested in optimizing my 2003 Disco 2 as a daily driver and minimalist overlander and am interested in getting input from the community as to whether my potential strategy makes sense.

My primary targets for improvement are reliability and fuel economy with output (i.e., HP/torque) gains as a secondary target. I initially considered an LS swap, but this is off the table since ACE Conversions is no longer producing conversion kits and the other shops that do the conversion are cost prohibitive. So after a bit of research I've developed an approach that goes some way toward accomplishing these goals while retaining the core or the stock powertrain.

I have already installed the inline thremostat (link here) upgrade to minimize the risk of overheating and an electric cooling fan conversion (link here) to improve fuel economy and engine output.

To further improve engine output and fuel economy I'm considering getting the ECU reprogrammed by Tornado (link here), who do reprogramming on the D2 ECU that claim to yield an increase torque along the cuvre by 15 lb-ft and improve fuel economy by 10-15%. I'm also considering a remap from Speed Tuning (link here). My first question is does anyone have firsthand experience with ECU reprogramming from either of these companies on the D2 or other companies that do this for D2's?

If the ECU reprogramming yields sufficient engine output gains, the next step I would consider taking is to regear the transfer case from the stock ratio 1.222 to 1.1 to further improve fuel economy, these parts are available from Ashcroft (link here). I understand this would sacrifice some performance in terms of acceleration but fuel economy is my primary concern. Does this approach make sense considering my priorities?

Thanks for your advice/input!

 

How much would all of these mods cost, and how much driving would you have to do to recoup that amount as a result to the fractional increase in fuel efficiency?

 

Not to poo all over this but you will realize little if any gains in performance/economy.

 

The main downfall is the 4spd gearbox. If you really want to make a meaningful increase in your economy, you'll want to go to a 6spd unit to really optimize the gearing. Beyond that, LRR tires and keeping your aero clean will make the next biggest difference. It'd be cheaper to get an economical daily and deal with the crap mpg for road trips.

 

This is truly a cost/benefit analysis and I can't help but think the for the cost of all of your mods you would be able to buy a tremendous amount of fuel, to say nothing of the fact that the mods don't get you closer to one of your stated end goals of reliability. I think the key here is regular, relatively easy maintenance items which will yield small gains, but won't be expensive and make for a better costs/benefit scenario. My list would include:
1) Front oxygen sensors. They read lean as they age so the ECU wants to dump more fuel to compensate so swapping them out can pay for itself quick if yours are old. Check the Long Term Fuel trim with a scanner to see how yours are doing. The truck will throw a code when it reaches +10% buts that's a lot considering how inefficient the truck is to start with!
2) Fresh oils in the diffs and transfer cases, as oils and additives break down friction increases
3) A secondary set of rims and tires might be a good way to approach it as well, have a tire with lower rolling resistance for your "daily driving" and another set with a more aggressive tread for overlanding/off roading.

 

I don't think anyone's done the tornado tuning thing or the speed remap, hard truth is that a discovery is a big v8 gas guzzler with a 4 speed automatic, nothing you do will change that, it's just the way it is. Honestly even a 10% difference in fuel won't make that much of a difference you'll go from 13mpg to 14mpg. The extra power you won't feel either. Honestly if you want fuel efficiency drive a CRV or something like that, rovers aren't fuel efficient and that's just the nature of them. But by all means if you want to pursue this go ahead in my opinion I don't think you'll ever really outweigh the costs with the benefits.

 

I've thought about what can be done to increase efficiency over the years. The engine is an old design with lots of internal friction (flat tappet lifters vs. roller lifters, standard rocker arms vs. roller rockers, pressed-on piston pins vs. floating piston pins, etc.). Addressing each one of these with more modern designs, surface treatments (REM finishing or WPC treatment), and/or coatings would be an interesting exercise, but certainly cost-prohibitive. You'd never recoup the costs from increased fuel efficiency before the engine needs a rebuild. If you've got more money than sense I'd love to know how it turns out because this kind of stuff interests me.

Maybe you don't want to go all-in on this, but what about a few parts here and there? If you're having to re-gear your front and rear axles, you could take the time to have the ring and pinions cryo-treated and WPC treated for a reasonable price. Engine needs a rebuild? Perhaps the same for the bearings, and cam and crankshaft? Need to pull the fuel injectors off? Send them out to get them cleaned and balanced. You're not going to see 20mpg with all of this, but 1 or 2mpg improvement? Yeah, maybe?

 

Forgive me if I sound negative, but in my opinion this is a losing battle. Two key things you must accept when getting into the Disco world are: you aren’t getting anywhere fast, and you will be using a lot of fuel.

Every 1k+ trip I’ve done in a Disco has forced me to accept these realities. Putting in a cam, headers, all the stuff you mentioned and whatever else end up being lipstick on a pig. In my opinion, the D2 is penultimate SUV that does EVERYTHING well…. Except for doing it in a hurry or economically.

When I sold my last Disco there was a slight sigh of relief as I wouldn’t have to worry about keeping up with traffic any longer on trips. The Jeep does WAY better at that, but I prefer the driving dynamics of the Disco. So then, in my opinion, the only solutions are: 1- accept the D2 for what it is and move forward with just keeping it going reliably, or 2- get another vehicle better suited to economy and expeditiousness.

 

If you consider the D2 the penultimate SUV, what in your opinion is the ultimate SUV (since penultimate means second best)? Would it be a 2016 or earlier Defender? Or something else?

 

I don’t think one should expect good fuel mileage in a vehicle like an LR, it just wasn’t designed that way and tossing thousands at it won’t magically improve the efficiency. If you want a good mileage daily get an older Honda civic and use the LR for weekends and fun and do things that make it more reliable.