To be honest I have only used old Range rover classic v8s, one had carbs one was efi, my experience was that they sound lovely, drank like a fish (not an issue in the US unless they have burnt all their fuel stations), were okish on the top end but a bit gutless towing trailers, especially up hills.
However, everyone on here is an expert, I will happily bow to your superior knowledge. I ran a 300tdi for 10 years, it was no F1 car, but drove well, towed well, and was very easy to fix.
My first car was a 300Tdi Defender in 1997. Currently own a highly modified 200Tdi pickup. But we've had Disco's and RR's with Tdi's in. They are good solid lumps, and make good torque low down. And respond very well to a few tweaks. However the op says they are in Phoenix Arizona. And despite being before 7am over there, it is already 30 degrees C.
Tweaking the Tdi's will generally make them run hotter. Sure you can improve cooling, but there is no denying the EGT's will be higher. Therefore, I wouldn't want to run my own setup in the sort of heat they have over there. Which will limit some of the tuning you can do to them. We get away with it more so in the UK, as we don't see the same kind of constant and high outside temps, nor generally have the sort of mountains and long climbs you see in certain parts of the US.
As for the RV8, were they auto V8s you drove? Remember a torque converter will sap power and you only have 4 gears. If it was a manual LT95 4-speed Range Rover, they have tall gearing too. All of this will blunt performance. And an RR/Disco typically weighs more than a 90, again blunting the performance. Not to mention such vehicles are more refined, so will hide the speed more so than a raw Defender will.
We had a dyno day earlier in the year. My standard (bar exhaust) 4.6 p38 Range Rover made more power at the wheels than a standard Tdi does at the crank!!!
This is actually a Td5 90 and a tuned one too. It is making nearly 160hp on the dyno. The V8 Range Rover only has a performance exhaust and nothing else.
Now remember:
1. The 90 is a heck of a lot lighter, somewhere in the region of 500-600kg!
2. The 90 accelerated first and was in an optimum gear and rev range to do so. The RR was in D, had to wait for the driver to respond, kickdown and then go. And due to only having 4 gears, was not remotely in the optimum rev band to do this.
3. Imagine how this engine would go in a manual 5 speed car with much better gearing, no powered sapped from a torque converter and in a vehicles weighing 600kg less?
