I'll chime in here with my .02 cents worth, maybe worth even less!
I see lots of folks touting the attributes of the venerable 1HD-T/1HD-FT engines, however, the torque is less than a 1FZ-FE while having the same HP (all be it, at different RPMS) . The folks that tout their 20+mpg diesel engine are averaging <=65 mph, which for some people is great but not for me. I'm not getting buzzed my semis for hours on end, too annoying. Yeah, spare me the "it's the journey, not the destination" speech. I tend to leave work, haul booty to the trailhead on fridays, then haul booty back home on sunday evenings. That's just the reality for most of us working stiffs.
Yeah sure, you can turn up the fuel and roll some coal but you ain't getting 20+ mpg doing 75-80 mph. Of course there are exceptions to this rule, particularly if you spend $$$$ on a "proper" turbo/intercooler/lift pump/etc upgrade. Everyone freaks about EGTs at the higher RPMs and rightfully so. The1FZ-FE gets horrible mileage and with a turbo, at least you're able to maintain USA hwy speeds while still getting crappy mileage! Actually, the mileage is a tad better with the turbo due to the transmission staying on 4th gear most of the time. It's rather amazing how sweet the A343F tranny is once you add 100hp to the engine.
If anything, I might consider going a H151 5 speed tranny in my turboe'd 80 just to eek out a little more fuel economy and become a more active driver.
Again, just my exteremely biased opinion here
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