Quote:
Originally Posted by t vago
I have considered a taller gear ratio, as well as a Laycock-type overdrive unit. I could go down to a 3.23 rear end with a taller gear, or I could effectively go to a 2.77 rear end with the Laycock unit.
Trouble is, I'm not sure if doing either of these things would actually gain any FE on my truck. Either option would push my engine speed well below 2000 RPM at cruise (1800 with the 3.23 diff, and 1560 with the Laycock unit), and any gain from running at lower engine speeds may likely be offset by the fact that the engine would be running well into the bad part of the torque curve. Nobody's been really able to produce a dyno chart for my engine (apart from the OEM propaganda), showing torque at speeds below 2000 RPM, so I can't really tell for certain.
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How big is your engine? My Frontier only has a 4.0L, and I get better FE running shifting at 1500rpm than I do shifting at 2000rpm when running around town- so at least in the city I'm sure you could benefit from a lower final drive ratio. I'm sure your engine is larger and has even more low end torque than my VQ40, especially since my engine is derived from the 350z and really made to rev. On the highway it may be a different story, but again- you HAVE to have more useable torque under 2k than I do- and I'm still pushing a 4500lb truck.