Quote:
Originally Posted by mpg_numbers_guy
What do you mean by more linear? Just the change of the ratios themselves? How does this improve ease of driving? I thought the HCH1 manual transmission was just shorter and less fuel efficient..
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The final drive is a little shorter on the HCH so yeah, you'd have a little worse highway economy. I probably wouldn't make that trade. Ideally you'd put the HCH gears 1-5 into the Insight box, or the Insight final drive into the HCH box for the best of both worlds. Might be worth doing if it ever develops a grind and you decide to fix it. I'm still driving mine with a downshift grind and it's fine, the compensation is long since in muscle memory.
While the Insight transmission will spin slower on the highway, due to the spacing of the gears you end up needing to rev higher in the lower gears.
Only graph I have on my phone:
Notice how gears 1-3 are further apart than gears 3-5 and have almost zero overlap, whereas the higher gears have a lot of overlap.
When shifting from 1st to 2nd you need to get up to maybe 2200rpm in first gear so that you're above idle in 2nd. If you're climbing a hill without hybrid assist you might need to rev as high as 4000 in 1st (or 2nd) so you don't begin losing speed in the next gear. Sometimes you really just want a gear that's in between. If those gears were closer together you wouldn't need to rev as high, and the lack of torque without electric assist exacerbates it.
Meanwhile, I usually downshift from 5th to 3rd when passing on the highway because 4th is so close to 5th as to not be enough of a power increase. I still use 4th sometimes but I'd use it more if it were spaced more from 5th.
The HCH gearbox has more even spacing between the gears, so 3rd gear is more like gear 2.5 in the Insight box. I'm being nit-picky and really the Insight box is fine, this is more of an ideal world sort of thing. You'd probably get a little better city fuel economy while also being able to accelerate better in city driving with the HCH gear spacing. With the Insight's final drive you'd sacrifice no highway economy.
Edit: I'm actually getting both in my engine swap. I'm putting in a 6 speed transmission which has linear spacing between all of the gears, while also having what amounts to an entire extra gear beyond the Insight's 5th, for extra efficient cruising. This should partly offset the losses of having a bigger engine.