Quote:
Originally Posted by ke5aux
So should I look for a bigger or smaller final drive ratio?
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You want a taller FD ratio if you want to slow the engine down for the same vehicle speed.
The HF transmissions for the D-series are all the same gearing, through all 4 years. The 84-87 HF Carb'd transmissions won't fit, and have different ratios.
The available gear ratios for USDM Civic/CRX are as follows, from shortest overall to longest:
Si
EX (90-91 only)
DX/LX (Not the same exactly, but so close that they're interchangeable.)
HF
I'm not sure where the Std falls in there, but IIRC, the Std transmission is just a 5 speed with one gear removed. Honda used the 4 spd on base models because no other car at the time had a base model 5 spd (comparable vehicle), so there was no demand for it. They saved a buck, but the transaxle was designed around the then-available 5 speed gear box. I'm not sure what's necessary to change it to a 5 speed, but I don't believe any of the gears will mesh up.
There are several hybrid options to make longer/shorter gear ratios for your transaxle, if you have two or more available.
For instance, if you intend to run a turbo, HF transmissions keep the engine loaded as long as possible in each gear to spool the turbo and utilize the torque available, but they're extremely long in the gears... a good swap is to use the HF's 5th gear in the Si transmission, so you get faster acceleration when N/A, and you still get a longer 5th gear for cruising. You can also swap final drive assemblies between transaxles, making what would essentially be custom ratios.
If you're going all out on modding, it's a great idea to figure out exactly what you want, and where your "sweet spot" is, and build your own transaxle using available parts to suit your needs.
If you're just looking for a tranny swap, use the HF tranny if you can find one. (They're usually able to be gotten fairly cheap, as they lack in performance if you're not boosted.)
Other options include swapping tranny from 92-00 Civics, but this also requires that you either swap to hydraulic clutch assembly, or use an adapter to keep your cable clutch. You can also sometimes swap guts from one case into another, allowing you to use your cable trans with the hydro gears... Not sure if you can do this with the D-series trans though. I know the B-series can do it.e