California98Civ

Quick question I hope you'll help with. Is it possible to swap the final driven gear for the 5th Gen CX/VX transmission into the 6th Gen DX transmission on my 1998 DX coupe? I have a 4.058:1 final reduction while the 5th Gen CX and VX had a 3.250:1 final ratio. For MPG I would like the taller gearing. I know the transmissions are different otherwise (cable versus hydraulic). But this is just the final reduction. Can I swap it? Will it fit?

California98Civ

bump. anyone have an answer to this one? thnks!

mayfly

yes it will. and they are both hydrolic. but it really wont make to much of a diffrence

California98Civ

Thanks very much for the response. So even though the engine was a little bigger for the 6th Gen, the transmission was kept about the same?

BTW, why do you think the swap won't make much difference? The VX gearing is about 20% taller than my DX coupe. Here is a road test that suggests a 20% RPM reduction at steady speed could mean as much as 10 MPG improvement: http://www.metrompg.com/posts/rpm-mpg.htm . See what I mean?

Relic1

http://hondaswap.com/reference-mater...n-specs-29132/

CX/VX ratios:
1 - 3.250
2 - 1.761
3 - 1.066
4 - 0.853
5 - 0.702
R - 3.153
Final - 3.250

DX trans ratios:
1 - 3.250
2 - 1.762
3 - 1.172
4 - 0.909
5 - 0.702
R - 3.153
Final -
coupe/sedan: 4.058
Hatch: 3.722


so swapping 5th will get you literally nothing. The VX gets it's lower RPMs from it's very high final drive.
Keep in mind lower RPM does not always mean better mpg, it's been shown many times that swapping to a JDM ITR trans from a USDM ITR trans will net better mpg despite the increase of about 500rpm on the highway.

Lower load on the engine means less fuel injected.
Higher foot position on the go pedal will get you the best result.

California98Civ

If you look more carefully at my question, you'll see it is the final drive I am asking about. I noted that the trans itself is mostly the same.

As you said, not always. I'd like to see the tests and their methods. I think you missed the test I posted above. Not a Civic but interesting anyway.

Sometimes. Lower load on the engine also means a less efficient burn relative to production of power. Depending on the engine, the sweet spot may be fairly high in load (not for cruise but for the most efficient place in the BSFC map). I have learned that my 1998 DX has its BSFC "island" around 2000rpm and 70-75% load. But that's not for cruise, that's for acceleration to speed.

But basically I agree that load is important, that the final drive is what makes the VX different, and that lower RPMs do not *always* produce better efficiency. For $140 or so I can get that final drive gear (new) and have a fairly close match to the VX transmission. Might be worth the experiment. Thanks.