Best trans combo for a CRX DX?
 

Any Honda gurus, I'm really hoping you'll chime in on this one, but everybody is welcome to comment of course.

OK, I've just picked up a replacement (manual DX) trans for my '88 CRX DX (auto), and I have an HF final drive on the way that I can swap in to really leg the trans out if needed.... BUT.

To date, all the indicators show that I'm getting the best FE at around 3300-3500 rpm. With my auto, that puts me at around 73-76 mph or so. I'm assuming that the stock DX manual will have a similar final drive ratio. So will it really serve me well to add the HF final drive and drop my freeway rpm down below that point? I haven't crunched the numbers yet, but I'm thinking that the only way it would pay off will be if the HF final drive will put me in the butter zone in 4th gear and leave 5th for the flats and downhills where I can let the rpm drop when the engine isn't under any load (I live in a very mountainous area, which complicates my efforts some)... Is that in line with what other people are doing?

Also, does anybody know the most efficient rpm of the D15 VX engines? I'm giving some serious thought to picking one up eventually to stuff in my CRX. Maybe the HF final drive would be a better mate to that than to my stock engine....

Thanks in advance for your advice everybody....

Not sure on the trans questions but my VX's upshift light would be on around 2000rpms +/- I could drive that all day without ever needing to go above that point and get 40+ easily...even when i felt like revving it out to pass people I was get mid to low 40mpgs, HTH Matt

I know your 88 DX has fuel injection, but my carbed 87 civic 1.5 DX likes the HF trans in the 60-75 mph range, but stick with the DX final drive if you are going to do a lot of city driving.

An added bonus of the HF trans on the interstate is the reduction in engine noise/vibration. My engine only turns about 2200 rpms at 70 mph.

I would wait with the HF final drive until you get the VX engine. The VX has a lot more low end torque than your DX does so starting out is a lot easier. I have an HF transmission behind a VX engine in a 90 hatch and even with the VX, I often wish 1st gear was a little lower, especially when starting out on hills. Otherwise I love the low RPMs at speed. I know there are some here who have done the HF/DX combo and are OK with it, but I'm not that big a masochist. My ideal transmission would be an HF with a lower 1st.

I have a '95 DX hatch and swapped in a VX tranny 15 months ago. Although my DX has equivalent torque to my former '95 VX, it just doesn't have the same giddy up as the VX. The VX seems to have the right torque in the lower RPMs, making it quite driveable. The DX with the VX tranny is sluggish in the lower RPMs. That said, I wouldn't trade the tall gearing for anything because it improved my FE by about 10-15% and there's much less noise now, unlike the high RPM blender noise it had w/ the DX tranny. I'll bet my DX w/ the DX tranny had similar RPMs to your CRX DX, so I think you can expect similar FE improvements with an HF tranny. But it may make the car less "driveable."

If memory serves (I have a memory like a rusty trap... so I could be wrong), my DX trans has lower gearing throughout the gears, as well as a much lower final drive, so mating the final drive to the trans would yield a trans with a lower overall gearing than the normal HF trans, but would be much higher than the DX trans when all is said and done.

I'm torn about wether or not to swap the HF final drive in right off the bat, or to wait. I do commute to work with the car, but 80%+ of my driving is on the highway (albeit at 7000 ft altitude and in a very hilly area).

I'm just wary about having the engine/trans mis-matched too severely and actually hurting my FE... Right now I can manage about 45 on the highway if I drive conservatively. That's a surprise since the EPA FE rating for this model CRX is only in the mid 30s.....

Has anybody tried the HF trans, or an HF final drive in another trans and NOT had good results?

As long as you stay with the D15B2, stick with the DX transmission. The D15B2 DOES NOT like the HF transmission. I thought I might pick up some MPG with this swap, but only lost some. Save the HF transmission for a VX swap.