1988-1991 Civic DX transmission on D15Z1?
 

I'm actually finally getting ready to drop in the D15Z1. But as alot of you know, I really don't like the HF transmission. I think it is one of the WORST engineered transmissions in terms of gear ratios EVER. I just don't like starts that are harder than second gear starts on my CRX. And while the CRX will happily creep at walking speeds in first gear with the clutch out in rush hour traffic, trying such a thing with an HF transmission will just kill the engine. And having just two usable gears (maybe three at best) for city driving neither makes things enjoyable OR efficient. Which brings me to my BIG question: would it be SO bad to use a 1988-1991 DX transmission on a D15Z1? Gear ratios would be INFINITELY better around town. Of course, revs would be higher on the freeway. But I know that this alone doesn't hurt MPG by MUCH. However, would they be SO high as to run the car in VTEC or bring it out of lean burn?

You should be able to do this okay. An alternate solution would be to drop a CA HF transmission in. Lower gearing means less MPG (which you were expecting with the DX) but it would mean better MPG than the DX, basically a compromise between the two.

CA HF tranny should still give you lean burn on the highway, faster starts than a Federal HF tranny, but better mileage than the DX.

i use an si transmission, much more livable except at highway speeds my rpms are 3000-3500! dx would be a little better. HF 5th in a dx transmission would be much nicer than both the si and hf.

You might want to give the HF trans a try first. The CA HF trans has pretty much the exact gearing as the VX trans. I hated my HF tranny till I got the car running right. Now that it perfoms correctly at low RPMs I can just drive it like a normal car. Hold the rpms to 1000 RPM and pull out the clutch easily and it goes. It's not so bad around town. You cruise 2nd at 20 3rd at 30 4th at 40 and 5th at 50. If you need to accel quickly you just skip a gear and then cruise. Take it up to 45 mph in 2nd and then shift to 4th and cruise

lol i remember i could get up to 70(redline) before i had to shift into 3rd.

Couple of things. First, if your having those issues with the HF transmission, I am thinking maybe I'll just keep my DX transmission, for now. Second, if you put in a DX, you could pull 5th gear from the HF and put in. It wouldn't be as low a rpm as the HF, but it would give you a lower rpm 5th. I think I'm turning about 3,000 at 60 mph.

Actually, 3000RPM at 60MPH sounds more like an SI transmission than a DX transmission. As for the fifth gear swap, I have thought about that. It would actually make fifth gear about the same as fourth gear is on an HF transmission. Yet another option might be to use an HF fifth gear and final drive in a DX transmission. Unfortunately, this transmission would still have the tall 'burn-out-your-clutch-in-a-month' first gear. BUT, it would have a MUCH better gap between first and second. It would also have the same overall ratio in fifth gear (obviously). And the gear ratio spacing would be closer to what Honda should have used in the first place.

first gear on a dx, si, and hf are all the same at least according to my factory service manual.

It is true that first gears are all the same (as I said before). BUT, at least with this transmission, you would have a better second gear (1.894 vs 1.65).

Well the deal is that the differentials are different. That is a part of where they get the rpm/torque difference's from. The problem with the HF transmission is that the differential is so tall that it makes it so you have to slip the clutch, more to get the HF rolling. Then it takes longer between gear shifts, because of the taller differential, as well.

Additionally, the HF has a taller 5th gear, as well. That's why I had suggested using a 5th from a HF combined with a DX box. The down side to that is that you have to open up two transmissions, take them largely apart, swap the parts and fit it all back together. It's something that can be done, but whether it is worth the hassle or not becomes a pretty subjective question.:rolleyes: