Honda VX/HX / VTEC-E swap MPG?

[phunky.buddha]

I've been hunting around the 'net for quite some time to see what kind of gas mileage the VX swap gets into different platforms. I've seen the CRX that gets 70mpg with the HF transmission- has anyone put it into something else, like a heavier Civic chassis or an Integra? What are your mileage figures at a steady cruise on the highway? Do you find it lacking torque in the taller gears? Has anyone (besides Full-Race) turbocharged a VTEC-E for the interests of fuel economy? I've searched around this forum and a few others, and answers are hard to find...

I'm asking because I'm thinking of putting a D15Z1 into my 88 Civic sedan chassis with an HF transmission (yeah, been done before), but I'm going to be towing about 500-600 pounds of extra weight. The car will be used as a normal commuter, so I have to be able to get up to speed in normal fashion, and still be able to cruise on the highway at low rpm without bogging the engine.

All input is appreciated!

[phunky.buddha]

Thinking about it a bit more, I guess I'd like to know what experiences people have been putting just the HF transmission onto other engines besides the VTEC-Es, like maybe a D16A6 (Si/EX engine) or the SOHC ZC. Also how the VX might have performed hooked up to a transmission not as tall as the HF, like the standard EF hatcback or sedan transmission.

[SVOboy]

Hey there,

I had the HF transmission hooked up to a modified d15b2 for a long time before I did the d15z1 swap. Basically, any combination of HF trans. and d15z1 is going to give you less power and more fuel economy, with both just giving you even less power and more fuel economy. However, they work well together since the tq. curve is so low on the d15z1.

Anyway, if you're putting it into a civic and driving slightly conservatively, I'd think you could expect 50s. People get that with the VX itself, after all, and the sedans are actually more aerodynamic than the hatchbacks were.

[phunky.buddha]

Hmm. I guess it makes sense that the sedan is more aerodynamic than the hatch- it has a tail to help break the wake a little bit. I'm thinking that taking 10-11 inches out of the overall height of the car will help too.

I'd like to go with the D15Z1, but I already have a SOHC ZC. If I could get 50mpg with just taller gearing an an optimized tune on the ZC, I'd like to just do that since it saves me the trouble of wiring in VTEC and the 5 wire O2 sensor. I can turbocharge the SOHC ZC almost without spending any cash with a small snail that would spool almost off idle and be perfect for a bit of vacuum reduction starting at 1500rpm- installing the Z1 and then doing that would be a bit harder. The wideband VX ECUs are a little more difficult to hack, so tuning a turbo properly on one would be a bit more difficult.

OK, I'm rambling. Sorry. More feedback from the Honda junkies please?

[SVOboy]

I can honestly say that wiring the o2 and vtec are about the easiest things you could do with wires on a car. If you know where the ECU is, it's even easier than wiring a stereo

But then I've done some crazy stuff with wiring so my perspective might be a little off.

Yeah, the z1 would be difficult to tune unless you went CA version and didn't run lean-burn at all, but then you're really defeating the purpose.

Anyway, the HF engine with the ZC would probably do well, but if you really ride it hard probably not so much .

[phunky.buddha]

Oh, no worries- I've done quite a bit of wiring myself. I do work at a company that build military spec electronics, including wiring harnesses.



You should see my old Civic's ECU harness.... with all the stuff that was added into the car, there were about double the wires compared to stock. It barely fit back into the wire sheath that was used to make a flat bundle out of it!

Oh, I guess what I was really thinking was that I didn't want to go back through and have to add all OBD1 hardware (distributor) to the car. If I can get 50mpg (or 60) in a flat cruise with the HF transmission and a leaned out tune on the ZC, I'd be more than happy with that.

Do you have any experience tuning Honda ECUs for running in the lean condition without a wideband O2 sensor to monitor ratios in closed loop? I've never worried about partial throttle tuning TOO much as long as the engine was happy and not tearing itself to shreds. I just don't know how lean I can go on the SOHC ZC without detonating since its pistons aren't coated and since the cam isn't designed for low rpm operation.

I guess I'll start with the HF transmission since it's basically free (to me) and can be used to get the car back onto the street without waiting for an engine to come in. If that doesn't get me there I'll try and drop one of these on:



I have a good spare (and all the support hardware) sitting around. Quickie spreadsheet math shows that I should be running spooling a little on the ZC by around 2000rpm, so that would increase efficiency in the intake tract at partial throttle cruise. I could probably get near to 200whp on the high end, and maybe boost mileage on the low end since it's such a small turbo. Have you had any experience with setups like that? I haven't really seen all that much around the site for using turbochargers to boost efficiency...

[SVOboy]

Tuning without a wideband can be a bit tricky, and I probably wouldn't recommend it anyway. I suppose you could just lean it out a hair, but you could just as easily buy a wideband for like 40 bucks (one of the crappy VW ones that don't work well enough to actually be used in a honda) and hook it up to a DMM to get your info.

Generally I wouldn't call for adding a turbo unless you're downsizing the engine. While it can be more efficient in certain ways, the primary efficiency we're concerned with is fuel efficiency and not thermodynamic . Most ECU tables I've programmed will really start to dump fuel on when you get anywhere near boostland, which isn't want you want. I haven't explored the possibilities exhaustively, but I suppose that's because I never say much possibility there.

[phunky.buddha]

Oh no... sorry- I meant without using a wideband ON the ECU to control the fuel ratio upwards past stoichiometric during normal driving since the normal narrow band O2 sensor is really only effective between 14.0 and 15.0. I always tune on a dyno and on the street with a wideband sensor plugged in for fuel/timing map manipulation.

I'm more worried about a tuned ECU being able to maintain air/fuel ratios in the 17-18:1 range or higher while running on a narrow-band sensor. I've never tried to tune for that.

As far as boost tables, I could probably set the ECU to run lean with very conservative timing up to zero manifold pressure and hope to avoid detonation- then start tipping in the fuel to keep the engine from puking on itself. I guess I'll just have to try it out.

Basically... I have all the tuning facilities and equipment at my disposal whenever I want to use them- and I want to modify as little of the car's configuration as possible to save myself some cash on parts. I'm sure I could add a wideband sensor to the car and hook up my Hondata S200 to really get the most fuel economy out of the ZC, but I'd like to sell the S200 and not have to convert up to OBD1 (which I really should) to do everything.

I can pretty much do the turbo install and tune on a non-OBD ECU without spending (or losing opportunity to gain) any cash at all... maybe I should just bite the bullet and throw in the Hondata and an OBD1 system to go for the best mileage possible. Honestly, the 50mpg goal is pretty minor compared to the overall scope of what I want to do to this car!

[some_other_dave]

One of the guys on the crxcommunity.com BBS has done just what you're talking about, at least as far as boost and lean operation are concerned. It's been a while since I've been over there, but I think "Mister Bone" may be the guy I'm thinking about who did that. He got good freeway MPG at light throttle settings (and no boost), and could rip off good drag strip passes by getting into the boost and richening the mixture to keep detonation at bay.

I don't remember if he ran a WBO2 full time or not.

-soD

[phunky.buddha]

Ah. I've read tons of stuff by Mista Bone. I don't really want to sign up for an account over there though... just tried to look him up on crxcommunity.com. I'll go roll over to d-series.org and hit him up. Thanks for the heads up!