Why the Civic VX is a superior highway fuel economy (FE) machine

[MetroMPG]

(Originally written October 28/06)

The seed for this post was planted by Dan saying...

Now, if there were a high speed FE ranking, the VX would be hard to beat. Even without drafting, I can maintain leanburn at 75 MPH.

No doubt, it's the king. It's what I started out looking for when I decided to go all out looking for a fuel efficient ar 2 years ago. And the fact is it would better suit the type of driving I do normally do.

I tell you, if one ever turns up that's in good shape and not too rusty, I'll be sorely tempted to pick it up.

[MetroMPG]

Why would a VX have greater potential than a Metro?

I'm mainly talking about highway FE performance. Despite the ability to achieve ridiculously good efficiency in city driving, I normally use my car more on the highway, where the VX excels and the Metro suffers.

It's about the speed at which the 2 cars attain their EPA highway ratings.

With wheel skirts & grill block (+5% mpg), the Firefly met its EPA rating of 49 mpg at 60 mph (flat road, steady speed). At 55 mph, I saw about 54 mpg. Dan, on the other hand has shown he can keep the VX in lean burn (without drafting) and get 75 mpg at 55 mph. Nuff said.

If we made a top 10 list topic of: "MPG / avg MPH", the VX would be on top.

I think I'd kick his butt in the city/suburbia though So if that's where you do most of your driving, the Metro may be the one to have.

EDIT: I shouldn't be so brash: Dan says he hasn't P&G'd the VX much. maybe it's got monster potential in town too...

[MetroMPG]

Dan chimes in with some critical VX info:

http://72.14.209.104/search?q=cache:...&ct=clnk&cd=11

A good read on the VX. This compares the 92 VX to the 91 DX, although there are some references to the 92 CX. The interesting stuff begins on page 22.

To answer your question,

Table 4: Technologies Used to Increase Fuel Economy in 1992 VX
Fuel EconomyImprovement (%) '91 DX to '92 VX

Multi-point fuel injection 1.5%
Low rolling resistance tires 1%
variable valve timing 2.5%
lean burn 5 -10%
reduced friction 1.5%
roller cam followers 1%
Weight reduction 2.5
Aerodynamic improvements 1.5%
Gearing and drive ratio changes 2%
Reduced idle speed/rpm 3%
Shift indicator light 5%

Total 45.5% - 50.5%

When comparing to a CX, I would guess that only the VVT, lean burn, reduced friction and roller cam followers would apply. That adds up to 10-15%. Somehow I have a difficult time believing that.

Perhaps iyou could to put your aero mods on my car to test it out before taking the plunge with a swap.

[MetroMPG]

Notable (p. 16)

According
to estimates from Honda Corporation, about 5% of '92 Civic sales were VXs (Pollack
1992).

vs...

Despite its perennial mileage championship, the XFi made up less than 10% of Metro sales, and the Metro team decided that the sacrifices made in comfort to achieve the higher mileage numbers weren't worth the candle. Also, economy numbers are now so good for all Metros that GM'll let the Honda Civic VX wear the mileage crown - source

Interesting, just as a comparison of VX's sold vs. XFi's as a proportion of their respective "regular" models. "Less than 10%" suggests to me somewhere between 5 and 10%. Too bad it's not specific.

[MetroMPG]

Another interesting quote (p. 23)

The VX operates at wider gear ratios and, thus, lower engine speeds than the 1991 and 1992 DX. This is made possible by the enhanced low-end torque resulting from the use of variable-valve timing. The combination of axle and gear ratio changes accounts for a 21% improvement in fuel economy (Harrington 1992).

That's an enormous jump. Another one I find hard to believe, given I gained roughly 5% better MPG with my fairly extreme transmission swap - one which probably "hurt" the car's driveability in the eyes of a regular driver.

[MetroMPG]

Another VX plus...

Apparently the tuner crowd is throwing VX engines to the curb in their zeal for power. Making used working engines free / cheap.

[TomO]

I can attest to the tuner crowd throwing/giving away the D15Z1 motors. That is exactly how I got my spare VX motor with only 110K miles on it for free. The poor kid didn't even want to try and save money/gas, he was too smitten with lust over the false promise of speed and glory.

The real problem with the tuner crowd going after VXs is the fact that they ruin the harness so it's harder for people to install a VX motor into non VX Civic.

[DAN]

a look at what the tuner crowd shows how lost you can get re maping a engine management system computer.

[crx driver]

How well do you think a vx motor would do for a crx with an hf tranny?

[crx driver]

Also, is there a way to program a 90 crx hf for lean burn?