2000 Focus ZX3 - The SLOcus

[LocoJason]

Hello! Long time lurker and first time poster here. I've been into cars for as long as I can remember, and I have too many of them.

I purchased a 2000 Ford Focus ZX3 with a manual transmission last year to save on gas with my regular commute and to take on short trips out of state. It was cheap, well maintained, and under 100K miles. I decided on a focus after a lot of research. The Focus is hard (if not impossible) to beat in terms of initial investment cost, replacement parts cost, insurance, and last but not least: fuel economy. With a 25/33 rating, it's not too bad to begin with. I found after just a few weeks of owning it, that I was averaging more like 34mpg on the highway and ~28 around town for a total of 32 combined, and that's ON E10 fuel! Not bad for a car that cost me less than $3000. With ~20K miles per year being my average, the car would actually pay for itself in 3 years vs my previous commuter vehicle. Win-Win.

For many years I had been into performance cars of many types. I never really focused on fuel economy until I bought this Focus. Now, the reasons may not be obvious to all... but here is what pulled me into ecomodding my Focus. The Focus is an extremely slow car from my perspective. It has 130hp... that's 120hp LESS than my next-slowest car.

After a couple very small modifications, addition of a scangauge and some big modification to my driving habits, I now average around 35 mpg per fill-up.

Mods so far:
Front underpanels made from coroplast
Front lower grill opening blocked ~50%
Front tire spats
Tires at 40PSIg
Mobil 1 0w-20 AFE
Lots of coasting/modified driving/scangauge

Now, like most people before getting the scangauge I thought "slower is better, right"? That was very true for other cars of mine in the past... NOPE. Not for this Focus. After reading into it, I found it is apparently not so in all cases; especially with a well-tuned engine. An interesting thing to note is I consistently averaged better fuel economy at 70mph than I do at 65mph. I verified what the scangauge was telling me by continuing to monitor my fill-up MPG's and changing my target highway speeds between fill-ups. This seems counter-intuitive, but I have tested it many times and normally get ~.5mpg better at 70mph. I tested this again (scangauge only) using 60mph vs 65mph when driving back roads. 65mph delivered another .5mpg improvement over 60mph, again showing that the engine was in its prime operating speed/load when the car is closer to 70MPH in 5th gear. I have not tested slower and I still wonder at what speed the aerodynamic drag has reduced enough to offset the lower efficiency of the engine and actually deliver an increase in economy? Maybe around 50 or 45?

I've thought about some of the things that could be done to further improve fuel economy. Engine mods like a custom intake cam, adjustable cam gears, etc. were all major turn-offs to me. Why? This car can hardly get out of its own way as it is, I doubt I could tolerate driving a vehicle much slower.

So that leaves me with aero mods and rolling resistance to focus on...

[Daox]

Welcome to the site.

While I do find it hard to believe faster is indeed better, there are exceptions out there and will admit is is possible. However, .5 mpg variance is tiny and I would say that is well within the 'noise' from test to test. Would you care to share your testing procedure?

[JRMichler]

We used to have a 1995 Dodge Neon. That car averaged 41 MPG highway in the summer at 60 MPH. I once got the exact same mileage at 80 MPH. At the time, I was not paying attention to the weather, but I do remember that it was a hot summer day (no AC in the car). There may have been a tailwind.

The engine in the Neon had fixed camshaft timing, so was more efficient at higher speeds.

Anyway, better mileage at higher speeds is believable, but unlikely. Temperature and wind have a large effect on mileage, and you need to include them in your testing.

[ksa8907]

With electronic spark advance it could happen, id try a few different runs at those speeds and see. I get the same mpg at 55 as I do at 60, but 65 drops from 40 to 38-39. 70 is about 36mpg.

[redorchestra]

I changed my 205-50-16 tires to 205-55-16 and my fuel economy jumped. I am back to OEM size now though. my best mileage was 41mpg with smoothed hub caps, upper and lower grill block, and the lower block acting as a airdam. A Focus-friendly tire diameter chart

[LocoJason]

Thanks guys,

I will post my testing method as well as the spreadsheet I have been building in due time. My commute is over 20 miles largely without traffic and only two stoplights, which makes it pretty good for testing changes.

I also 'tested' a hot air intake on a trip last month, which was very easy to do on the focus by moving the fresh air duct down behind the radiator. This was not an ABA test, but on a 90 degree day the intake air temps jumped from ~98 to ~140. Ignition timing at the same load was about 2 degrees lower (27 vs 29btdc). No notable difference in fuel economy compared to the last trip up there (35.1 on both trips), but a notable power loss. Only one tank (400 miles) was burnt in this condition driving 70-75mph all highway to Michigan. On the way back (back to stock 'cold air' configuration) I managed 1.5mpg better, due largely to filling up with non-ethanol fuel while in Michigan.

Thanks for the link to the tire compatibility chart. The tires I have now are nearly new Michelin primacy MX4V in 195/50-15. They are supposed to last at least 50K miles, so I doubt I will be buying new/LRR tires any time soon. I wish I had a set of wheels/tires so I could test the effect of gearing changes though.

Not wanting to sacrifice power or make large investments for a small return in fuel savings, I'm looking mostly at aerodynamic improvements. I think between a passenger mirror delete, more under-panels, and some sort of rear airfoil I could get a 5%+ improvement.

[redorchestra]

I would love to see pics of your mods

[redorchestra]

I am making a trip from Nova Scotia to Southern Ontario 2000km and I am toying with the idea of a box cavity for my trip. http://www.google.com/url?url=http:/...sxZ2nEblrruScw

[LocoJason]

Yes! Thanks for sharing that presentation; very interesting. The box cavity was exactly what I was thinking about trying. Any vehicle with a steep rear window angle could benefit. I've been seeing them on the back of tractor trailers more and more frequently. Could use card board and duct tape as a test prototype, but could eventually be made in clear polycarbonite to be more visually appealing.

"Adding a shallow, 2°
diffuser under the
rear bumper
reduced CD by a
further 6%"

No picture of this diffuser though? For a whopping 6% change, I would think it would be shown.

Originally Posted by redorchestra

I would love to see pics of your mods

Sure, no problem. I will snap some pictures for you (all) this weekend.

[UltArc]

Very cool. What are your other vehicles? I am interested in seeing your under panels, I am very interested in beginning that project after the winter.