Geo Metro Modification List for Mileage

This is a work in progress list of all the modifications that are reasonably possible to get the best MPG out of a Metro. I will assume the starting point is a standard base Metro 3cyl/5spd for this article so if you have an XFi you are already well on your way.

I will try to keep the list in order of what I think the easiest/biggest gains first and harder smaller gains last. This list is not addressing the driving style changes. I am keeping it strictly about car modifications.

  1. Grille block and front air dam – very easy to add, just use stiff plastic and cover all of the grille opening except for a small 3×5 or so area in front of the radiator. Also don’t forget to seal the gap between the bumper and hood. Cost less than 10 bucks probably depending on materials.
  2. Weight reduction – get everything not required out of the car. Carry a can of fix a flat and toss the spare and jack. Rip out the back seat and seatbelts. Even the passenger seat and belt if you don’t need it. After getting all that stuff out take the carpet up and scrape off the asphalt like soundproofing on the floor, there is at least 25lbs of it in the car. All this stuff adds weight that you can use for faster acceleration or the same acceleration with less engine load. Also the car will go up a hill easier without downshifting.
  3. Advance the ignition timing a few degrees over factory. Just make sure to listen for knock and not blast the radio so you don’t damage the engine over time. 2-3 degrees is a pretty safe amount to advance it.
  4. IMAGE_00023 Use the 93-94 flat front bumper instead of the earlier 90s bumper with a rounded bottom. These are easy to find in a junkyard cheap. The left one in the picture is best.
  5. Take the passenger mirror off and mount one inside the car. Check local laws first before doing this.
  6. Acetone 3oz per fill up – This will show an improvement in mileage if your car has a weak fuel system. It cleans it out pretty well so after a few tanks just put it in once every dozen or so tanks just to keep the system clean. It is much cheaper than those little bottles of injector cleaner.
  7. Water injection – Use a fish tank gang valve to get water into a ported vacuum source on the engine. It works and you can pick up 3-5mpg with it but it is a pain to keep regulated and is probably the most annoying thing to keep right but it is cheap and easy to set up. There is lots of information about it online just search for ‘water injection fish tank gang valve’ or something to find information. I have used this in the past but it is impossible to keep tuned and running properly the way I did it and I gave up on the idea before trying to make it work better.
  8. XFi camshaft – under 100 bucks but can give you an easy 8mpg and make the car run a lot better on the bottom end. This mod works well with changing the gear ratios
  9. Find a 3.52 final drive transmission – The 3.52 is the tallest gear available. I have an article on here detailing the transmission ratios.
  10. Change to a larger diameter tire – this also helps lower highway rpms and if you are careful with your tire and wheel selection and stay as narrow as possible on the tire can gain a few mpg. Just make sure you change speedometer gears to keep it accurate. Also make sure to pick a good low rolling resistance tire.
  11. Advance the camshaft timing to suit your driving style – this one can take some time and testing to get right. Drill a new indexing hole in a different location to change the cam timing. Typically 3-5 degrees advance for an XFi cam and 5-10 for a standard cam. If you don’t want to do it yourself they are available on pretty cheap.
  12. Wire up a toggle switch to disable the alternator. This has shown as much as 10% increase in mileage. I have not tried it yet but when I do I will post a full writeup on it. Taking the alternator out totally is also possible but then it can limit your range in case you have to drive longer than normal.
  13. Rear wheel skirts – use something like aluminum flashing with something to stiffen it and cover the back wheels. It is a small increase in mileage but not that difficult if you don’t mind drilling a few holes in the body and pretty cheap really.
  14. Rear wing off a swift. The small wing that extends the top of the hatch is a pretty easy thing to install the holes are already marked for it inside the hatch. Just drill them out and install it. There is a tiny aerodynamic improvement from it but every little bit counts right?
  15. Smooth belly pan – using coroplast or some other material cover the entire underside of the car making it smooth. It is cheap to do but takes hours to install and makes working on the car a pain. But it can pick up a few mpg. Also trim the front air dam to be pretty short after doing this.
  16. Remove radio antenna and fill the hole in smoothly. Probably nothing that can be measured but every little bit counts. The antenna can be put inside the car and work almost as good as stock.
  17. Lexan covers glued to cover the headlight buckets. A 2 liter clear bottle works well for the material to glue on. Again probably not measurable but every little bit…
  18. Smooth wheel covers. These look cool and can be something as simple as a pizza pan bolted to the rim so they should be cheap to do. The salt flat racers always run these for some reason so they have to help some.
  19. MSD or similar ignition and bigger coil. Easier starts and smoother idle. The car can pull better at lower rpms with this so if you adjust your shifting down 100rpms or so lower than normal it can show gains.

All of the stuff listed here should help improve mileage. But before doing any mods it is best to get a baseline mileage by either driving a few tanks of gas before/after or using a mpg computer like the new open source mpg computer MPGuino. If anyone has any other ideas or can see anything I forgot let me know and I will add them to the list.

7 Responses to “Geo Metro Modification List for Mileage”

  1. I have a 94 Geo Metro, took the carpet out for some other mods: No soundproofing on floor! Some was on the sidewalls, I scraped it off and put lighter and better quality soundproofing on it, but I am going to fill in that huge space to the side of the rear passengers with a bass expander for my stereo: Not a lot of extra weight, but a real nice noise!

    Thanks for your web-site, it’s what inspired me to buy a Geo (automatic, unfortunately) and I get 50 pretty easy already with no real mods. I am not convinced I want to remove the spare and jack, but I am thinking about something along those lines… Maybe put it in for long long trips?

    I also wondered about the alternator, I may put an automatic system on it, but one thing to remember is this: Generic lead-acid batteries need to always be topped off. If you plan on really leaving the alternator off, you should consider replacing the battery with some type of “deep cycle”, so it won’t harm it leaving it low (potentially) for long periods. I know farmers wear theirs down and leave them down all the time (with their machinery) but they also have to replace the battery quite frequently.

    Right now I have the working a/c model, and I am not really convinced I want to remove it… I don’t actually use it anyway, it runs the engine down so bad and I am sure it really eats up the mileage, I just don’t know which is worse — both windows down, or a/c on…

  2. Is there a higher final-drive gear setup available that can be used in the automatic Geo Metro 1 L. to help with the MPG? I bought a ’92 convertible and got 35 MPG on the interstate driving 65-70 MPH on the trip home with the car. I will be installing the XFI cam grind from Delta Camshafts in a few days. Here are 2 sources for new OEM-like cams and other Metro engine rebuild parts including crankshafts: and .

  3. I have read your ways to save on a geo. I have a 91 Geo metro. I have done a few things that you have listed. And they WORK!!! Also you may try a what I call a pre heater for the fuel. My brother-in-law came up with this. And i got about 5 mpg more with it. It’s to bad you cann’t use it on newer cars.

  4. I have a 93 Metro, 3 cylinder. Was 4 cylinders an option?
    This is a great site with great ideas. However;
    If you increase the rim and tire size from 12″ to 13″, won’t you lose some low end power. Won’t the car have slower acceleration?

  5. YES but if your shooting for max mpg you would not be accelerating hard anyway 🙂

  6. I have run 185/70-14 tires on the front of my 1991 for over a yr. that’s 15% greater distance per axle revolution. so 15% more MPG. 155-12 on the rear. I also run 10% above the Max. PSI on tires less than 3 yrs old. a bit harder ride. The bad news is they rub on some bumps and corners. To the point of bending the fender and cutting the tire. It may be the old springs but next time I will go with 175/70-14. The 14 wheel is off a Swift GT. ATV lug nuts are necessary as the holes are bigger.

  7. I ran oem 15’s from a 2008 yaris i used to own… KILLED acceleration, and braking.
    And i didnt do the math involving tire diameter, circumfrence, and %ages but if o remember correctly i was getting like 25mpg so if someone could do the math.