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Old 02-23-2008, 09:40 PM   #1 (permalink)
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MetroMPG's Avatar
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,488

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 63.96 mpg (US)
Thanks: 4,032
Thanked 6,938 Times in 3,592 Posts
MetroMPG.com mailbag: various questions (final drive, exhaust, underdrive pulleys...)

Rec'd a message from a MetroMPG.com visitor who's written to me several times. Decided to post my reply here, in case it can prove useful to others who may be searching out this info...

I've followed your mods and tranny swap. I have to believe that you know (knew) about the possibility of simply changing the final drive ratio:


Why didn't you go this route, as opposed to swapping out the entire tranny?
Actually, I didn't know about the ability to buy those parts. In any case, it still requires removal of the transmission to do the job, and because I had the extra transmission (as a result of buying a Swift 1.3 that I was going to convert to electric), I took the path of least resistance. I also knew the Swift transmission worked well, having driven it before pulling it out.

Another point: the numerically lowest ratio that site offers is 3.93, which is still higher than the final drive from the Swift 1.3: 3.52. The lower, the better.

Also, I'm considering some other mods and would love to hear your thoughts vis-a-vis their value as fuel efficiently mods:
- Exhaust headers
- Aluminum flywheel
- Undersized pulley
I don't know enough about exhaust theory to say much more than: most exhaust mods improve flow at high RPM, which is something a fuel efficient driver doesn't do (high RPM). The stock exhaust is probably minimally restrictive at the engine speeds I commonly use.

As for the lighter flywheel aiding efficiency - If you're a pulse & glide driver, it may help marginally, since it may permit you to accelerate the vehicle more efficiently. Other than that, it's probably a wash, and I know someone else will likely chime in and say the engine may run poorly without the damping effects of the OEM flywheel's mass.

Undersized pulleys will help slightly at the water pump, probably won't make any difference at the alternator (since the voltage regulator may simply strengthen the field to compensate for the lower RPM).

Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown

has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
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