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Old 12-21-2010, 01:33 AM   #1 (permalink)
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Build Thread: Max City MPG from a $250 1991 Geo Metro

Through a fluke of availability I now own 2 Geo Metros: a 4 door 3 cyl/5 speed I bought yesterday for $250 and a 2 door 3/auto I got a month ago for $350. The 2 door needs an engine and I was building one. However, I needed a 5 speed setup so I answered an ad for a $300 4 door. It turns out that the 4 door is in fairly good shape and already runs and drives as is. It needs some sorting, but that is to be expected at this price. I offered $250 and the owner accepted. As of today, I have installed the battery from my 2 door, paid for the title and tag and it is now on the road. It had sat in this guy's yard for about a year or so but it seems to be none the worse for wear. It needs something in the front suspension, a properly hooked up and cleaned EGR system, an intake air temp sensor and it's plug, and a good general cleaning. So far I have pressure washed the majority of the car-including the interior. I took it out today and worked on it with some Simple Green and a scrub brush first. It seems that all my cheap Metros are doomed to smell like dog. It all turned out to be in decent shape except for the carpet and driver's seat. I'll deal with them later as I hope to find replacements in the junkyard.

The goal for this car is to improve my economic situation as a pizza delivery driver/returning college student. I figure it should save me $150-200 a month in fuel costs over my Nissan Frontier. I believe it should be capable of 40+ mpg under these circumstances but my goal will be 50 mpg city. As such, I feel that the stock gearing is adequate as a lower gear should permit the car to accelerate with less throttle opening than it would with a taller gear. I do plan to experiment with taller tires though in order to try and fine tune the sweet spot where mileage and my driving needs mesh the closest. It is a harder task in some ways than maximizing highway mileage as you cannot just tune for steady state speeds. You also don't get too much benefit from aerodynamic tweaks either as the giant magnetic sign on the roof pretty much stands to negate any gains you might see.

The engine in this car is a big, giant question right now. I was planning a new engine for my 2 door Metro and had shipped the head off to Suzuki G10 guru 3 Tech Performance for a fuel economy head and cam package with stainless exhaust valves. I do plan to complete this engine. However, which car should I put it in? If this engine is good then it will probably go into this car and this engine will go into the other car and it will be sold off. If the compression check does not come back good tomorrow then the new engine goes in the 2 door, the 5 speed comes out of this one and I will sell the 4 door shell off to an individual who has expressed interest. This then is a tentative build as things may yet change dramatically in my little Geo universe. One thing will remain the same though ans that is that I WILL build a car and chronicle it here. Without further ado then, here are the pictures.












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(Note: the car sees 100% city driving and is EPA rated at 37 mpg city)
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Old 12-21-2010, 08:53 AM   #2 (permalink)
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Sounds like an interesting build. Looking forward to the progress.

I think you are a bit mistaken (or I read your post wrong) on how gearing and throttle works. As an engine gets loaded more it operates more efficiently. Having taller gearing tends to load the engine more thereby increasing efficiency. So, you want to have to use a lot of throttle. I believe the manual trans from the 4 door is the one you want to use because of this, though I am no Metro expert.

Anyway, I don't think you'll have much problem hitting 50 mpg if you combine your modifications with some good driving techniques.
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Old 12-21-2010, 04:46 PM   #3 (permalink)
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Your 5-speed has a 4.10 final drive. The two taller options are the 3.79 from the Metro XFi and 1995-2001 Metro/Swift 4-cyl, and the rare 3.52 from the 1989-1994 SOHC 4-cyl Swift.
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Old 12-21-2010, 05:58 PM   #4 (permalink)
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Quote:
Originally Posted by Gasoline Fumes View Post
Your 5-speed has a 4.10 final drive. The two taller options are the 3.79 from the Metro XFi and 1995-2001 Metro/Swift 4-cyl, and the rare 3.52 from the 1989-1994 SOHC 4-cyl Swift.
I plan to try some taller 13 inch wheels and tires up front to see if the XFI gear ratio would improve things.
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No green technology will ever make a substantive environmental impact until it is economically viable for most people to use it. This must be from a reduction in net cost of the new technology, not an increase in the cost of the old technology through taxation



(Note: the car sees 100% city driving and is EPA rated at 37 mpg city)
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Old 12-21-2010, 06:05 PM   #5 (permalink)
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Quote:
Originally Posted by Daox View Post
Sounds like an interesting build. Looking forward to the progress.

I think you are a bit mistaken (or I read your post wrong) on how gearing and throttle works. As an engine gets loaded more it operates more efficiently. Having taller gearing tends to load the engine more thereby increasing efficiency. So, you want to have to use a lot of throttle. I believe the manual trans from the 4 door is the one you want to use because of this, though I am no Metro expert.

Anyway, I don't think you'll have much problem hitting 50 mpg if you combine your modifications with some good driving techniques.
Everything in moderation though. I have a 1985 Cutlass with a 355 Chevy that picked up 2-3 city mpg by going from a 2.41 gear to a 3.23. In a car that was getting 12 mpg, that is a very significant change. Also, while pumping efficiency may be compromised by a throttle being closed the fact remains that the engine is still ingesting less air and fuel than it would need to sustain higher RPMs with a throttle more open. Ideally then, you would like to eliminate the throttle like Fiat did in the Multiair engine, but in a throttled engine you will still generally use less fuel with less throttle and less RPM. Are there mathematical exceptions to the rule? Yes. A car is a complex system and thus has many more variables than any one simple axiomatic answer can provide. All in all though it is an experimental process to optimize the car for a variety of situations.
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No green technology will ever make a substantive environmental impact until it is economically viable for most people to use it. This must be from a reduction in net cost of the new technology, not an increase in the cost of the old technology through taxation



(Note: the car sees 100% city driving and is EPA rated at 37 mpg city)
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Old 12-22-2010, 11:47 AM   #6 (permalink)
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Quote:
Originally Posted by Jim-Bob View Post
I have a 1985 Cutlass with a 355 Chevy that picked up 2-3 city mpg by going from a 2.41 gear to a 3.23. In a car that was getting 12 mpg, that is a very significant change.
Is it possible that the gearing change allowed the torque converter to lock up at city speeds? Or even just allowed the trans to shift into top gear more often?
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Old 12-22-2010, 12:24 PM   #7 (permalink)
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Sounds like the perfect place for a scan guage or MPGuino... Being able to see MPG instantly seems invaluable to your situation.

Lightweight effective aerodynamic mods will almost always help the mpg, even at low city speeds, see:
Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

A hybrid would probably help a lot in the driving you plan to do, though your budget would have to allow for it. It's an interesting "problem" though, you wouldn't want to give up a good tip by being late... I suppose shifting early and keeping it at full throttle until you reach your desired speed would work well enough. An efficient (if there is such a thing) CVT would be the perfect transmission for you because of the quicker acceleration (I bet just making a light really helps with the delivery time.)

Really interesting build thread, good luck!
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Old 12-22-2010, 12:37 PM   #8 (permalink)
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Quote:
Originally Posted by Gasoline Fumes View Post
Is it possible that the gearing change allowed the torque converter to lock up at city speeds? Or even just allowed the trans to shift into top gear more often?
I do not have the torque converter clutch hooked up in that car as I eliminated the computer and went with a Quadrajet from a 1979 Chevy van. The Quadrajet is another secret with that car. The small primaries of a Q-Jet give very good throttle response due to higher velocity through the small venturi and allow the car to run at basically a high idle in most circumstances.

The car now has more than three times the stock horsepower and double the torque ( 390 ft/lbs from off idle and a flat torque curve in excess of 400 ft/lbs until 5,000 RPM) that it had with the 231 V6 and 2 barrel it came with. Yet, it is better on gas in the city that it was with the V6 by about 1 or 2 mpg. It is worse on the highway though where the V6 got 29 mpg on a trip from Florida to New York and the V8 struggles to top 20 mpg. The small, low power engine is really at it's best in a car this size at steady state speeds where you do not need to accelerate often. This car took 22 seconds to hit 60 with the stock V6 with the gas pinned to the floor, or about 7 seconds longer than a 3 cylinder Metro. Merging onto the highway was a terrifying prospect and thus when it was used for delivery work with the V6 it only returned 14 mpg. The V8 means I don't have to work the engine as hard to get it up to speed and keep up with traffic.

The Cutlass is another of my "theory" cars but not optimized totally for fuel economy. Fuel economy played into the equation but so did performance. It was intended to be fun to drive around corners and comfortable for long trips. Then again, it was initially built when gas was $1 a gallon and I could afford to drive it everywhere. The Metro is a car for the new reality and the Cutlass will likely get sold next year as I simply cannot afford to use it anymore. It's a shame too as I had more plans for it- like a 5 speed conversion using 3rd gen Camaro parts.
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(Note: the car sees 100% city driving and is EPA rated at 37 mpg city)
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Old 12-22-2010, 12:45 PM   #9 (permalink)
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Drop a 6.2L diesel in the Cutlass! Combined with a 5-speed, it should beat 30 MPG. But there goes your power.
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Old 12-22-2010, 12:49 PM   #10 (permalink)
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Quote:
Originally Posted by mnmarcus View Post
Sounds like the perfect place for a scan guage or MPGuino... Being able to see MPG instantly seems invaluable to your situation.

Lightweight effective aerodynamic mods will almost always help the mpg, even at low city speeds, see:
Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

A hybrid would probably help a lot in the driving you plan to do, though your budget would have to allow for it. It's an interesting "problem" though, you wouldn't want to give up a good tip by being late... I suppose shifting early and keeping it at full throttle until you reach your desired speed would work well enough. An efficient (if there is such a thing) CVT would be the perfect transmission for you because of the quicker acceleration (I bet just making a light really helps with the delivery time.)

Really interesting build thread, good luck!
Thanks! It is an interesting equation to balance which is why it's sort of fun to do ( at least for me). As for a hybrid, I considered an early Insight but the price of the car coupled with a technical complexity that could get expensive to fix nixed the idea. I can buy 15 Metros for the price of 1 good Insight and it would take me a long time to make up the price difference ( once you get past 50 mpg you run into the law of diminishing returns at $3 a gallon). Don't get me wrong: I like the Insight better. It's a safer car and probably doesn't feel like something from the third world to drive. It's just too expensive right now.

I will also say that the store you choose to work at determines a lot. My store is primarily suburban driving and 90% of my deliveries see no more than a 1 mile stretch between stop lights. I also have an easy merge from the main road from my store that helps as does the fact that I really only need to do 50 mph at most on all but a few deliveries. I plan on trying the Metro tonight to get a proper baseline and to see if it works well enough to keep driving it as I fix it.

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(Note: the car sees 100% city driving and is EPA rated at 37 mpg city)
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