Modding the Geo Metro

[JohnAh]

I've been hypermiling my old Saab for some years now and have reached absolutely magic numbers I first found hard to believe. I roughly HALVED what is a normal fuel consumption for this type of car! First step was to reduce travelling speed a bit, then try to plan my driving to minimise the use of braking (engine braking included). This did gave some improvement.

Then I started to experiment with larger wheels, since the car has a 4-speed transmission with quite high revs on top gear. I also increased the tire pressure. I could clearly see a tiny improvement from this, but what really changed the game was to introduce "Burn & glide" driving in continous cycles of acceleration with almost full throttle, followed by coasting. When I started doing this the fuel consumtion decreased way more than by anything else, and I could not even see any difference from changing wheels or tire pressure.

The final very rewarding step was to introduce engine shut-down while coasting. This is just as extreme as it is rewarding! Fuel consumption made a huge dive again. An average burn & glide cycle has 15 20 seconds acceleration followed by 30-40 seconds of coasting with the engine shut off. Driving this crazy way is a lot of work, but you definitely get something back! :-)

I have installed two push-buttons on the gear stick and two relays. One button kills the engine by switches off the ignition. One of the relays "stick" in this position until the other button is pushed, together with the activation of the starter. I have a good engine that most times start in just one piston stroke so the load on the battery is not too heavy.

Note: I have a +40 year old carburetted car with no electronics what so ever. This makes starting and stopping easier/quicker than with some modern "electronic" engines that must rotate at least a full turn or two before finding the actual position of the pistons and camshaft. I have no air conditioning and no power steering. I do have a vaccuum servo for the brakes and that can sometimes be a problem or an unpleasant surprise.

[JohnAh]

My old Saab is lowered quite a bit, but thats mainly to improve road handling and not the least to give it a meaner look. I have also quite fat tyres, 225/55R15 instead of original 155R15. I get absolutely amazing road holding and a firm but still comfortable suspension. It's a narrow track car but behaves more like a gocart! I made the lowering simply by cutting the springs and grinding the cut ends flat. I did not cut the rubber stops at all so they come to action softly, helping to give a nice progressive suspension.

There's no sway bar on these cars and with original suspension they roll a lot due to narrow track width and soft suspension. Even if the roll centre is dropping more than desired when lowering a car this is something I have not noticed. The car is stiff and stable, but still comfortable at about 2" lower ride height than original.

Improved road holding may be a big benefit while performing Burn & Glide, since you can keep your speed in the turns, around corners and in roundabouts. -It also adds a great portion of fun while ecodriving! :-D

[freebeard]

Bellypan/boat tail — I'd say generally true, with caveats.

The area under the car experiences interference drag between road and undercarriage. A rake exposes the undercarriage to the low pressure wake, a tail-dragger exposes to the front. I think a relative rake is preferable.

https://ecomodder.com/forum/showthre...rag-31649.html

https://ecomodder.com/forum/showthre...ges-13199.html



Compare the images in the first post. The problem isn't so much the gross area, but how the wheelwells (especially the fronts) are handled.

[arcosine]

The camber plates wont fix the roll center, an extended ball joint is needed.



Iv'e had belly pans on 3 cars and a boat tail on one.

Ive gotten 63 mpg in my Saturn sc1.

The Saab 96 must have a high roll center then.

https://en.wikipedia.org/wiki/Saab_96

http://www.saabnet.com/tsn/models/1967/pr4.html

Front wheel suspension is accomplished by the stub axle carried in a single angular contact ball bearing. The rubber bearings are of the type in which angular movements take place without any sliding motion whatever. All the relative movement is absorbed elastically in the rubber, with the roll center somewhat above ground level. The coil spring is on top of the upper suspension arm. A stabilizer (anti-roll bar) connects the two lower suspen- sion arms, with the outer ends of these arms connected to the steering knuckle housing by means of ball and socket joints.

The U-section rigid axle of the rear suspension system is joined to the body by a resilient bearing in the car's plane of symmetry and by two longitudinal links at the sides. The central bearing is designed to take up lateral forces and, together with the springx, the braking torque. The side links keep the rear axle at right angles to the longitudinal axis of the car and carry over the braking forces transmitted from the rear wheels.

Shock absorber movement is approximately half that of the wheels when the spring system functions without roll. When roll does occur, however, movement of the shock absorbers-which are attached to the rear axle-is considerably greater, approximately 80% of wheel movement.

The rear axle design eliminates rear-end lift under braking because brake torque produces a spring compression which compensates for this. It also eliminates sway in S-bends, as the shock absorbers react sufflciently to damp roll and thus stabilize the car.

With two people in the car the weight distribution is approximately 58% on the front wheels and 42% on the rear wheels. This weight distribution ensures good drivingwheel adhesion, keeping the load on the front wheels greater than that on the rear wheels, as long as the up gradient does not exceed 25O.

[California98Civic]

Originally Posted by JohnAh

... I do have a vaccuum servo for the brakes and that can sometimes be a problem or an unpleasant surprise.

I have a very similar story, though with a mildly electronic 98 Civic. For braking, I made an enlarged vacuum canister using PVC from the hardware store. Put it inline with the existing system. No problems. Big help to braking, too.

[MetroMPG]

I forgot about that mod! Such a good idea.

[arcosine]

On sc1, I used an ajustable check valve on the crank case breather, which pumped down the crank case to a predetermined level. Never ran out of vacuum. Oil seal squeaked at idle. Had it that way for 7 years, no problems. I figure it degassed the oil as well.

Originally Posted by California98Civic

I have a very similar story, though with a mildly electronic 98 Civic. For braking, I made an enlarged vacuum canister using PVC from the hardware store. Put it inline with the existing system. No problems. Big help to braking, too.

[arcosine]

I changed the oil, someone had written 122k on the filter, car has 142 k now, so its been 20 k miles since the last oil change. I used 0w20 synthetic and a fram tough guard and filter thats about 3 inches longer than stock(TG2870A).

I removed the back seat, front seat, third brake light and glove compartment to fit the SWB Coroliner inside. Races this weekend in Indiana, 170 mile drive. Duct tapped the extraneous holes in the front bumper.

No MPG reading yet as wife doesn't take down odometer reading at fill ups.

[MetroMPG]

Ha - I just had all the seats out of mine to move a bunch of steel boat jack stands. (OK, OK, the rear seats are out all the time anyway.)


The car sat much lower than I'm used to seeing, and for the first time ever the rear bottomed out on one bump. (Suspension is already lowered, though).



Good luck at the races!

[arcosine]

Avg 25 mph, fastest lap around the high school building, 28 mph. Lap is about 1/3 mile with 3 sharp turns.