The most common questions asked about engine or cylinder head replacement would be about fuel economy. Its important to realize how efficient a Metro already is. Yes you can do some custom work and change the horse power. Also you can change the gas mileage. The issue is you cant have more power and better mileage.
99% of all Geo metro owners are commuting to work. Were all budget minded trying to take advantage of the lower cost of ownership and maintaining a Geo Metro. There is very little reason to build and spend on custom engine builds and after market parts if your commuting to work. The Geo Metro has performed very well for many years and will continue to do so in its stock configuration. This also is true on engines converted to aircraft that have been sized to the correct aircraft weight.
We recommend building to stock specifications unless you have a special need for your Geo Metro. Driving to work is not a special need. Most owners that option for more power regret the loss of power even for small decreases in fuel economy. Every one regrets chasing better fuel economy as it costs upper end power (passing power). Geo's run strong and hard when there fresh. If your down on power or fuel economy. More than likely the engine is just not performing having high mileage.
A 10% percent change on a Geo metro engine is much different than other engines in economy and power to scale. If you have a v-8 engine and it gets 20mpg. Then you alter it to get 10% more power. These results likely will cost you at least a loss in economy equal to the gains in horse power. Bringing your fuel economy down to 18mpg. Increasing your v-8 engine now to 220 hp which you might not even notice. Your initial 200 hp was more than sufficient as a commuter car.
The Geo metro engine on the other hand altered for 10% more power loses 4 to 5 mpg in scale. The loss in fuel economy is more than double that of a V-8. The increase in the extra 5.5 hp or 10% is almost UN-noticeable. You need to be running the car up in the 4500 rpm range or higher to even use that extra power. That's 50% higher than your cruising RPM of 2600 rpm to 3000 rpm. Its very rare to even run in that range. You only need about 30 hp to maintain 60 mph on flat level ground at 2600/3000 RPM depending on your gear ratio and tire size. The small engine cubic inch size, lightest car out there and reasonable cruising rpm. This is the reason your Geo can gets such amazing fuel economy. So once your up to highway speed 60mph 30hp 2900 rpm. You still have available in a stock Geo Metro about 50% more power. You simply have to turn the rpm up to access this power. Stepping on the throttle pedal alone is not how you get to that power. A person must shift down a gear and raise the rpm to access this power that is already there. This would be a very steep hill and not freeway driving or commuting. There is plenty of power there for you to use.
A Geo has great highway power. You dont need to build in more power its already there. Geo's love to run hard all day and many do in aircraft engine conversions. Planes run at about 70% of full power and the cars run about 30% to 50% of that. Aircraft run several minutes at full power during take off and climb out of large airport patterns. Also while climbing to altitude. These little motors dont mind being run hard when its called for. The point here is dont spend money on HP upgrades when your not using the power you have. Take advantage of the power and fuel economy the metro already has. When you have a small car. Lowering the power to create more economy is never a good idea. This is the premise of the XFI model. It was de-tuned to 49 hp from 55hp. It was so disliked it only lasted 2 years or about. Its not necessary either. You already have this option its the gas pedal. Slowing 5 mph on a commute will get you as much as any upgrade at no additional cost. Or what I refer to as doing the speed limit.
If your engine is down to 70% of its rated power having high mileage. Your off by 30% of your power and fuel economy. Getting back to 100% power will be like building a hot rod engine for your commuter car. This will also raise your fuel economy back to like new.
You simply do not need to do any thing other than a stock engine. I promote this route of common sense building and driving. This is why the Geo Metro is the most cost effective highest fuel economy commuter car in North America. Its a great tool to have if purchasing fuel is a issue for you.
The club asks you to absolutely respect that you to set up a time to stop in for some help or meeting with the group for the first time. Some meets we do at restaurants or our camping/cruising weekends. Not every meet up is a project or tinker day "We may not be big, but we're small."