[prodigit]

Originally Posted by qwertydude

Unfortunately it's simply not that easy. We do have the technology to make 50-60 mpg cars these days. Problem is nobody would buy them. Even back in the day when you could get a 45 mpg Geo Metro 3 cylinder no one wanted them because they were vastly underpowered and most people considered them unsafe to boot because they were made so lightweight they compromised crash worthiness and to keep them lightweight they were extremely spartan, no options basically.

Right now we do have 40+ mpg cars that aren't hybrids. The Ford Fiesta is one of them but you don't see many of the people who long for the MPG's of back in those days even wanting to drive a Fiesta. I think it's purely nostalgia because even now the good MPG cars are equaling or bettering what we had back then but with actual safety, options and not as anemic performance.

As for the 100 mpg carburetor. Simply a myth. Simple physics will tell you that you can't get a "vapor" carburetor to work. Try jetting your scooter lean and see what happens. And that's all those vapor carbs were doing.

There was Smokey Yunicks adiabatic engine but that was experimental only. It was designed to run extremely hot in order to extract efficiency and even then it proved to unreliable to bring to market. There was experimentation in trying to build all ceramic piston and cylinders to combat the high temperature failures of Smokey's adiabatic design but simply put the oil would coke up and seize the engine because of the heat.

It's not some vast oil company conspiracy. Oil is selling at an all time high and oil companies know it's a limited resource. In fact some of the biggest investors in alternative energy are the oil companies themselves. Only an idiot in an oil company would think they don't need to invest in a diversified energy portfolio.

Right now one of the biggest revolutions in fuel efficiency technology are direct injection high compression engines. These new engines are running higher compression on regular octane fuel than you can even dream of. Compression ratios that would detonate normal engines. IF you take a look the modern small engines now are making the similar fuel efficiencies of what diesel engines used to do just 20 years ago and doing so more reliably and without nearly as much tail pipe emissions to boot.

My Chevrolet Cruze is a well engineered piece of art! It gets an average between 35 and 38MPG, gets 50MPG on the highway when staying below 60MPH, and 70MPG when going 35-40MPH on continuous roads (where there are no stops or slow downs).

There is nothing like setting a carburetor too lean. When you set it too lean, it'll lose performance, and your MPG will go down as well, as you'll need to open the throttle more to achieve the same performance out of it.

There's an optimal setting where performance is maximized. It can be achieved with a slightly lean jetted carb, and a choke. You can use the choke to compensate for the lean setting, to achieve optimal performance, and often by cutting air, get a few HP extra (or a few MPH extra top end).

As far as 100MPG, my 127cc roketa achieves 118MPG, and someone else on another forum gets 120-125MPG out of his BMS BMI 110 (which is the same engine as mine, only mine has a 17cc bigger BBK on it or so.

It's not hard to achieve 120MPG with gears; it is hard to achieve with a CVT.
The question is, how much torque you are willing to trade for MPG.
Gear them higher, and most of the time you'll gain MPG, and top speed, but lose torque.

Then there's also the issue of what kind of engine will work best.
Well, usually between 35-45MPH you get the best gas mileage on almost ALL vehicles. Wind resistance is minimal there. Above 35MPH wind resistance increases a lot for every increase in speed.
With a 50cc, you're basically have to run the engine in the powerband to maintain speeds of 35-45 MPH, and there's a lot of engine wear at those high RPMs.

Increase engine size by 25-50cc, and you almost doubled the power output, while increasing the weight by only a few pounds, as it generally does not need bigger tires, brakes handlebars, suspension... All that mostly stays the same.
Since weight does not double but only increases by a few percent of the overall weight the engine has to pull, and wind resistance is pretty much the same on a 110cc scooter compared to the same size 50cc scooter at the same speeds,
With a 100cc, you can decrease RPMs from 6-7k RPM, to 2.5-3k RPM to maintain these speeds easily.
That means, despite doubling the cc's, your RPMs go down by mpre than half, and at the same time, the throttle can be moved from WOT to 1/4th to halfway open. In other words, not only does a 110cc engine have more overall power, better top speed, but by choosing the gearing right, it can also have higher MPG than a 50cc, all thanks to running the engine at lower RPM.

So, the sweet spot would be somewhere between a 75cc and a 100cc, it has the power to run at just above idle RPMs and maintain speeds of upto 45MPH easily (all day).

Increase CC's and you'll increase torque, and decrease MPG, unless you change gearing (put taller gears on). But when you'd swap a 50cc scooter with a 250cc scooter, not only will the 250cc scooter weigh almost 50% more because it must go faster, (better bigger brakes and shocks, better handlebars, bigger tires), but also because the engine is bigger and more powerful, if you want to maximize MPG, you'll have to put such a tall gearing on them, that at 2-3k RPM the scooter will be doing over 45MPH, where wind resistance becomes a big factor.

For that reason, a 75cc-100cc carbed bike can easily reach beyond 120MPG. I believe for a skinny small guy, under 150lbs, a small, manually geared scooter can be made that could be running a 75cc engine, running at over 125MPG (130MPG even when torque is virtually zero at final gear), with top speeds of upto 50-53 MPH.

Going lower than 75cc, and the scooter will struggle to maintain 45MPH at lower RPMs, plus, you still have the same weight on tires, brakes, a seat, handlebars, lights, and the rider is not going to lose weight, so the overall weight the engine needs to pull remains pretty much the same if you go below 75cc compared to a 50cc scooter (or lower, like some 33cc mopeds).

Going higher than 125cc, and the engine can be optimized to run higher than 45MPH at 2,5-3k RPM, but on the other hand, wind resistance increases at those speeds, and thus gearing can not be doubled when doubling the cc's, and MPG will be forced down.

For that reason I think they should categorize a 50cc scooter as a moped, and have a special, cheap license for 75-125 cc scooters, that's much cheaper than a motorcycle license, and easy to get.
the upper limit of 125cc would only be necessary if the rider is of big posture, or you're riding with 2 people on a bike, or you're living in a hilly terrain, and a 75cc will bring you into trouble (eg: ride below 35 or 45MPH) going uphill.


And then finally, something NONE of the scooters have yet, is like a bicycle, a cruising neutral gear!
Scooters and tiny motorcycles, could benefit from a neutral gear when approaching a red light in the distance. This allows the engine to go into idle mode, while the ODO still counts the miles as you're rolling to a stop.
Instead of having the engine brake (engine braking not only loses energy that gets converted to hot air, and makes use of the vacuum of the cylinder, but also makes you waste more gas than when the engine was idling).

Instead of looking into regenerative braking, engineers would do well in investing in a neutral on those machines (or have a scooter with automatic neutral, meaning whenever you roll off the throttle, the clutch will disconnect, and the engine will go into idle RPM, even if the scooter is still going at a high speed).
For the very simple reason that at idle, the engine uses just as much fuel per stroke as when the engine is used to brake the vehicle. Only in the latter, the engine is sucking 5000 RPM / 4 (for a 4stroke) times fuel, while at idle it's 1200 RPM / 4.

Those moments will add at least 5-10% to MPG numbers, especially if you're in the city; but also on the suburbs where you can speed up to 45MPH on a 40MPH road, then roll to 35MPH in neutral, and accelerate again.
This type of cruising is called hypermiling, and could be applied to scooters as well.