This is my first post, so I figured I would start by sharing a few mods that I haven't seen mentioned yet, there may already be posts on this stuff, but like I said I haven't found it yet.
1.Underdrive pulleys. Made from lightweight aluminum, they have a smaller diameter than a stock pulley, which offers up to a 20% reduction in spinning ratio, which means up to 20% less drag on the pulley. The pulleys are also a lot lighter than stock cast pulleys, which reduces the spinning mass on the crank. The most common underdrive pulley is a crank pulley, but you can also find alternator and power steering underdrive pulleys. The one drawback is a potential reduction in alternator efficiency, which can be solved with a deep cycle battery or a higher amp rated alternator, and water pump efficiency(if your water pump is belt driven) I haven't tested this, however it's along the idea of an alternator or power steering delete, but not as dramatic. Also for winter drivers, if you have A/C, see if you can get a belt for a non A/C version of your car to use in winter, it will bypass the A/C compressor to free up some drag on the crank.
2.Air Flow Converters. Mostly used for increasing hp, air flow converters have the ability to tune the engine for FE. Apexi makes a few different versions, from the low end with turn dials that you can usually find pretty cheap on ebay, to the advanced with an electronic display. The idea is pretty simple, it uses the knock, rpm, throttle position, and airflow/pressure sensors, and changes the signal to the ECU to change the fuel management. The S-AFC II offers a +/- 50% fuel adjustment, which can be set in 200 rpm sections, and the settings are divided between high and low rpm range, so with a scangauge and an AFC, fuel trim can be adjusted to increase FE. Also, you can change settings for different weather conditions, to stay efficient in those cold winter months.
3.Ignition Systems. I have seen some posts about ignition upgrades, but I wanted to share my results from this upgrade. I haven't made a gaslog, however I drive the same route to and from work every day, 17 miles there and 17 miles back, and in my '92 thunderbird with a 3.8 V6, I was getting a consistent 19 mpg every fill up for almost a year, not so good(a lot of it is my driving habits). I replaced the stock ignition coil with an MSD coil, used Accel spiral core plug wires, and stock plugs, gapped slightly wider than the largest gap setting to increase the size of the spark. After this mod, I gained a consitent 2 mpg over 6 months of fill ups, which in my car is amazing.
An under drive pulley on power steering would work. it would only slightly decrease output. Hell I don't even have power steering and I'm not complaining.
An alt. pulley would decrease output which might cause the electromagnet to stay full fielded longer, which would increase the parasitic drag. Which would defeat the purpose. you'd have to some math on the time it's full fielding normally.
crank pulley. some crank pulleys are balanced and you could ruin your motor.
but the cost of these pulleys new wouldn't even be worth the gas mileage increase if at all.
I'm all about dreasing the afr to 15's instead of the normal 14.7 if possible. msd ignition. I don't necessarly believe in that. a fresh tune-up should do the same thing.
Like I said I haven't tested the pulleys. It has some potential, but could negate the gains, especially with the alternator like you said. I have a couple friends who swear by the crank pulleys they bought on ebay, however they bought them for hp, and didn't keep track of their mpg. They lucked out buying cheap pulleys, becuase also as you said, cranks pulleys are balanced.
I went with the msd coil becuase of the higher output to the plug, which allows a wider plug gap, also it was $50 cheaper than the OE replacement. I've never had any mpg gains on any of my cars with OE replacement plugs, wires, or coils, but it's different vehicle to vehicle.
I agree about the cost of new aluminum pulleys. If there was gain to be had, you might as well do it with cheap used steel pulleys, which I'd guess (but don't know) should be easy to find and interchange.
The rotating weight of the pulleys is not an issue. If it was, then we could all gain lots more FE by changing to a lighter flywheel, which certainly carries a lot more inertia than pulleys.
The "Air Flow Converter" sounds like a much better version of a device called an "EFIE", which is often used by HHO experimenters. How much do they cost?
An upgraded ignition system will be unlikely to pay for itself on a mostly stock engine, or probably eny engine. That stuff is expensive. (Though, if you have to replace broken stuff, it might be close.)
the air flow converters go for $50-$400 on ebay, the more expensive are the brand new super air flow converter II, or S-AFC II, the more affordable are the earlier versions, the origional afc, which is a series of back lit knobs with a + range and a - range, each knob represents an rpm range, and dialing + increases fuel in that rpm range, and dialing - decreases fuel in that range, which gives you the option to dial down fuel while driving, to almost give yourself a lean burn mode, like honda engines have. There's also the first version of the safc, which has a digital display, those are usually on the less expensive side. If you want to get all the technical info and see all the different models, go to www.apexi.com
they also make a v-tec air flow converter for hondas with v-tec
like i said on the ignition, the performance replacement parts were less expensive than the OE replacement parts, so I figured I was better off paying less and getting more, but that was my experiance
I've never had any mpg gains on any of my cars with OE replacement plugs, wires, or coils, but it's different vehicle to vehicle.
Its not so much an increase as its a not losing any mpg thing. not having any worn out old parts in the car. keeping up with maintenance. How many people really keep up with maintenance... hell brake fluid and coolant should be changed every 2 year or sooner with coolant ( depends). power steering fluid flush, tranny filter (auto), etc.