Re: 1991 honda CRX Daily Driver Rebuid....Open for Suggestions/Comments...
If you are looking for cheap mods that will help FE some, there are quite a few (the sticky post at the top of this forum is a good place to start).
As others have mentioned, the mods that make good FE are often not the same mods that give good performance (however there is some overlap). And some of the cheapest FE mods are very easy to do (and easy to overlook). For example:
1) Increase tire pressure (but not beyond the rating of the tires themselves). Doing so will increase FE by lowering rolling resistance.
2) Look into aerodynamic issues. In general, the easier the car cuts through the air stream, the less fuel you waste to pushing the air out of the way (and therefore the better your FE). Even something as simple as putting duct tape over rough surfaces on the car's underbelly (thereby improving the air flow on the bottom of the car) has giving some of us noticeable FE improvements.
3) Consider at least a partial grill block. They are cheap to do, and generally help FE a little bit (mostly by helping car aerodynamics). Just be careful to not block too much, or you may have overheating problems (or at least excessive cooling fan usage). As an added bonus, grill blocks also help the car heat up better in the winter!
4) Drop weight when possible, as extra mass generally means extra fuel. NOTE: Your fiber wheel idea really would help some in this case. However, as another poster mentioned, it might not help enough to justify the cost.
5) Keep the engine clean. A cleaner engine is a more efficient engine. NOTE: A good synthetic oil will usually keep an engine cleaner (and more free of varnish) than most normal "dino" oils.
6) Index your spark plugs (i.e. carefully point them at the right angle, instead of just screwing them in at any angle they go to naturally). Yes, I know this is a racer's trick, but in this case it really does tend to give you a small FE boost as well (presumably by making combustion slightly smoother). And it's not as if indexing plugs is difficult or costly...
7) Save electricity when possible. Yes, alternator load on the engine isn't the biggest thing consuming fuel, but it is still engine load that is proportional to how much electrical power you are using. So if you can lower electrical usage, you will save some fuel (because lower electrical usage translates into less alternator drag). For example, some of us have converted our car lights over to energy efficient LED modules to save a lot of electricity. And it makes sense to turn off accessories, when you don't need them (i.e. for example, only run the vent fan when it helps comfort, not all the time simply "because"). And some really ambitious members of this forum (not me) go all the way and disconnect the alternator completely (and therefore run their electrical needs completely off of batteries, instead of using fuel and engine drag for that electricity).
NOTE: Not all alternators are equally efficient. Alternators with noticeably higher efficiency than stock are on the market, and should help FE some (by resulting in less car drag for any given amount of electricity used). However, when I recently looked into this issue for my 1991 CRX-DX (which had its alternator die this year), I ended up just going with a (rebuilt) stock design alternator due to purchase cost. Specifically I could only find the efficient alternator models new for over $1000, whereas I could get a rebuilt stock design alternator for a small fraction of that cost.
8) A really high end synthetic oil, combined with an extra good oil filter, is usually good for a small FE gain. And the nice thing about this mod, is that it already pays for itself in longer times between oil changes. i.e. The extra oil/filter costs are balanced by the fact that you save money by doing oil changes less often (which is possible due to the high end oil and filters), leaving the minor FE gain all a "bonus".
9) Look for sources of drag, and try to reduce them when feasible. It's amazing how much difference a little high end grease in a wheel's barrings can make, for example. Remember, if the wheel can't turn easily, you are constantly using fuel to overcome that wheel friction. Likewise, a little effort put into minimizing brake drag can also pay off in FE (again by avoiding wasting fuel to overcome static friction).
And those are just some of the EASY mods. If you want to get fancy, there are a number of other things you can do to help. However, at some point you reach "the point of diminishing returns". So you do have to weigh the cost/hassle of a mod, against the expected benefit.