I have a 89 CRX HF, fresh rering, aluminum flywheel, aluminum underdrive pulley, AEM cam gear set to 0*, megan racing header, no cat, 2.25-2.5" ss exhaust, stock intake, 205/40R16 tires on aluminum rims, fiberglass hood.
I babied it on my last tank of gas. Barley accelerating, tons of tailgaters, shifting with the shift light. Cruising 60-65mpg, holding speed around corners. The best that I could get was about 45 mpg.
My commute is a lot of highways with a few stop signs, but I do have to go through town were there are several stop signs and lights.
The thing rolls great, hardly any rolling resistance, no stuck brakes.
I will say that I have added some weight to it with the sway bar, strut brace, sub, and I had to add my own seats so they aren't the super light HF ones. There is a little toe out, but like I said, rolling resistance is pretty good.
It was running good at the time, it wasn't raining at any time during that tank. I have no engine lights. I run regular through it (87 octane). The only thing that I think is that I might switch back to the stock manifold at some point because I've heard that the big diameter tubes could be causing me to lose low end torque and therefore mpg.
Along with mileage going up and down between tanks, if your car just had a ring job, it will take a few tanks for the rings to seat in and the bearings to wear in. See what you get after about a thousand miles or so...
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I'm only averaging about 43mpg with my 90 HF. (a CA model, which has a little shorter gearing then the FED model).
This is on a 45 mile each way commute that's probably 75% fwy/25% city. I'm driving too fast, (~75mph) which I'm sure is hurting the mileage. I coast with the engine idling down the hills on the fwy (it's in heavy traffic and I don't like the idea of not having the brake booster working at 75mph), and that is about the only "hypermiling" I do. While I don't doubt people's claims of their HFs getting 50mpg and better, I think it takes a real light foot on the accelerator, engine off coasting, and maybe pulse and glide driving to get those kind of figures.
I've got an '88 DX Automatic and to date I'm averaging about 40 mpg, but I've hit the high 40's on the highway a number of times and just hit 51 on the highway last week. The car is bone stock except for the 16" wheels that the PO installed.
I agree that you have to let the engine get broken in, but let me ask this. Why add all the high performance goodies to a car that you want economy out of? I'd lose the headers (they probably are hurting your low end torque like you think, but the Alu FW is probably hurting you more than the headers in that dept.) and anything that adds weight to the car if it was me. The adjustable cam gear could come in useful, and so can the underdrive pulley and hood, but other than that, I think that you're better suited keeping the car as mild as possible.