If there are hills, cruise will be less efficient than a foot controlled by an observant driver. Driver's using their foot can predict hills/slopes and modulate throttle accordingly.... cruise doesn't. It just maintains a certain speed and downshifts when neccessary to keep that speed.
Even on flat ground, in my testing w/ a vac gauge, cruise would lower vacuum 2-3" more than a steady foot to keep the same speed on level ground. IDK why that is, it just is.
I want to address everyone's concerns, if practicable. Not all concerns are fixable, but I'll try, and I appreciate all your input.
kit352, yes, the WAI clears the hood without mashing anything. I can't make a WAI for my SE-R because of space constraints. Its air intake splits into a 3" circular horn above a larger rectangular horn, and those horns are boxed in by battery, radiator, fender, and hood.
philip1, GPH varies too much and too frequently to be a useful measure. It will be all over the map from 3+ gph accelerating up hills, to .15 gph at idle coasting down hills. I can record total fuel consumed at the end of each test drive, but it will also be incorporated in the current trip average mileage when I record trip distance and average mpg.
John (project84), I'll double the route to 20 miles from its current 10, and I'll add a (or some) hypermiling ABA test(s). The first change should even out variability, and the second should show us more what real-world changes come from the WAI. I don't normally drive with cruise control, but it does eliminate variability. A couple of hypermiling P&G ABA runs should tell us a lot about what real FE changes I'll likely see from a WAI.
Tire psi should be the same for each trip, but I'll check them a couple of times during the test session. I plan to do all the tests the same morning or afternoon, and I'll make sure the xB is warmed up before I do the first run. Once the engine and tires are warmed up, everything should be relatively consistent for the rest of the testing session. My Scangauge is very accurate over 400 mile tanks, and 20 mile tests are nearly 5% of a full tank, so the differences, if any, should show up clearly in the results.
I'll record water temperature, too. It normally runs 185-204, IIRC.
Resetting my ScanGauge each trip is a given. I have to do it to start each test clean.
My frontage road has no traffic. If I see any, it passes me. The highway does have traffic, but it's all going faster than me. I'll abort and re-run any test leg where I end up following someone closely enough for drafting to be an issue.
Contrary to popular belief, northern California does get cold enough weather to affect fuel economy. I'll pull 60 mpg on my test route in the summer, but will often have difficulty topping 50 mpg in the winter on the same route.
I haven't got a clue how high my IAT's will be. Mods (if necessary) to top 60*F above ambient, are in the future. Ditto heat shields. For now, let's see what results we get. If the WAI isn't very effective on the first attempt, I'm willing to try insulating and/or shielding it.
Re: cruise control. It doesn't matter whether it's a little worse than DWL. We're doing ABA testing, so we want repeatability. In my case, I can barely beat cruise control with DWL. I'll check my cruise control against a GPS for speed. Once I set it, I'll just keep using the same setting for all my tests. My cruise control doesn't lose its setting during P&G..
My route is at sea level. There are a couple of hills on the route, but the highest is probably under 100'.
I looked it up in my repair manual, and the electrical doohickey atop the air intake hose near the air filter is the MAF, which contains both a heated platinum wire and a temperature sensing thermister. From reading the description, I am directly reading IAT from the internal thermister, and indirectly calculating mass air flow from the voltage applied to the heated wire and the thermister, rather than v.v.
I've said before, I don't doubt that WAIs work - they should. I've just questioned how much, and wanted to see ABA testing. The only WAI ABA testing I've seen is Darin's on metrompg.com, and he didn't find any benefits. I hope I do, but I have no money bet on the outcome, and no preference for the outcome. I've complained (perhaps too much) about poor testing to support claims. Now it's my turn to put up or shut up. That's why I want your input on doing a nearly bullet-proof test.
I'll tape up the air horn/WAI connection today. I'll continue to accept input/suggestions at least through today, and hope to run the testing Thursday or early next week. Keep your comments and suggestions coming.
It's far too cold outside to need AC. I'll run the test on dry roads so there won't be a need for lights or wipers.
The only other thing to consider is the weather - presumably you're doing 2-way testing (i.e. x miles northbound then x miles southbound) so that will cancel out if there is any wind. Or you are doing the testing directly back-to-back so there is minimal change in weather.
I look forward to the results. I've been totally slacking on making a WAI and maybe this is the kick in the pants I'll need!