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Originally Posted by brucepick
Good on all the work you've done so far. With EPA Highway of 17 and you're getting 20.5 approx, that's a really good improvement - more than 20% above EPA already.
I think aero mods are definitely going to help you. I'm guessing that in Texas you do lots of highway miles, 60 mph and above. I got a lot of benefit from my belly pan on the Civic, and most of that benefit seemed to come from the front section between bumper and firewall. The planned wheel covers are a good idea.
Think about a tapered cap, one that gets shorter at the rear. I saw some discussions and pics of those in the Aerodynamics subforum. Should be pretty easy to build one that actually helps your aerodynamics. If you want to make it look cool or macho, you'll need to tackle that separately.
Oh yeah - tires. If yours are knobby off road capable ones, consider tires with a smoother highway tread. And in any case, air them up to the max imprinted on the sidewall. And check pressure often.
Mostly we find that better flowing intake and exhaust don't help fuel economy a whole lot. They improve the max power output you can achieve, if the original provided some restriction. Remember, you're likely only using a tiny percentage of the engine's available power. At the low throttle levels used in hypermiling, the amounts of air in and exhaust out are far below the capacity of even a bone stock system - in my humble opinion, of course. Three inch pipes can help at wide open throttle at max rpm. You're likely at 1/3 throttle and 1/3 max rpm most of the time, so 1/3 * 1/3 = 1/9 of max/max air and gas flow. Am I close in my guess?
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Yes! In fact, I noticed that my engine is only showing like 12-14% throttle opening when going down the highway; that was a real eye-opener.
I do want a tapered cap but the spousal unit likes the one we have now (stnd Leer type).
I did a new aero mod this weekend, which seemed to help. I put some fairings in front of the rear wheels, as I have done with the front wheels. I have not been able to test this ABA style yet, but on my trip back from OKC Sunday the truck got 20mpg into a 12-20mph headwind, while I was traveling @63mph. I've never gotten that good FE into that much wind before. Now, it was 90* out, and I would not use cruise much, and did let the truck slow down to about 58mph up most hills. I plan to rig up something to help me maintain a 90* air stream into the intake, and ABA test that as well as the new fairings. Any ideas on the hot air intake? I tried one briefly, but my exhaust manifolds have an exhaust wrap on them and I didn't see any intake air temperature difference...
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Originally Posted by mcrews
good job!!!
trucks are tough.
Think about going up a size on the tires (ex 245 to 255) when you go to buy them again. as brucepick said, it's about lowering the rpm on the road
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I am actually considering some 255/55R20s; a little shorter and a little narrower. My truck's tires are 33" tall (275/60R20) and wide, and give me an effective 3.55 rear end...which is pretty tall for my 4.7L. These would bring my gearing to about 3.78 and would be nearly an inch narrower each. Plus less rotating weight...
But that is only after these tires wear out. 46K and they still look good!