Nice video! :thumbup: One word of caution, the more efficient you make your truck, the more inefficient you make the engine. Eventually, you'll hit a wall in terms of aero/rolling resistance modifications. However, because you've been making the truck so inefficient in terms of engine operation, once you hit that wall, you can generally pick up what you've already picked up w/ an appropriate OD gear. On the highway at least. For instance, lets say you make a canvas bed cover, get some LRR tires, etc... and get up 26mpg hwy from 20mpg hwy. With a gearing change, you should easily be able to get up to 30+mpg hwy, if not more depending on what level of acceleration compared to mileage you're willing to have. For a truck like that, I figure optimum is somewhere around 40+mpg cruising at 50-60mph, but you may not like being at half throttle on the highway at those speeds. My take is, everything my truck can do now, it could do w/ an extra OD gear, and I'll be able to get into the 40mpg highway range. If I want to accelerate, I'll drop it into fourth. But, you may not find this acceptable. YMMV.
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Glad you liked the first gas mileage video. The second one is on the way. What I'm also going to do is driving techniques - with a manual transmission you really have a lot more options for saving gas; clutch in downhill, short shifting, skipping gears, etc.. Should be pretty entertaining. Might work in a burnout or two. :D
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Hmmm... Ime, I figure that 1500rpm for a 3L engine seems to be the sweet spot for a normal car, or even an efficient Phil Knox kinda truck. For an engine that big, at ~50-60mph peak efficiency could be had at ~1000rpm, if not lower depending on what the mods do. Provided of course it's a dohc gasser with a relatively flat torque curve. I'm guessing that right now, BSFC is in the 400-500g/kwh range, while ideally, it could be around the 300g/kwh. When you're cruising at 55mph in OD, assuming flat ground and no wind, about how much throttle (%) would you say you're at?
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I'm going to start another thread with the cab spoiler video. |
If you really are that light at a 55mph flat cruise, engine eff is probably about half of what it could be. Have you checked the mileage at different speeds by using bi-directional runs within minutes of each other at whatever average speed in the same gear? I haven't seen an engine that will decrease in efficiency compared to speed faster than power levels climb compared to speed, so I'm thinking there may be some confounding factors influencing your speed versus mpg results.
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Well, I see everyone has that glazed look in their eyes so it's time for another beer. Beer is the perfect food. It's a fluid, has carbs, fiber, relaxes you and tastes good as well is an excellent substitute for common sense in many cases. I started a new thread with my videos. |
It's just the nature of most gasoline and older diesel engines ime. Unless it's a newer diesel, or an Atkinson cycle gasser, BSFC will always be poor at lower loads. Peak efficiency is around 250g/kwh, but if what you're saying is true about throttle position, then you're in the 400-500g/kwh range. It's just something I've noticed that's pretty consistent across the years. Be it older diesels, or newer gassers, anything below ~half throttle will be less than ideal, and at a quarter or less throttle, horrible. The intake and exhaust will move these ovals around slightly, but it's just a matter of low load pumping losses in general. Ideally, we want a little more or less than half throttle and whatever our desired cruising speed. Any more, and we only gain a little bit of efficiency while losing a big chunk of available power. Any less, and efficiency goes in the ****ter at an increasing rate. Even economy cars these days are sometimes geared way high. For example, the Honda Accord and Element both have the same engine, and for the conditions on the EPA highway test, need nearly the same amount of power, with a little more required for the Element. But because the Element is geared so high in terms of OD, probably due to the market it's being sold to, it looses nearly 10mpg on the highway compared to the Accord. Naturally the downside to taller gearing is less available power, but I'd give up being able to go 75-85mph in OD for an extra ~7-15mpg.
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I'm playing devils advocate here with this response, so bear with me. I'm trying to simplify this as much as possible - I'm going to use it in my next full episode of "This Old Shack". Doing my reporter BS, I am.
But if that's the case why would I be seeing 35-36 mpg at 25-35 mph where my throttle is so much lighter? Even at 40 mph, I'm seeing mpg in the 30s. I understand the aero drag causes big losses in mpg but even in a tail wind I only see another 1-2 mpg at highway speeds. If we take the inefficiencies of the engine to be a truism I wouldn't be seeing the mileage rate that I do at lower speeds but would see less. Now, with the drive train taken into account (I'm in 5th gear as low as 25 mph), I'm just loping along at 900 or 1,100 rpms at low speeds and I see higher mpg. That just seems to scream higher efficiency at lower speeds. If the efficiency is lower at lower throttle levels, one would expect to see lower mpg. At a gut level here's what I'm saying: at low speeds, I get higher gas mileage. At higher speeds, it's lower. Logic dictates no matter what the efficiency of the engine, if I get higher mileage at "X" speed, then the drive train is more efficient at that particular speed, which is in the 25-35 mph range. ---- At the one end, without the aero drag at low speeds, we see high mpg (even though the efficiency of the engine might be at its lowest), at the other end we see lower mpg with higher aero drag even though the engine might be operating at its peak efficiency. As we decrease the aero drag, mileage increases until we reach a break even point in engine efficiency at "X" rpms. The key point is to get your rpms, engine efficiency and aero drag to be as co-equal as possible at the highest speed possible given all of the parameters. --- As I said, I'm trying to simplify this for the average viewer so I can communicate it to others. |
I think the most important think to note for the average person is that engine efficiency and fuel economy do not correlate exactly, :p
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The important point that I make to myself as I've learned after jumping with both feet into the aero deal after pissing around with it for a year is that getting the two as close as possible is the key. The hard part for me is to actually get in front of the camera and explain this for the layperson. I keep asking myself if I should dumb it down or gradually ramp the theory up until the viewer understands the concept. I prefer the latter. But that's the hard part because I like to screw around. :sigh: I need some PMs to discuss this. Once I get the theory together I'm going to need some people to check my point of view. |
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