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Old 07-28-2017, 10:42 PM   #31 (permalink)
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I have a fully modern suv with direct injection, a modern 6 speed with double oveedrive, and quite extensive aero treatments, and if I go 70, I lose 10% fuel economy over going 62. Imho, 70mph speed limit should not be allowed, for safety and environmental reasons.

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Old 07-28-2017, 11:29 PM   #32 (permalink)
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Originally Posted by Isoldmysaturn:( View Post
Imho, 70mph speed limit should not be allowed, for safety and environmental reasons.
I'm not totally unfavorable to a 70 MPH speed limit, even though it does adversely affect fuel-efficiency. Anyway, though I'm not an eco-nazi, I understand that a relatively lower speed is advantageous on that matter too, not just because of the lower emissions out of the tailpipe but also due to the fewer energy spent on oil drilling, refining and the supply to the fuel stations.
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Old 07-29-2017, 01:08 PM   #33 (permalink)
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under 70 mph

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Originally Posted by Merlyn2220 View Post
So I started hacking off some of the rear of the shell, in an attempt to figure out what was going on with the cavity and taper. I removed the center upper section (with taper) at about 100 miles into a tank, and ended up with 14.27mpg. With the 12 degree side taper and upper section and A/C use I was around 13.9-13.9mpg. So the center was a definite negative, even with a reasonable taper.

At 240 miles into the next tank, I hacked off the sides to be ~4" long, following the general shape of the body from a side view. 15.24mpg is a dramatic improvement over the previous tanks. HOWEVER....part of that is because I was having overheating problems and not running the A/C much, and driving slow to keep the highway temps down. This followed up with 15.67mpg for the next tank, with no other aero changes. I'd attribute the extra 0.5mpg to mostly driving well under 70mph on the highway while I swapped parts (thermostat, pump, hoses and radiator) and it seems to be back to normal. So this tank should tell me what real impact there is from hacking off my abomination of a tail!
*Driving 70 mph vs 55 mph would effectively increase your drag by 1.619 X
*It 's like increasing the Cd by the same factor.
The 'naked van,@ Cd 0.38 would go to Cd 0.619.
*Aero power and fuel would increase by 2.061 X.
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Old 07-29-2017, 09:30 PM   #34 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
I'm not totally unfavorable to a 70 MPH speed limit, even though it does adversely affect fuel-efficiency. Anyway, though I'm not an eco-nazi, I understand that a relatively lower speed is advantageous on that matter too, not just because of the lower emissions out of the tailpipe but also due to the fewer energy spent on oil drilling, refining and the supply to the fuel stations.
I understand the desire to get places faster, there were times in Germany I only had one day to go see some sight, and going 144MPH was hugely advantageous to that goal, but a: that car didn't get the same extreme a difference in economy like this one, and b: that was the only way I could see the country. at the same time, people who only wanted to go 60 were allowed to without getting harassed by the police, unlike the united states.
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Old 08-07-2017, 05:00 PM   #35 (permalink)
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Amazing work! No skirts yet? will you do front skirts also? Would love to see those.
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Old 10-12-2017, 12:02 PM   #36 (permalink)
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So here’s a summary of the “rear shell” and other changes since fall of 2016:
  • Larger rear tires with a 15.8% gear reduction = no change in fuel economy. Any gains were offset by the wider tread (225 vs 285) and resulting worse aerodynamics.
  • Removing the giant 3 point towing mirrors and replacing with 2003+ paddle style = 5% improvement in FE. Also drastically easier to draft and keep up speed on the highway.
  • Adding a driver’s side axle-axle bellypan = no change in FE, likely because you really need front-back to see a significant improvement.
  • Having a failing 25-30psi fuel pump = 10% better FE. I didn’t have an AFR meter at the time, but I bet it was running really lean.
  • Addition of a squared-off rear shell = 5% worse FE.
  • Completed driver’s side side skirts (with rear shell unchanged) = 10% improvement in FE
  • Addition of huge Class IV rear hitch = 5% worse FE
  • A/C use = 4.5% worse FE
  • Changing rear shell from squared off to ~12 degree taper = 5% improvement in FE
  • Driving ~60-65mph due to overheating = 7% better FE than driving 70-80mph
  • 180F thermostat vs 195F thermostat = 2% worse, likely no significant change
  • Completely removed rear shell taper = within 1% of the 4” long 12 degree “short taper” but noticeably less stable in crosswinds and while drafting

I’m currently at about 14.8mpg and easily keeping up with 70-80mph traffic. Driving 60mph on the highway here is, like almost everywhere, extremely risky. I turn into a rolling roadblock that only causes problems for myself and other drivers who are expecting consistent traffic flow while texting. A ~7% improvement in FE is not worth risking my life on a daily basis, and it causes me to be unable to meet my delivery schedules.

Modifying the rear shape to add taper was spectacularly unsuccessful and a complete waste of time. The only thing I’ve concluded is that a “trip line” like used on the back of a Volt or Prius does seem to help highway stability. It’s especially noticeable when drafting a semi, where the alternating left-right vortexes coming off the semis push the van a LOT. I did get a chance to draft a semi with the “TrailerTails” installed, and it was quite a bit nicer on me, with a lot less buffeting.

A couple of other interesting conclusions:
  • Adding a big honkin’ hitch to the back, dangling out in free air is pretty noticeable.
  • Changing the thermostat from 195F (stock) to 180F made almost no difference.
  • Running lean due to a failing fuel pump is *probably* a significant improvement

One thing I noted is the consistency from tank-tank when I did a few back-back with no changes. Some people have said you have to run 2-3 tanks to be sure that the mileage is consistent. I’m filling a 35 gallon tank, so 1 of mine = 2 for most vehicles, and 3 for some like my Miata. So unless I get really odd numbers due to traffic jams I’m going to go back to 1 tank = 1 mod.
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Old 10-12-2017, 02:56 PM   #37 (permalink)
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One of the bigger shifts in FE was a relatively simple one, installing paddle mirrors instead of the big 3 point towing mirrors. This one change meant the difference of only 5% improvement in FE, but it also meant that I could keep up and stay in the draft with other vehicles. Before that change I'd have to go close to full throttle any time someone ahead of me stepped on the gas or we started going up a hill. A lot of times I'd just have to wait for someone to pass me before I could catch up into the draft again.

I have a Dodge Neon mirror that I'm going to hack up and install on the driver's side. The stock paddle mirrors are so tall because they don't tilt vertically, so half of the height is totally useless. I know this will probably be a small change in FE, but it should only take a couple of days of fiberglass work to make a new mirror housing.
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Old 10-14-2017, 12:50 PM   #38 (permalink)
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mirrors

With the T-100,going from stock,to racing mirrors netted a drop in drag,from 0.027,to,0.010.
I think you'll like the NEON unit.
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Old 10-15-2017, 02:35 PM   #39 (permalink)
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There's no "risk" in running 58-62. Big trucks run 62-66. A little above them, but below the idiots in cars is "the rocking chair". (That van won't stop or handle worth s%^* above 65). Mixing with cars means throttle changes, more steering inputs, plus brake use. All of those a fail.

Thus, need to analyze engine run time versus distance. And then look at travel speed. Average MPH will tell you best trade-off.

Get an engine hour meter

I've been running to customers for years. It isn't the travel speed, it's the road design and traffic percentage. Year after year the time won't really change unless one switches from daylight to dark (far less traffic = higher average mph. But night running has its own dangers).

What is open to manipulation is cruise control set speed based on average mph. There's a sweet spot on the graph where time en route vs fuel consumption meet. (Burning thru tires kills fuel savings; you are getting 70k plus from tires, right?)

The ironclad determinant -- as always -- is vehicle spacing. If one is ever surrounded by other vehicles, one has screwed up. Severely. The speed which allows consistent 200' spacing (minimum) out ahead, and if one drives otherwise to avoid pack formation around one, is what really finishes set speed determination. Safety, then fuel economy.

Find the averages. Hit the sweet spot.

As to towing, you didn't need a Class V hitch. Class IV would have worked. Just need to set up a weight-distributing hitch properly. (Leave van springs alone unless you're changing them all). Trailer tongue weight IS NOT the same as cargo weight. Use of a CAT Scale is key. Be glad to walk thru that. Better handling and braking is the result.

That crap out of the way, it's really impressive the amount of work you've done. I really like straight sixes. V8s have their place, but a big six is sweet.

Towing plus A/C use: HD clutched mechanical fan.

The downside of a straight six is weight. A lot of Iron to keep cool. I wouldn't screw with old school in this. In fact I'd get the radiator, fan shroud and fan from a big block van.

Then you can mess with thermostat temps.

I'd also add a second A/T cooler (plate and fin) downstream from radiator that will bypass cold fluid (B&M Racing). Centered low across rad face, but "within" fan shroud profile and out ahead of all else.

And a Derale power steering cooler. (Same).

Mount both with metal strap or similar. Not with zip tie to radiator.

Filters for each downstream again.

A bug screen also a good idea.

(You can see where big capacity radiator a better choice, now).

This is how we followed MoPar guidelines and factory build starting in 1960s. Just as effective now.

And it's "aero" as intake openings should "work" with all the other fine work you've done. I'm old enough to remember the heyday of vans. Things didn't always work on that score once towing was involved. Gotta have engine room airflow. Vans are sensitive to this.

To take it back to where I started (as this is the aero thread), a consistent travel speed -- verified by averages -- will put all other aero changes in proper light.

.
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Last edited by slowmover; 10-15-2017 at 02:42 PM..
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Old Yesterday, 11:56 PM   #40 (permalink)
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Quote:
Originally Posted by slowmover View Post
Towing plus A/C use: HD clutched mechanical fan.
As long as you may find one (or two) with enough flow, there's no actual reason for a mechanical fan to be better than an electric one.

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