AeroRanger (brother to AeroJeep) boat-tail
 

Just put the boattail on yesterday. I haven't driven enough miles to get a decent fill-up yet, but it sure drives differently. I normally coast down a hill, between exact points, and go from 55 mph to 52/53 depending on the headwind (always a headwind there). Last night I hit the coast at 55 and came out at 57 mph. Today, the headwind was fierce and I came out at 55. Definitely a longer coast. I'll have to do a test run soon. The temps are dropping a bit here in Jackson, WY. I'm hoping that won't affect the results much.
PICS:
picasaweb.google.com/consmiller/Ecomodding#5514669072007210610

Now THAT'S a boat-tail.

Thanks Big Dave, I went to fill it up this morning to start with a clean slate and a ring of people surrounded me inquiring. People were actually stoked this time too, which was cool (I think because they think I'm racing it, looks like it should be fast but the engine is only 2.3L). A lot of people ask if it's electric too. Hoping for mid-50s hwy mpg. We'll see this weekend.

Looking GREAT!

Please do some testing and post up the data, I will add it to the wiki.
For the wiki I also would like cost and time for the mod :)

Thanks and keep up the good work!

Thanks Weather Spotter. In total, everything costs $600 (for everything on the truck, half that for the boattail). I probably only needed to spend 500 though. The screws, bolts, nuts, & washers really add up. The polycarbonate was like $120 too.
Time wise, my head was constantly working on it all day for weeks. The boattail took probably 12 hours of hands on time. The aerotopper twice that (no power tools then).

Thanks for that data, I will add it to the wiki once you get MPG results.

Nice, man. Now I'll have to get my game on to finish mine!

What Wiki please? :)

Cheers
KB

Good, I can't wait to hear the results Big Cheese!

NICE!! :thumbup:
I am impressed.

I took the liberty of browsing through the other pictures in that gallery and the VW looks interesting. Is there another thread about it?

Matt's VW got a 12% increase in mpg with the rear wheel skirts, pizza pans, and grill block. His boattail/kammback is stalled because he didn't like the aluminum flashing (it's loud and doesn't bend well). So he is waiting on plastic or foam to finish it.

Just did an 82 mile hwy loop , 60 degrees out, a bit windy, had to stop 5 times, sometimes for a few minutes. When I filled up, I waited a couple minutes so no gas in the tank was sloshing. Then filled it. Let it settle another minute, then topped it off a click, trying to be as precise as possible for a short fill. Got 60 mpg.
Now, as Frank Lee will point out, it was a small fill, so it's something to take with a grain of salt. But, beforehand, after getting some pure city driving out of the way, I filled it up, got in 1/4 of a gallon, with 16 mpg. So I think there is some truth to this. Further testing is needed to verify the 60 mpg, but it's a great start. And with the 5 stops (all coming to a stop from 60 mph, and not a long coast down), I feel more strongly that there is some truth to it. We'll see.
Lastly, I have a feeling being at 6,200 feet elevation might play a role in the generally excellent mpg this summer, over my spring mpg in Seattle.

I'll do another test run Monday. I might drive 100 miles to see if that improves accuracy. But I don't want to drive all day to get a big fill-up. Anybody have an opinion on how many miles it takes to get a solid reading?
Also, the truck is 1,500 miles overdue for an oil change. So I'm hoping that could boost it a wee bit too.
At the gas station again, so many people were inquiring. I might print out a bunch of business card type sheets with this website and some basic drag stuff to hand out. A magazine might be interested in doing an article on ecomodding. I'll try to steer them to Darin and Phil for more accurate statements.

Very nice! Alot of duct tape holding it together, but if it works, it works! That would be amazing if you could pull 60mpg with a pickup!

I'm curious, did you leave a way to access the bed?

Also, the way your wheel covers mount up are a really good idea!

Thanks Zerohour. Yeah I can still access the bed because the boattail is on a hinge.
I'm still not officially saying 60 because it's a small fill, one-time event. I got 50 mpg though on the test run without the boattail, so I am optimistic.

But you need to consider the boat based on original highway. If you get 5mpg, thats 20% of the original highway rating. If you're even touching 60 on occasion its just awesome!

Kudos to you, can't wait to see the data results!

Yeah I was wondering if I should expect increases off original EPA ratings or after the mods. Still not sure on that. Is it the law of diminishing returns or the sum is greater than all the parts? I think it's the latter.
Also, after further thought, something tells me this is all just way too high. Maybe these short fills, which are consistently 60ish, just aren't accurate as Frank Lee always says. I don't know. I don't know how they couldn't be (even when I'll max the tank out on the return), but I don't know how it'd gain so much. So I'm just going to drive half the tank out, which will take a couple weeks. After that, I've got a long road trip and will get a really good idea. But I don't want to be disappointed to be getting only 40 mpg then.
A big problem has been people at work putting gas in and out of my tank, reducing me to these short runs when I fill up before and after. I just bought a locking gas cap today though so that'll stop. And I got an oil change and it feels much smoother.
So, I think I am hitting 60 in ideal flat, non-windy conditions, but I'm not too confident on it. If the aerocivic can hit 120 though, I think 60 could possibly be what I 'm getting. I'm just remaining skeptical for the moment.

40 mpg with any pickup is nothing to be disappointed about. You're greedy. But I like it. ;)

Cheers
KB

YEAH BABYYYYYYYY!
Just did another test run, same stretch, 60.56 mpg!
I really feel like there's something to it since the previous run, same stretch was 59.77 mpg. Here's the differences:
1st run: had to stop 5 times from full speed, some slower driving involved.
2nd run: little windier, ran the fan a little bit, noticed the pass. side mirror was opened (closed it half-way through run w/o stopping!), had an oil change couple days ago, drove 45-60 the whole way, no slow downs, no braking.
Did the same fill-up style for precision: pull up, wash the windshield so the gas has time to settle, fill-up, start filling out mileage details on my chart (kills another minute), then top off one click. Same gas station.
Before this, here's the following fill-ups:
0.25 gallons, 16 mpg (purely slow driving and lots of stop signs)
1.372 gallons, 59.77 mpg (pure hwy)
1.530 gallons, 23.53 mpg (mostly town)
2.114 gallons, 36.899 mpg (mostly hwy, but a bit of town)
1.321 gallons, 60.56 mpg, pure hwy, pretty ideal conditions except for some cross-winds

NOW, I'm ready to calm down and do a bigger tank for my commute. But I really feel strongly about this. Lastly, I DO believe being at 6,500 feet elevation helps. Think about how baseballs and golfballs fly way further up here. The air is less dense so it gets pushed around the car easier. Maybe the oxygen/fuel ratio is the same, but that's only part of the equation.

Thoughts?

Usually thinner air at elevation leads to richer mixture and less efficient. The rule I recall is a normally aspirated engine loses 2% max power per 1000' elevation. So 6500' should pay a 13% handicap compared to sea level by all rights. Then again, maybe you know something others don't... ;)

Cheers
KB

The engine adjusts gas according to how much air is going in though... not volume but actual mass... right? That's the basis for hot air intakes.

When I had a Grand Cherokee I got much higher gas mileage driving around Montana and Wyoming than Texas.

Interesting. Maybe that explains why my city mpg up here is terrible, but at hwy speeds air density is more important than engine efficiency.
I don't know, but I was really skeptical about that first 60 mpg run, and coming so close again on the same run seems like there is some accuracy to it.
And if that mirror was folded in the whole time, if it wasn't windy at all, and I didn't run the fan but wore clothes fresh from the freezer, I think I could do even better.
Lastly, I've been using mid-grade fuel and that seems to have helped some. Has anybody else noticed a difference?

Now I'm excited to do a full belly pan, boat tails behind each tire, a major plexiglass sheet to extend from the top of the cab in a straight line, resting on the hood, and extending out to below bumper level (only for road trips), LED lights, alternator delete, AC delete. Then it could be 70 plus range. That stuff will be a ways away though.

Glad to hear that. That makes me feel a little more grounded in this 60 mpg thing because it still seems unbelievable and when I drive to MA in the fall, I feel confident my mpgs will be going down. (Then I'll just have to add some more things to get them back up though!) This is also a higher valley of the Rockies. Most of MT is around 3,000 feet.

"One thing you should know is that I'm at high altitude (~7000 ft average).
That definitely plays a role as it effectively turns my 3.5L engine into a
2.8L (there's about 21% less air up here...less air means less fuel) and it means less wind resistance." From 5speed5 today

If true, me being at 6,500 feet turns my 2.3 into a 1.85L engine, helping to explain to me why these numbers seem a little too high.
I've heard you can't even throw a curve-ball at high altitude because the threads don't get grip on the air. I've asked others out here who say they get way better mileage up here too.

SO, these numbers seem way high. I don't want fellow ecomodders thinking I'm full of BS. I would be a skeptic hearing about a truck doing 60 mpg.
But remember, I think altitude plays a big role, and these 60 mpg are under pretty ideal conditions on only HWY (roundtrips uphill and downhill, upwind and downwind).

It might not be that out there for a small truck with a small engine.

That last explanation rings true. Mostly I hear about altitude derating of (NA-IC) engines in the context of RVing. Scenario 1 is the rig's ability to crest a 10,000' pass with effectively one piston on the bench. Scenario 2 is the generator's ability to run same appliances at elevation as sea level. I wonder if more efficient operation at altitude applies mainly to overpowered vehicles as opposed to say a frugal car with a tight nut behind the wheel. :)

Cheers
KB

The way I understand it is that the closed loop mode is called closed loop because it uses sensors to get feedback on the A/F ratio, among other things. That is the main purpose of the oxygen sensor. It lets the ECU know how close to stoich it is running, so it can correct the amount of fuel injected. (sorry, I had to explain)


Thus, if you take an engine up high, with low air pressure, there will be less oxygen and the O2 sensor will pick up on it, then the ECU will just put in less fuel. This argument only holds true for fuel injection (and electronic at that) because a carburetor doesn't adjust itself :p

Yes, altitude is your friend if you're an ecomodder/hypermiler and you have either a fuel-injected engine or an engine with a carb that is jetted for the altitude. Of course, you have to use it wisely. I imagine there are some people that just step on it harder to make up for the lowered power and they probably use more fuel.

cons, nice work on your aero mods. I live over a mile above sea level and I do believe it helps with highway mpg but you are doing something right too with your mods. Bicycle racers go to Mexico City for their high altitude velodrome (The hour record for bicycles is the record for the longest distance cycled in one hour on a bicycle. It is one of the most prestigious in cycling. Hour-record attempts are made in a velodrome, frequently at high altitude for the aerodynamic benefit of thinner air.- from Wikipedia) You seem to be getting some good results from your full boat-tail even with the square corners. Ingenious design with the hinge for tailgate access. I hope you can talk your buddy with the TDI Golf to start a build thread too. The photos in your web album are interesting.

Thanks Cocyclist for that aero info. Squared is just way easier for me. I'm not a very talented builder of things.
I'm getting on Matt's case to finish his boat tail. If he doesn't do a thread, I'll do one for him. He's searching for the right material to put on it. The aluminum flashing didn't work out, he's a perfectionist, and there's not much to pick from in Jackson. He might just do a cheap, short-term solution like cardboard until he gets to San Fran in a month.

Can you salvage some large used coroplast political signs? I used a 4x8 sign for my belly pan.

We found a small yard sign of coroplast, but that's it for now. That'd be funny to make it out of political signs.

Especially if you got signs from all parties in your area - and kept them showing when installed.

numbers
 

cons,sorry just getting back to town.
I'm in agreement that short test runs can be problematic as to accuracy.
I'm also in agreement that EFI is probably 'smart' enough now to lean mixtures at altitude whereas in the days of carburetors you might have to re-jet to avoid rich conditions.
Somewhere,I did a thread on elevation vs air density which may help on that issue.
If you have an established baseline mpg at say,a constant 55-mph ( forget EPA numbers ) you can do your comparisons against that realizing that weather and road conditions will affect it.
If you're going to do your testing at 55-MPH,then there is a relationship already established which you can use to reverse-engineer your new Cd.
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A 10 % drag reduction will net you a 5 % mpg improvement at a constant 55-MPH ( no stops! no messin' around! ).
If say the Ranger originally had a Cd 0.44 like my T-100,the if you were to streamline it down to Cd 0.12 ( like GM's Solaraycer ) that would get you down to only 27 % of the original drag,a 73 % reduction.
At a 73 % drag reduction,this should improve MPG at 55-MPH by half the percentage,or 36.5 %.
I'm not sure what the Rangers original baseline would be at a constant 55-MPH,but say it was for example, 27 MPG,then the Cd 0.12 would get you 36.85 mpg.

Road Trip
 

Thanks for the input Aerohead. I've just driven cross-country and have a great idea on what the truck gets with all my life's load in the back and in the cab. I'm guessing it's around 700 pounds. Don't know how much of an effect that should result in.
The first day, there was no wind, got 39 mpg on 15.7 gallons, usually going 60-75 mph, but had a slow construction zone for an hour. Went from 6,200 ft-4,000 ft
2nd day, 15.5 gallons, removed grill block due to it being a hot day and big load, got 34 mpg, at 65-75 mph, down to 2,000 ft.
3rd day, 14.3 gallons, 37.5 mpg, did the grill block for the second half, crazy cross wind, down to sea level
Then went 75 mph purely for 4 gallons, got 22.7 mpg, bad crosswind, hard rain, lights
Then purely 60, needed headlights, wipers high speed due to hard rain, bad crosswind, 37.1 mpg, that difference seems too big.
4th day, 14.9 gallons, 34.7 mpg, very stiff head wind all day, constantly watching the flags to verify that direction. It sucks, I only had a tail wind for a couple hours on the second day! And I went from west to east!

These were not ideal conditions (warm and calm would've been great). Also huge load (I'll put pics up soon). So to be getting 37 in it wasn't a big disappointment. But I'm still really curious on those 60 mpg runs.

Did some coast down testing in Jackson before the trip and used the tool here for that. Seemed to be around .24 to .26 on the graph. Factory is .49

My tires are at 38-40 psi (max is 44), might have gotten lower due to the colder temps and coming down from the higher altitude. I don't know how much that would effect the long drive. Also, the load in Odd is so heavy the boat tail is at least a foot lower than it was pre-load. That might have thrown off my angles a little. Going on a sailing trip for the next month and might not get in a good long highway run to see how Odd does, empty, at sea level. But I might be too damn curious and have to try anyway.

People at the pump were always stoked to see Odd, and I direct them all to this site. Cheers to this site!