Weight Reduction VS Aero Mods
 

Hey guys,

I bought a 1984 Carbureted inline 4 Mazda B2000 truck. When I got it, it was in DIRE need of a tune up. I have replaced the plugs, wires and air filter, getting supplies for an oil change and fuel filter.

Onto my question: I totally removed my truck bed and topper and have gone from 100 miles per quarter tank to 170 miles per quarter tank (small engines greatly benefit from weight reduction, this reduction equaled -500lbs) And I have started to fabricate a very basic ply wood boat tail.

Does anyone know if the added weight from the boat tail will change the mpg in a considerable amount and where will I see the most gains? I'm assuming highway will be the best.

I just need some input, Thanks guys!

** UPDATE **

I found this pic on google, cant find a camera right now haha

Tail -

White = PlyWood
Red = 3/4in Conduit frame sitting inside plywood

All Around -

Orange - Wind resistance
Light Blue - Drag and Wind Resistance
Dark Blue - Drag with minimal wind resistance/ negative space

http://i271.photobucket.com/albums/j...pscb49f522.jpg

If the tail fit the Profile, I would expect improved aerodynamics to more than compensate for the added weight.

Fits the profile? I am pretty new to this. Its going to be boxy and simple (3/4 conduit frame and plywood covering it) It matched to the top just fine but falls about 4 inches short on either side.

Should I attempt to expand the width of the base to cover these 4 inches of play or do those not really matter?

Sorry for all the questions!!

+1

Plus, your boat tail should weigh nowhere near the 500 lbs you already shed. Keep us posted, you've got my interest and moral support!

Oh, and as to where you will see the most gains.. I find that the aero factor kicks in (significantly) around 40 mph and above. Also the boat tail ought to give you a very significant improvement in coast-down if you use that technique.

One thing to consider when doing aero mods...wind direction. You can do all the aero mods you want but the effectiveness is quickly diminished by a good side panel or 1/4 panel wind.

I live in the Colorado rockies (black hawk) and I spend about 50% of my driving in neutral and the other times going 35-50mph at 2k to 2.5k rpm

Im going to open a new thread for high altitude driving, I got questions about tuning my carb haha

When you removed your bed topper, you may have also improved aero. So the recent gains could be coming both from reduced weight and better aerodynamics.

Aero trumps weight ... unless you do exclusively stop & go, and never go over ~30 mph. Go for it.

Weight reduction will come in handy more at lower speeds than it will at high speeds... That's when aerodynamics really plays it's role. At the speeds you drive, you should see some decent gains from a boat-tail, which should (as other's said) weigh much less than the 500lbs you have removed. When it comes to aero mods, if you go by the aero template it's hard to go wrong.

I thought about this later and thought "You could only go a hundred miles per tank?!" Quarter-tank! :)

With a curb weight of 2,788 pounds, you removed about eighteen percent of the weight. In order to see a 70% decrease in fuel usage with an 18% fuel reduction, you would have had a terrible power-to-weight ratio, or there are confounding ratios.

Of course, fuel gauges are not very accurate, but hopefully they would be less than 44% off (1.7/1.18, your mileage improvement divided by your weight reduction). Please consider sending a private message to Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Profile: JellyBeanDriver to order an MPGuino in order to have an accurate measurement of your mileage. I highly respect my associates on here and everyone seems to agree that an MPGuino is more accurate than dividing your mileage by how much fuel you pumped.

As for the template, please take a picture of your truck (hopefully not in grass!) and upload it here: Aero Template Overlay ver.0.6.2-alpha

This is an example: https://sphotos-b.xx.fbcdn.net/hphot...58296011_n.jpg

Maybe another day I would have "photochopped" off the bed, but the weight reduction would change its angle, this is not accurate for you.

Just try to make sure that your wheels are level when you use the tool and if you try to build according to the template, that just seems complicated, because you would add weight back, but less, so if you are serious about it, I would plan it out the best that you can, figure out all of the materials that you need, and then take a picture with that stuff sitting on the back of the truck, weighing it down about as much it should when finished.

Please note that the Template is only really useful for the top. Please look at what I did for my Forester--as a joke:http://ecomodder.com/forum/attachmen...5&d=1367238665

Also, you would want to taper in the sides accordingly.
Did I create more questions than I answered? :)

Next time you go 100miles on a tank you might try loading the rear to simulate the previous ride hight to check if the level sensor might be a contributing factor

I have been highly considering the new angle messing the sensor position. I have noticed though that at half a tank, I just hit 300 miles.. where as in the past I would have hit 300 at near empty.

Ill be filling up today to get appropriate numbers at the same gas station and pump I normally attend.

As for the earlier template demo, thats much more advanced than the boxy shell I am fabricating. Would I then benefit more from a half boat tail and ending in a half kammaback?

Jot your odometer reading down on your gas pump reciept, then work out the math- or start a fuel log here. You'll get better numbers.

+1 on the "pump & pencil" method of bookkeeping!

Pickup truck beds are hardly aerodynamic, especially with the gate up. Should have tried some trips with tailgate down to see difference

I've always checked my MPG at the pump. Miles driven/ amount of gallons to fill up.

I just did this and achieved 34.4 mpg!! Thats coming from ~24 mpg. And all you critical thinkers, yes I filled up with the bed off once already for accurate numbers.

I got an extra 10 mpg from the weight reduction alone :D

That's impressive!

Not to thread jack or anything, but this is how I have been logging my mileage forever. I am just curious about how much gas to put in. I only fill my tank until the pump stops itself and then I close it up, or is it more accurate to top it completely off? I have been thinking about this because I am not sure that all station's pumps stop at the same point.

I am kind of surprised that nobody else is encouraging the MPGuino. If you open the "65+ Efficiency Mods" page, it is the very first suggestion!

Doesn't everyone talk about "Adjusting the nut behind the wheel?"

I know that the MPGuino is very different than my Ultragauge, but I rely on that to tell me when to fill up, not the fuel gauge, since it is far more accurate.

At least with the MPGuino, you can do A-B-A testing and see if there is a difference without filling up, which would not necessarily fill to the same level every time.

If you do rely on topping off to see how much fuel you used, they always say to use the same pump at the same station.

I actually just ordered my MPGuino on sunday. Still waiting for it to come in. Then I get to go through the pain of installation and finding a good spot to mount it. As I don't have the MPGuino yet, I cannot say anothing good or bad about it. The main reason I got one is so that I can do A-B-A testing once I start putting on my aero mods. Only have an adjustable grill block so far that I need to test and an MPGuino will help greatly. Along with helping me test my upcoming belly pan and mirror delete. Not to mention adjusting the nut behind the wheel.

I go by the auto off. A lot of people use the same pump at the same station. I know by using different pumps/stations, one tank (or all) may be a little off- but when we track thousands of miles, the average is the same if your tank is off a little here or there. The next tank will correct, or the one after that.

Everyone has their own specific way, but my suggestion is just to stay consistant. Pick a way, and keep doing that. Since we do not have labs and an exact science, it's really the best we can do. Make a plan/system and stick with it.

Stick with aero mods, any kind of weight reduction mod beyond deletions will never pay for them selves.

I keep wondering about a grill block here in Arizona. I would install a fan indicator light first, although I do plan on trying it.

I am running 100% grille block, and my engine temp gauge never hits the half way point- it's always a hair to the left (cold). In 80-82* weather, for hours driving, it balances between 212-220* on the Scanguage, the UG just adds one degree. I am not sure if the fan is coming on, but I have not had any issues with over heating.

I know Arizona is wicked hot, but thought my experience may help.

The MPGuino is a great device for a fuel injected vehicle.

Unfortunately coltanandrew's Mazda uses a carby (first post), so has no injector signal for the MPGuino to use.

Yesterday was 101°F.

Something wicked this way comes.

Someone posted that they had better efficiency with the grill blocked and the fan blowing, but I couldn't live with that.

Wow. I couldn't fathom living in that climate. Have you thought about using a mesh? I remember reading it lets air in, but when moving, the air more so flows over the mesh- it seems like kind of an in between.

Like a partial grill-block? :)

Thanks for the idea.

coltonandrew -- I'm curious about the 3/4" conduit frame and plywood box. Will it have any function other than wake filling?

The reason I ask is those materials could make an efficient shape or a vortex-inducing nightmare. There is a lot of opportunity in this, most of people are hamstrung when they can't let go of the un-tapered bed.

Those 4"s you mention should be dealt with. How far along are you with that?

This is what you should emulate:
http://i.imgur.com/26TKSTY.jpg

The best example of aero drag vs weight that I know of is the streamliner Honda built by Allert Jacobs:

214 mpg with DIY aerodynamic fairings on a Honda 125cc motorbike

It gained 43% of it's original weight, and yet with the streamliner fairing (and the taller gearing that the lower drag makes possible) more than doubles the FE of the motorcycle.

So, I say that aero drag improvements trump weight savings - by a lot.

http://ecomodder.com/forum/member-fr...lboxlayout.jpghttp://ecomodder.com/forum/member-fr...ticuda-tb5.jpg
Thin curved plywood will give you more strength with less weight.

Just updated the op for visuals, how does it look?

Use a finer pen :)

You've got the general idea, but to confirm your accuracy would require tuft testing. About half the drag comes from the tires and wheel wells so it pays to consider those carefully.

I had trouble finding a picture of a B2000 without the bed and at the right angle. so this doesn't show as much plan taper as should be possible.

http://ecomodder.com/forum/member-fr...0-boattail.jpg

I'd give it a shallow curved cab-over about 4-6" thick at the center. There is a low pressure area just abaft the windshield header, from the angle of the windshield. Also the square edges of the cab top induce vortexes and you could soften those. So even though it would increase the frontal area marginally, it might show some benefit.

Here's a quick, easy way to find the length of the boat-tail necessary to accommodate the width of the cab at the back of the doors. Get some flexible strips, the longer the better—12-14'. Clamp them together at 45° ( 2x the optimal plan taper). Prop up the end and lash the fronts to the door handles. Then slide it back and forth to eyeball the curve. 'If it looks right, it is right.'

http://ecomodder.com/forum/member-fr...1-100-0577.jpg
On my car, I get a little head start on the plan taper.