Weight Reduction VS Aero Mods

[coltonandrew]

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

[Xist]

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

[coltonandrew]

Originally Posted by Xist

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!!

[Mira]

Originally Posted by Xist

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

+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!

[Mira]

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.

[LeanBurn]

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.

[coltonandrew]

Originally Posted by connorkeyser

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.

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

[MetroMPG]

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.

[Shortie771]

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.

[Xist]

Originally Posted by coltonandrew

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)

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:

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:

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