Skid plate/belly pan

[Billett]

I see an awful lot of posts about improving mpgs in these trucks by doing all kinds of crazy things, but has anyone ever decided to build a skid plate or belly pan for these trucks to try and improve the absolute lack of aerodynamics on these things? I would think there's enough room to build a pan all the way back, not just the front. i know a lot of the eco-modding crowd does this and claims 2-3 mpg increase on cars that are already pretty slippery.

[71swb4x4]

I think the key is that they are fixing their weakest link. If you have a car where you are losing a significant amount of MPG's on the underside, a belly pan will help a lot. If you have a car where most of your MPG's are lost because it's shaped like a brick, I don't think you will see much of an improvement with a belly pan.
Now I am just a guy on a keyboard. Go out and prove me wrong. The car hobby is great because people have different ideas.

[Keith Seymore]

Originally Posted by 71swb4x4

I think the key is that they are fixing their weakest link. If you have a car where you are losing a significant amount of MPG's on the underside, a belly pan will help a lot. If you have a car where most of your MPG's are lost because it's shaped like a brick, I don't think you will see much of an improvement with a belly pan.
Now I am just a guy on a keyboard. Go out and prove me wrong. The car hobby is great because people have different ideas.

My first thought exactly.

Well said.

High frontal area, Camper mirrors, door handles, roof drip rails, big tires - all that stuff adds up.

You might see the biggest gain by (a) lowering the truck and (b) chopping the top!

K

[cdowns]

if yoiu do like the nascar guys and slam it with less than 1/2 inch clearance you might see a few MPG increase at over 150MPH// at 30-70 mph tthere aint that much to b gotten in the aero dept

[Billett]

I'm thinking about it. Might be a fun winter project. I'm just thinking about how much drag is created by that massive crossmember and all the air swirling under the bed.

[PanelDeland]

I think payback on the other mods would be a lot quicker than aerodynamics.There's a lot of MPG in EFI,OD and other mods before aerodynamics will help.
A flying brick is mostly good for going thru your ex's window.

[Billett]

Already got EFI and OD with the LS swap Like I said I was mainly curious to see if anyone had done it before, but I'd be happy to be a guinea pig.

[Prematuregrey]

You'd be better off using a bed cover or removing the tailgate (mythbusters proven?). If you were to do a "skid" plate, I would think the size of it would be weight prohibitive and possibly cause heat issues due to air flow and the inability for under hood air to escape.

I would be interested in seeing your results, but skeptical of the advantages. I know when I panned my 4Runner from the bumper back, it had no gain in mileage. Although with the lift, long travel front end and tires sticking out, it's not really a platform to judge mpg adders.

[Billett]

Got the bed cover too! I'm thinking of making it from carbon fiber to keep the weight down. Not sure about underhood heat. I could probably do some research on where I could drill some holes to let the heat out and not affect air flow

[BrianG]

Seems like you are more curious than anything and that's cool. I say if your interested, go for it. Seems like the overwhelming question among many is why??? But we all have our 'crazy' ideas running around in our head (different seats, diesel motors, turbos, dropped to the ground, etc.) Seems like the money spent researching and fabbing it would take a long time to pay off in fuel savings. But perhaps you'll discover some amazing easy way to deflect air under these vehicles. You may be able to patent your idea and even make some money off your time spent. If someone were looking for a super fuel mileage truck it would most likely NOT be a 67-72 chevy(gmc). But same goes for ride, hauling capacity, etc. We all know that there is much more to it than purely function. Why not make the best of it.

Good luck to you Billet, keep us posted on your progress.

[BrianG]

He may not have his truck sitting on the ground though.

Differnet type of vehicle, but perhaps some of the concepts would be the same as in the following study;
http://www.solusinc.com/pdf/2003-01-3377.pdf

Also, look at all of those air deflectors under semi trailers these days. Here's a company that has a few different options, but the one's underneath are what I've seen a lot of. They seem to have proof of the effectiveness of such products.
http://freightwing.com/on-aerodynamics.php

Some of these things may actually work but I'm not sure if you would end up with a very desirable look on a pickup in the end.

I know the big automakers spend a lot of money tuning the outside of their new truck to get the fuel milage and sound reductions that are found on new trucks.

The idea is to get air to flow around the vehicle (or maybe better stated, the vehicle to cut through the air) with as little disturbance as possible. I think udercariage deflectors would help. How much that might be is debatable and in most opinions would not be very much. Most of us don't drive an old C-10 for the fuel milage anyhow.

[Fitz]

Originally Posted by Billett

I see an awful lot of posts about improving mpgs in these trucks by doing all kinds of crazy things, but has anyone ever decided to build a skid plate or belly pan for these trucks to try and improve the absolute lack of aerodynamics on these things? I would think there's enough room to build a pan all the way back, not just the front. i know a lot of the eco-modding crowd does this and claims 2-3 mpg increase on cars that are already pretty slippery.

The body has the aerodynamics of a brick. A belly pan won't improve that.

[Billett]

I'm seeing an awful lot of nay-sayers, but not a lot of proof. I'm not saying I'll suddenly get 30mpg, but if you could improve your mileage by even 2-3 mpg with a bolt on wouldn't you at least be interested?

[Keith Seymore]

Originally Posted by Billett

I'm seeing an awful lot of nay-sayers, but not a lot of proof.

It's gonna be somewhat tough to prove out in the real world.

I should preface this by saying I was the engineering manager on the Chevy Volt program (both domestic and export; and related variants: Opel Ampera, Vauxhall Ampera). CdA for the Volt was .284 which at the time was the lowest GM had ever done for a midsize sedan. We spent a ton of time in the wind tunnels (we have two: the aero tunnel that the NASCAR boys borrow, and a Climatic tunnel for hot/cold operation).

The problems with doing a truck program on the outside as I see it are:

a) Airflow over a vehicle is not intuitive. You don't really know what's going to happen 'til you smoke it. Example: We introduced a duct at the front of the vehicle one time, looking for a ram air effect. It wasn't working like we expected so we brought it into the tunnel for evaluation. With the smoke, you could see the air was actually hitting the inside corner of the inlet, scooting across the opening and shooting out the outboard side of the inlet and around the vehicle. No air was actually going into the duct and in the hose. We would never had known (or even guessed this) without the smoke and video. The whole "tailgate up vs down" and bedcover debates that just won't die (in spite of objective data) are a symptom of this.

b) You need to be able to focus on one small area. On the road testing incorporates the overall vehicle, which is fine for a final "capping run" evaluation, but for development work you need to isolate one area and gage the effects that can be attributable to those specific changes. Sure - the NASCAR and Bonneville guys to some testing on site with duct tape and cardboard - but if they're smart it's after spending hours and hours iterating and developing inside a tunnel like ours.

c) Things change while you are looking somewhere else. So - the bad news is while you are focus on one area of the vehicle the other end can be changing without you knowing it. Hopefully you find out and can nuetralize the effects but if not it can generate a lot of confusion.

We had been working for years on prototype and preproduction vehicles so we were quite anxious to do a "sense check" on the first saleable vehicles off the line. We put them in the tunnel and the results were .289 - not good because it was higher than expected but also because the media reports the values rounded to two decimal places = .29. We very much wanted the .28 value reported, so we had to be below .285 to achieve this.

After much angst and diagnosis it turns out the cars were building 5mm too high. This change in trim height was affecting our test scores, the advertising numbers and our fuel economy certification. Dropping the cars down 5mm brought everything back into line. Note that's 1 count of aero drag for every 1 mm of trim height, in this case (your results may vary).

With my duct example above, we could've changed something at the rear of the vehicle, changed the flow under or around the truck and suddenly our front duct could've started working. You never know.

d) Small changes have big results and big changes can have small results, like the example above. My boss used to joke that he would give his finger for .001 CdA (one "count" of drag). Little scallops and skegs and flanges that look like styling features can actually be aero enablers. Things like mirrors and door handles and grille openings are fairly significant aero disenablers.

e) If you are using fuel economy as your measurement you don't have a great linkage between the design change and the result. There are too many variables in your fuel economy even without changing anything, the least of which is the refueling and calculation process. As an anology - it's like trying to figure out how fast you are driving by looking at the gas gage. There's a relationship - but it's somewhat removed. You are better served looking at a more appropriate gage: the speedometer, in this analogy. Normally what you will find is that any results from your design changes will be statistically buried within the variation of the fuel economy measurement.


Can it be done? Yes.

Will it be particularly rigorous (in terms of proof)? No.

My $0.03 -

K

[Keith Seymore]

Given the benefit of further thought: you want the biggest bang for your buck?

Slow the H.E.L.L down!

(lol)

The aerodynamic drag increases with the square of the speed.

No other physical dimension or attribute has that much power by comparison.

K

[68gmsee]

Sacrilegious!

Joking aside and not knocking anyone that wants to make changes to their trucks -I've done the same in the past. However, I always stop to consider that the reason I bought it was because it was a 1968 -trucks I grew up with. I drove one in my teens and after I got out of the service. Also, my dad owned a 1970. I figure if I absolutely have to have better mpg's I'll get me a smaller newer vehicle and leave this old truck like it was intended to be.

[Fitz]

Originally Posted by 68gmsee

Sacrilegious!

Joking aside and not knocking anyone that wants to make changes to their trucks -I've done the same in the past. However, I always stop to consider that the reason I bought it was because it was a 1968 -trucks I grew up with. I drove one in my teens and after I got out of the service. Also, my dad owned a 1970. I figure if I absolutely have to have better mpg's I'll get me a smaller newer vehicle and leave this old truck like it was intended to be.

I'll vote for that! My truck is a TOY. I use it to play not work so the MPG, drag, reliability, towing ability, payload and all the rest of the stuff related to using that truck to do a job simply do not matter.

[In The Ten Ring]

Originally Posted by Keith Seymore

Given the benefit of further thought: you want the biggest bang for your buck?

Slow the H.E.L.L down!

(lol)

The aerodynamic drag increases with the square of the speed.

No other physical dimension or attribute has that much power by comparison.

K

Slowing down works so well, I don't understand why more people refuse to do it.

In 2006, I was driving back to WV from Mt. Airy, NC, and I decided to see if dropping from my normal 70 mph to 55 mph would have much effect.

In that 2003, 4 banger Honda Civic (gasoline engine, automatic), if I did 70 mph on the interstate I saw 38 miles per gallon. When I began to drive 55 mph, I SAW 50 MPG. After I had the factory spoiler attached (looked killer!), my mpg dropped and stayed at 46 to 48.

In my current "lead sled," 2002 Honda Accord, 4 banger auto, if I do my standard 55 mph on the interstate, I see 34 mpg. Speeding up to 70 mph drops that to 24 mpg. Now a lot of people simply say, "I can't drive that slow" but I feel they are very immature. The fuel savings will add up and I have to tell you, it's much more relaxing to drive 55. There is more reaction time, much more. I'd like to see a return to the 70's and 80's national speed limit of 55 mph.

[Fitz]

Originally Posted by Billett

I'm seeing an awful lot of nay-sayers, but not a lot of proof. I'm not saying I'll suddenly get 30mpg, but if you could improve your mileage by even 2-3 mpg with a bolt on wouldn't you at least be interested?

When drag count is low, a skid plate helps because the contribution of the rough underside is a significant part of the total drag. When the drag counts are enormous, as in one of our trucks the undersurface is such a small percentage of the total that it is insignificant.

My corvette benefitted greatly when the Engineers at GM gave it a belly pan. The Cd dropped from around 0.33 to about 0.286.
Compare that to the "typical" 66-72 pickup of 0.7 and you can see the differences but that isn't the total story. To get a valid comparison of drag between the two you must use Cda, which is drag coefficient multiplied by frontal area.

My Corvette has a very small frontal area and your truck has the frontal area of a Seven-Eleven. I'm not being negative about your idea; I am laughing so hard it is difficult to type. They just don't look the same, do they?
My 3100 pound banana is sleek and low, my 67 stepper is huge, square and aerodynamically resembeles the third picture more than the first.

[Billett]

This really did start out as a hypothetical, or asking if anyone had even tried it, but I really might talk to some of my friends and see if anyone is willing to help out. My college has an FSAE program with an awful lot of spare carbon fiber and fiberglass. Hell, even scrap aluminum would probably work ok. If it doesn't work I'll give it back and they still get their scrap, and if it does work I'll take measurements and make a cleaner one.

It isn't about making a brick aerodynamic. It's about making it just a little less un-aerodynamic haha.

[WIDESIDE72]

Dont overlook a simple air dam mounted below the front bumper. It would divert air aroumd the truck before it ever got a chance to get under it.

[Billett]

I did think about that as well. Could help with handling too if done right. But my truck is a longbed so the air would definitely get back under at least the bed.

[ulakovic22]

I too have been thinking about a belly pan. Ultimately I would like to take my truck to the Texas Mile and see how it does, so a belly pan/difuser is an obvious choice. There are a lot of seams on the front of the truck that could be cleaned up as well to keep air from getting trapped up front. Shaved drip rail and smooth cowl. I'm not sure on the bed cover though. It's been said that the air turbulence in the bed actually creates a better buffer for air to go over versus a cover.

[Billett]

I don't think I plan on going crazy with seams as this is still a DD. I would like to shave the drip rail though. I really like the look of it, but the road noise is terrible. Not to mention mine is full of rust anyway.

[ulakovic22]

I wasn't talking about filling/welding seems, just making the observation that on the older vehicles there are a lot of parts that get bolted together, hence a lot of seams and very large ones at that. On newer vehicles with the advancements in urethane molding, stamping, etc. the seams are fewer and much tighter. Most guys who DD and go to the mile just tape up there seems for the weekend, nothing permanent.