Flat bottom (belly pan)

[Jeremy]

I thought I would share some pics of my belly pan. It started off as a way to stiffen the car to take some of the flex from t t-tops out. As I got into the project, it came apparent that I could get everything flush with the subframe connectors.

I have the majority of it completed. I have the patterns made to fill in the area around the a arms and exhaust down pipes but I just did not have time to cut and bend them today. I need to prep and undercoat everything, but you can see what it will look like.

The benefits are real. The car is sooo much quieter going down the road. I guess the smoother airlfow makes for less noise. The car pulls better at higher speeds and is much more stable above 100.

The pans also add a lot of tordional stiffness. Each piece is probably 5 to 7 pounds for a total weight added of 15 to 20 ish pounds. With the weight I have dropped in other places, the net effect to the car is about a wash or slightly lighter. To me the increased stiffness and aerodynamics are worth the weight gain.

[ilovefirstgens]

Sweet!

I had been considering this as a project for mine but to incorperate venturis running into the tail of the car...

[Sue]

I've been considering this too.

Have you guys thought about air exits the engine compartment? Depending on how much of the bottom of the engine bay you cover it seems, (particularly with our camaros and their huge open front end that catches a lot of air) that you have to be aware of dumping it out under the car.
Obviously that is where it is going now, but to make it most effective it seems getting the air to exit the engine bay toward the sides would be better for aero dynamics as well as air flow in the bay.
Thoughts?

[BluEyes]

That looks awesome! Where'd you pick up sheetmetal that big?
Any concerns about lack of airflow over the oilpan/trans/exhaust leading to heat problems?

do you keep fuel records with each fillup? Any change in fuel economy? Not exactly the kind of performance we tend to focus on I know, but a reduction in drag would also manifest itself in increased effeciency (and is a welcome return thesedays!)

Sue: very good point. I have considered a heat extractor vent in the hood either like the old GT40's, or vents in the fender as used on '70's Trans Ams. Either way, it gives the air coming through the radiator somewhere to go other than under the car. If you put a vent in the hood though, it's gotta be near the front or else you pick up the cowl induction effect and start forcing more air under the car.

[Jeremy]

I plan on header wrapping the exhaust if needed to control heat.

Airflow through the radiator and out the engine compartment should be very efficient. The air comes in on the bottom and exits out the upper rear of the engine compartment through the fender vents.

From the front, the plates sit about 1/2 inch higher than the bottom of the front spoilers.

Truthfully I am expecting some increase in gas mileage as well. I kept good records on my last trip to TA Nats and will check again this April when we go to STARS.

The local rental store actually stocks the sheet.

[Sue]

BluEyes thats exactly what i was thinking.
But those vents would have to be big enough to reduce air pressure at speed, and i don't know how big that is.
In order to keep air flowing back and around the oil pan and headers, i've actually considered a dual layer belly pan that lets air travel down the block under the car and then pushed out the sides

The fuel savings are very real. A drop in drag coefficient of 0.01 is approximately equal to an improvement in fuel economy of 0.1 mpg.

[CAMAROBOY69]

Looks like a good idea but like mentioned above, I would be really really concerned about the build up of heat. Especially if you are just sitting in traffic. The oil pan, mufflers, and transmission would be my main convern. I bet if you sat in traffic on a 80+ day, the floor would get very hot. Mabey you could run some duct work from your engine fan that would force air down thru the bottom. Or even some air ducts that run from the front of your car under the lower valance that force air thru the lower custom pan at all times.
Do you have a tranny temperature gauge installed?

[BluEyes]

A hot floor isn't nessacarily so bad (don't Vipers have this problem?), it would depend on whether it is a daily driver or a weekend fun car. My worry about the exhaust is possibly causing the exhaust system to wear out faster due to the heat.
Oil temps is my biggest concern. An engine oil cooler can take care of the motor, but for a manual trans you'd need a pump to run an external cooler.

Sue, any air vent (that is not in a pressurized area like the cowl) will reduce pressure at speed, the question is by how much. Lots of testing would be needed there, or you could just seal off the bottom of the engine bay so virtually no air can get out that way. Then just enlarge the vents if you get a temperature problem, lol. Obviously, any reduction in undercar pressure is good though.
Are there any general estimates of the reduction in CD due to a bellypan?

[Jeremy]

The pics don't show, but the mufflers are not enclosed. One, I was not sure that the pan would clear and second, I was worried about the heat. The pan is notched around the mufflers and they are fully exposed.

The pans don't seal to the factory floor. Air can circulate from the engine compartment, between the pans and the factory floor and out the back just in front of the axle.

[CAMAROBOY69]

Another thing to consider.
You might also want to drill a few holes or mabey make a couple small vents so that water and debri can escape. Last thing you want is sand and dirt collecting up there. Not knocking your idea at all, just helping you consider every precaution.

[Sue]

"Where there's absolutely no attention paid to that in the underbody area, you can get about 5% to 6% improvement in drag by treating the underbody."
Max Schenkel - GM technology integration engineer

I'm not sure what our cars start out at but it probably between a 1/4 and 1/2 more MPG.

[David Pozzi]

cool!
How hard is it to change your oil?

[Sue]

wait i think i'm wrong.
Poeple that are smarter than me say, "According to the industry's rough measure, that's a performance increase of 2 mpg."

[Jeremy]

To change the oil as it stands right now, I would have to remove the front pan. This takes four bolts and around 5 minutes. When my dad and I fabbed it, we talked about cutting a small hole big enough to get a socket on the drain plug, but did not feel it was worth it as easy as it was to remove the pan. Furthermore, I don't drive that much so oil changes are every six months as I don't get 3K in that amount of time.

The front pan overlaps the middle pan and is 1/4 lower letting air and mositure out at this joint. The middle pan has two drain holes towards the center, rear.

Furthermore, the car is really for the most part a fair weather driver. It never sees snow and will only see rain if I get caught suddenly out or on the way to a show.

Please keep firing away with the questions and suggestions. I think the idea has merit and I really don't want to give up the improved aerodynamics and structural rigidty. The car is so nice and stiff now.

[Damn True]

I'd like to see a couple more photos, thanks.

[BluEyes]

Please keep firing away with the questions and suggestions.

Extend it further back! Particularly under the trunk area where the 1/4 panels and trunk panel come down and make a neat scoop under the car. Covering around the axle would be tougher, but something could be attempted. Maybe a sheet of roughly 1/8" thick semi-flexible plastic attached to the leafs on either side?

Nice to hear there is a noticable gain in stiffness, what gauge sheet did you use? I assume stiff enough to keep it from flexing at speed? Some sort of stamped ribbing running in the axis of the vehicle would be ideal to keep flex under controll and reduce weight, but that would be hard to do that at home.

Sue, 2 mpg is still a tidy little gain. Plus the sound reduction and increased acceleration (although a tiny bit slower at low speeds due to weight, but I assume we aren't talking too many #'s here).
If that's a current industry measure, the gain is likely to be even more on an older vehicle. I know the stock underside of my '92 LeBaron looks a whole lot 'cleaner' than under my '77 Camaro for example.

[Jeremy]

The front two plates are made of 5/32 steel. The rear is out of 20 guage. The middle and rear plate have 1 1/4 x 1 1/4 angle iron welded on the top sides to make triangular strengthening ribs.

I would have loved to have access to a bead roller. I would have put beads in the metal to strengthen the plates and look better but as it is, once it is all black, it should look nice.

[element180]

Sweet!

I had been considering this as a project for mine but to incorperate venturis running into the tail of the car...

I don't see how that could be done taking the rearend/rear suspension into consideration.Unless you're using in IRS that is.I remember seeing a 3rd gen Camaro with a Porsche independant rear (pushrod shocks I believe) and a full length belly pan with venturis but can't seem to find and more info on it.Either that or I have'nt looked hard enough

[Mean 69]

Bravo, nicely done young man. You can bet your bottom dollar that the efforts will pay off in greatly reduced drag. It is worth the effort for sure. I'd really like to see what difference you get in terms of mileage, it will be a darned good indicator of how the car cuts through the air better. I plan on doing something very similar when I can get new headers for improved ground clearance (drag race headers are not road race headers....).

Another idea that you can try for the exhaust is to have the pipes coated. It's not terribly cheap, but not horrible in terms of cost. I had my headers done, and it made a really big difference in underhood temps. I'd consider that before the wrap idea, but either/both are probably going to be needed.

Mark

[SoCal69]

That's an excellent idea. There's an awful lot of "stuff" hanging down in the breeze under our older cars. I notice the luxurycars are covering up and incorporating a pebble finish to further deaden the road noise. I made up some aluminum parts for my first-gen Camaro to take the place of the missing factory A/C car panels, the ends of the core support and underneath the radiator. I extended mine all the way to the top of the front spoiler so all air has to come in the front. I also made the panel that GM forgot that covers up the space in front of the core support to the header panel. Now the only air going into the engine compartment is cooling air, not recycled air from the back of the radiator or extra air that isn't cooling anything. This is an area I've been looking at for some time, glad to see somebody else is too. I'm selling some of these panels on Ebay if you're interested. They have generated a LOT of interest at car shows.
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