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...

[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.
[/IMG]

[Damn True]

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.
[/IMG]

Very nice! Ya know...you'd probably be able to sell a few of those around here as well...particularly if you made one that fit a '68 (hint hint).

Let's see some pics of the metalwork you did under the car as well.

[element180]

A good way to bring the pan all the way back to the tail would be to use an underslung type of tail section where frame rails pass under the rear axle.This design may have ground clearance issues but with careful engineering,anything is possible

[Jeremy]

I went for a trip today and got 20 mpg. This is a huge improvement. On the trip to TA Nats, I got 15 to 17 with the majority of the driving at 15. This was mostly highway driving at 80-85.

I tried to keep the speed today at 80 the whole trip. In town I tried to ease through the gears shifting at 2K.

To really put it in perspective, I have increased jetting 6 or 9 percent richer since I last checked mileage. I am also running my winter tires/rim which weigh 4 pounds heavier per wheel. Neither of these are the way to go for better mileage.

I don't think airflow through the engine compartment will be a problem. The outside temp was 45 and I have never seen the temp gauge so low going down the highway. I don't believe the thermostat (180) was open while I was going down the highway.

When I got to my destination, I was curious how warm the exhaust was and the mufflers were cool enough that I could touch them for a few seconds. Not scientific, but I thought it was a good indicator that sufficient airflow is getting between the pans.

[ilovefirstgens]

I don't see how that could be done taking the rearend/rear suspension into consideration.Unless you're using in IRS that is.

Just so happens that i am.

[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."