Flat bottom (belly pan) [Archive]

Jeremy

03-19-2006, 03:53 PM

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

03-19-2006, 04:20 PM

Sweet!

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

Sue

03-19-2006, 10:45 PM

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

03-20-2006, 04:15 AM

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

03-20-2006, 04:45 AM

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

03-20-2006, 10:56 AM

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

03-20-2006, 11:06 AM

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

03-20-2006, 11:58 AM

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

03-20-2006, 12:32 PM

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

03-20-2006, 12:40 PM

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

03-20-2006, 12:55 PM

"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

03-20-2006, 01:07 PM

cool!
How hard is it to change your oil?

Sue

03-20-2006, 01:23 PM

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

03-20-2006, 01:47 PM

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

03-20-2006, 01:59 PM

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

BluEyes

03-20-2006, 03:31 PM

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

03-20-2006, 03:39 PM

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

03-20-2006, 03:40 PM

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 :dunno:

Mean 69

03-20-2006, 04:48 PM

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

03-20-2006, 05:48 PM

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.
https://www.pro-touring.com/forum/http://xs73.xs.to/pics/06122/DSCN0079.jpg.xs.jpg (http://xs.to/xs.php?h=xs73&d=06122&f=DSCN0079.jpg)

Damn True

03-20-2006, 05:52 PM

element180

03-20-2006, 05:53 PM

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

Damn True

03-20-2006, 06:04 PM

Jeremey, how did you secure the pans to the chassis?

Jeremy

03-20-2006, 10:02 PM

Starting at the front, we welded a plate to the bottom of the front crossmember. The leading edge of the front plate sits on top of this and 3/8 bolts hold them together.

The rear of the front plate and the front of the middle plate use a 3/8 bolt that goes up through the subframe. Right now I use a nut and washer on top but future plans call for a L bracket with a nut welded on or the bracket itself threaded to avoid having to use a wrench.

The back of the middle plate has a bolt going all the way through the subframe as well and it too calls for a hidden nut in the future.

The rear plate is the easiest as it bolts right to the bottom of the subframe connectors using self tapping bolts.

The nice thing is that each plate can be removed without taking another plate off.

ilovefirstgens

03-20-2006, 10:18 PM

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.:woot:

SoCal69

03-21-2006, 06:10 AM

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.

I didn't know if I should even mention it since I'm not a sponsor. These panels fit all first gen Camaros. I will take pics next time I put my car on the lift. I was experimenting with it, found it to lower my coolant temp and tranny temp besides it looks good.

Rick Dorion

03-21-2006, 09:13 AM

I made the top piece too. Your bottom and side pieces are interesting. Will you be selling those?

SoCal69

03-21-2006, 04:17 PM

Yep! Those are coming. I got so many orders for the closeouts I have to get them going before I start something else. I'll let you know when I list them.

Jeremy

03-22-2006, 01:43 PM

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.

Sue

03-22-2006, 08:35 PM

I'm stoked to hear that. Thats a big improvement.
Good work on that mod.

hotroddr

03-23-2006, 11:50 PM

good to see another guy after my own heart. My fiancee probably thinks Im crazy. I take my windshield wipers antennae and passenger mirror off for roadtrips. I also experimented with taping cardboard over my grill to minimize airflow to the engine compartment, now I made a permanent cover and extended the airdam to compensate. Im glad the belly pan made a difference, I have been planning on doing this on all of my projects but have been dragging my feet because its a lot of work without knowing if its worth it. I also am going to go to a single sport bike aerodynamic mirror to minimize wind noise and wind resistance while still keeping street legal. My 56 gmc will have a functional rear diffuser/venturi setup since I hate wings and will need all the downforce on the back that I can get.

What about sheets of abs plastic to minimize weight, as well as foam filling between the belly pan and floor to cut road noise more and insulate better?

Jeremy

03-24-2006, 05:32 AM

The abs sheets are an interesting thought. They would not work for me as the plates are there to stiffen my structure as well. With the t-tops I need all the help I can get and a 4 or 6 point cafe is out (ask the wife). Actually I don't think I would want to live with a cage/bar either.

I had thought about filling the void but after hearing all the discussion about heat, I think its best that the air can flow through the space to cool the exhaust and tranny.

I have seen some people mention diffuser/venturi for the rear. I have to confess that I am not sure what these are or what they do.

Anyone care to enlighten me?

hotroddr

03-24-2006, 05:58 AM

https://www.pro-touring.com/forum/attachment.php?attachmentid=8023&d=1140196867

The back portion is a diffuser which is basically a venturi. It works just like a venturi in a carburetor which squeezes down the opening of the carburetor in order to increase velocity of the air which decreases the pressure to suck out gas. On the bottom of the car it sucks the car to the ground.

Here is a thread that gets into it a little.
https://www.pro-touring.com/forum/showthread.php?t=15348&highlight=belly+pan

BluEyes

03-24-2006, 06:10 AM

It's only a model, but you can get a really good view of the diffuser/venturi on an Ferrari Enzo here: http://tamiya.com/english/products/24260enzo/enzo6.jpg
Basically, as the air passes under the car, it gets to the venturi area and expands to fill the larger space, causing a reduction in pressure under the car. Low pressure underneath = downforce.
The diffuser I think is technically the part at the very back where one attempts to reintroduce this airflow into the general airflow around the car in such as way as to minimize drag at the tail.

hotroddr

03-24-2006, 07:55 AM

The diffuser I think is technically the part at the very back where one attempts to reintroduce this airflow into the general airflow around the car in such as way as to minimize drag at the tail.

Good point...I mixed that up in my last post, you are right.

Jeremy

04-10-2006, 02:25 PM

I finished the hidden mounts yesterday and with an air ratchet I can get all of the pans off in under 10 minutes.

While I had them off for painting I went for a drive and my vibration problem was back. It was very pronounced again and I thought I had it fixed. The only change was leaving the belly pans off.

I had groaning in the dash and A-posts without the pans over uneven bumps. They apparently help tighten the structure as I thought they would.

I weighed them and the total weight added is 100 pounds. The wight is low and probably doesn't hurt the CG, but a 100 pounds is a lot I would guess.

Does anyone now how much a 6 point roll bar/cage would weigh for a comparison?

I am guessing that I need to put the front two pans back as I have driven the car with just them and no vibration. This will cost me 63 pounds.

Damn True

04-10-2006, 03:56 PM

Let's see some photos of the complete package.

Jeremy

04-11-2006, 03:31 PM

I'll get finished pics in the next week or so. I put the pans back in today and all vibration is gone. Any thoughts as to why the difference?

Damn True

04-11-2006, 09:06 PM

Hard to say. Describe the vibration for us.

Jeremy

04-12-2006, 06:19 PM

The vibration is tied to an rpm range of 2500 to 3000. Without the pans, I can feel the vibration in neutral, in all gears, and it is most pronounced when cruising in that range.

When I put the pans in, the vibration is gone in all gears and neutral. It makes me wonder if there is something in my structure that does not like that frequency range.

I did replace the floor pans as the first thing on my buildup. I left the floor supports and peeled the old pans away. The others fit perfectly and I put 1/4 inch bolts through all the factory spot weld holes to bolt the new pans to the supports. In theory, this should have been nearly as strong as the spot welds I would have thought. I then welded the pans in.

Besides that, I have solid body mounts, subframe connectors welded in, and the front structure braces from pro touring f body.

I have been through everything. It is not the motor, tranny, driveshaft, axles, tires/wheels, flywheel or clutch. The front end is properly aligned and all new moog parts.

Any thoughts? Worst case is I have an extra 100 pounds of bracing and all is good. I just would like to know what the problem is.

BonzoHansen

04-13-2006, 03:11 AM

Maybe a newly exposed mount is in an airflow somewhere.

You need to hook up with ks71z28 and make carbopn fiber under pans. :)

Mean 69

04-13-2006, 07:01 AM

If it is specific to an engine RPM versus a road speed, then the motor is exciting some frequency in the car, somewhere. At that frequency, it is something pretty stiff, probably the body structure, etc. Chasing resonant vibrations is not terribly fun. Are you sure it isn't the engine itself?

M

Jeremy

04-13-2006, 09:17 AM

The problem came about after driving the car for a few months after getting it back together. The motor was fine before and it is fine with the pans installed.

You can feel the vibration in all five gears without the pans. During the small window of vibration it is nasty and feels like the car is going to come apart. With pans, no problems.

The vibration is worst at 75 to 80 which happens to be 2500 to 3000 rpms. I really think it is frequency related more so than speed related as it does it in neutral and all gears.

As I said every rotating part is new and quality parts. No low level stuff.

I have also attached some finished pics.

trackrat79

04-15-2006, 10:25 AM

Every structure has a specifice frequncy that it will resonate at. The more flexable a structure is the easier for it to achieve that resonance. By adding you under plating you may have stiffend it enough to change were the chassi will resonate at. My truck does the same thing. But mine seams to be a more specific rpm. Right around 1200 my truck vibrates like a palm sander. I love it, it makes it sound like I am in a cave or an eco chamber. The exaust note sounds like it is coming out of an amplifier. I hope this sets you at ease a little.

Jeremy

04-15-2006, 05:40 PM

I may have found the problem. I did shim the front springs ever so slightly at the same time I removed the plates. I got more time to drive the car today and it still vibrates a little at 75 to 85 and more than it did before.

I checked the torque on all the lug nuts and they were fine. While looking at the tires, I noticed some scuffs farther down the side of the tread than normal. I believe shimming the front end was enough to change the alignment.

I have an appointment for an alignment an Tuesday, but will probably remove the shims tomorrow and see if that makes a difference.

David Pozzi

04-15-2006, 09:43 PM

You should try a coast down test, it will tell you the actual drag reduction. All you need is a level road and a stopwatch.

Here's a link to the page:
http://www.mustangsandmore.com/ubb/DanJonesAerodynamics.html

"So what can you do if you don't have access to a wind tunnel? Several years ago I
copied down this coast down formula which can be used to test aerodynamic and rolling
resistance drag. I've never tried it, so caveat emptor.
CDHP = (WEIGHT*MPH)/(823.3*CDTIME)
Where:
CDTIME = coast down time in seconds
CDHP = coast down horsepower (i.e. the horsepower required to maintain a given speed.

This formula can be used in determining the effects of changes made to a vehicle
to alter its aerodynamic drag or rolling resistance. As an example, assume you
have taken coast down measurements from 65 to 55 mph (under similar atmospheric
conditions) before and after making changes to reduce aerodynamic drag (e.g. lowered
the vehicle and added an air dam). In the before case, it takes 15 seconds to
coast down. In the after case it takes 20 seconds. Assume the vehicle weighs 3400 lbs.
Plugging this data into the formula yields:
Before: CDHP = (WEIGHT*MPH)/(823.3*CDTIME)
= (3400*60)/(823.3*15)
= 16.51 hp

After: CDHP = (3400*60)/(823.3*20)
= 12.39 hp

Net Change: 16.51 - 12.39 = 4.12 hp @ 60 mph.

This formula indicates that the changes result in 4.12 hp less required to maintain
the vehicle at 60 mph. Since aerodynamic drag varies with the square of speed,
the effect will be greatly accentuated at higher speeds. To minimize the effects
of internal engine drag, coast down times for aerodynamics effects should be taken
with the transmission in neutral. When testing the effects of lubricants or the
effects of accessory drag (an air conditioning compressor, for instance), leave
the transmission engaged.
Coast down time should be measured on a flat, smooth, road with no wind or drafting,
using a 2 way average, under similar atmospheric conditions. I wouldn't put much
faith in the absolute numbers provided by this formula, but I think it might be
a good tool for assessing relative changes.
Off the top of my head, I can think of several things that might be worth testing
using these formulas:
*lowering the car
*adding a lip spoiler/air dam
*raking the body with a slight nose down attitude (primarily for stability)
*fitting a Capri hatch (supposed to be more aerodynamic than a Mustang one)
*fitting a belly pan to the rear skirt on GT's (factory skirt looks draggy)
*taping over door and hood seams
*convertible top up and down
*roll bar "

David Pozzi

04-16-2006, 10:25 AM

Here is an on-line calculator for aero drag. It requires two readings, a high speed and a low speed. This calculator allows for rolling drag, so you can see the true aero drag.

http://www.race-technology.com/WebPage2/Other/Utilities/Coastdown/CoastDownCalcs.html

Sue

04-16-2006, 10:27 PM

That's a cool link. I'm going to try that out when i get a chance.

Jeremy

04-17-2006, 09:30 AM

I'll try the cost down test the next time we get a calm day. Right now everyday is really windy.

Vibration problem found and fixed. I guess when I was greaing everything, I got some old grease and grit between the mounting surface and the back of the wheel. It was thick enough to keep the wheel from sitting flush. I cleaned this up and all is good.

gonein67bird

04-18-2006, 04:57 AM

That is so cool, nice work. I so want to do that to my Bird but I think I will use alum.Might not be as stiff but I think lighter.

ks71z28

04-18-2006, 08:19 AM

My role cage weighs about 90 lbs. 100 is a bit much. I think this is where a composite aluminum type pan would work best. ABS won't handle the heat and is heavy. How far are you from Northern California, ha ha.

Keith

atomicjoe23

05-14-2007, 01:26 PM

Jeremy

05-14-2007, 01:44 PM

I'll see if I have any pics stil. I had to abandon the idea due to heat retention.

atomicjoe23

05-14-2007, 02:02 PM

Jeremy,

thanks for taking a look!

What were your heat retention problems? Was it in the engine bay or under the car?

I have a few ideas of how I'm going to address heat retention due to the belly pan. . .I've put quite a bit of though into it actually.

Engine Bay
-The belly pan (I will be making it out of aluminum) in the front of the car will have will have louvers in it in the rear section. . .let's say from the area of the oil pan on back probably just beyond the firewall.
-The hood will have heat reflective lining on the underside
-The headers will be ceramic coated (I am going to be using thermal and friction reducing coatings extensively in my project).
-The engine bay is going to have aluminum close out panels to help control the airflow in the engine bay itself. . .part of this will consist of aluminum intake ducting for the tubo air inlets and the radiator and intercooler(s) and there will be a fan shroud as well. . .part of the air from the engine bay will exit out the louvers in the belly pan (low pressure area) and part of it will be directed through ducts to the brakes where it will keep the brakes cool and will exity out the wheel wells (another low pressure area).
-turbos will make for some heat management issues of their own but I'll work that out as well. . .

Firewall back
-the entire exhaust system will be ceramic coated to hold the heat inside the exhaust.
-floor pans will have a thermal barrier coating on the underside and use dynaliner above
-the aluminum belly pan will be coated in a heat radiating coating on both sides to help shed the heat from the area between the belly pan and the floor board

I'll have to see how it works out. . .I'm sure I will probably have to make some changes here and there but I think with the use of thermal coatings and proper air routing into and out of the belly pan/floor pan area I can make it work so that I can realize the aerodynamic benefits.

Looking forward to seeing your pics.