A belly pan question

[CamaroAJ]

on alot of high end newer cars they are running full length belly pans that also enclose the exhaust system. how are they controlling the heat in the tunnel? i know i won't be able to make a full pan like they are but i was wondering how they were doing it.

if i were to try a full pan my exhaust will be stainless and i though about having it coated and then wrapping it to help but it will still get hot.

[JEFFTATE]

Well , they just downright get hot ..
My 2007 Z06 has the exhaust through the driveshaft tunnel and above a belly pan .
The console gets hot enough to be uncomfortable on my arm..
I could keep my lunch hot in there !
I don't know how to cool the area , or keep the heat from transmitting except , like you said , ceramic coating and heat wrap.
I think the wrap can cause corrosion issues with the exhaust ??
Because of moisture condensation from the hot gasses /cold metal at startup.. ( I could be wrong about this )
I would think that after the exhaust heats up , it would vaporize any moisture.
Stainless steel piping would be a must.

[Nessumsar]

You could incorporate a vent for the driveshaft tunnel, much like a brake-duct; but I can't think of a way to make this work with a rear-exiting exhaust, they would have to exit infront of the rear tires. I have been pondering this as I have a huge sheet of alluminum that I could use for this.

I would think that as long as you seal (paint) the exhaust, you wouldn't have to worry about corrosion.

[CamaroAJ]

Well , they just downright get hot ..
My 2007 Z06 has the exhaust through the driveshaft tunnel and above a belly pan .

the vette doesn't really have a belly pan. the trans tunnel plate doesn't count since its part of the cars structure and doesn't do anything aero wise for the car.

and i know what you mean about the heat, i left chapstick in the cup holder once at a track day in my old C5Z and it melted lol.

You could incorporate a vent for the driveshaft tunnel, much like a brake-duct; but I can't think of a way to make this work with a rear-exiting exhaust, they would have to exit infront of the rear tires. I have been pondering this as I have a huge sheet of alluminum that I could use for this.

I would think that as long as you seal (paint) the exhaust, you wouldn't have to worry about corrosion.

i was thinking maybe loovers facing the rear of the car to draw heat out.

i'm not sure adding air into the trans tunnel would be a good idea because that air would go under the car. i did read though that adding air at the back into the defuser helps speed up the air comming under the car though. i'm not sure that would be far enough back though.

[Nessumsar]

i'm not sure adding air into the trans tunnel would be a good idea because that air would go under the car. i did read though that adding air at the back into the defuser helps speed up the air comming under the car though. i'm not sure that would be far enough back though.

I was thinking along the lines of building a box (for lack of a better term) around the exhaust itself and curve it so the exhaust and cooling air exit out the side in front of the rear tires.

This wouldn't introduce any air under the car as it would be contained and exited from underneath.

[CamaroAJ]

it could be built like corvettes. they have flat floors and down the center the exhaust and torque tube. its not ideal but it works.

[69496]

If the exhaust is stainless wrapping it should be ok, it would atleast last long enough. If its not stainless it will rust out pretty quick if you wrap it, like someone mentioned earlier.

[LeighP]

Guy I know on another board did this with a 2nd gen T/A. He made up a three piece belly pan from the front to just in front of the rear axle. All mounted to a triangulated brace he fabbed up. Stiffened the car nicely, but it was so hot he ended up taking it off as the car was too hot to drive in for any long distance runs (which was why he built it in he first place).....Last I heard he was trying to figure some way of using the airflow to extract exhaust heat.

[overZealous1]

simple, louver it.

[CamaroAJ]

that was my thinking too. however sitting in traffic no air is going to move so it will get hot with the quickness.

[wmhjr]

How do they design them from the factory?

With massive computer modeling to determine all the thermal and fluid dynamics. You have to worry about all kinds of variables, and it would take some serious track time and constant modifications to try and trial and error it. I would be very concerned about creating hot spots where heat would not extract, as well as unintended lift at speeds. You would also very possibly increase engine temp if done incorrectly, as you might create a high pressure area in the engine compartment, decreasing air flow through the cooling system

[CamaroAJ]

air flow through the radiator will not be a problem with my car. i wish i could get my hands on a car full belly pans to see what they did with the exhaust.

[wmhjr]

You think air flow through the radiator will not be a problem until you close off the belly of the car, creating a pressure area which restricts air flow. IOW, you still have plenty of surface area in the front, but unless you're ducting air from the engine side out somewhere the air does not flow. Same reason top race cooling guys want you to retain your cowl seal, etc. Force the air flow along the path it was designed to go. Not saying there WILL be a problem. Just saying you can't say there WON'T be a problem. Not unless you've modeled it.

What is the problem you're trying to solve? If it's just to be like "some high end cars" I think they've spent millions of dollars figuring it out for their specific design. The variables at play here are very significant. You could certainly do it via trial and error, but I think heat, high speed handling and noise would all be factors to deal with. You just might be creating a very heavy airfoil, generating lift at speed. Of course, the other thing would be that it may not pass tech at some tracks.

Interesting thought.

[CamaroAJ]

the air flow will be venting through the hood from the radiator so its not going to be a problem. and there will be hood and fender vents to get the pressure out from under the hood with as much of the grill blocked as possible to keep alot of air from building up.

belly pans are mainly smooth with a few ribs to direct air flow and need to be angled up in the rear to create an expansion are to help suck the car down and end in a defuser at the rear.

thats the easy part of the big picture. heat is the hardest part. the exhaust can be coated and warpped to help but it won't take care of it 100%. another option taken from corvette racing is to use vented mirrors and pipe air into the space between the belly pan and then control the exit of that air to the rear of the belly pan at the defuser (corvette vents the spot where the plate goes with a screen.)

there would have to be alot of trial and error to see if any gains would to be had. but if it wasn't worth it then do you think all the race teams would do it?

[wmhjr]

I do think it can be worth it, but the race teams spend hundreds of thousands of dollars in computer research before just trial and error. Like I said, interesting, but probably pretty difficult to deal with unless there are more metrics available.

[vette427-sbc]

What front engine cars actually have full belly pans though? I wouldnt think any production cars would have a fully enclosed exhaust due to the heat generated when idling in traffic or other similar situations. You would think that GM would have put a belly pan on the 190+ MPH Z06 or ZR1 if they could. Same with the Viper. Also... most full belly pan cars are mid/rear engine layout and dont really have to deal with this problem.
I know this doesnt really help in your quest to put a belly pan on your car, but maybe the manufacturers leave them out for good reason.

[CamaroAJ]

thats a good point chris, i never really thought about that. i'll prolly just do a front pan and enclose behind the axle.

[exwestracer]

thats a good point chris, i never really thought about that. i'll prolly just do a front pan and enclose behind the axle.

Donohue and Penske recessed the exhaust into the floor of the 1969 Trans-Am Camaro, but they didn't have to worry much about sitting in traffic...

If you really want to sell your soul for a flat undertray, how about side pipes with skirts inboard of the exhaust? No different than rocker panel extensions, really...

There is a hell of a lot to be gained with a well-designed flat floor concept, because the air pressures are relatively constant as compared to a wing.

[Bjkadron]

Belly pans can be very complicated to design. Especially if your needs require that it be able to sit in traffic. I would look into ceramic coatings to control the heat. Some companies that do exhaust coatings claim that you can touch the pipes with your bare hands. Sounds nuts.. But I would say it is possible.

That said I am putting a full bellypan on my car. But other areas of the car will be radically changed to compensate for cooling and such. Also I am working to use the cooling air to help add downforce where I want it.

Whether or not you should do it could be answered with a simple question. How much is the benefit worth to you?

[vette427-sbc]

Some of the ceramic coatings do keep the heat way down, but Ive found that only to be true with open headers (on my car at least) I could hold my hand on the sidepipe for a 5 or so seconds without cooking my fingers. As soon as I put mufflers in, they would get hot enough where you couldnt hold your hand on there for more than a second without getting a nice burn. To end my story, the ceramic started rusting, I sanded it off, painted with regular high temp paint, mufflers out, and they are still too hot to touch.

Like exwestracer said, sidepipes may be your ticket to a full belly pan. I havent looked under a first gen f-body in a while, but could you run the exhaust on the outside of the subframe connectors and have it come out of a hole in the rocker? Might look pretty bad ass too if you could pull it off.