After market exhaust effect on rear aerodynamics - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Avalnch · 11-07-2015, 02:07 PM

I've always wondered if there are any noticeable negative affects of deleting the OEM mufflers. As I recall the OEM mufflers are supposed to be part of the rear diffuser aerodynamics where by wind flowing under the car flows over the shaped mufflers and is dispersed by the diffuser.

When the OEM mufflers are deleted or replaced, there is a big gaping hole where the air flow can create all sorts of currents and eddies.

Has anyone consider a rear belly pan to replace the function of the OEM mufflers?

JOHNSONROD · 11-07-2015, 02:55 PM

the rear of the car can catch up to 1.21 mega newton jewels of quantum friction if not diffused. this Jrod motorsports patented diffused diffuser relieves over half of the potential negative effects of the a fore mentioned scavenging residuals. im not an aerodynamics expert but none of these other internet know it alls are either. lol i figured id relieve the tension before they all come in here out talking one another.
i took a hole saw to my rear diffuser to let any pressure out that might be there. a rear belly pan might help. it would probably be best if a man could make an incorporated pan/real diffuser like a race car has. the rear diffuser would be a part of the rear pan. it would angle up way sooner than the factory one. the factory rear diffuser is cosmetic at best and only catches air.

L99CAMA2011 · 11-07-2015, 03:49 PM

Quote:

Originally Posted by JOHNSONROD

the rear of the car can catch up to 1.21 mega newton jewels of quantum friction if not diffused. this Jrod motorsports patented diffused diffuser relieves over half of the potential negative effects of the a fore mentioned scavenging residuals. im not an aerodynamics expert but none of these other internet know it alls are either. lol i figured id relieve the tension before they all come in here out talking one another.
i took a hole saw to my rear diffuser to let any pressure out that might be there. a rear belly pan might help. it would probably be best if a man could make an incorporated pan/real diffuser like a race car has. the rear diffuser would be a part of the rear pan. it would angle up way sooner than the factory one. the factory rear diffuser is cosmetic at best and only catches air.

I mentioned how this was nothing but a cosmetic parachute years ago on this forum when some Idiot asked me for proof that it holds back our cars WOW. I mentioned taking off the rear defuser during events.

rockrau · 11-07-2015, 07:05 PM

My understanding is that the rear valance becomes a parachute.

VTSummit · 11-07-2015, 07:21 PM

I studied aerodynamics at Embry-Riddle... and I still won't make an assertion as to what the best setup is but I think the OP's concern is valid. I've also seen wind tunnel tests where the "bunch-o-holes" approach pictured above cause extreme extra drag since the outer surface of the valence was a low pressure area- it sucked the air back IN the holes.

JusticePete · 11-07-2015, 08:15 PM

I spoke with some Camaro TEAM engineers about this way back in 2009. Removing the OE exhaust does increase drag. I can't remember the exact amount. It wasn't much, something like 2 MPH at top speed.

White_SS/RS · 11-07-2015, 08:20 PM

The dead space behind the diffuser has the same aerodynamic principles at work that the bed of a truck has.

JusticePete · 11-07-2015, 08:21 PM

Quote:

Originally Posted by White_SS/RS

The dead space behind the diffuser has the same aerodynamic principles at work that the bed of a truck has.

Meaning?

White_SS/RS · 11-07-2015, 08:36 PM

A pocket of air is created that allows faster moving air to flow over it much like it was solid. Of course actual solid material such as the role the mufflers play is better. Think of them somewhat as a tonneau cover. Probably why they said removing them only causes minor drag issues.

Avalnch · 11-07-2015, 08:39 PM

Great comments everyone. Keep em coming.

Problem with a rear "pan" would mean hiding the exhaust. But then, if Pete is right about the 2 mph, I don't think I'll lose sleep over that.

VTSummit · 11-07-2015, 08:54 PM

Let's dispose of the term "pocket of air" as it's nonsense. There is high and low pressure, high and low velocities or stagnation. If you look at most well done diffusers in a wind tunnel, you'll see they are trying to marry the air passing under with the air passing over without creating undue turbulence. This isn't easy to do.

White_SS/RS · 11-08-2015, 12:24 AM

Quote:

Originally Posted by VTSummit

Let's dispose of the term "pocket of air" as it's nonsense. There is high and low pressure, high and low velocities or stagnation. If you look at most well done diffusers in a wind tunnel, you'll see they are trying to marry the air passing under with the air passing over without creating undue turbulence. This isn't easy to do.

I agree it's a laymen term for sure.

JOHNSONROD · 11-08-2015, 11:04 AM

Quote:

Originally Posted by VTSummit

I studied aerodynamics at Embry-Riddle... and I still won't make an assertion as to what the best setup is but I think the OP's concern is valid. I've also seen wind tunnel tests where the "bunch-o-holes" approach pictured above cause extreme extra drag since the outer surface of the valence was a low pressure area- it sucked the air back IN the holes.

which of the many wind tunnel tests you have witnessed of camaros that have holey diffusers was the worst lolololol.

JusticePete · 11-08-2015, 11:19 AM

Quote:

Originally Posted by Avalnch

Great comments everyone. Keep em coming.

Problem with a rear "pan" would mean hiding the exhaust. But then, if Pete is right about the 2 mph, I don't think I'll lose sleep over that.

Give or take a 1/2 mile an hour it is accurate. If the rear fascia really did become a full on drag item it would blow off at some speed in triple digits. I have not heard of this happening.

Quote:

Originally Posted by VTSummit

Let's dispose of the term "pocket of air" as it's nonsense. There is high and low pressure, high and low velocities or stagnation. If you look at most well done diffusers in a wind tunnel, you'll see they are trying to marry the air passing under with the air passing over without creating undue turbulence. This isn't easy to do.

I was looking for the Myth Busters version, but the photo in this GMC test make clear the concepts under discussion. This is not a complete answer, but it is a good illustration of flow.

http://www.foxnews.com/leisure/2013/...truck-mystery/

11-07-2015, 02:07 PM	#1
Avalnch Drives: Rally Yellow Camaro+Avalanche Join Date: Dec 2009 Location: Vancouver Posts: 1,110	After market exhaust effect on rear aerodynamics I've always wondered if there are any noticeable negative affects of deleting the OEM mufflers. As I recall the OEM mufflers are supposed to be part of the rear diffuser aerodynamics where by wind flowing under the car flows over the shaped mufflers and is dispersed by the diffuser. When the OEM mufflers are deleted or replaced, there is a big gaping hole where the air flow can create all sorts of currents and eddies. Has anyone consider a rear belly pan to replace the function of the OEM mufflers? __________________ Vengeance Kaotik Cam, C.A.I., ARH LT, Pypes Cat Back, ZL1 Shifter+2012LS3VERT bushing, Quantum Brake Ducts, JDP Tow Hook Scorch Yellow Trim Kit, Shark Fin, AAC DRLs+ABLs+SMDs, ZTA Rear Spoiler, R.Y. 1LE Splitter. Pfadt coilovers, camber plates, trailing arms, Pegasus Solid Subframe. Pedders ZL1 barz, radius arm & steering rack bushings. BMR adjustable toe-rods. Hotchkis Max Chassis Brace. ZL1 GMPP Driveline Upgrade. TurnOne P/S pump. CTS-V 6 pistons. 447 HP @ 6180 RPM / 418 TQ @ 5100 RPM

11-07-2015, 02:55 PM	#2
JOHNSONROD Drives: 62 Chevy & 2021 1SS/1LE manual Join Date: Aug 2010 Location: Kentucky Posts: 893	the rear of the car can catch up to 1.21 mega newton jewels of quantum friction if not diffused. this Jrod motorsports patented diffused diffuser relieves over half of the potential negative effects of the a fore mentioned scavenging residuals. im not an aerodynamics expert but none of these other internet know it alls are either. lol i figured id relieve the tension before they all come in here out talking one another. i took a hole saw to my rear diffuser to let any pressure out that might be there. a rear belly pan might help. it would probably be best if a man could make an incorporated pan/real diffuser like a race car has. the rear diffuser would be a part of the rear pan. it would angle up way sooner than the factory one. the factory rear diffuser is cosmetic at best and only catches air. Attached Images

11-07-2015, 07:05 PM	#4
rockrau Drives: 2010 2ss red LS3 Join Date: Aug 2011 Location: perkasie pa Posts: 533	My understanding is that the rear valance becomes a parachute. __________________ Pedders Pace Car Kit with ZL1 sway bar conversion & camber bolt kit.Lowered 1.5". 1LE tires & wheels. CAI air intake. Anvil CF rear spoiler.MGW shifter. 1 7/8" Kooks LT headers & HF cats.V-Max ported TB. Tuned.

11-07-2015, 07:21 PM	#5
VTSummit Consistently inconsistent Drives: 2015 2LT Summit White Join Date: May 2015 Location: United States Posts: 1,364	I studied aerodynamics at Embry-Riddle... and I still won't make an assertion as to what the best setup is but I think the OP's concern is valid. I've also seen wind tunnel tests where the "bunch-o-holes" approach pictured above cause extreme extra drag since the outer surface of the valence was a low pressure area- it sucked the air back IN the holes. __________________ Thanks to MRR, I have some SWEET wheels! Thank you! 2015 2LT Ported TB, Ported intake, JACFAB intake spacer, Borla exhaust, IPF 91 tune, Complete 1/LE suspension, Brembo brakes, Goodridge lines, Elite catch can, CAI with Thermo-wrap, 275/40-20 x 10's all around, Z/28 spoiler, GM splitter, Alpine/Polk stereo with AudiControl interface.

11-07-2015, 08:20 PM	#7
White_SS/RS Drives: 14 1LE Join Date: Mar 2013 Location: Spokane, WA Posts: 1,567	The dead space behind the diffuser has the same aerodynamic principles at work that the bed of a truck has. __________________ LMS Engineering

11-07-2015, 08:15 PM	#6
JusticePete Drives: Camaro Justice Join Date: Jun 2007 Location: Virginia Posts: 20,174	I spoke with some Camaro TEAM engineers about this way back in 2009. Removing the OE exhaust does increase drag. I can't remember the exact amount. It wasn't much, something like 2 MPH at top speed.

11-07-2015, 08:36 PM	#9
White_SS/RS Drives: 14 1LE Join Date: Mar 2013 Location: Spokane, WA Posts: 1,567	A pocket of air is created that allows faster moving air to flow over it much like it was solid. Of course actual solid material such as the role the mufflers play is better. Think of them somewhat as a tonneau cover. Probably why they said removing them only causes minor drag issues. __________________ LMS Engineering

11-07-2015, 08:39 PM	#10
Avalnch Drives: Rally Yellow Camaro+Avalanche Join Date: Dec 2009 Location: Vancouver Posts: 1,110	Great comments everyone. Keep em coming. Problem with a rear "pan" would mean hiding the exhaust. But then, if Pete is right about the 2 mph, I don't think I'll lose sleep over that.

11-07-2015, 08:54 PM	#11
VTSummit Consistently inconsistent Drives: 2015 2LT Summit White Join Date: May 2015 Location: United States Posts: 1,364	Let's dispose of the term "pocket of air" as it's nonsense. There is high and low pressure, high and low velocities or stagnation. If you look at most well done diffusers in a wind tunnel, you'll see they are trying to marry the air passing under with the air passing over without creating undue turbulence. This isn't easy to do. __________________ Thanks to MRR, I have some SWEET wheels! Thank you! 2015 2LT Ported TB, Ported intake, JACFAB intake spacer, Borla exhaust, IPF 91 tune, Complete 1/LE suspension, Brembo brakes, Goodridge lines, Elite catch can, CAI with Thermo-wrap, 275/40-20 x 10's all around, Z/28 spoiler, GM splitter, Alpine/Polk stereo with AudiControl interface.