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exhaust rerouting question #4564352
11/04/17 09:40 PM
11/04/17 09:40 PM
Joined: Jun 2005
Posts: 1,785
Saint Paul (ex-San Diego)
Tornado Red Offline OP
Tornado Red  Offline OP

Joined: Jun 2005
Posts: 1,785
Saint Paul (ex-San Diego)
I have a Mk4 Golf TDI that I use almost entirely as a courier vehicle -- so much so that I have removed the front passenger seat. The rear seats are folded flat and they and the hatch area are covered with 1/2" plywood so I can haul more cargo. A lot of my deliveries are electrical, plumbing, HVAC and other parts and supplies for contractors. Generally it works out very well, because if what needs to be transported is more than my Golf can handle, we have other drivers with pickups, vans, and box trucks. I typically drive about 5000 miles a month.

Often I need to haul bundles of 10' PVC pipe, copper or galvanized conduit, or threaded rod. With the front seat removed, I can get about 9' of these pieces inside the vehicle, with about 1' sticking out the back. I use a bungee cord to hold the hatch down, strapping it to the tow bar.

Fumes sometimes get sucked into the cabin, so I have to crank up the fan and lower the front windows. But with winter coming on, I'd prefer to keep those windows up. So my question is, where should I reroute the exhaust pipe to prevent the exhaust fumes from entering the cabin?

My options seem to be 1) to the side, exiting behind the rear wheel, or 2) extending the pipe several inches straight out the back. But which is more likely to work? and if I extend the pipe, how far?

Other than trial and error, how should I determine which option is most likely to work?


'03 Golf TDI, 728k miles: Bosio DLC764, GT1749VB, Malone Tuning, G60/VR6 clutch/flywheel, Bilstein HD, Recaros, Akebonos, Brembos, Pirellis, DG Panzer & FMJ, Delvac 1 5W40
Re: exhaust rerouting question [Re: Tornado Red] #4564356
11/04/17 09:48 PM
11/04/17 09:48 PM
Joined: Jun 2003
Posts: 34,073
ME
eljefino Offline
eljefino  Offline

Joined: Jun 2003
Posts: 34,073
ME
Your problem is the air pressure caused by the bubble shape of your car. How air closes around the rear of the car at speed is as important aerodynamically as the front... which is why the "Prius shape" is a thing.

I wonder how hard it would be to modify your hatch so just the glass opens, but the metal frame stays closed. That would be more of a buffer between the interior and the exhaust pipe.

But to answer your question, mess around with the pipe as you're doing. You'll be blasting the heat anyway, on vent. You can get random pipe pieces and clamps for $10 to extend beyond your muffler. They come with a slip fit fitting that'll go over your current exhaust tip. Maybe a good "turn down" will get the smoke into the under-car slip stream instead of the dead eddy it's in now.

The only other idea would be a long tube mounted on the side or roof of your car-- I've seen them for pole vaulters. That would cut into your MPG though.

Re: exhaust rerouting question [Re: Tornado Red] #4564379
11/04/17 10:23 PM
11/04/17 10:23 PM
Joined: May 2010
Posts: 9,854
out there
spasm3 Offline
spasm3  Offline

Joined: May 2010
Posts: 9,854
out there
eljefino, nailed it. There is a low pressure area at the hatch created by air moving over the top of the car. Mythbusters found the same thing with pickup truck tailgates. More drag with the tailgate down than up.

That low pressure area sucks in the exhaust when the hatch/window is open/down. To get exhaust out of the low pressure area, you would need a long pipe, it would look silly, and probably not legal.

Your option really is roof carry, or keep the front windows open with full blast heat/ac.

EDIT; I wonder what the effect of a rear hitch rack would be on the airflow, one of those might work with an attached solid plexi or plywood floor.




Last edited by spasm3; 11/04/17 10:32 PM.

13 elantra 75k 5w30 QSUD
03 chevy avalanche 80k synpwr 5w30
17 mazda cx-5 9500 miles m1 0w30
Re: exhaust rerouting question [Re: Tornado Red] #4564381
11/04/17 10:27 PM
11/04/17 10:27 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline

Joined: Jan 2007
Posts: 17,501
Clovis, CA
Having the exhaust routed straight up to slightly above the cabin like a semi truck would work the best.

Re: exhaust rerouting question [Re: Merkava_4] #4564387
11/04/17 10:38 PM
11/04/17 10:38 PM
Joined: May 2010
Posts: 9,854
out there
spasm3 Offline
spasm3  Offline

Joined: May 2010
Posts: 9,854
out there
Originally Posted By: Merkava_4
Having the exhaust routed straight up to slightly above the cabin like a semi truck would work the best.




LOL

Last edited by spasm3; 11/04/17 10:39 PM.

13 elantra 75k 5w30 QSUD
03 chevy avalanche 80k synpwr 5w30
17 mazda cx-5 9500 miles m1 0w30
Re: exhaust rerouting question [Re: spasm3] #4564409
11/04/17 11:36 PM
11/04/17 11:36 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline

Joined: Jan 2007
Posts: 17,501
Clovis, CA
LOL! LOL That would work.

Re: exhaust rerouting question [Re: Tornado Red] #4564436
11/05/17 01:46 AM
11/05/17 01:46 AM
Joined: Jul 2014
Posts: 583
Wisconsin
Srt20 Offline
Srt20  Offline

Joined: Jul 2014
Posts: 583
Wisconsin
Drive with your windows open. Problem solved.

Re: exhaust rerouting question [Re: Tornado Red] #4564440
11/05/17 02:14 AM
11/05/17 02:14 AM
Joined: Dec 2016
Posts: 8,006
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,006
Waco, TX
Exhaust out the side in FRONT of the rear tire... but a vertical stack like a "deuce and a half" would be best.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: exhaust rerouting question [Re: Tornado Red] #4564444
11/05/17 02:46 AM
11/05/17 02:46 AM
Joined: May 2012
Posts: 6,158
Fort Lauderdale, FL
DoubleWasp Offline
DoubleWasp  Offline

Joined: May 2012
Posts: 6,158
Fort Lauderdale, FL
You have to get the exhaust out of the boundary layer that surrounds your vehicle at speed. Doesn't matter where you route the exhaust. If it doesn't escape the boundary layer, it's going into the hatch.

Is there a reasonable way to get the exhaust to esxapw the boundary layer? No, there isn't.


07 Lincoln Navigator M1 0w-40/FU
68 Charger R/T / Supercharged 440 VR1/DBL7349
07 Ram 3500 4x4 / Cummins 6.7 /DBL7349
17 Maserati GranTurismo Cabrio
Re: exhaust rerouting question [Re: Tornado Red] #4564519
11/05/17 07:29 AM
11/05/17 07:29 AM
Joined: May 2012
Posts: 6,158
Fort Lauderdale, FL
DoubleWasp Offline
DoubleWasp  Offline

Joined: May 2012
Posts: 6,158
Fort Lauderdale, FL
Oops. Double post

Last edited by DoubleWasp; 11/05/17 07:30 AM.
Re: exhaust rerouting question [Re: Tornado Red] #4564520
11/05/17 07:30 AM
11/05/17 07:30 AM
Joined: Feb 2003
Posts: 8,077
Jupiter, Florida
Cujet Offline
Cujet  Offline

Joined: Feb 2003
Posts: 8,077
Jupiter, Florida
I think the best result would be a small pipe exiting to the side. Using the exhaust velocity to push it away from the car's aerodynamics. Piston powered aircraft use the exhaust's directional blast to prevent CO from entering the cabin. However, I don't think that's a complete solution, as at light throttle, exhaust velocity will be lower. In much the same way that piston powered aircraft on descent (with throttle pulled back) often get fumes in the cabin.


People who count on their fingers should maintain a discreet silence.
Re: exhaust rerouting question [Re: Tornado Red] #4564630
11/05/17 09:41 AM
11/05/17 09:41 AM
Joined: Oct 2005
Posts: 7,094
Colorado
Kuato Offline
Kuato  Offline

Joined: Oct 2005
Posts: 7,094
Colorado
I'd go out the side, or the long exhaust above the vehicle.

How about some sort of custom foam fitted to fill the gap?


Thick vs Thin test: 15k / 43k miles complete
Re: exhaust rerouting question [Re: Linctex] #4564928
11/05/17 02:47 PM
11/05/17 02:47 PM
Joined: Jun 2005
Posts: 1,785
Saint Paul (ex-San Diego)
Tornado Red Offline OP
Tornado Red  Offline OP

Joined: Jun 2005
Posts: 1,785
Saint Paul (ex-San Diego)
Originally Posted By: Linctex
Exhaust out the side in FRONT of the rear tire... but a vertical stack like a "deuce and a half" would be best.


So you think in front of the rear tire would be better than behind? I could do that, but I'm interested in hearing your reasons.


'03 Golf TDI, 728k miles: Bosio DLC764, GT1749VB, Malone Tuning, G60/VR6 clutch/flywheel, Bilstein HD, Recaros, Akebonos, Brembos, Pirellis, DG Panzer & FMJ, Delvac 1 5W40
Re: exhaust rerouting question [Re: Tornado Red] #4566005
11/06/17 04:23 PM
11/06/17 04:23 PM
Joined: Oct 2012
Posts: 4,825
Taiwan
Ducked Offline
Ducked  Offline

Joined: Oct 2012
Posts: 4,825
Taiwan
You might try a scoop that entrains higher pressure air around the exhaust, say a halved traffic cone, or metal equivalent if the exhaust is too hot to be plastic friendly.

Or do a lateral-thinking body swerve around the problem and rig yourself (not your engine) a schnorkel (and a nose clip) so you'll be able to breathe with the car full of fumes (or water).

No need to provide for passengers since there are no available seats.

Re: exhaust rerouting question [Re: Tornado Red] #4568837
11/09/17 12:57 PM
11/09/17 12:57 PM
Joined: Dec 2016
Posts: 8,006
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,006
Waco, TX
Originally Posted By: Tornado Red
Originally Posted By: Linctex
Exhaust out the side in FRONT of the rear tire... but a vertical stack like a "deuce and a half" would be best.


So you think in front of the rear tire would be better than behind? I could do that, but I'm interested in hearing your reasons.


Turbulent airflow, and the "bow wave" in front of each tire. It's also the easiest way. Make the exit 12"/30 cm in front of the rear tire and make it a good 2-3 inches out past the outside sidewall.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
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