Exhaust entering cabin after engine braking

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bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Exhaust entering cabin after engine braking

Post by bobhattler » Sun Dec 30, 2012 5:51 am

My passengers are being smoked by fumes as I decelerate. I am thinking of having the last several feet of my exhaust pipe bent to direct the fumes to the side behind the rear wheel similar to some pickups. The convertible is more suseptible to this problem than the closed car that I had at an earlier time. The judges will deduct for this modification, maybe I need a swiveling pipe. Any thoughts would be appretiated.
Bob Hattler
1940 sedan convertible

jacko
Posts: 146
Joined: Sun Jul 19, 2009 12:55 pm

Re: Exhaust entering cabin after engine braking

Post by jacko » Sun Dec 30, 2012 1:05 pm

Bob, As you probably know, the rear of the car as it moves down the road is subjected to a substantial negative static pressure thus causing fumes from the tailpipe to "crawl" up the back of the car. That is why it is important to have a good seal on the trunk lid so the fumes don't get sucked into the trunk and ultimately end up in the passenger compartment. As the car moves forward, these fumes are entrained in vortices that "shed" off the rear of the car. This is all fundamental fluid mechanics at the rear of the car. First, check the entire length of your exhaust pipe for any pin holes or obvious leaks and fix them. Second, make sure the end of your tail pipe is at least even with the rear of the back bumper. If not, consider adding length to it so it sticks out from the plane of the bumper. Third, consider adding a downward deflecting nozzle on the end of the tailpipe. These are available from many sources and are usually chromed and rather fancy.

Here is a somewhat related story: As a Cessna 210 pilot, I would carry a small battery operated carbon monoxide alarm in the cockpit with me since the heater in the plane is a muffler around the exhaust pipe. Any leaks in the exhaust pipe over the length of a flight can enter the cockpit and could render the pilot and passengers unconscious. I never got an alarm when in level flight and with all the landing gear doors closed. However, in the winter with the heater on and doing an approach to an airfield, as soon as I lowered the landing gear which also opens the gear doors, the carbon monoxide alarm would go off. Thus I knew exhaust fumes were entering the cockpit. The fix was to redo the seals in the gear door compartments. This is sealant material similar to what we use on our cars between sheets of body steel. So take a good look at the seal material integrity under the car body. Let me know how these suggestions work out.

Bob Jacko

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Exhaust entering cabin after engine braking

Post by bobhattler » Sun Dec 30, 2012 2:13 pm

Thank you, I tried the exhaust extention with a down\ward curve, switched to side ward curve. It's bit better but not good enough. I'll take another look a my trunk seal, it's relatively new but may not be sealing properly. To be continued.
Bob Hattler

John Harley
Posts: 219
Joined: Mon Jul 06, 2009 3:44 pm
Location: Dumont, NJ

Re: Exhaust entering cabin after engine braking

Post by John Harley » Mon Dec 31, 2012 2:31 pm

Bob

I work with a compay that sells musical instruments to schools. The repairmen use feeler gauges of mylar tape or cigarette paper glued to a small stick to test the seating of pads on woodwind instruments. Perhaps if you close the trunk on a piece of copy paper or some such you can find the areas that don't grip the paper

Happy New Year

John Harley

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Exhaust entering cabin after engine braking

Post by bobhattler » Sat Jan 12, 2013 10:11 am

I purchased a 5/8" stick-on roll of weatherstrip from Lowe's and stuck it on the truck lid to meet up with the factory strip on the body. It seems to help. I added it to the door bottoms on the body and it is now fairly air tight. Air can still enter through the back window seams on the convertible top. Thatis all I'm going to do for now.
Thanks again for your help.
Bob Hattler

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Exhaust entering cabin after engine braking

Post by bobhattler » Thu Jan 17, 2013 12:29 pm

I just added the exhaust downward extention as far out as possible. The fumes are lessened to a tolerable level.
Thanks for your help,
Bob

jacko
Posts: 146
Joined: Sun Jul 19, 2009 12:55 pm

Re: Exhaust entering cabin after engine braking

Post by jacko » Fri Jan 18, 2013 1:31 am

Bob, Sounds like your on the road to minimizing the sucking of exhaust fumes into the car.

Take Care, Bob Jacko

JWL115C
Posts: 196
Joined: Sat Jul 11, 2009 9:02 am

Re: Exhaust entering cabin after engine braking

Post by JWL115C » Sat Jan 19, 2013 5:11 pm

I had the same problem with a 1973 Datsun 240Z. Replacing the hatch gasket fixed it.

(o{}o)

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