Exhaust smell in car

[RoyBatty]

I am getting the odor of a rich exhaust mixture inside the passenger compartment of my BC coupe only when decelerating with the car in gear. If I pull it out of gear, or engage the clutch before letting off the gas, then there is no odor. The exhaust system is all new and I have double clamped both slip joints and then leak checked the same. There is no leakage from either joint.
I understand why the mixture is rich under deceleration on a 71 vintage car, just trying to stop the odor from getting into the passenger compartment.
The muffler tailpipe is not extended past the bumper. I am thinking of clamping on a temporary extension as a test.
Any other ideas?


Thanks.

[baltobernie]

FWIW, I found a huge difference in cabin exhaust fumes between a downturn and straight tailpipe. The downturn was the clear (non-eye-watering ) winner. The further rearward from the body you can exit gasses, the fewer will get sucked back into the car. Try a downturn extension and see what results you get.

BTW, the wind blocker on the Spider does a great job in reducing exhaust fumes in the cabin.

[RoyBatty]

Thank you Bernie.
I'll install a test piece to see if that cures the rest.

[TStark]

After exhausting (heh) all conventional methods, and optimizing tuning, i installed a magnaflow mini spun converter, it eliminated all remnants of odors, under all conditions. Something to consider if you reach that point.

[RoyBatty]

Where in your system did you install the cat?
As I understand it, the converter should installed not too far back from the down pipe so that it has the required temps to work properly.
Thanks for the idea, I'll keep that in mind.

[RoyBatty]

Here are the three different phases of the exhaust tailpipe length.
By the way, with the windows up, NO exhaust smell enters the passenger compartment.
Stock length, much exhaust odor in the car with the windows down.


Extended test, huge improvement in reducing the exhaust smell.


Since the first extension worked so well, I decided to go a bit longer. This could not be accomplished with the stock pieces. So I went to the local parts store and cobbles this together. Unfortunately the only tailpipe extension they had that was close to the right diameter was this twin tip affair.
Results were very good. Exhaust odor in the car is now almost non existent.

[TStark]

Where in your system did you install the cat?
As I understand it, the converter should installed not too far back from the down pipe so that it has the required temps to work properly.
Thanks for the idea, I'll keep that in mind.

Good to hear you have marked inprovement!

To answer your question, indeed, closer is best. I would have rather right off the header, that would have been optimal but ended up with it much rearward, just before the hump for the axle.

It worked immediatly, very well as is, but to improve its heat up time and continuous effectiveness at idle, I then wrapped the exhaust pipe from the header to the cat.

The spun cats have a wire screen inside, impossible to clog unlike the older style!

My worse scenario prior was top up, windows partially down.

[4uall]

amazing how much of a difference is made with different exhausts

Mine is just a slightly angled down and never smells, there may be another reason