Tailpipe exhaust back into passenger compartment

[Healey_Z]

When I first picked up this project, one of the first things I had to do was replace the exhaust. I tried to replicate the look of the angled Healey exhaust from this picture.

Here is my local exhaust man, happy to do something besides 1992 Honda Accords.

Here is the car as it sits today:

The problem I am having is that the exhaust seems to just naturally travel back into the passenger compartment. Not an issue on the freeway or when I have the top up, but around town it is definitely noticeable. Did I do the exhaust wrong and if so, what should I change?

 

[Patrick67BJ8]

When I first picked up this project, one of the first things I had to do was replace the exhaust. I tried to replicate the look of the angled Healey exhaust from this picture.

Here is my local exhaust man, happy to do something besides 1992 Honda Accords.

Here is the car as it sits today:

The problem I am having is that the exhaust seems to just naturally travel back into the passenger compartment. Not an issue on the freeway or when I have the top up, but around town it is definitely noticeable. Did I do the exhaust wrong and if so, what should I change?

I once saw some chrome tips that took the exhaust at it's present angle per your photo, and then straight back, not too much, but enough to do the job. I'll look for the photo and post if I can find it.

 

[Bob_Spidell]

My BJ8's exhaust--part Ansa, part home-rolled--is very close to your 'design' (except on the other side, of course). I don't have any problem with exhaust fumes in the cockpit, and your exhaust looks plenty long to me (and you've got the 'correct' bevel at the end). What exactly are you smelling? You could have a leak in the engine compartment--though you'd certainly get that with the top up--or underneath.

A well-tuned Healey's exhaust won't smell bad--the main ingredients being CO and CO2, which are odorless--if you're smelling something (hydrocarbons?) I'd check the mixture, etc. Are you burning oil?

 

[Johnny]

I have the same problem with my BJ7. You might check the rubber seal on top (or side on early cars) to access the transmission dip stick is on correctly, it should be a tight fit to seal out fumes.

Without the over riders on it's hard for me to judge how far back your pipes extend.

Most likely you have an exhaust leak around the muffler, or the manifold pipes aren't sealed properly.

 

[RAC68]

I would not be surprised if the vortex created at the back of the car is picking up the exhaust and pulling it back into the car. If this is the case, I would install a small deflector somewhere under the car and toward the rear shroud edge. This deflector would disturb the air flow sufficiently to move the vortex, hopefully, further back and out of the area of the exhaust tips. Shortening the pipe could also do the trick.

Hope this helps,
Ray (64BJ8P1)

 

[Healey_Z]

I do not get exhaust fumes with the top up, so I do not think there is an exhaust leak. I'm not having any excess unburnt gas or oil.

RAC68, I think you may have hit it on the head. I think the natural flow of the air is to come back into the passenger compartment and my exhaust is exiting in that path. I can certainly clamp some pipe on there and see if re-directing it helps at all.

Here is a side shot with a better view on how far it extends.

And one of my favorite pictures, my Mom and Dad taking it out for a spin.

 

[Cottontop]

THIS is from a posting that I made last April (2011). It still applies.

"I'm not an aeronautical engineer, but I have a Classic Mustang buddy who works for Boeing in Bellingham, Washington who is and in discussing the airflow over, around, and under a Healey with him, he pointed out several things.

The rear of nearly all cars have a very thin layer of air, called the boundry layer, that flows UP and forward under the main rush of air flowing down and rearward over the trunk lid. In the Healey, this may be exagerrated because of the rounded back end and long sloping trunk.

At speed, because of the air flowing up over the bonnet, then up over and around the ends of the windshield, the entire cockpit is a low pressure area.

Depending on the vehicle speed, wind direction and speed, it is possible that low pressure of the cockpit area is pulling the boundry layer all the way up the trunk lid and into the cockpit.

One reason that many modern cars have have a small "lip" spoiler on the trunk lid is to help merge the air flow over the car into the merged airflow at the rear of the car and prevent the boundry layer from advancing farther forward.

If your exhaust pipe is angled upward and/or too short, you might be introducing exhaust fumes into the boundry layer which then get sucked up to the cockpit.

Many performance cars (Porsche, Crossfire) have a small, servo driven spoiler, that raises at speed to disrupt and stop the boundry layer.

I'd lower the angle and/or lengthen pipe so that the tip protrudes more into the airflow from over and under the car and farther from the area that feeds the boundry layer."

You might try to attach some temporary extensions (paper towel tubes) and drive around the block to see what happens to the smell.

Please let us know what you do and what happens.

Tim

 

[Cottontop]

As I said above, I am NOT an areo-engineer. I wish I was.

Since your exhaust pipes "look" OK, another thing that I would try is to get a 3-4 foot piece of wooden dowel (or a yardstick) and tape 6-8 inches of knitting yarn to one end.

Have your someone (your dad?) take you for a drive and while you are sitting in the passenger seat like a monkey, stick the yarn into the airflow coming over the top and around the ends of the windshield.

Pay particular attention to where the air stream/flow LANDS after it comes over the windshield.

I have a question that the seemingly high stance of your convertible top may have something to do with the airflow and the boundry layer on/around the back end.

Another thing to try is to "Yarn" or "Tuft" the car. That is to scotch tape a couple dozen 3 inch lengths of yarn in a grid pattern all over the back end and trunk lid. Then have someone (your dad?) drive the Healey and you follow him in another car, preferably on a wide or 3-lane road and observe the Healey's rear air flow at varying speeds and wind directions. Communicate by cell phone.

If possible, photo or video the airflow for later review.

I have done both the above. It's amazing what you can learn about a Healey's airflow.
That is how we sorted out the proper airflow for Richard Wright's "Radiator-in-the-Trunk".

Good luck and let us know how it goes.

Tim

 

[Brinkerhoff]

Your exhaust should turn up at the rear bumper and then make a noticable bend toward the left side of the car, not to the right like yours. If you had an overrider fitted ( right where the bolt is at) the exhaust should be on the left side of that. You are probably exiting fumes into a "Healey dead zone" of sorts. Just my thoughts fwiw.

 

[elrey]

Or leave the choke out and read the spots on the boot lid.

 

[Bob_Spidell]

Your exhaust should turn up at the rear bumper and then make a noticable bend toward the left side of the car, not to the right like yours. If you had an overrider fitted ( right where the bolt is at) the exhaust should be on the left side of that. You are probably exiting fumes into a "Healey dead zone" of sorts. Just my thoughts fwiw.

Good point. On my BJ8, the pipes are canted towards the outside by maybe 10-15 degrees. I think if the overriders had been installed when this muffler was fab'd the shop would have canted them out to avoid the overriders.

 

[Keoke]

Well if the joint between the exhaust pipe and the tip is not tight it may be possible for this to occur. However, based on my experience this is not a characteristic of the BJ8 Car.-Fwiw--Keoke

Elrey the boundary layer will not allow spots to develop on the boot lid.--- :laugh:

 

[Healey_Z]

Your exhaust should turn up at the rear bumper and then make a noticable bend toward the left side of the car, not to the right like yours. If you had an overrider fitted ( right where the bolt is at) the exhaust should be on the left side of that. You are probably exiting fumes into a "Healey dead zone" of sorts. Just my thoughts fwiw.

Good point. On my BJ8, the pipes are canted towards the outside by maybe 10-15 degrees. I think if the overriders had been installed when this muffler was fab'd the shop would have canted them out to avoid the overriders.

Does the exhaust on the original BJ7 come out on the left side and slanted outward? I can't blame this on the muffler guy. If you notice in the picture above, the overriders were on the bumper when the exhaust was welded. He followed my direction perfectly and he put them spot on to where I told him to put them and it took him a while to get it to my liking. The good thing is that this is something I could fix in the garage.

 

[Legal Bill]

Your exhaust should turn up at the rear bumper and then make a noticable bend toward the left side of the car, not to the right like yours. If you had an overrider fitted ( right where the bolt is at) the exhaust should be on the left side of that. You are probably exiting fumes into a "Healey dead zone" of sorts. Just my thoughts fwiw.

I agree, plus the tips are sticking out and up to far. On my BJ8 they are shorter and lower. I believe the bumper does the job of the spoiler as described above. Your tips extend into the line that the air would follow up into your cockpit. Just my .02

 

[Healey_Z]

Thank you for the responses. Here is one more picture after I installed the exhaust, but before I took the car apart to paint it.

It confirms the slant in and it does extend an inch or so past the bumper. I will put this on the winter list; rotate out and shorten to below the bumper's edge.

 

[Johnny]

I wouldn't shorten them. Then they'll blacken the bumpers and over riders.

 

[red57]

I have a side exhaust now but many years ago I had a stock exhaust and wanted to run without bumpers. When I took the rear bumper off the pea shooters were a definate hazard walking around the back of the car so I shortened them about 6-8". Looked fine and was a lot easier to avoid bashing your shins but the exhaust in the cockpit with the top down was beyond tolerable & I added extentions a few days later to bring them back out to where they were originally & only rarely would smell exhaust. This problem does not exist with side exhaust.

I think Cottontop and Brinkerhoff nailed it. If you move the ends outward you will get out of the heavy turbulence in the center of the rear of the car. The air is coming together at the rear and is coming inward from the sides as well as down over the top & up from the bottom so the further outward they are the better.

I would not shorten them at all - in fact you will find if you extend them a bit it will get even better... eg, if you left them where they are and added a foot to them you probably would solve the problem by getting the tips out into clean air.

I am not any kind of aero-expert either

Dave

 

[RAC68]

Dave,

If he adds a foot to the length of the pipes as you suggest, wouldn’t the warning flag required to be hang off the end disturb air flow in a positive way?

Ray (64BJ8P1)

 

[red57]

Ray,

Just re-read my post.... No, I was NOT advocating making them a foot longer , only trying to clarify what I was saying (and typically not doing a very good job).

However the warning flag may not be such a bad idea since most folks out there have a hard time seeing us anyway...

Dave

 

[Cottontop]

Maybe the correct way to attack the problem is NOT to lengthen or re-position the pipes, but to disrupt the boundry layer that is sucking the exhaust up onto the cockpit.

Maybe adding a Porsche-esque Whale Tail is the answer...

YEA..... That's the ticket!

Tim :thumbsup: