Exhaust fumes in cabin solved!!!

[EScanlon]

...Below you can see where my muffler ends.I have ZERO fumes in the cabin issues.Translation:Length of your tail pipe is NOT the problem.

I suppose if you choose to ignore the effect of that ice scraper you're using for a spoiler AND the increased diameter of your tailpipe in your hypothesis regarding length of tailpipe NOT having an effect on fumes in the cabin then the theory might be .... naah... the translation is off.

That spoiler changes the air flow behind the car considerably. I believe that that is the PRIMARY reason for putting them on, to change the air flow. I'll bet that the spoiler is more likely the reason you're not getting fumes than the length of your tail-pipe.

The discussions regarding exhaust fumes in the cabin, the causes and solutions have been going on for years. Spoilers AND / OR length of tail-pipe have been tried all with moderate success. So have louvers, both side and rear window, as well as front/rear/side skirts, all to some measure of success... or at least that's what's been reported.

Of all the ones that have been written about, and you can do a search here, the downward pointing tail-pipe that's been extended just a couple of inches (just to knee scraping protrusion) is the one that's (purportedly) worked for more people.

2¢

E

[Z train]

I suppose1) if you choose to ignore the effect of that ice scraper you're using for a spoiler AND the increased diameter of your tailpipe in your hypothesis regarding length of tailpipe NOT having an effect on fumes in the cabin then the theory might be .... naah... the translation is off.

2)That spoiler changes the air flow behind the car considerably. 3)I believe that that is the PRIMARY reason for putting them on, to change the air flow. 4)I'll bet that the spoiler is more likely the reason you're not getting fumes than the length of your tail-pipe.

5)Of all the ones that have been written about, and you can do a search here, the downward pointing tail-pipe that's been extended just a couple of inches (just to knee scraping protrusion) is the one that's (purportedly) worked for more people.

E

1)I'm not ignoring anything.Diameter has zero effect.My muffler/pipe(however you want to call it)ends in just about the same(or shorter) location as the stock one.

2)Yes it does.In fact it creates MORE negative pressure behind the car.which shoots YOUR theory in the arse.

3)The primary reason for spoilers is downforce over the rear tires.

4)This defies logic.

5)This is nothing more than a band-aid solution.The cause is still there.Now if some don't have the skills or inclination to re-seal everything,it is understandable for them to go the "extended pipe route".

This is my 4th Z dating back to 1977.I have NEVER had any fume issue that wasn't attributed to a leaking cabin.

Edited October 3, 2010 by Z train

[EScanlon]

1)I'm not ignoring anything.Diameter has zero effect.My muffler/pipe(however you want to call it)ends in just about the same(or shorter) location as the stock one.

2)Yes it does.In fact it creates MORE negative pressure behind the car.which shoots YOUR theory in the arse.

3)The primary reason for spoilers is downforce over the rear tires.

4)This defies logic.

5)This is nothing more than a band-aid solution.The cause is still there.Now if some don't have the skills or inclination to re-seal everything,it is understandable for them to go the "extended pipe route".

This is my 4th Z dating back to 1977.I have NEVER had any fume issue that wasn't attributed to a leaking cabin.

Ahh... you're an enlightened scientist... that is, if it doesn't match your idea of what it's supposed to mean then it's inconsequential. That is, ignore the facts if it contradicts your hypothesis.

1) Different diameter exhaust tubing is used to allow for less back pressure. Less back pressure means that the exhaust isn't being pushed out with as much force towards the air turbulence behind the car.

2) My theory as you put it, is that your translation is off ... which it is. YOUR theory is that the length of the pipe in your non-stock diameter exhaust pipe in a STOCK location has no effect and therefore that's why you don't smell fumes. But your theory is based on your ignoring the effect of the spoiler, which by your admission creates more negative pressure behind the car. More negative pressure and less exhaust pressure and you have the reason you're NOT smelling fumes. They're being blown away by the shear forces behind the car.

3) Yes, you're right... by disrupting the air flow over the car.

4) Not if you are capable of logical thought.

5) I'll agree with you there. That is the main reason that so many people do have a problem with this. But, the extended pipe still proves to alleviate the problem for many.

The design of the car is such that there is a vortex of turbulence behind the car. That turbulence traps the exhaust behind the car so that at certain speeds the vortex actually engulfs the rear section of the car. Any opening into the cabin (which is at a lower air pressure than the vortex) is literally sucking that exhaust rich air into the car. The extended and downward pipe puts the exhaust on the lower and outer portion of the vortex, allowing it to dissipate more than if it's positioned near the middle of the vortex.

Congratulations on being a long time Z owner. Have you been Arizona the whole time? Maybe the reason you've not noticed the fumes is that you're mostly running with the A/C on, and the windows closed. Which would explain why you only notice the fumes when the car has a leaky cabin.

If the cause could be effectively pinpointed and the solution(s) documented then maybe this wouldn't be such a divisive subject. As it is, it's mostly conjecture based on individual, non-reproducible results.

I've never smelt the fumes in my Z, with a straight stock length tailpipe, without a spoiler, air dam or skirts, window(s) open but with both hatch and side window louvers... could they be the proper fix?

You can choose to argue it, but the theory is far from being properly phrased, let alone solved.

I will agree that properly sealing the cabin is of the utmost importance, and probably the single most important preventative measure to avoiding the fume problem. But some supposedly still encounter problems, so go figure.

Let's not get this thread closed. We can agree to disagree, but insults or expletives are not required.

E

[Z train]

Bottom line:If a Z(1st gen) is in perfect order(perfect order meaning in as "left the factory condition",then how does adding a spoiler introduce exhaust fumes to the cabin?

By the way,i have used no expletives or insults.

[olzed]

Does anyone know if all the rear hatches on an early and later 240 are the same. My 72 has an earlier hatch which fits the body perfectly, but where the hinges are there is a gap caused by a dip in the body to accomodate the hinges. This results is a gap between the hatch and the rubber about quater inch wide at this point.

[steve91tt]

Does anyone know if all the rear hatches on an early and later 240 are the same. My 72 has an earlier hatch which fits the body perfectly, but where the hinges are there is a gap caused by a dip in the body to accomodate the hinges. This results is a gap between the hatch and the rubber about quater inch wide at this point.

I think I have the same hinge dip that you describe with my 1973 with the original hatch. I spent a few hours getting the rubber to fit tightly in that location.

For me cabin fumes were 95% related to the hatch panel. I put plastic behind it and It didn't look like it was leaking but it was.

I found my leaks with temporary bits of tape and plastic. I simply taped up areas of the car until the fumes went away. Great way of narrowing this down.

[doradox]

A spoiler could both cause or stop a leak from allowing fumes into the cabin. (notice that I am not talking about a well sealed Z)

A spoiler spoils lift. It does so by changing the air pressure distribution on the outside of the car. There is also to some extent a conservation of momentum effect when you change the direction of airflow but I'll not go into that. So generally speaking adding a spoiler means increasing pressure on the top of the car and decreasing it on the bottom. So depending on where the leak is it could begin letting in fumes if it were in an area that experienced a pressure increase or stop leaking in an area that experienced a pressure decrease.

Since there are so many places that can leak there is no one magic bullet that "solves" the fume problem. That's why you see so many different solutions and why one persons solution may not work for another. Unless, of course, that solution is to seal the car properly.

Steve

Edited October 3, 2010 by doradox
spelling

[Bcalvosa]

Attached is a write up with some pics of how to do the smoke testing, and a method of using a hose to pinpoint the exact source of the leak. It also shows and notes areas where I found leaks...

http://www.classiczcars.com/forums/showthread.php?t=34205

Good Luck,

Bob

[Inf]

Some fun tests could be done by someone with the time and interest...

You could mount something emitting a colored smoke in your exhaust pipe and drive along a track or something at various speeds while video taping the flow patterns. Could be interesting.

We have a small scale wind tunnel in my building on campus. I wish I had been interested in this topic back then, I could have bought a 240Z model and done some testing for my undergraduate fluid mechanics lab. Would have been a fun project.

Of course, testing this in a wind tunnel may not be accurate in two ways that immediately come to mind:

1) The air would be moving relative to any static "ground" you installed in the test section (unlike in real life, where it could just be sitting above the road on a windless day). This could be important because air flow under the car would be very different.

2) You couldn't effectively explore what happens when you slow down for a stop sign or stop light. The smoke-filled air lingering behind your car would have some forward momentum in the real world, which may carry it forward around your car as you slow down. This would not occur in a wind tunnel when you ramp the speed down.

Anyway, I'm getting off track. The real world testing would be superior (and a lot more fun!).

Caveat emptor: fluid mechanics is not my technical area

[racer88]

I am not sure if this is the right thread for this, but why do our cars smell that bad in the first place. Anybody got any ideas. My engine is a fresh rebuid, the carbs are perfect, the plugs look great and it still has a certain amount of smell???????

Bob

[Z train]

Some fun tests could be done by someone with the time and interest...

You could mount something emitting a colored smoke in your exhaust pipe and drive along a track or something at various speeds while video taping the flow patterns. Could be interesting.

We have a small scale wind tunnel in my building on campus. I wish I had been interested in this topic back then, I could have bought a 240Z model and done some testing for my undergraduate fluid mechanics lab. Would have been a fun project.

Of course, testing this in a wind tunnel may not be accurate in two ways that immediately come to mind:

1) The air would be moving relative to any static "ground" you installed in the test section (unlike in real life, where it could just be sitting above the road on a windless day). This could be important because air flow under the car would be very different.

2) You couldn't effectively explore what happens when you slow down for a stop sign or stop light. The smoke-filled air lingering behind your car would have some forward momentum in the real world, which may carry it forward around your car as you slow down. This would not occur in a wind tunnel when you ramp the speed down.

Anyway, I'm getting off track. The real world testing would be superior (and a lot more fun!).

Caveat emptor: fluid mechanics is not my technical area

That would be really neat to see done.

I am not sure if this is the right thread for this, but why do our cars smell that bad in the first place. Anybody got any ideas. My engine is a fresh rebuid, the carbs are perfect, the plugs look great and it still has a certain amount of smell???????

Bob

You have a leak in the cabin somewhere.At the age of these cars,seam sealant has dried and cracked and other gasket types have become porous.

[Davey G]

You have a leak in the cabin somewhere.At the age of these cars,seam sealant has dried and cracked and other gasket types have become porous.

My leak between the exhaust manifold and downpipe doesn't help either, but that's being fixed as I type. Hopefully that will make some difference.