What..cough,cough, Do You Think....

[mally002]

I know, I know, not another exhaust smell in the cabin beat the dead horse question again.......

It kind of is, but also want some opinions on my idea.

My 71 240 which I just aquired about 8 months ago does have the wonderful smell of exhaust BUT only when the windows are down....windows up equals perfect, smell free cabin.

I have done the basics on seals, leaks, etc, but the PO who put on the muffler used this twin pipe out the back that didn't quite reach the bumper. This weekend I went and bought two extensions...(see picture) and ran them a good ways past the bumper......guess what.....still has the exhaust smell.

So I was thinking, and this is where you guys come in, maybe the smell is because of the twin pipes going straight and what if I ran down to the muffler shop and had them remove this setup and put on one pipe with a down bend 1-2 inches past the bumper. Do you think it would be worth the $75-150 dollars to see if this "cures" the problem, or does this twin setup have anything to do with the issue at hand.

Thanks for any input.

Randy

[Derek]

Make sure you look really good for any holes in the rear area. I had exhaust smell and found it was coming in through some 6MM screw holes that I missed. I plugged them and the smell was gone.

Derek

[bigoak]

Check the seals around your tail lights. Another common spot for exhaust fume ingress.

[AZ-240z]

If I were you, and this is what I did, I would take out the plastic interior finisher panels at the quarter panels and tail lights. Then you can see the seals around tail lights and unfilled tail light screw holes/ the edges of the rear deck floor at quarter panels where there is historically a gap on both sides/ grommets around all hoses and stand pipes going through floor, and beneath fuel evap tank/ grommet, or lack of, for antenna drain tube. This covers almost all likely areas. Whether you extend to tail pipe, point it down, or whatever, the culprit is still a hole in your car. With the window down, there is a negative pressure created in the car which draws the fumes in through any hole.

This comment may contain errors in reasoning, maybe, but it worked for me and I can't even close a door without the window cracked.

Also, Banzai Motorworks at www.zzxdatsun.com has grommets for all of those hoses in the rear floor, and worth the money.

Hope this helps.

Dan

[Arne]

Checking seals is a fine idea, but in my experience, fumes that are present ONLY WHEN THE WINDOWS ARE DOWN is an exhaust and aerodynamics issue. Many people have cured this by extending their tailpipe to a bit beyond the bumper bar. Worked for me.

[AZ-240z]

Oh, and to answer your original questions, and this is, again, just my opinion, I do not think it would be worth the money to modify the exhaust tip, length, etc. I am no expert, but I think that air flow over the car creates a fairly large turbulent zone behind the car where these exhaust gases churn and linger just waiting to get sucked back in.

In racing, drafting closely behind another car allows the following car to get sucked along in this negative pressure turbulent zone.

Dan

[EScanlon]

Have you tried opening the Fresh Air Vents on either side of the dash?

E

[mally002]

Hey guys,

Thanks for the input. Yes, I did open both both air vents and checked all my seals. I went through about every thread using the search function to tap any untried ideas as well.

In reading the older post I focused on the smell only with the WINDOWS DOWN. Like Arne had said most were cured with the tailpipe extension, but since mine was not I was wondering if it was because of the current twin straight pipe.

I'm going to go back out there in a bit and re-check for any holes, screws, etc. I am assuming that when these cars were new this was never an issue, which is why I can't understand this problem......

Thanks again.

[Arne]

Sorry, I couldn't see the attached pictures the first time I read this, and was in a hurry so I apparently didn't read it all either.

Since extending the tips didn't help, I'm still wondering about aerodynamics. Is the green car still on stock suspension? Not lowered? And no front spoiler of any kind? It's certainly possible that the second pipe down exiting a couple inches lower than normal could have an affect. Reducing the amount of airflow under the car may help as well, by either adding a front spoiler or lowering the front ride height in comparison to the rear.

[Arne]

Just to recap, my '71 did have this problem when I bought it, but does not now. I did extend my exhaust, but not even as far as you have. But at about the same time as I did the tip extension, I also added a front Spook, and readjusted my ride height. Most stock 240Zs sit a touch lower in the rear than the front. While it is pretty much at the stock height, mine is now the other way, a small amount lower in front. I can't honestly say which of these things cured my problem, or if it was a combination of some of them. But I do know that seals and weatherstripping was NOT part of my cure, as those are unchanged (for now).

[AZ-240z]

mally002,

Probably all recommendations seen here in reply to your problem would eventually work.

I have no exhaust gases in my car, windows up, or down. To smell exhaust, it has to find a way into the car. For my money, I would seal up the car rather than try to find that sweet spot where exhaust will be swept away at all driving speeds and conditions.

Just my opinion.

Dan

[Arne]

mally002,

Probably all recommendations seen here in reply to your problem would eventually work.

I have no exhaust gases in my car, windows up, or down. To smell exhaust, it has to find a way into the car. For my money, I would seal up the car rather than try to find that sweet spot where exhaust will be swept away at all driving speeds and conditions.

Just my opinion.

Dan

The only problem with that idea, Dan, is that I'm convinced that with the windows down, the fumes were actually coming in the window opening, not leaking past seals and such. I'm not convinced that sealing a 240Z completely will always fix this, as there seems to be other issues in play.