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You have to seal EVERYTHING in the back and repair any rust or poor body work (such as unlevel panels or rust around rear window} also check the top hatch seal carefully and make sure the rubber is not twisted and that all molding is good and glued in place properly If there is any leak the exhaust will find it
 

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The turn down tip is the only way to go but that's not all of it. The very end of the turn down tip HAS to be BEFORE the end of the bumper by at least an inch. Read the writeup on my website at www.zspecialties.com Hit the tips and info tab then hit the Exhaust tab. That will explain it more. Extending the length of the pipe doesn't do anything except push it right into the vortex at the back of the car even better than when they were new. All first gen z's have this problem, it's there by design. If the exhaust is being pushed into the vortex then it also eats up the chrome on the bumper and tail lights as well. Making sure that your gaskets and grommets in the back of the car is also important. Making sure that the rear hatch interior panel is sealed is also critical. Z Man of Washington
 

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Going to a turn down tip is the correct way to do it but it has to be done properly. The end of the tip has to be at least half an inch BEFORE the end of the bumper. If there is no bumper then it has to be before the end of the body by half an inch. Sealing up all the gaps in the body is very important as well. There are hose grommets in the back, there is also one right next to the muffler for the antenna. Look at the floor of the car from the underside and see if you can see any gaps. Having properly installed body gaskets in the back is important as is the hatch interior panel. The grommets on the fire wall have to be sealed and so does the rubber shift boot. Stopping all exhaust leaks is important and making sure that the engine runs as clean as possible is also important. Most of this is covered in a writeup on my website at www.zspecialties.com Click on the tips and info tab then click on the exhaust tab for enlightenment. This is critical stuff, CO is known as the silent killer for a good reason. If there is a way for exhaust to get into the cockpit, it will get in. Every one of these categories I've mentioned are all very important. Overlook any one of them and you could be getting poisoned. For those that have the 70-71 hatch on your car then there are internal flappers inside the hatch that may need to be replaced. If you think that you've been getting poisoned by CO from your car go to a clinic and have them do a blood test and check for CO in your blood. There is a vortex at the back of the car and the exhaust goes right into it. Putting on a longer pipe just puts more exhaust into the vortex. Look at the back of any z that has older chrome on the bumpers and the tail light trim and you'll see the left side of the car is always worse than the right because there is more concentration of CO on the left side of the vortex. That's proof enough right there about this topic. Don't have the exhaust exiting your z properly and you're screwing your car up. It's not just your health but your z's health as well. Personally my health is more important to me than my z's health but not by all that much. Z man of Washington
 

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Discussion Starter #24
Thanks so much for all the info zman I'll check out your site's writeup shortly
 

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With all due respect for knowledgeable experience, I must beg to differ, at least in the specific case of the mega-bumpered 280Z.

The stock tailpipe configuration fit Mr.z.m.o.w.'s specifications exactly, and always made a mess of the tail. Without the benefit of a credible wind tunnel, I theorized that the area below the ledge of the bumper and its apron was a low pressure zone, trapping the exhaust and subjugating it to the whims of the turbulance that follows the car.

My solution was to extend the tail pipe with an angle-cut end, a couple inches past the rear bumper face to inject into the turbulence of the corner of the tail, to better diffuse the outflow.

Well, that was the idea anyway. Curiously enough, the tactic seems to work pretty well. But then, I make no claim to fame about aero; it's just one fellow's anecdotal evidence.

Of course, were it not for the gas tank placement, I would have gone with my personal Plan A, and run the pipe out the side to exit behind a rear wheel.
 

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ensys, first of all there was NEVER a 70-78 z that came out of the factory with a turn down tip therefore your statement of them fitting my specs exactly is without merit. They all had a straight tip and some of the early ones even had a chrome shroud that was suspended around the actual tip which was useless other than for looks.
I didn't just stumble across this theory, I spent hundreds and hundreds of hours studying these cars and trying just about everything you could think of. I ran tests on these cars while driving them and driving behind them. Making the engine deliberately smoke by hooking up a poor mans oil injection so I could see the air travel at the end of the car in relation to the exhaust. There is without a doubt a vortex at the end of these cars, every single one of them. It's very pronounced, and it's much more than just turbulence. Now making the 90 degree bend at the end of the exhaust like some people have mentioned will also cure the phenomenon with the exhaust but who wants to drive a z around looking like a dog in heat. Know what it means when a female dog is in heat and her tail bends totally to one side and she holds it there.
An angle cut tip is mostly for aesthetics, yes the exhaust will very slightly start to expand on the short end of the angle tip but not enough to make any difference. In my early days I tried that tip and many others when I started building exhaust systems on these cars. I've been doing my technique for the turn down tips and their specific position for over 35 years and have only done it on way north of 100 z's and that's a conservative estimate. The first car that I did it on was on my own mega bumpered 1978 black pearl Z that I bought brand new. After a few years of driving it, I noticed all the chrome deterioration in the back on my car and saw it on almost every single other z that I looked at. That compounded with the exhaust smell in the Z's that I found that to be more noticeable in the 240's because they don't run as clean as the injected cars and the body seals had more chance to wear because they were older. That is why I started looking into it deeper and experimenting on different things. I found that the only difference in the back end between a 70-73 and a 75-78 mega bumpered car is that the vortex sits back a little farther on the 75-78's because the bumper sticks back farther. If you made even an ounce of sense with your claims on your one single car I'd give some credit to you, but your claim isn't worth 2 cents. ZMOW
 

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Discussion Starter #27
ensys, first of all there was NEVER a 70-78 z that came out of the factory with a turn down tip therefore your statement of them fitting my specs exactly is without merit. They all had a straight tip and some of the early ones even had a chrome shroud that was suspended around the actual tip which was useless other than for looks.
I didn't just stumble across this theory, I spent hundreds and hundreds of hours studying these cars and trying just about everything you could think of. I ran tests on these cars while driving them and driving behind them. Making the engine deliberately smoke by hooking up a poor mans oil injection so I could see the air travel at the end of the car in relation to the exhaust. There is without a doubt a vortex at the end of these cars, every single one of them. It's very pronounced, and it's much more than just turbulence. Now making the 90 degree bend at the end of the exhaust like some people have mentioned will also cure the phenomenon with the exhaust but who wants to drive a z around looking like a dog in heat. Know what it means when a female dog is in heat and her tail bends totally to one side and she holds it there.
An angle cut tip is mostly for aesthetics, yes the exhaust will very slightly start to expand on the short end of the angle tip but not enough to make any difference. In my early days I tried that tip and many others when I started building exhaust systems on these cars. I've been doing my technique for the turn down tips and their specific position for over 35 years and have only done it on way north of 100 z's and that's a conservative estimate. The first car that I did it on was on my own mega bumpered 1978 black pearl Z that I bought brand new. After a few years of driving it, I noticed all the chrome deterioration in the back on my car and saw it on almost every single other z that I looked at. That compounded with the exhaust smell in the Z's that I found that to be more noticeable in the 240's because they don't run as clean as the injected cars and the body seals had more chance to wear because they were older. That is why I started looking into it deeper and experimenting on different things. I found that the only difference in the back end between a 70-73 and a 75-78 mega bumpered car is that the vortex sits back a little farther on the 75-78's because the bumper sticks back farther. If you made even an ounce of sense with your claims on your one single car I'd give some credit to you, but your claim isn't worth 2 cents. ZMOW
Zman, thanks for all the info. Do you have/could you take a picture of one of your cars with the turndown tip so I can also see how far it should (or shouldn't) stick out from the bumper?

Also - did these cars pull exhaust into the cabin off the showroom floor? I mean the series 1 240s had vents right there on the hatch...
 

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chasincats, when these cars were new they didn't usually have the exhaust problem but a small number of them still had it in extreme circumstances. Going down a long hill slowing down on compression was probably the most noticeable, especially if the car was running dirty. It usually took a few years before it got really noticeable. Keep in mind that just because you don't smell the exhaust in your Z that doesn't necessarily mean that there isn't CO inside it. I've heard many people say that it only happens when I roll the window down. There are vents on the side and/or back of the car that allow air to come in just like when you roll down the window, just not as much air. If the exhaust leaks into your car with the window down you can bet that a small amount is still coming in with the window up. Just not enough for you to smell. What you're actually smelling is by products from the exhaust because CO doesn't have a smell to it. There are lots of factors to consider on this matter, it's not JUST the exhaust tip and it's position. When I redo my website next year I'm going to add a little bit more to the writeup and add some pics like these 2 that I added for you. I'm also going to be adding some pics that I have of a white 240 that was running very dirty which isn't uncommon. The left side of the hatch on the underside is black as coal and you can even see the fingerprint from the hatch gasket. There is a very slight leak on one spot where the seal had a wrinkle and you can see a black line about 2mm wide where the exhaust was getting in. As you pan towards the right side of the hatch, it gradually fades to light tan and then to white. A pic is worth a 1000 words. When installing the TD tips I usually end up cutting them in half or even a little shorter than that to get the desired length. ZMOW
 

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Discussion Starter #29
chasincats, when these cars were new they didn't usually have the exhaust problem but a small number of them still had it in extreme circumstances. Going down a long hill slowing down on compression was probably the most noticeable, especially if the car was running dirty. It usually took a few years before it got really noticeable. Keep in mind that just because you don't smell the exhaust in your Z that doesn't necessarily mean that there isn't CO inside it. I've heard many people say that it only happens when I roll the window down. There are vents on the side and/or back of the car that allow air to come in just like when you roll down the window, just not as much air. If the exhaust leaks into your car with the window down you can bet that a small amount is still coming in with the window up. Just not enough for you to smell. What you're actually smelling is by products from the exhaust because CO doesn't have a smell to it. There are lots of factors to consider on this matter, it's not JUST the exhaust tip and it's position. When I redo my website next year I'm going to add a little bit more to the writeup and add some pics like these 2 that I added for you. I'm also going to be adding some pics that I have of a white 240 that was running very dirty which isn't uncommon. The left side of the hatch on the underside is black as coal and you can even see the fingerprint from the hatch gasket. There is a very slight leak on one spot where the seal had a wrinkle and you can see a black line about 2mm wide where the exhaust was getting in. As you pan towards the right side of the hatch, it gradually fades to light tan and then to white. A pic is worth a 1000 words. When installing the TD tips I usually end up cutting them in half or even a little shorter than that to get the desired length. ZMOW
Thanks so much for the info/pics - that will help a lot. Since i kept the large bumpers on my '78, should I extend the tip to match the end of those bumpers or use your 240's picture as the proper length?

Also, will this simply help less exhaust into the cabin or is this the actual cure that datsun never thought of?
 

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Gee zmow, don't sugar coat it; tell me what you really think about other people's (mine, in this case) opinion/experience. But of course, when you know everything, the blather of us mere mortals must be truly annoying.

And certainly, it was my lack of precision that led you to mistakenly (gasp! say it isn't so!) assume I was talking about a turn-down pipe. Until I changed it recently, the exhaust in question was 100% original.

But let's not dwell on your error; I'd rather assert the full $.02 value of my own research, reported with a modicum of sense and a dedication to accuracy. Believe it or else, I have not had any infiltration issues since the change, and I'm running all-original seals around the hatch to boot.

Thus, I hope you will pardon me for having the temerity to go with my own personal experience over your elaborate dissertation of superior qualifications, delivered with a consummate condescension for any fool who would dare differ.

Rest assured that I will consider my untainted cabin air an "illusion" in honor of your pronouncement of my incompetence.

As a footnote to other mortals out there looking for less elaborate ways to cope, I would note that one can lessen infiltration by boosting cabin pressure with liberal use of the ventilation fan and judicious window deployment.

And that's two cents you can take to the bank.
 

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Gee zmow, don't sugar coat it; tell me what you really think about other people's (mine, in this case) opinion/experience. But of course, when you know everything, the blather of us mere mortals must be truly annoying.

And certainly, it was my lack of precision that led you to mistakenly (gasp! say it isn't so!) assume I was talking about a turn-down pipe. Until I changed it recently, the exhaust in question was 100% original.

But let's not dwell on your error; I'd rather assert the full $.02 value of my own research, reported with a modicum of sense and a dedication to accuracy. Believe it or else, I have not had any infiltration issues since the change, and I'm running all-original seals around the hatch to boot.

Thus, I hope you will pardon me for having the temerity to go with my own personal experience over your elaborate dissertation of superior qualifications, delivered with a consummate condescension for any fool who would dare differ.

Rest assured that I will consider my untainted cabin air an "illusion" in honor of your pronouncement of my incompetence.

As a footnote to other mortals out there looking for less elaborate ways to cope, I would note that one can lessen infiltration by boosting cabin pressure with liberal use of the ventilation fan and judicious window deployment.

And that's two cents you can take to the bank.
So you tried a turndown pipe and it fixed exhaust entering the cabin entirely? If that's the case, could you post the exhaust tip you purchased (was it from Amazon or something)?
 

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Well no Sir, I did not.

I guess the first post could have been clearer on the subject... I used a straight pipe with an end cut of about 60deg.

But if I had used a hook, I reckon I would have bought one commonly available at most FLAPS.
 

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As everyone has been noting here, the best solution is to check for leaks at the rear of the car. Most often it is the taillight gaskets or hatch weather stripping. It could also be bad or missing fuel line gaskets where the vapor tubes run thru the body and into the vapor tank above the fuel filler. As people noted, a smoke machine is the easiest to find the leaks. A turn-down pipe won't solve the problem. It just causes the exhaust to swirl under the car and into any leaking gaskets.
 

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Discussion Starter #34
Like I've said - all gaskets in the rear are new.
- hatch glass
- inner and outer hatch seal
- taillight gaskets
- vinyl piece sealed from behind
- hatch grommets taped shut
- antenna drain plugs taped shut
- taillight bulb socket o-rings

I will check for broken fuel line grommets but ive been in that area so much I'd be surprised if there were any

ZMOW made it sound like a turn down pipe would solve the issue - are you saying it wont?
 
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