At the request of my wife, I am going to try to quiet down my 240Z. It only has a tail muffler, so I am going to add a high-flow catalytic converter just after the trans crossmember. I suspect that the cat will substantially quiet down the exhaust to a deeper note. The reason I chose a converter is that I am hoping that it also cleans up the exhaust a little, to help stay green, and keep some of the smell out of the car.

With the 2.5" premium exhaust from MSA, there is not much room against the driver's side trans tunnel. There is plenty of room in the rest of the tunnel though.

I ended up measuring and found that this offset stainless unit from Magnaflow should clamp right into the existing system after I hack out a short section. I will need to make a heat shield as well.

Has anyone tried this?

http://www.race-mart.com/MagnaFlow_49_S ... 54906.html

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-Dave
76Z Turbo'd
72 In Progress---DONE!

I can pretty much assure you nobody's even THOUGHT about this!

Resonators, yes. Catalytic converters, no.

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1970 240Z

Agreed Frank. Got to let that Z BREATHE. I'd leave it as is, but if you must, a bullet resonator is the way to go. I dont think a converter will do any good as far as cleaning the air in that setup and it will restrict flow.

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John Taddonio
1970 240Z
1977 530Z
1984 300ZXT
zcarnut@hotmail.com
FB: Zccr zcarclubofrochester

We shall see. I don't think modern cats are as restrictive as they once were. I have it on pretty high authority (instructor at an auto tech school) that this will not noticeably rob power, and will clean the exhaust. Besides this one is specified to flow up to a 5.2 liter engine. That's PLENTY of flow capacity.

After all, the 77's and 78's had factory cats and ran well. If it slows the car down too much, I'll drive the turbo Z instead.

_________________
-Dave
76Z Turbo'd
72 In Progress---DONE!

[quote="Frank T"]I can pretty much assure you nobody's even THOUGHT about this!

quote]

Just married guyz,Frank...

[quote="CygnusX1"]At the request of my wife, ]quote]

Here's another angle...how much diamond jewelry could you buy for what your spending on this?

Al, you slay me.

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1970 240Z

Not much. I could buy some Walmart Jewelry though. That would certainly not get me any points.

All kidding aside, how many posts about fumes in the cabin are there? After sealing the car off, you still can't really drive around with the windows open unless you enjoy smelling like exhaust for a day.

When I was younger, louder always equaled better, but now, not so much. Why not try to kill two birds with one stone. Make a mellower note and breath cleaner air. I highly doubt a 4" round element is going to restrict anything in a 2.5" exhaust system.

Remember when the earth was flat?

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-Dave
76Z Turbo'd
72 In Progress---DONE!

I would be a bit concerned about the heat coming up thru the floorboard on an early Z.

My wife would find the diamond jewelry comment interesting. Of course, she has already made similar comments about my "investment" in the Z's resto effort.

Jim

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Jim Arnett
Richardson, Texas
HLS30-15320 12/1970 (original owner)
ZCON 2015 Gold Cup - Street Modified class

Modern, high flow cats are NOT what you remember from the 70's and 80's. They flow much greater volumes and are much more efficient. They also range in cost from $40 to $100 depending on the materials. Stainless is at the high end.

Heat shielding is a given, and considered mandatory around any cat. I will fabricate one.

Most modern cars such as the Subaru STi run 3 or more cats in the system, and make well over 100HP per liter. Cats are no longer considered evil.

here is my other cat


Having defended my position...I must admit, I have no idea if the exhaust will clean up at all. We will see.

_________________
-Dave
76Z Turbo'd
72 In Progress---DONE!

Hydrocarbons or Sulfur I chose Hydrocarbons. Unless the car runs at an optimum fuel ratio at all time, they are not that good and could eventually go bad. I am using 2 Cherry Bombs, at $30 a piece I think from Napa. Then a Thrust Muffler. Cheap and quite. Now it didn't start out that way.......It was loud at one time, I then took a Slice to a different direction......but I now have Wife approvale. Somethin about that smell of gas....it's old fashion.

I installed the "cataclysmic" converter today. It was very easy and fits perfectly. Since it's going to rain for the foreseeable future, I can't test drive it. Up on the stands, I started it and got it as hot as I could by revving and holding revs for a while. The sound is good, just about 25% quieter than before, with a much more even tone at all RPM's. Before, the sound would resonate badly at certain RPM's and be quiet at others.

Now I ran the car in my garage with the door open of course, and my eyes did not tear, and I did not come back to the house smelling like exhaust at all.

In fact, that distinctive Z smell, was totally absent. Replaced with a faint smell akin to what a more modern car smells like.

Maybe, just maybe, this will actually work. Time will tell. If it gets clogged in a few years, I'll put in another one. Easy to do, with the way it's setup now.

I am using a really nice heat/sound product to protect the underside of the car from heat.

_________________
-Dave
76Z Turbo'd
72 In Progress---DONE!

So far so good. Initially I did smell some sulfur while running it moderately hard. I knew it was running a little rich under load already and figured that's what was causing the sulfur reaction. I took the Weber main jets down from 135 to 125 and it's much better. Around town with the windows down and the vent completely off, I don't smell ANY exhaust. If I get on it really hard, or coast down a long steep hill at high revs, I can still smell a little sulfur. Not really bad at all. The pungent exhaust smell is totally gone and all I smell is country air while cruising around normally.

The real question, is, howlong will the cat last with iffy Weber fuel mixtures? My annual miles are pretty low, so I hope it lasts a while. I used stainless band clamps on it (replacing the U-bolt clamps in the photo above), so if I have to swap it out, it's easy.

_________________
-Dave
76Z Turbo'd
72 In Progress---DONE!

Well, I congratulate you, Dave. That sounds like you may have hit on a good new idea. I especially like that heat patch you stuck under there ~ it indicates that you're not just thinking of your wife, you're also thinking of your Z.

I suspect you'll get a few miles of 'burn-off' before the sulphur smell disappears altogether. As the Cat breaks in, pleaZe adviZe us if the sound changes.

Well done, sir.
I wish we had a "Thumbs Up" Emoticon to use here.
Frank

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1970 240Z

It didn't make much of an impact on the sound from the outside of the car, but the cabin is 20-25% quieter. No more booming around 2500rpm and no more "beats" as the rpms change resonance. Hard to explain unless you understand wave theory and/or music. It just sounds smoother inside the car.

_________________
-Dave
76Z Turbo'd
72 In Progress---DONE!