catalytic converter removalel

  • patanna2
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27 Oct 2012 22:04 #12049 by patanna2
catalytic converter removalel was created by patanna2
Thinking about removing catalytic converter and replacing it with a Y and straight pipe and leaving the muffler as is. I'm hoping to improve sound. Any thoughts on this. It's an 81 so no omission is required.
Pat

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28 Oct 2012 05:36 #12050 by Kiln_Red
Replied by Kiln_Red on topic catalytic converter removalel
It would be just slightly louder. I hollowed a cat once on my '84 auto. Marginal is the word that I would use to describe both the change in sound and performance.

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28 Oct 2012 12:37 #12060 by 928mac
Replied by 928mac on topic catalytic converter removalel
Opening up and exhaust will not help if the exhaust is all ready big enough to handle everything that the intake can deliver.

If the engine has a significant amount of back pressure, then opening up the exhaust will allow more intake air and fuel to pumped through the engine. (remember the engine is just a piston pump)

This also has a lot to do with intake design and efficiency.
When I removed my catalytic convertors and bolted on the same style pipe, I believe the engine breathed better and that there was a bit more seat of the pants umpf
I have no numbers to prove this, but some others have posted their dyno numbers on the net.

The sound did get throatier for me.
I later (just this year) removed my muffler and installed the same open pipe set-up which is called a RMB (Rear Muffler Bypass) but its really just sticking a pipe in-place of the muffler.
I got a lot loader (when floored) and just a bit when cruising.
Some people complain of a loud drone (head ache type) with the RMB.

I will note here that.
When I engineered the H pipe to replace my cats,

I moved the Y where they join, further back to expose the flywheel housing.
I do not need to remove my exhaust to remove my flywheel cover any more.
You can see this in the picture below.

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29 Oct 2012 17:56 #12108 by mm928
Replied by mm928 on topic catalytic converter removalel
My experience is that earlier cars (through 83 at least) seem to benefit a great deal from exhaust upgrades. However, also check your manifolds. The stock ones on my 83 were horrible iron straws.....so I purchased a used pair of 85/86 and blasted and painted them. I then added the 3-in y-pipe and a new SS hi-flow Cat from Roger at 928sRus. Big difference in breathability and quicker reaction time. I would say the performance must be better as well but I have no numbers. It will rumble like a 32v car.....and this is with keeping the stock pumpkin muffler and rear pipe section after the Cat.

SO I would say definitely consider it. Just check and see if you model year exhaust manifolds are considered pretty good or not and if another model years might fit. I think it is probably a decent bang-for-the-buck upgrade. The last section stock section is likely 2.5 in, I bought a 3in upgrade but did not use a reducer, there is fairly little overhang where they match up. You could do it either way I think. I think also that my write up on it is elsewhere on the site somewhere. Just do a search.

Good Luck!

1983 928S - 16v 4.7L L-Jetronic
Dark Grey w/ Blue Leather
85/86 exhaust manifolds
Y-Pipe
SS Hi-perf Cat
S4 springs
Bilstein shocks
Air pump delete
VIN: WP0JB0926DS861180
- - Isn't Life great? - -

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29 Oct 2012 18:27 #12111 by Kiln_Red
Replied by Kiln_Red on topic catalytic converter removalel
I agree with Michael. If you are considering a complete replacement of the exhaust, including the manifolds, you could see more significant gains. A lot of people have updated the manifolds to MY85/86 style and reported a boost in performance.

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29 Oct 2012 19:08 #12112 by patanna2
Replied by patanna2 on topic catalytic converter removalel
Thanks Guy's The response was great , but I'm not surprised. There sure is a vast amount of wisdom within an arms reach when there's a 928 owner's club you can turn to in a time of need..
Sincerely
Pat

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29 Oct 2012 20:57 #12116 by OBehave
Replied by OBehave on topic catalytic converter removalel
The replacement of the exhaust manifolds with 85/86 shorty headers and no cat will yield a noticable improvement in exhaust note and performance, But it would be irresponsible of us to not inform you that it may be illegal in your state to do so and you should research it before just doing it.I am not trying to be a buzzkill just a friend.

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29 Oct 2012 21:03 #12118 by pcar928fan
Replied by pcar928fan on topic catalytic converter removalel
Ed, you are a buzzkill! LOL! That said, a friend has an '88 S4 and this is the last year of the dual stage idle test for our cars. He fitted an X-pipe NO CATS and an RMB and he still passed his emissions test with flying colors! Go figure!

James
78 Silver / Black-white #295
84 Ruby Red / Black AO84
88 Dark Blue / Linen-Black
92 Polar Silver / Dark Blue 92EURO
93 Arrow Blue / Black

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29 Oct 2012 21:09 #12121 by OBehave
Replied by OBehave on topic catalytic converter removalel

Ed, you are a buzzkill! LOL! That said, a friend has an '88 S4 and this is the last year of the dual stage idle test for our cars. He fitted an X-pipe NO CATS and an RMB and he still passed his emissions test with flying colors! Go figure!


Note: "your results may vary!"

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29 Oct 2012 21:11 #12123 by pcar928fan
Replied by pcar928fan on topic catalytic converter removalel
LOL! SO TRUE!!! Our silly little EPA test is pretty sad actually! We do nothing like D/FW or CA or many other places. Just glad we can still get away with a little hooliganism here in Austin, TX!

Thanks Ed for all you do for the 928OC my friend! Getting back to you on your PM soon. SUPER BUSY this week so it might be next week before I can get you my tool write up. But you can mention it for The Shark Vibes that there is a Tire Pressure Monitor Sensor removal tool available on the loaner program... We will fill in the blanks later if anyone ever wants to borrow it!

James
78 Silver / Black-white #295
84 Ruby Red / Black AO84
88 Dark Blue / Linen-Black
92 Polar Silver / Dark Blue 92EURO
93 Arrow Blue / Black

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30 Oct 2012 14:01 #12144 by mm928
Replied by mm928 on topic catalytic converter removalel
If you do end up needing a cat, the SS hi-flow from Roger is a good one. 3 inch ! Passing a lot of gas... HA.

1983 928S - 16v 4.7L L-Jetronic
Dark Grey w/ Blue Leather
85/86 exhaust manifolds
Y-Pipe
SS Hi-perf Cat
S4 springs
Bilstein shocks
Air pump delete
VIN: WP0JB0926DS861180
- - Isn't Life great? - -

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04 Nov 2012 19:33 #12301 by Normy1
Replied by Normy1 on topic catalytic converter removalel

Ed, you are a buzzkill! LOL! That said, a friend has an '88 S4 and this is the last year of the dual stage idle test for our cars. He fitted an X-pipe NO CATS and an RMB and he still passed his emissions test with flying colors! Go figure!


That is correct.


Properly calibrated LH-jetronic [or even L-jetronic] fuel injection will produce at idle emissions WITHOUT a catalytic converter that will pass California emissions tests.

The cat was always intended as a "scrubber", in case the fuel system made a mistake.

-Cutting off your catalytic converter isn't a good idea. You can buy a catalytic converter right here: www.randomtechnology.com that can flow enough gas to equal over 500 hp. If you install these on your car, you will be following the law, and perserving air purity, all while not losing a single horsepower.

NO, I don't have these on my car, and NO I have nothing to do with Random Technology. But their products are GOOD. And a good idea!

N!

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