What does a cat bypass pipe get you?
 

I came across a cat bypass pipe that fits my 911 SC for sale locally. It is a factory unit in good shape from a euro SC I am told as they aparently did not have cats. It does have the hole for the 02 Senor too.

My question is, what is gained by installing this? Is it louder? More HP? Simply more air flow? What is the real gain and does the cost justify it?

Also, what is one of these worth? BTW, I'm in a smog exempt state so, I don't have to pass emissions.

I didn't notice that much difference on my '79 SC, but I was already running a big B&B muffler. It was much louder without the cat.
Rick
'78 930

I assume you mean it is a euro pre-muffler rather than a cat bypass. I just installed a Dansk euro pre-muffler on my 81 SC. Everything else is stock (ie muffler, etc.). I can tell very little difference in sound or performance with everything else stock. However, my purpose was only to allow me to increase the fuel mixture without destroying the cat. After removal of the cat, I changed my AFR from around 14.7 to 13.4. Performance is much better. As reference, that AFR change was caused by about a 1/8 turn of the mixture screw.

It's fun to tell my tree-hugger friends that I took off the cat.

It should make your car go faster because it will lighten your wallet, and the lighter the car the faster it will go.

How is it fun to announce to those who care about their/your air quality that you don't give a rip? I wouldn't tell anyone how to modify their car, but don't you think a little discretion would be in order Beavis?

Because tree-huggers, like the rest of us, apparently, are being fed a load of crap about the ozone layer, etc., just so we can be forced to choke the crap out of our cars. It's all scientific mumbo-jumbo force-fed to us by the scientists who rely on the grant money from the government that passes the laws that require the emissions controls. It's the circle of life, Simba!

Drop the cat, Beavis, have it bronzed and display it proudly on your mantle. Do it just for the statement. I'll drink a ceremonial beer for you and toss the can in the Bay.

Well actually it's not. I've been an environmental consultant over 10 years and the areas that have been put under vehicle emissions restrictions have seen dramatic improvements in air quality. So Cal is a good example where the air is much better than 25 years ago.

Of course those same areas went under industrial emissions restrictions at the same time so that's also part of the equation...

And I AM a bit of a hypocrit as my 84 has a cat-bypass. Vroom.

Zonanas, thats way off. You are incorrect. Anyway, I feel as long as your emissions are below the maximums it should be ok.

Re: What does a cat bypass pipe get you?
 

Nothing, compared to a good metal-core cat.

I noticed a significant sound difference with the fabspeed pipe with the stock muffler. It is definitely louder and just about perfect tone wise. I removed it for a change in tone and also believe it is cooler (less heat) than running a with a stock cat.

quote:Originally posted by Steve87-911
How is it fun to announce to those who care about their/your air quality that you don't give a rip? I wouldn't tell anyone how to modify their car, but don't you think a little discretion would be in order Beavis?

The truth is I have a cat bypass on my car and the O2 sensor unplugged and I just passed the emission control for the 4th consectutive year and they just made it tougher this year.

The truth is if your car is properly tuned and maintained it is as clean as any car on the road.

In my opinion it is about time to start cracking down on the the buses,trucks and other commercial vehicles and leave the 20 year plus vehicles alone.

Your car will run cooler without a CAT.

Didn't the native Americans back in the day call the LA basin, the Valley of Smoke? And, that was way before industrialization.

Global warming? Of course! Where else would the world's temp go from the Ice Age but up, duh!

The tsunami, in its short duration, caused more pollution in the region than the inhabitants themselves.

I'm with ZOANAS, it's the circle of life. Humans may be able to affect the natural processes but we are not the underlying cause nor are we the panacea.

Porsche content: go with the bypass and report the results, please. Thanks.

I installed a euro pre-muff on my '78. The changes were very subtle. Slightly stronger top end and slightly more 'music' from the rear.

I definitely noticed that the car was much cooler in the left rear, which can only be good for your valve seals, gaskets, etc. in that vicinity.

Prove it. Cite facts, not hypotheses.

Fact: One eruption of a volcano produces more "greenhouse gases" than the entire state of California in a year.

It's all about the money.

Ditto Zoanas!

I think the real problem is not with us (the enthusiast groups) it's the "average" person, those who never take care of their cars, "we don't need no stinkin tune ups or oil changes".
"WE" probably are overkill on maintainence, overkill on spark plug changes and oil changes etc.
Back in the early-mid 80's I imported a bunch (50-60) of the dreaded grey market cars.. a few 911's a bunch of 323i BMW's (E21 6 cylinder) and some M/B's. These cars were EPA exempt, but when registered in NYS and NJ passed the "sniffer" test with flying colors....no cats etc, just well maintained.
But WE all pay the price for the AVERAGE PERSON, who does nothing to maintain a vehicle. MAJORITY RULES, unfortunately the majority are fools who don't give a S**T about anything but themselves....need I only say, who stops for red lights, hogs the left lane, (ad nauseaum)....its not "US" (is it?)
OK soap box back in garage....

Ill make a deal. When the EPA actually cracks down on factories who pollute more than you could ever imagine because of "loop-holes" then ill put my cats back on. For down I say go screw yourself EPA cause these double standards are a load of crap.

not to comment on smog testing or the work required to beat it every two years here in the golden state but, on the cat bypass. i just put my cat back on for somg testing and the sound was very much affected by the reinstall of the cat. so much so i opted to not go out and drive last weekend. it did not sound like it had as much power, and i believed.

i installed the by pass for cooling reasons, which i can confirm it helps. but mostly it was to save my cat for a week or two of use every couple years. i am not going to run the thing and wear it our/soil it then be required to spend my whore money on a new cat. the by pass was $100 or so and a new cat is like a grand. where is the logic in keeping it on? it gets stored and reinstalled to work while at the smog tester. that and my 02 pump.

if they set the rules i will play along.

I have run every possible exhaust configuration on my car. I now run a pair of RandomTechnology catalytic converters.

Conclusions;

Before and after emissions show a staggering change in emissions.

Dyno shows no perceptible change in HP. Possible slight torque increase at lower RPM's with the cats.

Absolutely no increase in running temp with the cats.

your 3.6 is an entirely different animal though.

Truth, Amen brother!:cool: http://www.pelicanparts.com/support/...s/beerchug.gif

There's an interesting quote from the earliest Spanish explorers about the LA Basin's pollution phenom.

The EPA, founded by Richard Nixon, and the various federal and most state air quality laws today are all about power, controlling people, and stealing money from them.
:mad:

My 3.3 Turbo clearly ran 10-15 degrees cooler (oil temps about 175-180) without the CAT.

My turbo spooled faster too.

Please post photos of your installation.

Yes, good point. Mine was 130,000 miles and melted.

I still think it ran cooler sans CAT as the air (exhaust) wasn't restricted on the way out the back. It is pretty well known the turbo will spool faster without the CAT (dunno how much quicker though...).

Some data points to chew on:

3.5L Motronic twin-plug motor that runs PERFECT

with stock heat exchangers & catalytic convertor:

HC @ 15 mph (PPM) - 13
MAX allowed - 121

HC @ 25 mph (PPM) - 8
MAX allowed - 96

CO (%) @ 15 mph - .04
MAX allowed - .76

CO (%) @ 25 mph - .03
MAX allowed - .65

NO (PPM) @ 15 mph - 283
MAX allowed - 807

NO (PPM) @ 25 mph - 290
MAX allowed - 746


Now, with headers installed & no provison for catalyst:

HC @ 15 mph (PPM) - 95

HC @ 25 mph (PPM) - 90

CO (%) @ 15 mph - .44

CO (%) @ 25 mph - .44

NO (PPM) @ 15 mph - 769

NO (PPM) @ 25 mph - 743

Conclusions? The motor still passes, but just barely!

1. Motor is down on power with stock heat exchangers and catalyst installed due to exhaust restriction.

2. Motor runs much hotter (not good) with stock heat exchangers and catalyst installed. Approximate oil temp at 210-220 versus 195-200 with the headers.

3. Removing heat exchangers & catalyst and installing headers significantly sheds weight. Even removing just the catalyst in favor of a pre-muffler will shed some unwanted lbs. and the car will run slightly cooler. BTDT.

Do what you feel is right and best for you.

Ralph

Moses, do you have any photos of your latest configuration? All I found was the sharpie version:

http://forums.pelicanparts.com/showthread.php?s=&postid=593993&highlight=Random+T echnology#post593993

if you would rather not post them you could email me through the board.

Thanks,

I tried ('87) both the straight pipe cat elliminator from Bursch and the Dansk premuffler. The cheapo Bursch gave a noticable performance improvement, especially top end, while the Dansk actually seemed to do nothing at all for performance and it weighed more... My vote is for what works, the Bursh straight pipe, at half the cost. BTW, good idea to have it aluminized because the paint it comes with just burns off in a few days allowing it to rust.

Kevjandon,

I have an 82 911SC. When I got the car, it was fitted with an aftermarket converter and the stock muffler.

I have experimented with a Fab Speed pre muffler (flange welded @ incorrect angle - different story) as well as a Dansk single in dual out.

Summary:

1. Adding the premuff killed throttle perfomance. I now run the cat as top end is the same with increased throttle response and low end.
2. The pre muff was quieter. A little different sounding, but not loader.
3. I now run the cat with the Dansk for the best of both.

I have read that the Porsche version of the Euro Pre muff (Dansk same) performs better due to the volume of the enclosure. Fab Speed and straight pipe both have lower volumes. Might limit velocityandflow?

Additionally, keep in mind the O2 sensor needs heat to light off. Without converter, may cause issues.

Any newer style cat should flow well. Gains in removing the cat depend on how inefficient the unit is in the flow department as compared to the pipes, pre muffs, etc.

Marlin

Kev,
You musta been watchin the one on ebay that ended tonight...Were you the winner?

I considered it, but I elected to pass. Seems like money is better spent the muffler.

Re: Re: What does a cat bypass pipe get you?
 

___

Any problems with passing emmissions wht the metal core?

Re: Re: Re: What does a cat bypass pipe get you?
 

Not with mine. Great performance. Do a search for "Random Technology". I posted before and after #'s.