I don't understand cat by-pass pipes

[nkotselas]

Hello everyone,

I was just about to place an order for a bypass pipe thinking it would give me a somewhat significant power boost. I decided to do a search and found that most people say it will barely produce any more power and change the sound slightly. This confuses me.

I have a euro spec 3.2 engine, should put out 231 hp, but a cat was installed to pass my CA smog test so I thought that going to a by-pass would bring me up to 231 again, as I thought I was at about 217 with the cat. Will this be the case and was I just reading about US spec cars? Or did all euro cars have the euro pre muffler?

The exhaust has been something I haven't been able to understand quite yet

Thanks for any help in advance

[DRACO A5OG]

You need to put in on a Dynometer to really see if there is HP difference.

But your butt dyno will tell you, your current low end torque may be lost to give way to the higher end torque at the wheels.

Sound is definitely more throaty and you may experience back fires/gurgles on decel.

My experiences,

Jim

[rnln]

Not sure how much you will gain without dyno comparison, but it's definitely a lot lighter. Not producing heat at the area like the cat.
If you are interested in a used one, I have it available.

[911pcars]

I believe euro-spec 3.2 engines have higher compression, around +10:1. That's the main difference in torque/HP.

Thus, it's not just the addition or deletion of a converter.

Sherwood

[theclaw]

Removed the stock cat and installed a sweet looking stainless bypass. (Yeah, could of punched out it out but then I'd just have a corroded hollow piece of steel that looked like crap.) Removed the O2 sensor. Steve W remapped my chip and the butt dyno says, BAM! Nice job. Feels like a new car. Pulls much better.

[Flat6pac]

Most of the ROW are 9.5 not the 10.3 as believed because you cant get gas for 10.3 all around the world.
Bruce

[Swoboda]

Isn't there also a basic difference between a cat bypass and a pre-muffler?

I thought a cat bypass was essentially just a straight pipe while a pre-muffler included some baffling--changing the flow and sound profile.

[Peter Zimmermann]

There are cats, and then there are cats. Is your cat a factory unit designed for the car, or some after market piece? If your engine is a true RoW 930/20 unit, it did have 231 DIN hp (170kW) at one point. If your engine was converted to M 298 specs, it will have only 204 DIN hp (150kW). If it was converted by slick willy's conversion shop, using a modified ECU and a junk cat, it might only make 180-190 DIN hp (I've driven some converted 231 hp cars that were complete dogs!).

A test pipe might help, but it might do little more than making the car noisier. It all depends what else was done during EPA certification, you might not even have the ECU that was with the engine originally. A Euro pre-muffler is your best bet regarding the exhaust, but more info is needed regarding the ECU. I'll let the electronics gurus work on that with you.

Maybe I'm missing something here, but you also don't want to upset the car enough to fail future bi-annual tests.

[DRACO A5OG]

Baffles? interesting I would like to know?

[nkotselas]

From what I know the engine should be almost completely stock. It is a 930/20 and I figured it would not have been changed at all especially since it only ha 23,000 original miles when it came to me. Would the PO have had to change the compression ratio or anything like that?

Also I have a SW chip programmed for the euro spec version. If I do upgrade the exhaust, how much will the chip hold back until I can have him remap it?

[DRACO A5OG]

'78 chip? Is your car a 3.2 with a DME?

[nkotselas]

Sorry, the car is a 78 but the engine is 84 carrera 3.2 euro spec

[DRACO A5OG]

Oh I see, then should be possible was the oil tank also updated to a 3.2 oil tank?

[cbe060]

my 84 euro is the german version [m499] 10.3 comp which calls for ron 98 unleaded..i have the euro premuffler, no 0,2,a b&b 1in 2out, this is my second 84 911 euro . when retured to thier german configuration they become like a race car as it says on SW,s website. ive owned 87 and 89 3.2s and a 97 993 and for raw power you can beat a euro 3.2 for imho

[DRACO A5OG]

Damn to be a Euro, Hmmmm, but to obtain pure 98 octain unmolested by eth is impossible here in People Republic of Kalifornia

[nkotselas]

I think the tank has actually been updated
What I really want to know is what that "german configuration" is

[IROC]

Originally Posted by DRACO A5OG

Damn to be a Euro, Hmmmm, but to obtain pure 98 octain unmolested by eth is impossible here in People Republic of Kalifornia

He actually said ron 98. Our 93 (mon+ron/2) works just fine with 10.3:1.

[db_cooper]

With a cat bypass you will not be cooking the left exhaust valve cover and tire when parked..it gets hot under there!

[attamz]

I just like to pollute the environment.....kidding. I def. noticed a difference w/ the bypass, muffler and chip. The bypass gives the car more of a hollow muscle sound.

[PatrickB]

Best bang for the buck, without doing major changes, is cat-bypass with a SW Chip. better all around performance, and MPG's too! The OEM muffler actually flows fairly well, but a significant improvement can be had with the bypass!