Cat-Bypass Legality Questions
 

Ok guys well here i have another dilema regarding my '78 SC's exhaust.

From many of the fans of exhaust modifications on this forum, it seems to be a popular practice to removed the catalytic converter on the older models and replace them with a cat-bypass or "test" pipe.

Now for those of you who have done this here are my questions:

Was there a noticable sound difference? Power increase? And what did you have to do legally in order to run your car without an emission regulations?

The third question really goes for those who have done this and drive their car within California. When i purchased my SC i had to get it smogged, but i have heard from a friend that you only have to get the car smogged everytime it changes owners in California. I am curious as to if this is true or not. Before then i thought a '78 would be smog exempt but i am apparently mistaken.

So particularly older porsche owners within California are my prime source of answers here but i wish to hear about the performance and sound difference from others. So chime in, im curious to see if i can swap that old restrictive cat off and get some more power and sound.

Thanks guys,
Ken311

Re: Cat-Bypass Legality Questions
 

Any car ('cept diesel & electric), '76 & up, will require a biennial smog inspection in Calif. unless you reside in certain zip codes (e.g. Imperial County). Then, it's change of ownership checks only:

http://www.smogcheck.ca.gov/StdPage.asp?Body=/Smogcheck/doineed.htm

What Mr. Ocean said. But... a gutted cat will pass the visual part of the smog check and "may" pass the sniffer test too. It depends on the engine state of tune.

A word of caution here - if the engine fails the smog test, then it has to to go to a :testonly" station or to a state referee. They check the engie and exhaust a bit more closely. Ask for a "static"/"dry" test that is done prior to having the test machine linked to the CA State's system,

Re: Re: Cat-Bypass Legality Questions
 

ahh thats too bad...

[QUOTE]Was there a noticable sound difference? Power increase?[QUOTE]

Louder, a good louder. Better throttle response and seems to be more power in the lower rpms.

You may want to change the exhaust every two years for the inspection as I suspect many do here.

[QUOTE]Originally posted by bmgmd
[QUOTE]Was there a noticable sound difference? Power increase?

Quote:

Louder, a good louder. Better throttle response and seems to be more power in the lower rpms.

X2. As for the smogging thing, just move, or get a job working on cars and become a State Inspector.

this is easy...run a bypass pipe all the the time and swap in a good working cat when you need to do a smog test...some people around here loan good cats out when a smog test is needed....
my bypass is louder and gives the engine a bit of a rumble sound at idle which makes me feel like I have a car with a powerful engine...which it isn't.. there have been dyno sheets showing 4-6 hp gain at the top end.
I like having the cat out to avoid having that big hot thing sitting under there...I don't have the proper shield... that's my 0.02
-Henry
89 3.2 - recent (DIY) top end - cat out - stock chip

My 3.2 passes every two years with a chip, SSI's and no cat. But I live in an area where they do a sniffer and visual test only. I have heard the areas that have the rolling road test are more stringent.

My old 78 SC would not pass without a cat in the same area.

Is it hard to remove and replace the CAT when going in for a smog check? I mean, everyone would do that if it was so easy right?

Yes it's very easy to remove the cat and replace it with a bypass.

It's easy if your exhaust has been off the engine recently, or ever.

If it never has, then you might be in for a treat.

haha. thats what i was worried about.

it doesn't seem that the government would enforce a Catalytic Converter Law and then allow you to take it off for 2 years, then put it back on for the Smog Test. But i will have to see if it is easy or hard for me, i have no records that the exhaust has ever come off, so i may be in for a little somethin hahaha.

A good impact gun and some penetrating oil, possibley a Dremel tool, new gaskets and exhaust bolts is all you need. Once you do it it will be way easier the next time.

I used a Dremel to cut the bolts out of the exhaust. It is the only way to fly. Took about 10 min. to cut out all 10 bolts. Don't forget to unhook the 02 sensor and feed the wire through the body before trying to drop the cat. You should put a new 02 sensor in the bypass pipe, and leave the origional one in the cat. This will add $80 to the bill but will subtract a few grand from the aggrivation factor. Go for it, you will love the added deep tone, very subtle but nice.

Most people only notice a slight performance gain when running a bypass as compared to a cat, usually because the cat is old and clogged. A new or good condition cat will give you similar results, a bypass may give you a deeper exhaust note but no real hp gains vs a solid cat.....YMMV

IMO it is well worth the $250 or so for the cat-bypass pipe. A 25 year-old cat converter has to be somewhat clogged. I noticed a slight power improvement, sound is deeper, and, most importantly, the left exhaust side of the engine is cooler.