Street legal exhaust questions...

[FrankenStang]

Does a car really need 4 cat's? Is there a legal way to eliminate just two? (Or all of em? LOLL) I live in Az. Mine has 4. (stock h-pipe, I guess.) I looked at my exhaust when my mechanic dropped it to replace the tranny. There are holes in the mufflers and rear pipes. LOL I was wondering why it lost it's sound. I have Flowmasters. Sounds like an old beater tho. Not sure about the condition of the h-pipe but, it has 4 cats, it must go. LOL Any recommendations or opinions? I'm kinda sold on the Flowmaster sound.

My car is a 1980 Mercury Capri with a 1990 Ford Mustang 5.0 motor in it, fuel injected. So basically, my question is, does it have to have cats at all?

 

[Sicarius428]

Magnaflow I believe makes the only CARB approved aftermarket x pipe. It has only two cats which you want but it will change the sound more nascar like than muscle car.
Kevin

 

[cjman15]

depends on if you have to pass the sniffer or not, everywhere is different

 

[FrankenStang]

Eww, no nascar **** for me thank you.

Yeah, I have to go thru emissions.

 

[Michael Yount]

You can replace the 2-cat system (per side) on yours with a single 3-way cat, and you should be able to pass the sniffer. But you can't just remove one of your existing cats - the two different cats clean up different emissions - so by removing just one of them, you'll be dirty on whichever emission(s) it cleaned up.

In any event - if the visual inspection is done by someone who absolutely wants to see the 4 cats - then you may have a problem anyway. So before I explored the option of replacing 2 cats with 1 3-way, I'd have a talk with the inspectors to be sure they don't have a problem with that approach.

 

[Sicarius428]

Then your best bet is to replace the lower two cats with a 3 way like Michael said and gut the top two by beating the honeycomb into pieces... That way it also has the stock appearance if the inspector gets technical. Probably a lot cheaper than a new piece too.
Kevin

 

[Michael Yount]

ACtually you want the cat as close as possible to the front of the car for fast light-off, so it you go with the approach Kevin suggests, replace the front 2 cats with the 3-ways, and gut the rearmost cats.

 

[Deleted member 87397]

If you gut two of the cats you are going to slow down your exhaust flow when it hits the empty space where the substrate material used to Not good for performance.

 

[Michael Yount]

Not necessarily - brush up on your exhaust theory. An expansion space roughly equal to the displacement of the engine is recommended about 36" aft of the heads in order to kill the pressure waves generated by the exhaust. Part of the reason the cats do such a good job of making a system quieter is because the increased cross section serves to kill that pressure wave, and because the ceramic substrate provides lots of opportunity for reflected sound waves to cancel each other out. As long as it's gutted cleanly, that increased volume shouldn't hurt flow/velocity at all. After all - at the other end of the cat, everything that comes in has to leave - so the velocity speeds back up as soon as it re-enters the downstream pipe.

The thing to be careful of is to choose a high flow 3-way cat.

 

[TheUser]

if you have a way of hauling a mid-pipe (truck, SUV, etc) it might be worth your while to just get a CARB legal hi flow h pipe used semi-local and go that way. You could prob. find one for a couple hundred bucks, which is probably what those cats will run you. Not to mention, might be kinda difficult to fit a cat up there where the upper-most ones are...I haven't studied the replacement of those cats much, but just my opinion.

You my try the classifieds at www.corral.net: http://www.corral.net/forums/forumdisplay.php?s=&forumid=276