A cat and a pre-cat would definitely be quieter. No cat sounds like cars did in the good ol' days and is quite a bit louder on the inside in low revs. The catalytic converter gives you a smoother, quieter sound. So I assume a pre cat + a cat would do the same thing but more. But if you don't have to have one, that would be one heck of a hoop to jump through for a quieter car (why would you want a quiet car anyway ). I had a mini bike that was loud so I put fiberglass mat in the muffler which made is much quieter with no appreciable back pressure. No idea on whether or not that will work on a car.

Have fun!

Regards,

Thomas

 

I believe it would be quieter with a pre-cat. Check out videos of guys who have deleted the cat on their vehicle (any vehicle for that matter). Its louder without the cat. I don't see how with the pre-cat it would be even as loud as with just the one.

 

Well since this blazer i might possibly be getting has a precat in the y pipe (im thinking its a California emissions truck) can I swap out that y pipe and put mine in that doesent have one? Will it throw a code and still pass inspection?

 

Mine (to my knowledge) isn't a California model and it also has a pre-cat. My truck has neevr left Florida. But yes, what you are saying would throw a code. Its not a matter of the y-pipe having two cats, its a code in your PCM that detects the error. You can always buy the one cat and give PCM4Less or Wait4Me (PCM tuning sites) a call and order a replacement PCM custom tuned for your mods and they'll delete that code from the bank of errors.

 

You can do that?!?!?!?!

 

Yes. It actually is quite easy for them. It is not illegal for them to do the modification because they state that their PCMs are for offroad use only.

 

Is there the chance that one cat wont throw a code? The blazer I have now same year and model has only 1 cat and thats what im hopeing to do

 

I have only ever known vehicles with one cat. If it does throw a code, I read on a WRX forum: get a set of 18mm non foulers, chop one in half and weld a piece of EMT between the two halves that is longer than your down stream O2 probe, then screw that into the one you didn't chop and screw that into the down stream O2 sensor bung.
Or you could get a slimmer O2 sensor and just drill out the one non-fouler, no welding needed. I think a Denso will fit because people with Subarus don't have to do that cut&weld thing.

But it seems to me that a modern 3-way cat would be fine... because I read that a pre-cat was for oxidizing, so a 3-way cat is a cat with the pre-cat in it.

Regards,

Thomas