Getting a helix up pipe with a cat is really up to you. I know that in California a high flow cat will not pass smog. The only reason I would get a high flow cat would be to keep cops off my back. IMO, I would not get a high flow cat on my up pipe and down pipe, only on the mid section.

 

A high flow cat is still not technically emissions legal, as it is a federal violation to remove a working catalytic converter from any vehicle with less than a certain amount of mileage (may be 50K, not sure). In some cases you may be able to pass a sniffer test in your state with such a setup, but it's not 100% legal by any means.

 

im also concerned about this, does a high flow cat make the car quiter and if so how much? thats the only thing im worried, i dont want my exhaust to be to loud

 

A cat (hi flow or not) shouldn't noticably effect sound levels

 

Though by changing the cats to highflow you do make the sound louder

edit:
Its highly dependent on the make of the cat though some are like a few pieces of chicken wire in a bottle others are more dense.

 

I have a hi flow on an n/a car, and the only thing that's different is occasionally I'll get crackling sound when I rev it (kinda like an old muscle car), the rest of the sound is a function of the muffler (Magnaflow cat and muffler).

 

not true, a highflow cat will indeed PASS the first portion of california emmisions, but keep in mind you will fail the visual.....

as long as you keep the position of the cats on the stock locations it will do its job, therefore passing, onething to keep in mind is that it will only work efficently if the hi-flow cat is closer to the turbo.

a few exhaust that come in mind which work great are the mad-dad high-flow twin dump dp+ mad-dad 3ce pipe mated to the catback of your choice, this is the most stealthy option available and will pass ca emissions.... carb eo = dont think about it like i said visual will be your enemy..... but with a quick glane this is the best!

btw having a highflow will not take much power off, so dont worry you will not see an effect in power until you reach much higher hp levels greater then 400-500bhp....

 

Sorry, but a higlow cat will fail. Personal experience. Had a hiflow cat on a car, failed smog bad. Put the stock cats back on and they passed with flying colors. A friend of mine had the same problems. Until I see someone pass with a hiflow cat, I will not believe that they pass.

 

Littleboyblue,

There is a thread on NASIOC BAIC about a member who had a high-flow-catted MRT turboback and passed the sniffer with flying colors. I'm too lazy to search for it. "MRT smog" in that forum will find it.

-=eric

 

Interesting. I bet that they will pass the sniffer, but not the dyno.

 

what kind of cat was it? ceramic or metal substrate? and where did you have it placed? i will gaurantee you that it may have been a bad cat, or possibly the placement, it is really more effective only if it is near the turbo....

contact gruppe-s in regards to their helix dp with high-flow, there is also a proff of it, again it will not pass visual though....

 

even with an awd dyno it should pass, it is tested at idle and under load, in regards to californians there are not many awd dynometers available, so they have to from what i ahve seen lately test at idle and at a higher rpm, obdii as well...