Is it a good idea to just relace the cats on the stock exhuast or do you have to replace everything? I was just thinking if the cats or confining the breathing wouldn't just replacing the Cats be good?

 

you can put stright pipes in place of the cats and keep everything else stock and you will definatly notice a difference...

 

Aren't people having problems with sound and whistling by doing that?

 

well, putting in high flow cats or even straight pipes in place ofthe cats will raise the sound of the car...

whistling would be from a bad install where air is getting out from the connection points...

 

I got ya, So are the straight pipes better for power, Just thought the High flow cats will keep me legal and not be tooo loud. But than again here in Fla we don't have vehicle inspections like they do up north.

 

yeah... straight pipes will give you no resistance in the air flow there for technically more hp / tq...

people will say the z needs back pressure... but... i havent seen any power losses for straight pipes...

if you keep the stock muffler and put straight pipes then you dont have to worry about being too loud...

 

Our cats have been gaining 4 - 6 rwhp on an NA car.

The test pipes have been gaining 6 - 8.

So YES, test pipes will give more gain! Unfortunately they won't pass a visual inspection.

 

Please post dynos of no cats and the high flow cats. (anybody who has them)

 

Heres my dyno with testpipes. I think the HP numbers are a bit low because the AF didnt have any time to adjust. on the test pipes dyno run AF showed 18:1. I think as soon as the ECU adjusted it would have gained a bit more.

 

18:1!

 

Well lets just say I HOPE the ecu adjusted the AF ratio. Is there any other way of knowing if your car is running lean (aside from dyno sniffer)?

 

Evil, What's the difference between your pipes and the Test Pipes? And do yours pass inspection?