Hey guys, im looking at replacing my car with a high flow unit soon.I was just wondering what was better, a 2.5inch, or 3inch kit. My current sytem includes Pacemakers, and a 2.5inch cat back, mandrel bent. Ill get the flex pipe changed when I get the new cat aswell.

I was always under the impression that it is better to go one half ince bigger on the cat, then the rest of the system. Is this true ?

it is if you really need the flow

a 3inch cat wont hurt, and you can always get an entire 3inch sytem later down the track.

what ever you get make sure its a metal substrate and not a ceramic substrate that most cats are made of. The difference is about 100bucks for a 3inch unit but just about never having to replace it even if it takes a strike speaks for itself

I got a 3" magnaflow metal cat from a guy on ebay(tuffcarparts). It is recommended to go 1/2" bigger on cat than the rest of the system. This cat gave a nicer note too. Picked up from a guy at Mt gravatt Brisbane. had it fitted for $35 at an exhaust shop.(needs flanges welded on)

Yep, 1/2" larger than the system is the norm.

I went with a 2.5" high flow cat in my Rada...no probs whatsoever
Here's some more: High Flow Cat (http://www.aussiemagna.com/forums/showthread.php?t=53221)

The high flow cat of same bore to your pipework is fine - the gains on flow from going from 400cpi to larger 200cpi (high flow cat) core is very noticeable. There are even more gains to be had by the same pipework connected to a larger cat because the increased core cross-section is further reducing the restriction in the system.

If you're going to spend the $ and take the time, going the next size up will be a wise decision for the future. :cool:

Consider a cam upgrade where mid and top will be enhanced, the lowest restriction exhaust system will work well with such future upgrades.