What is it when some have 200 cell or 300-400 cell high flow cat? Is lower the better? I looked around google but couldn't find much. TIA.

 

The reason high-flow cats exist is because people have been able to get good efficiency using lower-cell structures inside the housing. Lower cell count ='s higher flow. The problem you run into is that if the quality isn't there then the cat won't heat up fast enough to burn off the gases and the O2 sensors will pick up on that. In that case, you might as well get a test pipe with anti-foulers.

To quote our friends at <a href="https://forums.audiworld.com/9080/msgs/279215.phtml">034 Motorsports</a>:
In regards to your flow question, a 400 cpi cat will typically add 'around' 2psi back pressure (I'm being VERY liberal in my numbers here...) where as a 300 cpi will drop that down to 1-1.5ish psi back pressure. With our 200cpi cats I have a customer who's measured .5psi backpressure in a domesitic V8 application...he didn't get anything better with the 100cpi unit from another vendor.

To be completely honest with you, your catalytic converter is NOT the big performance robbing piece of equipment everyone thinks it is. The first catalytic converters, in the late 70's early 80's were a 'bead' style desgin. The exhaust gasses were forced to move over a bed of beads and it was VERY restrictive. This is how catalytic converters got the bad rap for being so restrictive. Once everyone moved to the honey-comb ceramic design, with it's long channels that follow the path of exhaust flow, the performance drop became VERY small. To the point, that honestly, a cat _shouldn't_ be considered the worst offender in a system. Baffled mufflers and louvered resonators cause more performance drop then your cat. Having said that, however, in performance applications where one is pushing the motor some gains can be had by replacing the cat with a higher-flowing unit.

In our research we determined that the cost increase of going with anything lower then 200cpi wasn't at all reflected in a performance gain worth the money spent. I'm not talking 'average consumer' here...I'm talking about it not being worth it even for guys who are spending GOBS of money on race vehicles.&lt;/i&gt;

 

interesting...thanks Roger.