I totally agree that a high flow cat will in fact flow more than a stock cat.

I totally agree that when the stock cat gets clogged up with soot (which it does) then it's time for it to go, and a high-flow unit is cheaper than a stock replacement.

I totally agree that an ITR motor, or GSR motor that has been upgraded to at least ITR specs, will benefit from a high flow cat.

I totally agree that when an exhaust system is upgraded to 2.5" the cat should be as well, and high flow is the way to go.

BUT...

The plain and simple fact is that a GSR with a bolt-on intake, header and exhaust (and a non-clogged stock cat) will put about 155 hp to the wheel. Adding a high flow cat to the mix will produce...surprise surprise, about 155 hp to the wheel. You can debate the flow numbers till you're blue in the face but it doesn't change that fact.

 

I would indeed be surprised, but do you have a graph that actually shows zero gains from swaping out a stock cat for a Carsound on a mildly-modified GS-R? I'm actually very interested in seeing one, because finding a direct back-to-back comparision with the cat as the only variable is not an easy task. Most people either retain the stock cat or swap header and cat at the same time, making it difficult to break down the gains. Something like this would make an interesting test if someone could locate inexpensive dyno time.

 

Unfortunately the dyno plot which I used to make as my point of reference for the difference between a stock cat when clogged and a new high-flow unit was on g-speed.com which has been taken down. The car put down a number in the 140s with the old stock cat, and then with a high-flow unit it put down 155 hp. THIS IS BECAUSE THE STOCK CAT WAS CLOGGED.

There are a bazillion dyno graphs out there of GSRs with stock cats and i/h/e, here are a few examples. Variances of +/- 5 whp from car to car aren't really indicative of any trend.

 

Yes, dynos of GS-R's with bolt-ons are plentiful, but dynos of OEM cats vs. Caarsounds are unfortunately not.

 

well i'm going to be putting a carsound cat on my GSR soon and i already dynoed it. 148.8 at the wheels. i might do a dyno after to see the results but i dont know if i feel like spending that much money. 96 GSR with 100k on it so i assume the high flow cat would help out considerably

 

I had always thought that the emmission equipment was supposed to last the life of the car. I have driven many >200k mile vehicles with the original cat with no apparent degradation of performance. As an aside, it is against the law to remove and replace your catalytic convertor if it is still working. I think the point that Fats is making is that it does not matter if a high flow cat or test pipe is able to flow more, if this is not limiting the flow the engine(air pump, if you will) is able to pass through. I have always had a philosphy of upgrading parts when I replace because of failure or wear, but if the part is not worn or impeding performance, I would just spend the money on good beer:cheers:

 

As far as I know it's perfectly legal to replace your catalytic converter once the original unit racks up 50 thousand miles. Cats are a wear item and eventually their insides get all caked up with grime that's been cooked on to the matrix over time. It's hot as hell inside there and all of the carbon particles and such get like, baked onto the inside surfaces. Eventually this coating gets thicker and eventually chokes off the flow through the cat.