Originally Posted by fredtoast
I've heard this before, but when I look inside a cat I can't believe that it wouldn't effect the flow. Of course I've never used a highflow cat or compared them on a dyno, so my opinion doesn't mean that much. The main reason that I didn't get a high flow cat was the cost. They are very expensive, and don't last very long. So I replaced mine with a small glasspack ($25 plus labor to weld on flanges). Luckily no emissions tests here in Tennessee. My stock cat was all f***ed up. I had been running very rich (and boosted) for 30K miles. I was already getting code 67 when I had it replaced.
I must take back a bit of my statements.
At the time I did the dynoing with the hi flow cat and test pipe, I had a JDM DC 4-1 header. No change in power, noise, nothing.
Well....
I put my test pipe back on last night. I had been getting code 67's: One week it would be on, then off the next week. This happened for two months, every saturday it would go on/off! Weird.
Anyways, I now have a toda 4-2-1 and a mugen intake.
Well, um, hrm... my car is MUCH louder ESPECIALLY in vtec now. It screams, growls, snarls. I'm confused. The power is a bit different, I can feel a change, i'm not sure for better or worse, just different.
So. I have no idea what I say about test pipes and cats anylonger.
I refuse to believe that with one header there is no difference, yet with a different header and intake the test pipe would behave so differently.
Me - stumped....