This post is going to be full of ifs, buts, caveats, and an apology.
To sum up what I'd found so far:
PH2 oval cat 187cfm
PH1 twin cat 132cfm
2.5" ID pipe 380cfm
all at 10" H2O depression. Something didn't make sense. I did some sums to try and work out the backpressure that each cat would produce, no promises, but this is my best guess:
PH2 oval cat 0.6psi
PH1 twin cat 1.3psi
2.5" ID pipe 0.2psi
none of them much to write home about.
Anyway, a bit of internet research led me to a Magnaflow 59926 200 cell metallic cat. Do a search it comes quite well rated (and currently very cheap on ebay), and with various quoted CFM from impressive to unbelievable. It came in a sexy box with a picture of a Corvette and 'racing legend Mario Andretti' on it. It had to be the dogs danglies. Now to put this in context, this cat has 2.5"ID ends just like the straight pipe, so much bigger diameter than the PH2 cat exit, and doesn't have the curved inlet pipe, just the bare cat. I'd optimistically estimated about 300cfm, so it was a bit disappointing to only get 215... (about 0.5psi pressure drop). At this point I'm ready to hurl the shiney piece of shite right back at the vendor. I then spent a couple of evenings on the net trying to see if I anyone else got the same result. Surprisingly there is very little about flow bench testing of cats, but the nearest I got was a similar result from a 300 cell metallic cat of the same size, the same tester found a 200 cell cat to be more like the 300cfm I expected. More head scratching and looking at larger magnaflow cats and 100 cell cats has followed. I still don't know what to do.
Anyway, the 182 cat turned up in the post today, this was going to sort the men from the boys, after all, it's known to be the mutts nuts. Again, time for another caveat, this wasn't a new cat, but I could shine a light through it and it's not blown or anything. The exit is also quite nasty, with a reverse lip and small pipe. However, it's a 200 cell jobbie so it'll rock. 110CFM (1.8psi) WTF!!!! Lets get this right, the best cat flows the worst on my bench, and the worst cat flows the best?? I must be going nuts...
I kicked around the room for a few minutes trying to make sense of things, the only thing that made any sense was that the I'd somehow stuffed up measuring the PH2 cat. I'd looked in the back of the cat and seen the honeycomb, and dangled a camera down the front and seen it from the other side. Just before putting it back on the flow bench I dangled my cliosport.net torch on a string back down inside the cat to look for light from the back. Hang on, I can see the whole damn torch.... It appears than my cat is just a bit of mesh at the back end and it's innards had disappeared in a previous life. I've put it through 2 MOTs like that (OBD1, not OBD11), but still. How it looked like it had lit up I don't know, I watched it, so maybe it was just coming off cold start? (not temp gauge in my car) - apologies Montana. Funny how in the cold hard light of day you suddenly notice things like how light the cat was, and how tinny it sounded....
I guess I need to test a PH2 with some innards to complete the set.
Anyway, I now really don't know what to do, clearly my car passed the MOT without a cat, I don't want to refit my PH2 as it's already been repaired and has a new crack forming (which is why I got the PH1 twin cat in the first place). I could get a decat and use that (although I feel I ought to use a cat with unleaded fuel), of fit the magnaflow into it, or sort out a 100cell job that should match the decat for flow... too many choices. I think the PH1 will go on for now whilst I think about it.
Apologies to all fro the confusion and long post, but I hope it's entertained
