Ben...good thread and topic here. My feelings are you would need to be outflowing the catalytic.

Say it can effectively pass 100 CFM and the car in question can push 120 CFM. If I were to look into it, I'd want a little extra capacity.

Simple...If you increase the power, then you increase the pipe size. That is the reason why Random offers two sizes for the GTP: 2.5" and 3.0" Since he runs a V-8, my friend used two Random cat'* with a custom dual exhaust for his F-Body Camaro.

So engine output has nothing to do with the efficiency of the converter, and it'* all based on displacement? Interesting.

So I feel safe in coming to the conclusion that a Magnaflow 91000 series is ideal for NA 3800s Series 1,2, and 3. What can we assume about L67s?

Efficiency of the cat still matters!!! What I meant is that if you have a mild to mid modded car, the use the high flow cat with the 2.5" pipe. For highly modded cars, use the same high flow cat, but with a larger pipe size.

I guess I should rephrase that....

The body size/style of the converter you use is determined by effective displacement, while the input/output pipe size is determined by engine output. Is this correct?

just thought id toss another coverter option in here, i actually have one of these on mine:
http://cgi.ebay.com/ebaymotors/3-Cat...40563226QQrdZ1

the Magnaflow converter i bought originally would not fit in the small opening for my cat, and it now belongs to harofreak00.

i honestly didnt notice too much difference with the cat, a little beefier sound, and perhaps some smoother power delivery.

my DP is actually a size between 2.5 and 3 inch, and to top it off, its actually double-walled pipe, so the actual pipe size is about 2.5, but the outside wall is closer to 3-inch, hence my converter choice.

I know my car isnt a Bonnie, but this is another cat option, that happens to be cheaper than the Magnaflow, and is also available in different sizes and w/ w/out and 02 bung built in.

BINGO!!!

It looks like a good quality converter and also made of stainless steel; looks like a great buy for the money. It is very similar in looks to the universal converter sold by Random Technology.

ssei1995 - Was that for me or for LittleHoov?

LittleHoov - Glad you posted. I don't want this thread to be dominated by Magnaflow if there are other legitimate options out there. Hopefully there are other people who find this thread and weigh in with their opinions. This knowledge needs to be available to everyone.

Wet noodle slap...