Any other recommendations on a high flow cat for a mildly modded motor?
"high flow cats" is a common marketing term and I would argue that the factory H pipe is hard to beat. In other words, I would save your money and just stay with stock.
Here is what Kenne Bell has to say about "high flow" cats:
"MUSTANG CATALYTIC CONVERTERS.
SHOULD I REMOVE, GUT OR REPLACE WITH HI-FLO CATS?
In our opinion NO, NO and NO! Removing the cats is illegal in all 50 States as doing so pollutes our environment. Ever close your garage doors and smell exhaust without cats. You won’t like it. All because some “think” there’s big HP gains in them.
Most important, we’ve seen “0” HP gain even at 775RWHP (387.5HP per cat) with our own ‘05 Mustang test car. See “Header, Cat, X Pipe & Exhaust Tests” in Ford Tech section.
EARL’S AUTOMOTIVE
Also “0” HP (stock vs. gutted) Earl’s Kenne Bell supercharged 700HP “First Cobra in the 9’s.”
ST MOTORSPORTS
Ran back to back tests at 600HP and 700HP. Gutted cats vs. stock was “0” HP on their ‘06 Mustang.
KARL’S EAST COAST SPEED
827HP Shelby. Headers, 3” x pipe and no cats. 2HP!
“Hi Flo” cats? Really? Show us your flow tests. HP tests. Our 1000HP air flow bench reads 407 cfm stock and 549 cfm gutted and no HP gain at 775RWHP. Besides turning on your engine light, gutting or removing cats has another drawback – the exhaust gets raspy (noisy).
Still want to gut those cats – or buy some “Hi Flo’s?” We welcome any magazine to come to Kenne Bell and test back to back on any Mustang – ours or theirs. We’ll hook up the data logger and record back pressure, air flow, temperature, etc. and, of course, HP with and without cats. All at no cost – IF it’s printed in a magazine. And we promise the tests won’t be skewed by changing ignition timing, AF ratio, pulley (boost), x pipe, headers, exhaust etc. to increase HP. You know how that can go. “Cats and a tune,” Cats and a pulley,” “Cats and cat back . . . “ Just a typical Kenne Bell back to back cat test."