You can quickly spot a catalyst 308 by the presence of the vented rear valance. The catalysts go where the mufflers used to, and the muffler goes behind the catalysts.
As a side note, people often confuse -- or obfuscate -- horsepower ratings for the carbureted catalyst 308s. Many (well, actually most) people selling them tend to claim 240hp like the non-cat cars, but it has been well documented since day one that the catalyst carb 308s were rated at 205 hp.
Replacing the cats with straight pipes will definitely help power. Better yet, spring for a pair of high-flow cats -- they claim to have 90%-95% the flow of straight pipes. Clean, legal, AND high performance!
If you have a pair of perfectly good cats, however, don't gut them; they are REALLY expensive, and there are owners who need them whose own cats are partially blocked from melting/fire/heat.
There are probably half a dozen readily available aftermarket exhausts for the 308; I don't know to what extent any of them improve flow over the stock system, and at what expense to noise (the 308 is already pretty loud!)..
I am pretty sure the catalyst 308s have different cam profiles than the non-cat cars, and that the difference in lift/duration/timing is significant. But I defer to someone more knowledgable than myself . . .
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