Join Date: Sep 1999
Location: Des Moines, IA
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I installed Borla cat-backs on my 90 4.2 and my 95 2.5. It seemed to help the highway performance of the 2.5, but I didn't notice much difference on the 4.2. I think it's because the 4.2 has a 2" factory exhaust pipe and cat, on the 2.5 they are 2.25", allowing the 2.5 to take better advantage of the lower restriction of the Borla. After instaling the Borla on the 4.2, highway mpg is 18, I don't know what it was before.
I had to some modifing to get the large exhaust tip to clear the hitch on the 95. And since the inlet on the Borla muffler is 2.25", I had to buy an adapter for the 4.2's 2" exhaust. I paid $200 each for mine when carparts.com had 1/3 off, and I think they were worth $200.
Before you buy anything, try searching the archives. A lot of people seem to like Flowmaster mufflers and they are a lot less expensive than Borlas.