I need a new muffler on my 89 305 TPI. A guy is parting out his 91 RS 305 TBI and offered to sell me his Magnaflow catback. Does anyone know off-hand before I go digging if this catback is interchangable with my 89?

 

The 87-92 TBI cars came with 2 1/4 in pipe ewerywere, smallest diameter for TPI cars was 2.5in. TPI intermediate pipe should be 2 3/4 in.

 

Not in '91-'92. Single cat 305 TPI got the small exhaust, same as TBI.

But, in the OP's case, it might be a downgrade. If the I-pipe and muffler inlet are 3", then the only issue will be the connection to the cat.

Only way to know is to check out exactly what he's got.

 

I never saw a 91-92 305TPI with single cat, though I have seen many but not all. They all have dual cat with aprox 2 3/4 to 3in intermediate pipe same exact as the 350TPI.

In the OP's case the intermediate pipe fitting/inlet of the 91RS muffler, will be smaller then his 89TPI intermediate pipe.

Yes definally mesure the intermediate pipe.