: 425 exhaust

03-15-06, 07:56 PM
I was wondering if anybody has purshased a dual exhaust kit for a 77 Fleetwood, or is this a muffler shop only job?

03-15-06, 08:16 PM
muffler shop job most likely.

Go with 2.5" pipe, that is all that is needed for low 11's, so you don't need to go fatter (which drives up costs). Mandrel bent is a must. You can buy mandrel bent bends at Summitracing.com, and have a shop do the work using them.

I recommend the Dr. Gas X Pipe crossover. Every dyno run I have seen on it has shown good worthy gains, 5-25 lb/ft torque across the whole powerband on average. If you are doing the work of an exhaust, it is worth it.

03-17-06, 05:21 AM
I'm not sure I'd go bigger than 2.25" mandrel bent pipe on a stock or mild 425. Anything, and I do mean ANYTHING would be better than the stock tiny single exhaust with the bead-catalyst convertor.

Muffler shop only.

03-17-06, 06:28 PM
I agree, 2.5" is probably overkill, if it is good for low 11's on a 473 CID motor, I don't think the 425 will ever make use of it. In reality, if you need costs down, or space is tight and you don't want to deal with the trans crossmember, then go with a 3in single, that would do nicely too.

03-17-06, 08:51 PM
The problem I had with going to duals on my '79 Deville is that there is only one "hump" in the transmission crossmember, so the other side has to go under it to clear. And if the pipe isn't squeezed a bit, it will bottom out over large bumps. I bought a transmission crossmember from a '95 Caprice that has the dual "humps" to fix that problem.