I am wanting to put Flowmasters on my F350 with a EFI 460. My Exhaust man recommended a single 3.5" pipe instead of dual. He said it will give me better fuel milage, like four more miles a gallon, and better performance. Please enlighten me!

 

Maybe he was referring to better mileage over the stock-sized single pipe, but I can't see how this would give you better mileage than duals (unless the duals were made using very small diameter pipe.)

To guesstimate, I would think a single 3.5" pipe would flow about the same as dual 2.25" pipes, but I may be off by a bit. (You'd still have the issue of the restriction at the Y-pipe.) He's probably more comfortable with sticking with the larger-diameter single pipe, as it's the legal means of improving your exhaust. (And, yes, a single 3.5" would give you more power and better economy over the stock-sized single exhaust.)

 

Thank you, I think I am going to go with the single 3.5", I'm not so worried about cosmetic appearance, I want power and economy. What series Flowmaster works best with that? He said something about the Big Block Flowmaster, and is $425 too much for the job?

 

$425.00 may be getting up there. What, exactly, is he proposing to do? If he is going to replace your catalytic converter with a high-flow model, run the 3.5" pipe out of it and into a Flowmaster, and out of the Flowmaster with a single tailpipe, then $425.00 is probably in the ballpark if he does quality work and uses quality pipe, although it may be pushing it. For doing less, I would say that it's pushing more and more on the high side. You may check with some other shops. If there aren't many in town, or few are willing to do custom work, then you may be stuck. Figure on the muffler and converter representing around $175.00 of the cost, with the rest being labor and pipe. (For the record, Summit Racing lists a 3" cat-back system for '88-'92 F250/350's with the Flowmaster 3" Big Block Series muffler for $199.95.) And, as another point of comparison, I just had a local shop fabricate a 3" pipe from the cat back, install it with a single 3" in / dual 2.5" out Flowmaster 50-series muffler, and fabricate and install two 2.5" tailpipes to cross over the rear axle and exit out of either side for $277.00 total. Definitely more labor involved than with a single tailpipe, for much less than $425.00. Again, though, local supply and demand may be a factor for you to consider. Good luck!

 

He is assuming I have a high flow cat, so he is only replacing from the cat back. With single 3.5" and Big Block Flowmaster. He is using luminized tubing and bending to fit and come out behind the rear passenger tire. Thanks alot for the info, I greatly appreciate it.

 

Sure thing..... I hope it helped. I would guess, with your scenario, that the muffler would be around $75.00 to $85.00 of the cost wholesale (and up to $135.00 retail) so the rest would be pipe and labor ($340.00 to $350.00 considering the wholesale cost of the muffler). Aluminized pipe is preferable to standard steel (which rusts out quicker), but your shop won't be needing to do a whole lot of work with just one pipe in and one pipe out. Shop around just for fun, and go ahead with the job once you find the best deal. Your truck will definitely sound better, and you should see improvements in both power and fuel economy.