[Sirrotica]

Almost all bending machines used in a muffler shop don't come with 3 inch dies, that is the major reason they try to talk you out of 3 inch, is because they have no capacity to bend that size pipe.

The dies to go up to 3 inch used to be about $400 back in the 70s, so think currently they would be double that roughly. Factor in how many times they would be used to bend 3 inch pipe and it becomes pretty obvious why few muffler shops recommend 3 inch exhaust. The investment would never pay for the upgrade to the 3 inch dies, or if it ever did it would be quite far down the road.

Having worked at a muffler shop in the mid 70s I heard all the salesmanship excuses as to why your hot rod would do better with 2 1/4 or 2 1/2 inch pipes.

FWIW, The middle signature pic shows my 67 GTO dirt car, in the rules we were required to run cast iron exhaust on the cars. I substituted a set of RA III manifolds and ran the stock GTO head pipes, of course no mufflers. Engine was a 400 with an 068 camshaft in it.

In the middle of the season I wanted to see if opening up the exhaust would produce any more power. I was working at the muffler shop and we had no 3 inch pipe so instead I cut the ends off of 3 driveshafts to get 3 inch tubing. Because I couldn't bend it because of no dies I mitered all the corners, and welded the pipes back together to make the bends. 2, 90 degree off the manifolds and a slight kickout to go around the vacuum modulator. I terminated the exhaust just short of the rear axle. Even though I used short 2 inch sections of 2 1/4 inch pipe off of the manifolds into the 3 inch I was rewarded with feeling seat of the pants performance increases. 3 inch wasn't at all common back in those times, 2 1/2 was as big as anyone was using. 3 inch will help any engine, even a mostly stock 400 with a factory 068 camshaft and cast manifolds. I won 4 features that year after switching the exhaust to 3 inch.