Mine had a stock 3.0” necked down to a 2.5” muffler, totally un@cceptable. I took a large (3.5” I think) pipe, shoved it through the cast flange and with a ball pien hammer, formed the pipe fl@nge to fit the tapered flange(easy), so now I have a 3.5” exhaust pipe hooked to stock 4” Cummins muffler(kid reject) so it is quieter now. If you ever have the head off, it will take a .090” reduction.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires. '47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle. '54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed. '55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
