Subject vehicle is a 2000 Chevy one ton van cutaway chassis motorhome with 15,500 miles on it. It's 28 feet long with a WB of approx 15 ft. Engine is 7.4L. Exhaust comes in 3" OD pipes from each cylinder bank, through cats, to a Y into a single 3" OD that runs several inches then enters the muffler (7"x9" by 24" long), then proceeds a considerable distance through 2.5" OD piping until behind the axle where it goes through another muffler/resonator (4" by 20" long) then out the tail pipe. I am looking at possibly getting better power/fuel economy if I free up the flow (without making a lot of noise though).
1) How restrictive is the stock muffler (the big one just behind the Y)?
2) How restrictive is the resonator (the little one behind the axle)?
3) How restrictive is the 2.5" pipe behind the muffler?
Or perhaps better question is why did they go from 3" pipe to 2.5" pipe. Shouldn't it be the same all the way? In fact, I thought the pipes should be maybe 2.5" to the Y, then step up to 3". They have essentially the reverse. OTOH, The 2.5" pipe may not be a problem, assuming the hot exhaust gasses cool enough after they work their way through the muffler that they have condensed and take up less space. The Banks system is a cat back and goes 3" piping all the way, which suggests that the 2.5 pipe is restrictive.
But maybe the big muffler is the main restriction (stock mufflers typically are restrictive) and that the resonator is more likely a straight through with sound absorbing perforations around the inner tube. In this case it would be a lot easier to just pop a new muffler in the existing piping, but don't want to do that unless it is going to help.
The other exhaust problem is the big muffler does not have much ground clearance and likely will get bashed off someday. I am considering taking to a muffler shop to have it turned so it stick upward more to get more ground clearance, but on the other hand, it might be easier to put an aftermarket muffler in it's place to get the ground clearance and improve exhaust flow for more power. Will this work?
Should I just turn the stock muffler or upgrade? Would like to keep cost relatively low, so just replacing the muffer is cheapest. Prefer not going all new piping cat back, but wonder what that smaller pipe is doing. I guess the 3" piping up front could be considered a sort-of resonator.
1) How restrictive is the stock muffler (the big one just behind the Y)?
2) How restrictive is the resonator (the little one behind the axle)?
3) How restrictive is the 2.5" pipe behind the muffler?
Or perhaps better question is why did they go from 3" pipe to 2.5" pipe. Shouldn't it be the same all the way? In fact, I thought the pipes should be maybe 2.5" to the Y, then step up to 3". They have essentially the reverse. OTOH, The 2.5" pipe may not be a problem, assuming the hot exhaust gasses cool enough after they work their way through the muffler that they have condensed and take up less space. The Banks system is a cat back and goes 3" piping all the way, which suggests that the 2.5 pipe is restrictive.
But maybe the big muffler is the main restriction (stock mufflers typically are restrictive) and that the resonator is more likely a straight through with sound absorbing perforations around the inner tube. In this case it would be a lot easier to just pop a new muffler in the existing piping, but don't want to do that unless it is going to help.
The other exhaust problem is the big muffler does not have much ground clearance and likely will get bashed off someday. I am considering taking to a muffler shop to have it turned so it stick upward more to get more ground clearance, but on the other hand, it might be easier to put an aftermarket muffler in it's place to get the ground clearance and improve exhaust flow for more power. Will this work?
Should I just turn the stock muffler or upgrade? Would like to keep cost relatively low, so just replacing the muffer is cheapest. Prefer not going all new piping cat back, but wonder what that smaller pipe is doing. I guess the 3" piping up front could be considered a sort-of resonator.
