marineusmc4

gotcha. so is the baffles inside rusting due to poor metal or is it an installation related issue such as poor/weaks welds at the muffler inlets/outlets? am i reading those percentages right, that those percentages are the amount the muffler allows to flow through it? such as something with a 82% flow, only allowing 82% of the exhaust entering the muffler to escape? cuz the Dunomax is showing 99% flow yet the magnaflow on the dyno comparison makes more power...im def thinking about switching to one of those now, prolly a magnaflow. btw, thats some good info for people picking a muffler based on dyno results

marineusmc4

also, does anyone know if the flowmaster muffler has had any improvements on design made in the last few years? i ask becuz that dyno sheet is from december of 2002.

Suburbazine

Flowmaster hasn't changed any of their designs at least in the past decade. It's not so much a baffle construction issue as it is that heat cycling + moisture weakens pretty much anything over time. Not having a baffle and being a straight-thru design keeps hold/cold pockets down and an even thermal spread.

The percentage numbers were calculated from a fixed CFM source thru a 2.5" open pipe vs. a muffler. I don't know what the supply CFM was but the percentage reflects how much CFM was able to exit the muffler, one muffler at a time.

This is Flowmaster's 40 Series baffle design:----------------------------------------------vs. a Dynomax Straight-Thru Design (Ultraflow):

black00chev

iTrader: (2)

While I cant speak for how long it was on before, but I bought my truck at the beginning of 07 and the weld on the back of muffler rusted out about 75% of the way around the muffler less than 3 years later. WAY too soon IMO. The case itself had a few rust spots but nothing that looked like it was all the way through.

marineusmc4

dont know if it makes a difference but the flowmaster pic u posted is of the 40 series delta flow. here is what i have, the original 40 series muffler. https://www.performancetrucks.net/fo..._mufflers1-png

gotcha. hey, is ur 1/8th mile time done in 4wd or 2wd?

SlowDude

iTrader: (4)

I ran a set of flows on a 1970 GTO with a 455 HO for 8 plus yrs and on two different K5 Blazers 4x4's with 383 and a 400 for years with no issues.. All were loud and non rusted but I kept my foot in it at all times. These were also of the late 80's and most of the 90's design so maybe metal used or construction has changed over the yrs. My 2003 1500HD, I chose the Magnaflow because it just sounded better plus I wasn't looking for the loudest anymore. Was told back then that with the change in the firing order of the LS platform, changed the sound characteristics of the Flowmasters. Up until then I was sold on Flows! .

726.0chevelle

iTrader: (17)

If you want a muffler that's going to last make sure its stainless steel. I had a dynomax start rusting out in 2 or 3 years now I only buy stainless.

black00chev

iTrader: (2)

4WD my friend

2WD just blows the tires off.

VegasJ

iTrader: (1)

40 series flowmaster here. Had one with pipes out the back when all was stock.

switched to just dumped before the axle - a lot of drone, read about restrictive blah blah - 2006 GMC Sierra crewcab 5.3L stock exhaust back to flowmaster super40 dumped before the axle - YouTube

added LT headers now 3" back, no cats - still some drone, but more flowmaster hollow poppy sound - GMC 5.3L Sierra CC w/LPP long tube headers - flowmaster super40 dumped @ axle - YouTube

switched to a Hooker AeroChamber dumped - sounded too straight-pipey - GMC 5.3L Sierra CC w/LPP LT headers - 3" Hooker Aerochamber dumped @ axle - YouTube

switched back to a 40-series but not dumped, turns out before passenger tire... (no vid yet)

and that's where I'm at now. I like it.

marineusmc4

gotcha. i have an 1/8th mile track 45 minutes from me that everyone goes to and a 1/4 mile track about an hour and some change away. have taken it to the track stock or modified yet. was thinking about doing the 8th mile in both 2 and 4wd to see if there is any difference. do u have the stock intake?

im with you. i like it loud but ive had loud pipes for so long that is sounds normal to me. but to everyone on here, to each their own, whatever you like and makes you happy is all that counts!