I have a non-Attitude hot juice equipped D/A. I still have the stock 3.5" exhaust system on an 03 LB7 - no cat converter.


I originally cut out the stock muffler and replaced it with a straight pipe (two 45* mandrel bent sections, so there was no restriction whatsoever). I felt that I actually lost some power with the straight pipe, and the EGT's barely dropped if it all. I could get 1400* at level 4 in 3rd and 4th gear. I also did NOT like the sound, it was too loud at full throttle and sounded kind of "farty".


I ordered the big Flowmaster muffler (not the one that says it's the Duramax replacement, but the longer one. I think it's 25" v.s. 28"). The lost performance came back and then some, I definitely feel like I gained a few HP with this muffler. The EGT's are about the same, maybe 1425* with the same level 4 in 3rd and 4th gear. The sound is almost as quiet as the stock muffler, almost too quiet. I like it, very stealthy.


Anyone else out there have any experince with the stock exhuast system and a Flowmaster muffler?

I think your SOP meter needs recalabratied. Muffler no muffler, aftermarket, stock, never noticed anything other than lower EGT's and more noise. *Maybe* a bit less turbo lag but that may have been in my head.


Even flowmasters marketing BS about using pusles of the exhaust to draw the next out so even though they are some of the worse cfm flowing perf mufflers out there they are still top performers goes out the window with a turbo. JMO


Tomac ran one for awhile IIRC

I love my Flowmaster. Great sound. Performance seems great to me. Stock exhaust otherwise.


I dynoed 494hp with 933 lbs of torque through the muffler. See sig for mods.


Edited by: gmccall

gmccall, which flowmaster do you have? 25" or 28", or do you know the part number?

I have the flowmaster listed for the Duramax on Flowmasters website. Don't know the length. The muffler shop had to use an extra piece of 3 1/2" pipe because I had them cut extra sections to save my original muffler.

When I started running nitrous I went with a 4" MBRP system to deal with the extra air the motor had to exhale

I still like the sound of the flowmaster muffler on the stock exhaust over the MBPR.

The part number for the longer muffler is 53553. I got this part number from a post by mtomac a long time ago... Thanks Mike!http://www.dieselplace.com/forum/smileys/hihi.gif The part number of the shorter muffler (Flowmaster's specified "replacement") is 53551.


When I first installed my Flowmaster, I was disappointed with the sound as I thought that it was too quiethttp://www.dieselplace.com/forum/smileys/smiley19.gif. Now a few thousand miles (and a lot of black smoke) later, I now love the sound and the "resonance" that I hear at power!http://www.dieselplace.com/forum/smileys/smiley32.gif

Where did you guys get yours from, and how much did you pay? On flowmasters website its list price is $195. Thats a lot of money for just a muffler IMO.

I ordered mine from Summit online, I think it was $120 or so

www.summitracing.com (http://www.summitracing.com)


go to "Online Store", then "exhaust", then "mufflers and resonators", then "flowmaster 50 series big block mufflers" and choose either FLO-953558 or FLO-53553


$125.95


The 553 muffler is the one I got, it is slightly longer than the 558 muffler. The 558 is what Flowmaster calls the Duramax replacement.

Can't get much easier than that.


have to appreciate this web site http://www.dieselplace.com/forum/smileys/smiley1.gif

I have Flowmaster race mufflers for sale!http://www.dieselplace.com/forum/smileys/smiley4.gif


http://dieselplace.com/forum/forum_posts.asp?TID=17161&P (http://dieselplace.com/forum/forum_posts.asp?TID=17161&PN=1) N=1

I got my Flowmaster installed at the local shop for $150.00 out the door. He had to order the muffler "special" as he had never seen, nor installed, a Flowmaster "that big"http://www.dieselplace.com/forum/smileys/smiley3.gif


He also stated that he was glad that I had done the research, because he would never had known what could've fit!


(All the thanks goes to mtomac and Dieselplace.com)http://www.dieselplace.com/forum/smileys/smiley32.gif