I recently installed a Magnaflow #12579 muffler on my stock exhaust and a UPD intake. With the muffler, I only noticed a stronger pull in the upper rpm ranges. With the UPD, I felt power everywhere (seat of the pants anyway).

Best ET before UPD and Magnaflow was 15.342 @ 88.36 mph with a 2.154 60' time.

I went out to HRP last night to take advantage of the cool weather. I knew I would go about 3 tenths faster due to the cooler weather (41 degrees vs. 65 degrees), but I was pleased to get the following ET.

2.018 60' time on stock tires! <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
6.010 330'
9.432 1/8
72.38 mph
12.357 1000'
14.834 1/4
90.29 mph

That's a solid 2 tenths gain for the muffler and UPD air box. I still can't believe the 2.0 60' times. I mean, for an F-Body, this would be no sweat, but for a 5400 lb SUV on stock radials, that's haulin' in my book. Gotta love that Yank converter. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

The Magnaflow muffler is a really big one. It has a 5x11" body and is 30" long (about the same size as the stock muffler). Inside it has two side by side tubes that are straight through with no restrictions. This makes this particular Magnaflow muffler the quietest muffler around with the highest flow. I don't see how there could possibly be any back pressure.

As for noise, it's a little throatier than stock, but there's absolutely no hint of drone at all. I kept the stock y-collector flange unmodified to keep the factory 2 bolt flange intact and to avoid any possible warranty issues in the future. I chose the 3" in and 3" out configuration mainly because the 3" in and dual 2.5" design did not perfectly match the dual outlet on the stock muffler (at least in my case). Did any of you know that exhaust only comes out of one of the pipes on the stock Tahoe muffler? The other one is a dummy (used to cancel out sound). So really, the stock Tahoe muffler has a single 2.5" outlet, haha. I figured one in and one out was better than one in, two out, then merged to one again (to each his own though).

I lost no low end torque and gained power above 4000 rpms with the muffler swap. I got mine installed at Southwestern Muffler and Brake in NW Houston. Mike's Muffler shop is also a big Magnaflow dealer here. Frank's Supply is the regional warehouse that most muffler shops buy from. The retail on the #12579 muffler is around $150. Wholesale is around $98. The muffler shop will normally charge around $200 for this muffler installed. Much cheaper than an aftermarket cat back and you get a quieter, more free-flowing muffler along with it. I call it a win-win deal. Those who want loud and don't care as much about performance would probably want a Flowmaster or something like that. For stealth performance, you can't beat my setup.

Patrick

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Did any of you know that exhaust only comes out of one of the pipes on the stock Tahoe muffler? The other one is a dummy (used to cancel out sound). </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yeah, I knew one outlet is actually an inlet to a resonation chamber, I've seen one of the mufflers cut open. The Magnaflow I was looking at is also the big 5x11x30 one, it's dual outlets are 5 3/4" apart. I measured the dual outlets out of the OEM muffler and they are also 5 3/4" apart, I figured the would be pretty close to lining and the dual 2.5" outlets would allow for a little play room with the installation. I really like the quiet though, so I don't know if I'm going to do the swap.
Jim

 

Man, that is cookin' for a heavy *** BLING BLING mobile. <img border="0" alt="[pimp]" title="" src="graemlins/gr_pimp.gif" /> <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

I've seen Mustangs run slower than that at the track. <img border="0" alt="[evil]" title="" src="graemlins/gr_devil.gif" />

John

 

NICE RUNS!!! I wish I was in the 14's <img border="0" alt="[burn out]" title="" src="graemlins/gr_burnout.gif" />
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

patric g, you've got the same setup as my 02 silverado and those 2 mods, upd and magnaflow are exactly what I want to do to my truck next. How'd you know which magnaflow you'd need, and where'd you get it, price, instalation etc.? I want to leave my stock exhaust alone also, just want a little noise w/o getting too loud. Also there is the back pressure/loss of torque issue I keep hearing about, apparently not a problem with the magnaflows. Thanks in advance. Kyle.

 

Patrick G. Great times! I hope to get back in the 14's, Sacramento raceway opens back up on February 5th, I can't wait. You put on Magnaflow muffler #12579 on your stock pipe? Did they cut off the 'Y' that comes out of the stock Tahoe muffler? I just put a stock Tahoe muffler and 3" tailpipe on my Silverado and I love it. It's nice and quiet, and actually performs better than the 70 Series Flowmaster I was using. I was however thinking about doing what you did, keeping the stock pipe and putting on a Magnaflow muffler. Did you loose low end? I was going to put muffler #12588, it's a dual out muffler that has 2.5" pipes. They are the exact width apart as the factory 'Y', I was going to remove the stock muffler and put in that muffler still using the 'Y'. The 2.5" pipes would slip right in the 3" factory 'Y', just a thought. Do you have any drone or resonation? That's why I ended up going to a stock muffler, I figured the Tahoe's 3" setup would be better than the trucks 2.75" setup, so far I like alot. Again, great times! So for this being so long.
Jim

 

That's quicker than my Impala SS. for shame. <img border="0" alt="[cry]" title="" src="graemlins/gr_cry.gif" />
babyhauler

 

Well hell that's new track record! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />