Just got Flowmaster!

Hutch · June 16, 2002

Ok, Just had a 70 Series (524703) installed. It's dual in/single out. It's way too loud inside the truck. Yes, sounds great outside, but too much resonance inside.....very "boomy" and gives me a headache. Now what? I hate to go back and tell them just to put my original back on!

Any ideas?

Thanks,

Hutch

Shaners · June 16, 2002

I thought the 70 series was the quietest muffler that Flowmaster makes. I wonder if you have a leak somewhere, or a loose hanger.?! Good luck... ???

Frank S · June 17, 2002

I can't hardly believe that you have a 70 series and it's too loud inside unless it's turned down underneath the truck with no pipe extending out of the back.If this is the case have a pipe run out the back or side of your truck because the bed causes an echo.

I have a 40 series on my truck and my brother has a 40 series on his Z71,both of which are turned underneath and neither of them are noticeable under acceleration if you have the radio so much as halfway turned up.

They may have mistakingly put the wrong one on your truck because a 70 series is barely more audible than a stock muffler.

gmcjoe · June 17, 2002

Ok, Just had a 70 Series (524703) installed. It's dual in/single out. It's way too loud inside the truck. Yes, sounds great outside, but too much resonance inside.....very "boomy" and gives me a headache. Now what? I hate to go back and tell them just to put my original back on!

Any ideas?

Thanks,

Hutch

Do you have a Tahoe/Yukon or a pickup? I can see how the resonance is worse in the SUV line. I have the 40 on my ext cab Sierra, and the only real resonance comes in around 2K RPM.

Maybe the installed the muffler too close to the front of he vehicle?

Hutch · June 17, 2002

This is on an '02 2500HD Crew Cab. The new muffler (model #524703) is right where the old one was and I'm using the stock tailpipe which exits out the side behind the right wheel. The resonance is very "boomy" in the cab between 1500 and 2000 RPM. It's terrible driving around town. Once I'm at cruising speed on a flat highway it's fine, but if I press down on the gas to maintain speed up an incline, here comes the resonance again! I can only imagine what it will be like pulling a trailer.

Does the resonating sound come from the muffler directly or does it come from the end of the tailpipe?

This may sound silly, but could some of the problem be that I'm dumping 2 large pipes from a 496cc engine into that one muffler?

What about other mufflers with better flow than the stock but not considered "performance" mufflers? I've heard about the Walker Quietflow, anyone have experience with this?

Thanks for the help, Guys, I hate to go back to stock!

Hutch

SteveSierra · June 17, 2002

I had true dual 40 series Flows on my 2500HD for about 2 weeks before I changed em out for some Turbo mufflers. The Turbo's are MUCH better. Nice and deep outside, very very little interior resonance. The 40's resonated so bad in the cab on my truck. When I would go up this long hill on my way home everyday, it would create this helicopter rotor wah wah noise that absolutely stunk. I live in a very hilly area and the drone and wah wah noise was commonplace everyday. I liked em for the first couple days, sounded cool, but after that, all they did was give me a headache. They're actually still sitting in my garage. Don't know why, I'll never have em on my truck again.

CMNTMXR81 · June 17, 2002

If you simply have it in place of the stock "muffler of death" it is still mixing both exhaust lines in the muffler and then mixing again at the Y-Pipe that is after the muffler exit. This is where your resonance is coming from. My suggestion would be to A) buy two individual mufflers and B) eliminate the stock y-pipe and have each line come out on their own. A welded in "balance" tube between the lines before the muffler probably wouldn't hurt either.

My Magnaflow's give off quite a bit of resonance too, but that's cause it all funnels into the Y-pipe after the mufflers.

Hutch · June 17, 2002

Steve,

What "Turbo" mufflers are you referring to? I would be interested in this option.

CMNTMXR81,

The 70 Series is a dual in/single out so I don't have a "Y" after the muffler anymore (they left that connected to my original muffler). But you're correct, both pipes are mixing into one muffler.

Hutch

chane · June 18, 2002

In response to your last post, here is a reply I recieved via email from Dave Cooper (aka Vette Hauler) who posted that his flowmaster setup had good results w/part #530504.

Email:

"I got it from 21st Century Exhaust at 1-800-276-6399. They are a Flowmaster

outlet. Part number is 530504.

It slipped right onto the factory duals and by cutting and rotating the

upper elbow on the rear "Y", I was able to utilize the factory stainless

system. My researched showed the single 3.5" out flows dual 2.5". The set-up

sounds GREAT! I plan on polishing the tail pipe one of these days to give it

a custom look, but right now we're in the middle of race season.

Later,

Dave"

His original post on GMTC:

"The factory 3" dual system back to the muffler would be hard to beat. I left in in place and installed Flowmaster's new dual 3" in's with dual 2.5"s out. By cutting the outside section of the rear "Y" close to the old muffler and then close to the "Y" and flipping it over, I was able to use all of the original SS tubing. The dual 2.5" out of the muffler were swelled out on the ends to match the 3" and welded in place. I still have the 2'5" openings at the muffler exit which is required to keep from loosing your lower end torque. The set-up looks factory and sounds GREAT! Nice and mellow at crusing speeds, but get out of the way when passing gear kicks in.

Total cost; Muffler $105.00 w/shipping, installation $15.00"

Located:

http://www.gm-trucks.com/cgi-bin....+hauler

dougsster · July 7, 2002

I would have to say i have the same result. Tremendously loud inside the cab at 1800 - 2200 rpm, right in my cruising range. I havent had time to go back and talk to shop that installed it yet. I thought the noise would improve when i added my shell but no reduction in noise. I have it plumbed out right in the same location as stock.

Dougsster

gandolphxx · July 7, 2002

I have the Magnaflow 12590 - dual 3" in and single 3" out, muffler handles the balance - nice sound, not bad in the truck.

Lil-Trkr · November 8, 2010

I drive a '08 GMC 2500HD with the 6.0L engine. Its an extended cab with a 8 foot box. I use the truck to pull a 28' fifth-wheel that has one slide.

Wanting more power I installed a K&N Performance Air System, #63-3067. I right away noticed much more pulling power but wanting more I decided to go to a Cat back exhaust system. I ordered a Flowmaster 12590 muffler. It has single 3" in and dual 3" out. I found a local exhaust shop who will install my muffler along with custom bent 3" aluminized steel pipes. He quoted me under $200 for the job so as soon as the muffler arrives I'll have it installed. I'll post on how it sounds and how, if any, change to the performance in my truck...