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Hi-Flow Cats Setup


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I know this topic has been discussed countless times before in various forums, but I'm going to post my experience here since all that information still did not give me a clear picture until i went and did it myself.


Basically, everything was great until I added a Lethal Performance X-pipe with hi-flow catalytic converters. These are the same cats found on the Magnaflow system, but the pipes are aluminized steel instead of stainless (saving me $150+). I was running the KR mufflers with an otherwise stock exhaust, which I still think is the best all around axle-back option for any 2005-2009 S197 Mustang, Shelby included. As many others have noted, once the hi-flow cats went on, the sound was stupid loud! My ears were bleeding at only 3,000 RPM. So I went on the hunt for a solution and here is what I found...


- 2007-09 OEM SVT GT500

Apparently these are the same muffler from the automatic version of the Mustang GT?! And the stockers on the manual version are louder?! Anyway, I didn't try these with the hi-flow cats so I can't speak to that configuration, but they are heavy and super quiet so they are not for me.


- Ford Racing Stingers (M-5230-5GT)

Didn't have these on my GT500, but I did have them for awhile on my 2006 Mustang GT. They sound like an exotic car. They are loud, they are deep, but they drone like a bitch. I couldn't take it anymore, so off they went. I'm quite sure they would be the same or worse on my GT500. And multiply that by a factor of 10, with hi-flow cats? Supposedly the M-5230-SGT has another baffle in it, which would reduce the drone and loudness a touch, but I determined I don't like the sound of Borla exhaust overall so I didn't bother with those.


- Ford Racing FR500S/KR (M-5230-S)

As noted above, these are painful to listen to with hi-flow cats. They are extremely shrill at high RPMs. However, on an otherwise stock exhaust, they kick ass. Deep and quiet at low RPMs and sing a loud song of ecstasy WOT. Not an ounce of drone anywhere, which is amazing for a straight-thru type muffler. Hands down the best axle-back setup for a stock exhaust.


- Borla Touring/Ford Racing (M-5230-SVT1)

I bought the Shelby Borla Touring catback system, but these are supposedly the same as the Ford Racing SVT1s but without the Ford Racing logo and you get the full catback system for the price of the Ford Racing mufflers alone. This is the same exhaust found on the 40th Anniversary GT500s and the Super Snakes. Surprisingly, these are very quiet, even with the hi-flow catted x. The sound is pretty good overall, but too quiet for what I wanted. Plus, they have a drone and regardless of how mild it is, I noticed it. At idle, they hum in a way that reminds me of a car that idles too high, even though the car is sitting at 800RPM. If I had to, I could live with this setup for everyday use, but compared to a Roush 427R, this exhaust setup sounds kinda weak.


- 2010 OEM SVT GT500

After reading countless online threads, I thought I had found the perfect solution. Unfortunately, they weren't. These mufflers look aggressive as hell on a '07-09 Mustang as the tips are 4" in diameter and stick out past the valence (due to the extended valence of the 2010 cars). They were simply too loud with the hi-flow catted x. Sounded much like a 70's bubba truck with straight pipes or glasspacks. I'm confident that on a an otherwise stock exhaust they would kick ass. No drone, quiet rumble at idle and loud at WOT.


- Ford Racing Bullitt (M-5230-GTB)

Again, thought these would be the answer, but they were a disappointment. They sound good on the Bullitt Mustang and weren't bad on my GT500 w/hi-flow cats, but I was surprised at how quiet they were at WOT on my car. No drone, deep idle, but WOT was too muffled for my taste. Figured the catted x would spice it up, but it didn't. This would be a great setup for someone who wants a slightly better than stock sound and doesn't care for the tone of the Borla exhaust kits.


- Ford Racing Shelby GT (M-5230-GTA)

And the winner is... these! I never would have guessed. These are standard mufflers on the Shelby GT and GT-H from '06-08. I figured they would be too loud. However, surprisingly, they have a good range of sound from quiet to loud (much broader sound range than the Bullits above). The exhaust note is deep, but at idle and at cruising speed you barely hear them. Partial and wide open throttle and these suckers sing loudly! Best of all, very little raspiness and sounds great with the windows up or down. For a loud, muscle-car sound with hi-flow cats and an X-pipe on a 2007-2009 Shelby GT500, these take the cake!

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All that being said, these items are now for sale in the Austin area...


These will fit any 2005-2009 Mustang GT/Shelby or 2007-2009 Shelby GT500:


2007 Ford Shelby GT500 Mufflers (OEM) Ford 5230A/B MSRP: $570 Sale: $100


2010 Ford Shelby GT500 Coupe SVT Mufflers (OEM) Ford 5230A/B MSRP: $734 Sale: $200

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Very interesting post, I was wondering what do you do with all the mufflers you have tried then taken off?


I gues you posted the answer while I was posting
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  • 9 months later...

UPDATE: the GTA's developed a small rattle on the driver side so i ended up putting on the Borla Touring as a backup. Been driving it like this for sometime and not pleased with the relatively dull sound. Finally decided to add some dynomax bullet resonator/mufflers right after the hi-flow catted x-pipe and then put the old FRPP 5230-S KRs back on and WOW! Back to sounding like a champ! NO DRONE. NO RASPINESS, quiet idle, and wicked WOT throughout the entire RPM range. FINALLY!


Now selling the following muffs:

Borla Touring (FRPP 5230-SVT1)

FRPP 5230-GTA (Shelby GT)

FRPP 5230-GTB (Bullit Edition)

FRPP 5230-SGT (Borla S-Type)

OEM 07 GT500

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