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Catless... Help with Rasp

7K views 15 replies 7 participants last post by  Robs_SRT8 
#1 ·
I've been running my Magnaflow Competition paired with Kooks long tube headers and catless midpipes. The exhaust note is extremely loud with a drag car note at WOT. The problem that's been nagging me has been rasp off throttle around 2800-3000rpms. There's also a buzz or tinny sound with light throttle in this area of the rpm brand.

I previously had dynomax mini bullet mufflers (#24250) 4" dia x 6.5" body welded to the midpipes where high flow cats are normally located. It made a small impact to the rasp but more so to the overall volume. I'm thinking of trying to max out the space with a set of kooks 4.5" dia x 10" long mufflers. Any thoughts?

It's probably worth mentioning that high flow cats aren't a long term option with a moderately high hp supercharged build in the near future.

Thanks for any input
Rob
 
#3 ·
I'm willing to sacrifice volume to calm the rasp, even if it doesn't get rid of it all. I've never tried a resonator but from my experience this would drastically change the whole exhaust note. The exhaust as is right now would be perfect if not for the metal tinny sound. I'm forced to shift and drive around this area of the rpm band.

I've debated about selling the Magnaflow Comp for a Corsa system but I'm just to much in love with the wide open sound of the Magnaflow. The corsa handles drone and rasp so much better.
 
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#4 ·
Catless mids and corsa sport will still be raspy. IMO, going catless for less restriction flow and adding additional mufflers which adds restriction seems bassackwards. Why not just use your SRT catted mids? I did the JBA catless mids, made it much louder, stunk and gave it a raspy sound. I only gained a few hundreths and 1 MPH so went back to the SRT catted mids. The 392 cats are very free flowing.
 
#5 ·
I'm running pypes race pro mufflers on my rt with catless mids and it sounds great. Before I put the race pros on I had pypes loudest muffler they call their violator. Let's just say it was so loud and crappy sounding without cats I didn't want to drive my car. I changed to a quieter muffler and boom I love it!


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#6 ·
I would put cats on in a minute if they could ultimately handle 700-800whp. Looking to step up my game at the strip eventually.
 
#7 ·
Not sure what your state's inspection requirements are but a lot of big HP guys around here use green cats when they have to. FI'd + LTs = Cat Failure over time.
700 - 800 HP will sound totally different than a N/A'd motor so what ever you do now will sound different after your build.
There was two different zones that my car was raspy (catless with the corsa). One when under heavy acceleration in the mid 2K range and then like crazy up top (5500).
Around town it wasn't bad but very cheap sounding at the track. Like others stated, a low flow chambered muffler where the resonators were sounds like the best/less epensive option. You could always use cutouts when you want no restricton.
 
#9 ·
Yeah, you know you’re shoveling the coal to her when you here it.
 
#10 ·
I run catless mids into the stock OEM bottle mufflers exiting through glasspacks . No tinny raspy sound for me, however it is loud when getting on it. Otherwise, it's pretty tame while in traffic.
 
#12 ·
by the way anybody running more than about 9 or 10 lbs of boost should not run cats or very restrictive exhaust, doing so is a sure recipe for disaster
Luke

ps, with higher boost, cats have a tendency to want to melt down and restrict heavily the exhaust causing additional boost to accumulate in the cylinders which will result in catastrophic failure
 
#16 ·
I actually just passed emissions while catless with the help of the diablo and my tuner. WI allows one sensor to be "not available" so long as the sensor is not reading "not ready". When it comes to the Kooks green cats I was advised to pass that they would fail sooner then later.

I'll look forward to the F/I engine build before I get to over board into this whole exhaust note thing. As of now it's manageable and really does sound mean as hell at WOT. The Magnaflow Comp catless really breaks loose at 3k as opposed to my old Mopar setup (around 4k).
 
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