Modifying the SRT8 OEM Exhaust System

[Hemissary]

After installing Kooks headers and hi-flow CAT's a few months ago, the existing Corsa CAT-back exhaust system then became too loud in my opinion. Way too brappy with a significant increase in dB (decibels) at various loads across the rpm range.

Previous to the Corsa I had installed an SRT8 OEM system, The sound quality was almost as nice as the Corsa system (different - full of base) and signifciantly lower dB levels...almost too quiet.

I re-acquired the SRT exhaust system in an effort to mix and match to see what I could come up with that would sound great (OK - I'm very picky) and demonstrate a reduction in dB (I'm not a kid anymore). First I tried adding the SRT resonators to the Corsa primary muffler system. Not bad, but still brappy and only a small decrease in (measured) dB.

What finally transpired was installing the entire SRT8 exhaust system, but with some very-much-needed modifications to at least be in par flow-wise as the Corsa.

Previously I had noticed that the outlets on the SRT8 suitcase muffler had a significantly smaller inside diameter (I.D.) than the rest of the entire exhaust system. Can you believe down to less than 2.1"?

The first pick shows cutting off the flange present on the left side that assists installation/removal at the factory:



This pic shows the pieces that were removed. The smaller of the three is what we actually pulled out with our fingers(!), these were what was protruding into the (major) exhaust flow, in this unit's case ~0.5"!! What this means is the exhaust gasses must back up near the inner lip to negotiate that intrusion into the existing X-pipe area. Basically two different types of restriction, interference drag by having to fight with the main exiting exhaust gasses, and a reduced outlet diameter to less than 2.2". Not good, especially the first problem.



This pic shows the actual I.D. of one on those pieces we removed by hand:



After removing part of the suitcase housing, the flange, and the inner tubing, this is what we were left with. A very nice radiused exit that we swaged up to match the outside diameter (O.D.) of the new 2.5" I.D. tubing we wished to incorporate:



After re-installing and aligning everything, a couple of lengths of 2.5" tubing were fitted. Notice also that the new 2.5" I.D. tubing enters the tail pipes (we swaged that up as well):



The end result is an even deeper exhaust note (lower frequencies) that is a little louder. Definitely not a stock SRT sound now by any means...and this is on a five-seven.

The finishing touch (after many iterations and styles) is a set of Ruf Porsche exhaust tips that fit the rear fascia's underside notches perfectly! The gap deviates less than 1/8" along the entire periphery:




Start-up clip (hope your playback system has good base):



The final result is a performance system that is now 2.5" I.D. throughout (up an appropriate 0.25" over stock), that rivals the Corsa's flow rates, sounds unique (more aggressive lower frequencies), and addresses those pesky 1st/2nd harmonics otherwise known as drone (Corsa being the only aftermarket firm to engineer-out this problem).

[GoofyTimL]

I'm thinking that would be a good thing to do on the SRTs as well for a deeper note.

[Jaak]

Nice... I've found the stock SRT cat back has really held my car back. (LOL!)

[viper3ez]

nice. that's one neat butt on her that magnum

[Hemissary]

	Quote:			Originally Posted by jaak
	Nice... I've found the stock SRT cat back has really held my car back. (LOL!)

...makes one wonder

[Jaak]

	Quote:			Originally Posted by Hemissary
	...makes one wonder

LOL, yeah, it actually does. I was looking at what you did and thought what a great way to improve an already underestimated system.

I know I underestimated it. I'm looking forward to comparing it to my SRT Corsa, which is basically a straight pipe with resonant cavities off it to create accoustic cancellations. That will be one of the things I do at the drag strip in the spring. Baseline a number of repeatable runs on the SRT system, then drop it at the track, bolt on the Corsa and do the same thing.

[hemiuberalles]

I don't know what a new SRT8 suitcase sells for... but you might could sell a lot of these modified and ready to install.

[Hemissary]

Nice idea hemiuberalles, however the system as it comes on the LX platforms has one resonator assembly permanently attached making it rather bulky.

The reason I elected to create the thread was to demonstrate what it would take to get your local muffler shop to perform the same work.

The end-result of the above modifications is an exhaust system that flows just as well as any of the aftermarket 2.5" I.D. systems (more than enough for a 5.7), sounds "really" nice, and lo-and-behold demonstrates a similar level of drone as the stock RT exhaust system when MDS engages (read as more than acceptable). This last point is important, as essentially the only other aftermarket exhaust system that (technically) addresses MDS is Corsa (and a good job at that).

Add to the plus column is that used OEM SRT8 exhaust sytems are not too difficult to find. So for say, a couple hundred pieces of cabbage one can have the cake with icing and even eat the cherry.

Although I payed less than half for a brand new Corsa exhaust system (the one I just removed), I was loathed to pay even "that" amount for what...some frick'in metal tubes!

I sold it, spent $200CAN for the SRT system, including the mods mentioned...and feel I have just eaten the canary. I bought a Power Bond 25% underdrive pulley for $170 (they supply them to SLP BTW) with money left over...

[stevesrt8]

great write up. Nice photos.

I quietly did this to my car over two years ago. I did not plan on modding up this car, but I spotted the suitcase "crimp" and me and my muffler man took care of it for 45 bucks.

I can't tell any difference, but it has to help on the top end of the power curve. I like the quiet cruise, and I have a nice bark when I get on it.

More than one person has asked me how the car can be so quiet!

Nothing wrong with a sleeper!

[Hemissary]

I have an article somewhere(!) about the engineering firm contracted to design the exhaust systems for the 5.7/6.1, apparently a significant amount of money had to be spent to modify the exhaust note, maintain a free-flowing system, and address the significant drone generated by the 5.7 (1st/2nd harmonics).

It appears that the two systems share the same configuration/layout, except for diameter/volume increases. The above modified system with headers/hi-flow CAT's, for me, is just as satisfactory sound-wise as the Corsa...with a bit less dBm.

	Quote:			Originally Posted by stevesrt8
	great write up. Nice photos. I quietly did this to my car over two years ago. I did not plan on modding up this car, but I spotted the suitcase "crimp" and me and my muffler man took care of it for 45 bucks. I can't tell any difference, but it has to help on the top end of the power curve. I like the quiet cruise, and I have a nice bark when I get on it. More than one person has asked me how the car can be so quiet! Nothing wrong with a sleeper!

[willtransco]

Sweet!!..Great Info..My Complete SRT exhaust is going on shortly..good info here..Thanks !! And I think the Bee might get a little opening up as well..Cool..Thanks!

[kaisersteiner]

On my 426 I was thinking of doing the exact thing. I also was going to put a 3 inch x before the suitcase that would more gradually go into 2.75. Any thoughts on that? I have American Racing long tubes with 3 inch catted mid pipes.

Nice write up...

[Hemissary]

The SRT suitcase muffler on my vehicle is, in itself, a huge perforated X-pipe within the confines of the suitcase muffler itself. I used my boroscope to explore the inside it and the resonators.

[willtransco]

Cool..I was wondering if that was the case with the SRT design...hence the Great Performance..versus the 5.7 struggle with restrictions/noise abatement issues. Cool..and Thanks for this Information..Looks like I will be doing Both cars and the R/T will have a full SRT8 exhaust added.

[Hemissary]

Actually the RT system is a similar design...