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This may be of use to those of us who own or have though about purchasing the inexpensive M2 exhaust for your ISx50, but have been hesitant from the negative reviews we have seen here.

I purchased the M2 exhaust for my 2008 IS350 last year after reading some mixed reviews here, at the time it was so cheap on eBay I thought I would give it a try.

It sounded great at idle, but during acceleration it was a little louder than I would have liked and it droned during highway travel, much as many people have also complained about here. So after a few weeks I took it back off.

This year after getting tired of looking at the M2 sitting in my garage, I spent some time researching into where the droning was coming from and did some acoustic tests on it playing specific frequencies through it from a speaker and frequency generator and ended up finding a lot of resonances within it. The resonances were specifically from the pipes, not the mufflers themselves. I also noticed that simply by holding the pipes with my hand, I could suppress many resonances I had been hearing. As a test I bolted a few pieces of steel bar with U bolts to the pipes at about midpoints to each muffler. As expected, many of the resonances had gone away.

Adding mass to exhaust systems is nothing new, I spent some time researching this as well and it is common for OEMs to do the exact same thing on vehicles to remove certain resonances and vibrations at specific rpms within the exhaust system. Looking at the stock IS350 exhaust, it actually has one itself. On the drivers side muffler there is a large rubber bushing clamped onto the back of the muffler that has no apparent function other than to suppress resonances.

So tonight I finally had time to swap out the exhaust again and the additional wights on the M2 have made a huge improvement. Acceleration sounds much more subdued, still louder than stock but significantly attenuated compared to the 'unmodified' M2. The droning at cruising is significantly quieter as well. With the addition of the weights to the M2 pipes I am definitely keeping this exhaust on the car.

The total weight I added is only about 3 pounds. Even with this the M2 weighs a lot less compared to the stock IS350 exhaust. Most of this weight is in the pipes. If you were to take any metal object and tap the stock exhaust pipes then the unmodified M2 pipes, you can hear a huge difference due to the thicker steel pipes the stock exhaust has. The stock exhaust sounds 'dead' compared to a ringing from the M2. With the weights, the M2 is much more dead when tapping as well.

Total cost for this modification was about $20. $12 was the cold rolled steel bar I purchased from onlinemetals, and a few U bolts from a local hardware store. If anyone is interested in this modification I can take some pictures showing how I added the weight onto the pipes. The weights cannot be seen as they clamp onto the front of the pipes, looking from the back of the car. I highly recommend this to anyone with the M2 exhaust that wants it to be better sounding.
 

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Definitely post some pictures! I plan on buying an M2 soon because I can't justify paying 800$ for the HKS.
 

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Hey bradthx, I just got the same exhaust set up. And I have terrible drone at 2300-2600 rpm. I want to try the same solution as you did. Can you post some pictures here? Would appreciate it :)
 
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