IPD catback exhaust experience

So I bought one early this year because it was on sale (as it is again now) for a very good price and was much cheaper than replacing the entire stock system. My stock exhaust was literally rusting off the car and had to be replaced. It was so rusty that I didn't even need a wrench to remove it, when I unhooked the hangers and pulled on it, it fell off in the garage floor. So, the IPD system...

Pros: Excellent fit and finish. I had to cut out the rear plastic bumper valence a little to fit the V70R style exhaust tips on the XC70, but otherwise it fit perfectly. Sounds amazing OUTSIDE the car. Looks great.

Con: On a wagon it creates an unbearable ear-bleeding drone inside in the car that renders it undriveable without ear plugs. It will literally give you an instant migraine. I am not a curmudgeon either, I have owned quite a few loud muscle cars in my time that would set off nearby car alarms and even required ear plugs to drive long distances. This was much worse than any of those, despite being attached to an engine less than half the size with less than half the power. Upon doing some investigation I learned that a smaller displacement engine actually has a lower frequency exhaust resonance than a larger engine. Who knew?!?! So now I had a car with a $600 sweet looking stainless exhaust that I couldn't stand to drive.
Further investigation led me to get a frequency analyzer app for my phone, figure out the worst frequency range, and fabricate a 1/4 wave tube out of pieces of the old exhaust (the original tubing was stainless and was not rusted, the rust was at the connector and the muffler). Although quite difficult (and impossible if you do not have a welder) this actually worked somewhat and made the car tolerable to drive, particularly on the highway where RPMs get out of the bad resonance range. BUT there is STILL an uncomfortable very low frequency drone, too low to be attenuated by the 1/4 wave tube, and carrying passengers in the backseat is not an option.

So now I'm faced with either removing the entire thing and spending twice as much again for a new factory system, or attempting to swap out the IPD muffler with a quieter muffler to try and further attenuate the low frequency drone. I am not sure that will actually work though though because the resonance may be more related to the 3" exhaust tube and such a low frequency has a very long wavelength that is not easily cancelled by a little metal box. All in all a very frustrating experience!

Thanks for this! I'd love more of an exhaust note but the drone would drive me crazy.
I just got back into a XC70 after my Forester got totaled and I was looking at that system. My resonator and muffler both are in need of replacement. I think I might just cut out the resonator and replace the muffler. Fortunately most of the piping is good.

If I had known, I would have just gone to a good exhaust shop and had the original resonator and muffler replaced with some quality aftermarket stuff. In the end that wouldn't cost any more $$. That may be where I end up anyway.

I had an experience similar to yours after installing an aftermarket performance exhaust, and fortunately was able to find a pretty simple solution.

Here is an article I wrote about using as side-branch "resonator" to eliminate exhaust drone.

If you can find room for the side-branch under your XC70 you can keep the cat-back and eliminate the drone - for little additional money.

You would need to adjust the calculations for the resonator length for five-cylinders.

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Originally Posted by Pennhaven

I had an experience similar to yours after installing an aftermarket performance exhaust, and fortunately was able to find a pretty simple solution.

Here is an article I wrote about using as side-branch "resonator" to eliminate exhaust drone.

If you can find room for the side-branch under your XC70 you can keep the cat-back and eliminate the drone - for little additional money.

You would need to adjust the calculations for the resonator length for five-cylinders.

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Check my original post... I actually did that with some success. I was able to eliminate the worst drone around ~120hz. There is still a lower frequency drone around 70-80 however that would require a very long 1/4 wave resonator tube to cancel. Too long to practically fit under the car. As it stands the one I built is around 48" long!

Quote:

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Originally Posted by brenglxc70

Check my original post... I actually did that with some success. I was able to eliminate the worst drone around ~120hz. There is still a lower frequency drone around 70-80 however that would require a very long 1/4 wave resonator tube to cancel. Too long to practically fit under the car. As it stands the one I built is around 48" long!

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My mistake! Sorry, I didn't pay more attention! Wish you success, without breaking the bank (somehow?). I know how frustrated you must feel at this point.

However, my math says the 1/4 wave length to cancel 75Hz would actually be about at the 48 inch length you now have. The length to cancel 120hz would be about 30 inches. So not sure how the 48 inch helped you at 120Hz, but left a problem at 75Hz.

Or maybe your originally had 30 inch and have since lengthened to 48? If not, have you correlated the drone to RPM to confirm what your sound analyzer software is telling you, to make sure you are working on the correct frequencies? With a five-cylinder engine, 120Hz should occur at 2880 RPM and 75 Hz at 1800.

Attachment 9024Attachment 9025Attachment 9026I installed one on the 2001 T5. It’s a car that I rebuilt for my son. He likes it. I don’t think I could stomach it for long drives.

Sounds great when you get on it, but, ugh, the highway drone is a lot...

It also requires some fiddling with the mounts to get it installed. It’s not a hard job.

But it’s not a modification I would recommend.

Pennhaven, I was mis-remembering my findings. The worse offending frequency was around 78-82, around 1800 rpms as you mentioned, which is right where the engine runs on the local 2 lane roads. On the highway if you could run 70-75 mph you could get out of the offending range.
As I recall I just made the 1/4 wave tube as long as I could without having it hang down lower than the main exhaust pipe. What I have now is a deep lower frequency drone, probably 50-60hz range.

Quote:

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Originally Posted by brenglxc70

Pennhaven, I was mis-remembering my findings. The worse offending frequency was around 78-82, around 1800 rpms as you mentioned, which is right where the engine runs on the local 2 lane roads. On the highway if you could run 70-75 mph you could get out of the offending range.
As I recall I just made the 1/4 wave tube as long as I could without having it hang down lower than the main exhaust pipe. What I have now is a deep lower frequency drone, probably 50-60hz range.

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Wish I had another idea, but best I can suggest is to manually downshift as required to keep the revs above the current 55 hz / 1300 RPM drone band. That at least is easy and costs very little.