Just finished replacing the resonator on my '04 Jag x-type because the oem unit was a baffled unit which created considerable backpressure. The results are amazing! Which leads me to this thread. Before I get under the xc 90 and unbolt the exhaust system, does tech or anyone else out there know if the oem resonator is baffled or a straight thru type?

Thanks.

I thought that the engines are designed to run w/ some back pressure, and removing it (resonator or muffler) will not increase HP. Is it true?

Correct! But the turbo and cats downstream provide that backpressure. The Jag has three cats, one for each manifold and an additional one after that. Replacing the resonator has provided faster 0 - 60 times, and slightly better gas mileage. Seems to me that if the Volvo resonator is restrictive, it should show even a slight improvement. If the oem resonator is a straight thru type, then I won't gain anything by replacing it.

I have replaced the catback exhaust systems on the previous 10 domestic vehicles I've owned and gotten improvements on all but one, a 2004 Ford Escape. The factory system on that SUV apparently was engineered differently. But, I don't want a noisier Volvo so I'll keep the factory muffler.

I wish I could tell you but I have never had one apart.

Well, crawled under and unbolted the resonator at the forward connection. Ran a borescope through the unit and discovered that it is straight thru. There are three restrictors in it, each one reduces the pipe to 1 1/2" ,but since the exhaust consists of a series of pulses and not a constant, high pressure stream, , I think I'll leave the resonator in place. Keeps things quiet.