I have a rattle on start up and acceleration. Infiniti dealer checked it out and diagnosed an exhaust leak from the right side of y pipe from the catalytic converter. Repair estimate is $1400 according to the them. By chance I've seen a part out and complete exhaust with y pipe from an 08 g35x sedan on Offerup for $80.

Would it be a direct fit.. Besides the cutout for the second exhaust tip?

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I could be wrong, but I'm pretty sure the only interchangeable exhaust part between the two generations is the y-pipe, and possibly the mid-pipe.

Also FYI, the catalytic converters are separate from the y-pipe, and the most common exhaust leak is from the flex pipes, which are a part of the y-pipe, so I'd say go for it!

Engine -> exhaust manifold (x2) -> catalytic converter (x2) -> y-pipe -> mid pipe -> muffler

 

not sure how the exhaust leak is causing a rattle? my y pipe flex joints are wide open bc low life and I have no rattle. I would think it would either be in your engine (hopefully not) or maybe the heat guards under the exhaust. if possible you should go under yourself and see if any of them are loose first.

 

The entire exhaust won't fit. The Y pipe will. The cats will if you have the HR manifolds.
you also can't use a dual exit exhaust without mods. You would have to work out the hangers,bumper cut out and evap canister delete or relocation. If you just need a y pipe then consider buying that one. If you need the cats and y pipe then consider it a chance to upgrade to high flow cats or test pipes and a aftermarket Y pipe. The HR style Y pipe will also give you a little power boost as well. Years ago it used to be one of the recommend budget mods.