audi rs4 or nismo 370z?

AlphaSnacks

Doesn't work. Audi takes the motor apart and uses something much, much stronger than seafoam to flush all of the gunk away - especially around the manifolds. A good friend of mine is the master tech at my local Audi, and his advice is to drive any 4.2L V8 Audi makes with some authority. He sees a lot of carbon buildup on S5s driven by women and older men, who admit to driving them really easy. The S5s that are driven hard on occasion don't have the build up.

Due to the rarity of the RS4, he's serviced a handful over time for carbon and once again, the ones running well are driven by younger and more enthusiastic guys, while others with carbon by older types just looking for a nice cruiser.

For whatever it's worth, my Audi A6 4.2L drives beautifully. All 340 ponies gallop proudly when I mash the throttle...and that's because I make sure to give the motor a nice workout sometimes.