2005 GTO or 2016 Z

Duc_Z09

The small amount of power per displacement argument with American cars used to be true, but not so much anymore. A 5.0 Mustang GT makes like 430hp these days bone stock, and check out the Focus RS if you want a pocket rocket Z killer. I'm not sure where you're getting your 4.5s and 12.9s numbers from, but those aren't realistic for a Z in stock trim. I've also read 5.2s and high 13s, so take magazine racing for what it's worth... pretty much nothing. Also, the aftermarket for domestics kicks our @ss. No getting around it, dollar per dollar it's waaaaaay cheaper to make big power with a Chevy v8 than anything else. And Ford isn't far behind. Check out American Muscle, CJ Pony Parts, etc. It's almost disgusting the kind of power $5k will buy on a domestic these days, and you can't even get into a Stillen SC kit for our cars for that. At least not if you want to do it right.

The Z is better looking for sure and comes with nicer components than you'd typically find on a domestic unless you shell out for a special edition of some sort.

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2009 370z #206 (all mods are Home Depot)
2009 Ducati 848 (full Ohlins, Termignoni, etc)
2003 Grand Cherokee (long arms, big tires, 4.56, lockers)