Just finished installing a set of Eddie Trotta C4 pipes on my '07 K9. No baffles so I was concerned about jetting. I was running a set of Mean Mother's using .031 intermediate jet and .78 main jet. Ran great but a bit mild for looks and sound. I stuck with the .031 intermediate but bumped the main to .080 and it runs perfect. Plugs look clean also. FYI for anyone searching through the jetting threads for specific advice on jet sizing.