Click here for full BSB FP1 results from Oulton Park
JG Speedfit Kawasaki's Leon Haslam and James Ellison made it a 1-2 in the opening free practice session at Oulton Park ahead of the Showdown decider triple-header.
Haslam enjoyed a late improvement to be the only rider to duck into the 1m 34s in FP1 to pull out a two-tenths advantage over team-mate Ellison, with Luke Mossey on the Quattro Plant Kawasaki making it a Japanese manufacturer top three lockout.
With the traditional late gains cranking up the pace over the final ten minutes a host of Showdown contenders rose to the top, with Ellison going top before quickly being displaced by his JG Speedfit Kawasaki team-mate Haslam.
Mossey jumped to third as the chequered flag came out with Haslam improving on his own top time to dip under the 1m 35s bracket with a 1m 34.953s. Byrne held on to fourth ahead of fellow Showdown contender Jason O'Halloran with Christian Iddon showing a return to form in sixth on the Tyco BMW.
Dan Linfoot claimed seventh on the FP1 timesheet on his Honda ahead of Buildbase BMW's Richard Cooper and Be Wiser Ducati's Glenn Irwin as Peter Hickman completed the top ten.
BSB Showdown contenders - who needs what?
Midway through the session a brief red flag period was required to inspect the track for oil at Shell bend after Tommy Bridewell's Bennetts Suzuki stopped with a technical issue. The Wiltshire rider was stranded on just six laps and eventually fell to 14th behind John Hopkins, Michael Laverty and Lee Jackson.