The official existing lap record around the 37.75-mile TT course stands at 135.452mph set by Peter Hickman in the 2018 Senior race.
As practice came to a close for TT 2023 ahead of the first race day on Saturday, Dunlop on his Hawk Racing Honda unofficially set the fastest-ever lap of the mountain course with 135.531 mph on his final lap of the Superbike/Superstock session.
Coming into Friday’s running, Hickman stood as the fastest rider of TT 2023 to that point, having posted a 133.7mph effort on Thursday evening from a standing start.
On Friday afternoon, Dunlop set the pace from a standing start in the pitlane at 134.270mph, with Hickman second at 133.195mph on his FHO Racing BMW.
Hickman was late away in the Superbike/Superstock session having been left stranded on the course in the Supersport/Supertwins session when his Yamaha bike in the latter class broke down.
This meant he was one of the last to get out on his Supersport bike and was still on his lap when the Superbike/Superstock session got underway.
Dunlop carried on for a flying lap on his second tour on the Superbike and started to light up the timing screens as his sector times suggested he was inside the outright lap record.
Pushing hard across the lap, with a moment going over Sulby Bridge and running wide into Ramsey Hairpin, Dunlop blasted over the mountain to complete the tour at a staggering 135.531mph.
For that to be counted as an official lap record, it has to be posted in a race.
Hickman’s second lap got him close to his own lap record, as the FHO rider posted a 134.910mph effort to end up second ahead of DAO Racing’s Dean Harrison at 134.216mph.
Padgetts Honda’s Davey Todd was fourth overall on his Superbike with his best-ever lap at the TT of 132.194mph, while John McGuinness was fifth on the factory Honda at 131.003mph.
Todd’s team-mate Conor Cummins has been ruled out of racing until next week having been admitted to hospital with an infection.
Dunlop’s domination of practice continued in the Supersport and Supertwins classes, with the Ulsterman fastest on his MD Racing Yamaha at 127.510mph, while he set an unofficial lap record in the Supertwins class at 123.474mph.
The Sidecars were first away on Friday afternoon, with the Peter Founds/Jevan Walmsley outfit leading the way with a 117.807mph.
That is still some way shy of the best Sidecar lap of practice week set by the Birchall brothers at 119.474mph – an unofficial lap record – on Thursday evening.
The Birchalls didn’t set a representative lap on Friday, with driver Ben and passenger Tom stopping for a wheel change at Ballacraine before setting off again to complete the tour.