Depending on conditions and the type vehicle and the tire you can use slip can be a lot or negligible. Our roadster was there also, not running a y-block but a different vintage engine. We fought gremlins I had never encountered in 45 years of attending many Speedweeks and World Final events. Our car runs in the 150-160’s and for a roadster is fairly light weight with 350 or so HP and normally does not slip. We use a 4 speed dog synchro G-Force transmission, a vertical gate shifter from Long and the driver doesn’t come off the throttle to shift. It sounds like an automatic for-as long as we can hear.
For us, this year the salt was hard and firm and did not see any slip of wheel spin. I’m sure with 800+ HP the conditions would be different. When running a spool or locked rear end your tires MUST HAVE THE EXACT CIRCUMSTANCE or you will be fighting it an more than likely get to see the entire course as your spinning once or twice trying to regain control.
I did not get over to Tim as we were thrashing….
56 Vic, B'Ville 200 MPH Club Member, So Cal.