IMO, there are other areas to work on instead of using softener.
We do some of these street style races that require true street radials.
We run a Mickey Thompson S/T 275/60/15 street tire (look the same as the Coopers) with 400 treadwear marked on the side set at 20 psi
Cal-Tracs help as does leaving in 2nd gear (manual valvebody) and weight in the trunk just ahead of the rear bumper. We use 110 lbs. and have run a 1.72 60 ft. Not great, but not spinning, either!
Weight is key to making this work as I know some of the cars that win our local events use up to 300 lbs. in the trunk! Getting high up and as far back as possible works best. Think shopping cart handle.
'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.
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