Underdrive pullies have been proven again and again for atleast 10RWHP, worth the money in my opinion and you can feel the difference in the Seat of the pant test
It was one of the first motor mods I did..that 70mm is killing the bottom end a little right now but should be fine for future mods.
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Check Out My Site 91GT,Holley SysteMAX II Kit-Heads 2.02" x 1.60" port matched to a 1262,Anderson N-61,24#,76mm C&L,Full MAC, No A/C or PS or emissions, 12" K&N Filter,RNH PERFORMANCE Ram Air,Ron Davis Radiator,Full Suspension, SPEC stage III clutch, Lakewood SFI bell, S&W 8pt "X" brace,JAZ seats,3:73's,Welds..etc,4:30's and 31 splines coming very soon!
[b]12.16 @ 113.5, 1.78 60ft..no traction in the 90 degree