Im using a Mallory 140 with about an inch of rubber between it and the lower bottom of the rear floor. It is every bit as loud as the Holley blue I had.
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
