I recently installed a wide ratio T56 to my Cobra powered '99GT with 3.73 rear gears. I had hoped the .50 6th gear reduction would help fuel mileage but all it got was 21.5mpg. Timing was pulled to under 10 degrees BTDC (which makes the motor run hotter aggravating the situation) even with light load on flat Florida roads. Is the effective 1.86 final drive too high or could a tune help. I am willing to go with 4.10'a or 4.30's as the best timing advance is at 2000 rpm. Stock Cobra has an effective 2.20 final drive and 4.10's would yield a 2.05 & 4.30's a 2.15 final drive. I think the tune could be an issue as it pulls more timing than it seems it should even in 3rd & 4th gears. Timing at WOT is 19 degrees and timing can be less under what seems to be light loads. Suggestions please. Thanks, Mark
