Selected ratios and ideas. Tremec has produced variety of ratios for OEM applications (TR6060) but in the aftermarket (T56 Magnum) for GM appliactions, only two are available.
1st 2nd 3rd 4th 5th 6th rev
3.01 2.07 1.43 1.00 0.84 0.57 3.28 SSR Truck
2.97 1.78 1.30 1.00 0.80 0.63 2.90 Camaro
2.66 1.82 1.30 1.00 0.77 0.50 3.98 Corvette
2.26 1.58 1.19 1.00 0.77 0.63 ? Viper
Using experience and ratio information from three of my cars (1986 Mustang 5.0, 1994 Nissan 300zxTT and 2007 Honda Civc Si), I selected the Corvette ratio above. Let us consider the Civic. Weighs about the same s the Solstice, 3000 lbs, and has a 2.0L NA engine the spins to 8500 rpm (with Hondata flash). 1st is circa 3.3 and diff ratio is over 4. 80 mph RPM is 3500+. The 200HP engine is very weak at the low end with anemic torque, just over 100 ft. lbs. This low gearing combination works well with a weak, high revving engine that can still get the car moving fast by spinning up the motor.
The Nissan has 400 HP (with some mods, boost, intake and exhaust) but engine is little at 3.0L and a max RPM of 7500 (with reprogrammed ECU chip). Weight is a porky 3400 lbs. 1st is 3.3x and diff is 3.69. 5th is .6x with cruising rpm at 80 mph under 3000 rpm, but close. In this case there is a heavy car (relatively speaking, about the same as a corvette) and a smallish motor that revs respectably. Having a turbo has benefits running revved up, as it keeps the car responsive, at the expense of wear and fuel consumption.
Come the Solstice. OEM weight with the 4 cyl was circa 3000 lbs. Let us estimate 3250 with the Ls7 and Tremec T56 Magnum. The engine is modestly revvy, 7100 (not bad for a pushrod V8) and produces over 400 HP and 400 lbs of torque. With this combo there is little need for the transmission to help the engine. The combination of gear ratios (2.66 ... .5), diff ratio (3.73) and car weight, resembles the factory configuration for pre 2015, Z06 Corvette.
The Ls7 has titanuim rods and a 30% lower weight reciprocating assembly. The reduced mass of its internals should allow it to change rpm quicker than a comparable motor with heavier internals. I also replaced the OEM flywheel with a Fidanza aluminum unit, seeking torque reduction off the line to reduce wheel spin. These are all fact based theoretical estimates, but non-the-less just good guesses. We shall see how this all works when put together.
Last edited by JMartz; 11-08-2015 at 09:58 AM.