First thing's first--literally....
First thing's first--literally. These are the 2.71-ratio First , 1.79 Second, 1.30 Third, and 1.00 Fourth G-Force Street gears that we selected for our six-speed. The factory '03-'04 Cobra Fifth (0.80) and Sixth (0.62) gears are retained, as Astro believes they will work well for our application.
Making serious horsepower with the Two-Valve 4.6-liter engines found in '99-'04 Mustang GTs has become popular in the last two years. With the safe rear-wheel-horsepower threshold for Ponies with stock bottom ends maxing out at around 420 or so, the new trend for New Edge owners has been to completely revamp their engines using stout short-blocks, and then jack up the power and torque levels far beyond the limits that Two-Valve (as well as some Three- and Four-Valve) stockers were meant to go.
Here are the factory First...
Here are the factory First through Fourth cogs, which are dramatically smaller (teeth face) than the upgrade gears, and more susceptible to breakage under the heavy torque loads of big-horsepower engines.
We've seen many a 'Stang's stock axles twist or break, their factory engine blocks split in half, and even witnessed many a Mustang's cracked unibody thanks to big-time horsepower and torque. The power thrown at some Mustangs easily can be more than two, three, or four times greater than the amount of force the OEM components are designed to support.
With the G-Force Street upgrade,...
With the G-Force Street upgrade, Astro swaps the OEM 11/16-inch 10-spline T56 input shaft (bottom) for a stout, billet, 26-spline shaft, which measures 1 1/8 inches in diameter.
Although the Tremec TR-3650's current state of functionality is good, we do realize that with the heavy amount of torque and big steam being sent to the rear wheels, the tranny is truly operating on borrowed time. It's best to address any issues now, before we have a serious (and expensive) problem later.
On the left is the 27-spline...
On the left is the 27-spline factory output shaft from our T56. The 9310-alloy upgrade piece has 30 splines, and again, is clearly more robust in diameter than the OEM unit.
Since all roads for plausible solutions lead to giving the 'Stang a six-speed transmission, a plan was set in motion to perform a swap. However, before doing anything, we asked Astro's owner, Tony Sarvis, for insights on how a Tremec T56, '03-'04 Cobra six-speed transmission should be built to withstand a high-torque workout, yet still maintain street manners. Tony explained that Astro can install billet synchronizer keys for Third and Fourth gear, a 4140-steel throwout-bearing retainer, bronze First and Fourth-gear shift-fork pads, upgrade cluster extensions, and replace the OEM 10-spline input/27-spline output shafts with a 26-spline-input-shaft/30-spline-output-shaft package, to increase the torque capacity (to 650 lb-ft) and improve the shifting characteristics of a T56.
These triple/double synchronizer...
These triple/double synchronizer rings and assemblies actually are the same ones used in a certain Brand-X sports car's six-speed tranny. Astro's owner, Tony Sarvis, says the synchros allow more "braking" action to the gears for clean, crisp high-rpm shifts. Billet-steel keys (for Third and Fourth gears) also are included with the G-Force synchronizer assembly.
Horse Sense: We've admitted many times that we know our race-blower/Two-Valve engine/street-'Stang concept is unorthodox (a D-1SC ProCharger unit makes great power and is easier to tune for the street), but now that our '02 Mustang GT is tuned, running well and throwing more than 550 hp and almost 540 lb-ft of torque at the ground every day (with the ability to put down a lot more with a simple pulley change, timing advance and race fuel), we can say the project was well worth the effort that the crew at B&D Racing and so many others put into making it happen.
Here are First... | 
...Second... |  ...and Third gears--the obvious...  ...and Third gears--the obvious major difference is size. G-Force uses 9310 alloy steel to enhance the durability of each gear. |
 Note the difference in the...  Note the difference in the factory cluster (left) and our new G-Force cluster with its upgraded coupler (right). The enhanced coupler is one of the keys to enabling Astro's G-Force-prepped six-speeds to stand up under 800 lb-ft of torque with no problem. |  Gerry has our G-Force Street...  Gerry has our G-Force Street output shaft assembled with First through Third gears, and ready for installation in the tranny's case once the necessary machining is completed. |  Once the output shaft and...  Once the output shaft and main shift rail are in place, Gerry installs Astro's steel, Third and Fourth-gear shift fork and slider assemblies onto the output shaft (most six-speeds feature aluminum, 3/4-inch forks). The steel unit is a $50 upgrade, but we think it's well worth the additional loot. |
 The countershaft extension...  The countershaft extension also gets a reverse-thrust washer that replaces the same piece for Sixth gear. The G-Force coupler upgrade also mandates the requirement for this washer. |  Our Astro Performance Warehouse,...  Our Astro Performance Warehouse, G-Force-upgraded six-speed is complete and ready for installation in our '02 ProCharged Mustang GT! Check out the sidebar for highlights of the process. | |