Project Acura NSX Final Drive Install - When You Can't Make Power, Change Gears

Real racers all know the value of gearing. It's what comes next when you've reached your power limit, whether regulated or not. The same applies to our NSX project. We don't have the money for a supercharger or turbo kit, nor want to deal the associated headaches. Instead, we're going to change gears-more specifically, the final drive ratio-which will give us better acceleration and torque at street speeds and is a welcome service after 120,000 miles of wear.

As always, the plan starts simple: put in a shorter (or numerically bigger) final drive. Unfortunately, the ring and pinion gears required to change the final drive ratio are as far buried in the car as it gets. Getting to it involves yanking the transmission and cracking it open. Since the pinion gear is part of the transmission countershaft, we're going to have to transfer all the gears over to the new shaft. If we're going that far, we might as well freshen up synchros, bearings and seals too, because putting new synchro springs and bearings also requires pulling apart the input and countershaft gear stacks. While we're changing the parts on the countershaft, we might as well freshen up the input shaft. Ah, what the hell, we're in there already-might as well change the oddly non-VTEC friendly spaced USM gears for the JDM/Euro-spec second through fourth gears which use a different input shaft altogether. Now we have new input and countershafts. To save the hassle of yanking the stock pressed fit ring gear off the stock differential, we might as well just replace the diff with an OS Giken unit that already comes with a tighter final drive and all necessary hardware.

With the transmission off, it's also a good time to replace the similarly beat-up OEM twin plate clutch. But because the OEM clutch costs almost as much as a really nice aftermarket piece, we settled for the OS Giken twin place STR clutch kit. Looking at the NSX and all the grime, oil leaks and grease from two exploded CV boots, we decided the prudent man would just drop the entire engine and rear subframe assembly and do the entire job on the ground where we can freshen up all the gaskets and give the entire powertrain a proper anal NSX-owner-style scrub down. After more parts are ordered for all-new engine gaskets and seals, belts, a water pump, thermostat and all new coolant lines, we were finally ready to start.

Now we have a parts list a mile long and almost as expensive as a supercharger kit. But we're happy because we're sticking with the NA plan and the car is still smog friendly. Getting the parts was the easy part. Doing the work is another story all together because dropping an NSX is on the garage floor is something reserved for the craziest or dumbest of mechanics. We had no idea what we were doing and couldn't afford to break any parts, so went to our good friend Mark DiBella of MD Automotive in Westminster, California, got on our knees and begged for his lift, tools and wisdom.

OS Super Lock LSD
We won't get into the nitty gritties, but it took a good six-hour day to drop the rear subframe along with the engine and trans. Once that was out, the engine and trans were pulled out from their cradle and separated for the scrub down. In terms of transmissions, the 5-speed transmission is just a burly version of what you would find in an Integra. With the bellhousing off and the transmission case apart, all the guts are exposed but nicely held intact sitting on top of the bellhousing. After running everything through the solvent tank, we started by replacing the stock differential.