When swapping an LSX engine into an RX-7, the weakest link in the car is the stock differential. As with most manufacturers, Mazda didn't design their base model components to handle more torque than they would ever be exposed to. However, they did design the differentials in S4 Turbo II models to handle more torque since the engine produced significantly more power. Although some owners have gotten away with using an NA rear in their V8 swapped RX-7's, they typically don't last long after they start launching the car. The S4 Turbo II clutch type differential is known for its ability to take abuse and since it's a clutch type, it's also easier to rebuild.
One day while looking through Craigslist, we found this 1987 Turbo II (TII) RX-7 shell. The asking price for the shell was nearly double of what a rear end would typically go for online. Quicksilver_s14's brother owns a truck and trailer and he was nice enough to drive all the way down to Lakewood, WA (2+ drive each way) to pick up the car. One of the distinguishing features on an S4 Turbo II differential is the number of cooling fins on the housing. The TII differential have 11 fins while the NA differentials have 9. The seller confirmed that the car had a TII differential installed on the car even though we were a bit skeptical since the price was so low.
The first thing we did when we arrived was count the fins on the housing. The differential had 11 fins which meant it was definitely a TII differential! After driving over 2 hours, it would have been very frustrating if it turned out the differential had been swapped by a previous owner. Even though the differential was the main reason for buying the car, it also came with the following valuable parts:
Ground Control coilovers
4 piston front and vented rear brakes (stock TII)
Front S4 control arms (stock TII)
Top Secret style fiberglass hood
TII transmission and driveshaft
1 usable TII mirror
TII seats (my shell was missing seats)
TII seatbelts (my shell has auto seatbelts that are broken)
Wheels with newer tires (stock TII painted black)
Driver door and passenger fender (both parts I needed to replace)
Miscellaneous extra parts that have been sold to recoup some of the cost
The only thing that would have made this deal better would have been if the car was black. I decided not to use the Ground Control coilovers and KYB struts since I plan on getting fully adjustable coilovers in the future. As you can see in the photo above, we dropped the subframe with the rear brakes and differential attached since they will be replacing the entire subframe in Project LSX-7.
We also removed the entire front lower suspension/brake assembly and swapped it over. I had heard good things about Corksport brake lines so I decided to order a full set of their stainless lines. Now was the perfect time to install these since we had to remove the stock lines during the swap.
Below you can see a comparison of the stock front brakes and the upgraded TII brakes with the front Corksport lines installed.
Before: Small single piston front brakes.
After: Larger 4 piston front brakes with Corksport stainless steel lines.
Prior to buying the parts car, I was already contemplating picking up a set of 4 piston fronts so that I could do a big brake upgrade in the future. Ronin Speedworks produces a big brake kit that uses 350Z rotors which is a huge upgrade over stock. This upgrade is reserved for stage 2 but for the time being the TII brakes will be significantly better than stock.
While the image below may upset diehard Turbo II fans, the parts car was sent to the metal recyclers after everything of value was stripped off of it. While some may think this was a waste, the remainder of the car was in pretty rough shape. Every body panel had rust developing and it had been hit in the rear which meant it would have required a quarter panel replacement. We didn't have leftover room in the shop so it was the logical thing to do.
Next week I will be going over the rear subframe modification and solid bushing installation.
Previous posts about Project LSX-7:
Update 9 – L33 Modifications and Preliminary Install
Update 8 – Ronin Speedworks LSX Mount Kit
Update 7 – Improved Racing Oil Pan Baffle Install
Update 6 – Parts Engine Teardown
Update 5 – 5.3L Engine Purchase
Update 4 – The New Shop
Update 3 – Drivetrain Choices
Update 2 – Interior and Wiring
Update 1 – Engine Bay Preparation
Introduction to the Project