FORD 8.8” AXLES / HALF SHAFT OPTIONS
As we learned in Part 14, power and torque “limits” and “ratings” depend on many factors, such as if the car is drag raced, road raced, drifted, driven on the street, tires used, bushings, clutch, shocks, etc… with wheel hop being a force multiplier by 3X. Having said that, the stock axle shafts can fail in the 400-550whp range, and the stock outer CV joint is good for around 600whp, and the stock outer hub can last upwards of 800whp.
Ronin Speedworks offers two axle solutions. Their ‘entry-level’ option includes 4340 heat treated axle bars/shafts, and reuses the stock FD’s outer CV joints and hubs, while requiring Ford Explorer inner stub axles/CV joints. Our diff did not come with the inner stub axles and they would need to be purchased. Thankfully, inner axle stubs and entire axles are not hard to find or expensive. This option is (loosely “rated”) to around 600whp, or the limit of the stock outer CV joint.
Their “Grande” Axle and Hub Kit includes 4340 heat treated axle shafts and new hubs equipped with ARP wheel studs that are designed to use the Ford Explorer outer CV joints. The kit also includes new wheel bearings. This option would require us to source Explorer inner and outer CV joints, or just factory axles. The limit of this option is (loosely “rated”) to over 1,000whp, or the limit of the Explorer CV joints.
We went with DriveShaft Shop’s new “Direct-Fit” Axle Kit for the 1993-1995 FD RX-7s equipped with 31-spline Ford Explorer 8.8” differentials. This is a bolt-in solution that requires zero assembly, reuse of 15-30 year old parts, and utilizes high-end materials and CV joints.
DSS ‘rates’ this axle at 800-1,000whp, which will be limited by the stock wheel hubs. By comparison, their “Pro-Level” Axle Kit uses a beefier outer spline and aftermarket hub and is rated for 1,400hp+.
The “Direct-Fit” axle uses the same 108mm Porsche-style inner CV joints with aerospace-grade 300M Chromoly Bolt-On Inner Differential Stubs, 300M axle bars/shafts, and 300M outer wheel stub splines that are found on their “Pro-Level” axles.
The main difference between the “Direct-Fit” axles and the “Pro-Level” axles is that the “Direct-Fit” axles come with an outer CV with 300M wheel spline stubs that fit the stock outer wheel hubs, while the “Pro-Level” axles have a larger 300M wheel splines and beefier aftermarket outer wheel hubs.
The stock FD axles weighed in at 18.3lbs each, or 36.6lbs in total.
The beefy DriveShaft Shop “Direct-Fit” Axle Kit for the 1993-1995 FD RX-7s equipped with 31-spline Ford Explorer 8.8” differentials, weighed in at 26.19lbs, or 52.38lbs. This is 15.78lbs more than stock. Fortunately, most of this weight increase is due to the massive 108mm Porsche-style inner CV, which is sprung weight. If we consider our 9.2lb weight savings from the aluminum Ford 8.8” diff and the mounting bracket; the entire swap (minus the driveshaft) cost us a 6.58lb weight penalty for improving the capability of the rear-end from 300whp to 800-1,000whp.
4 comments
This is vastly superior to any other 8.8 conversion I have seen for this car. Now to convince Jeff to do this to Project V8 FD!
We are spoiled to have so many updates on this amazing project lately! Keep up the hard work.
Great write-up and an impressive kit.
Although, it seems the support bridge could be easily revisioned to be at least half an inch lower so it wouldn’t necessitate beating up your pristine RX-7-s body.
Damn, great progress. 🙂
still loving the fact that this went from rest-mod to restless-mod.
been following from the beginning.