Out back, we bolted the Sikky differential brace to the diff. Then we used a jack to lift the front of the diff to bolt the crossmember to the chassis.
With all 8 bolts tight, the differential was now supported and ready to go.
With our drivetrain now secured with the Banzai Racing transmission mount and the Sikky Manufacturing HD Differential Brace, we were ready to take the car for a spin and see how it performed.
ROAD TEST
On the road, the improved shifting feel and consistency was immediately noticeable. The transmission is now far more secure and the shift lever no longer moves during heavy braking and cornering, which greatly reduces the chance of a costly mis-shift.
The entire drivetrain now feels more direct, responsive and solid without having hundreds of pounds of mass swaying inside the transmission tunnel. Even releasing the clutch, the car feels like there is less slop and is more immediate in its actions.
Now, project FD RX-7 “Restomod” is attempting to keep modifications refined and streetable without feeling like a ‘racecar for the street’ which can quickly become tiresome and takes away from the usability of the car. With a fairly stock suspension and a reasonably quiet exhaust on our car, there is a slight increase in NVH from the new rear differential mount. During light load when cruising on the freeway, the solid urethane differential bushing does transmit a little more vibrations and noise into the chassis of the car. For cars with loud exhausts or stiff suspension, this difference would likely go unnoticed.
Overall, we are extremely happy with the improvement in shifter feel and response by ditching the original Power Plant Fame for a traditional transmission mount from Banzai Racing and a differential mount from Sikky Manufacturing. The small tradeoff of NVH is a small price to pay for the improved durability of ditching the weak PPF to be able to handle the abuse of track use, significantly more power and sticky tires.
Stay tuned for the next installment of Project FD RX7 Restomod!
5 comments
Love it. Wild that there are so many new developments on 90s cars.
Good writeup guys! Is the FD PPF really that heavy? I only have experience with the NA/NB Miata PPF which is a very light aluminum piece. Maybe only 5-10lbs. Is the FD one steel instead?
It’s steel and weighs 20lbs. The new aluminum braces are much lighter.
I’m completely unfamiliar with Mazda’s ppf, so apologies if this is a dumb question. The ppf looks like it provides a bit of longitudinal stiffness that isn’t replaced with the new parts. Is there a risk of increasing the stress at some of the subframe connection points as a result?
Love the project regardless – thanks.
No worries at all, thanks for the feedback. The purpose of the PPF is to turn the entire drivetrain from the engine to the differential into one solid unit. So the entire drivetrain hangs off of the two engine mounts and the two differential mounts. The new setup changes this to a more traditional layout where the transmission is supported by a (new) bushing and the front of the differential is supported by a (new) bushing. Each additional bushing triangulates the engine/trans and the diff to provide longitudinal support and stiffness.