We have done many upgrades to our BRZ project car and this was one that I really looked forward to. A know on the Impreza chassis this upgrade makes a very noticeable difference. A few weeks ago we test a larger than stock driveshaft and with the car in the air we noticed a LARGE amount of rear differential movement. (by large amount I mean roughly 3/4 inch of upward movement from the front bushings and 1/2inch of rear downward movement in the stock rubber bushings).
Once on the ground and laying under the car as the clutch is engaged this is the same. So a fast shift at speed must be have a lot of movement as well.
The install took less than an hour. Instructions were simple and easy.
An initial test drive showed huge improvements when adjusting rpms mid corner( checking up). Now if you accelerate from a steady rpm you (seemingly) feel the car move forward without as much drive train flex/loss etc. Notice I said seemingly as there is no data to support this "feeling".
There is some additional NVH felt and heard now. When turning out of say a parking place at 1-3mph you do hear the differential transferring noise through the drivetrain and into the car. This was there before BUT the soft factory bushings insulate this sound. Its not loud at all, but if you listen for it with the radio off you can hear it.
At 3000 rpms there is a drivetrain rumble feeling that I can feel, but not at 2900 and not at 3100.
DISCLOSURE: I have a Cusco 4.55 final drive so this COULD be a result of THAT. None the less this isnt a big deal. On the "big deal scale" its a 2 with 10 being take it out NOW.
We also have the Whiteline trans insert installed and now with the 925 installed it "feels" like you can feel more transmission noise/grunt when shifting.
Alo keep in mind we have the subframe insert bushings installed also. So any thing that COULD keep these sounds from being heard and felt has been removed all in an effort to gain more feeling and handling potential.
DO NOT BE SCARED as what I am describing all falls under the " I want my car to handle better and are willing to incur some extra NVH to do so" category. With that said....this single mod
combined with some of the other key mods gives what is other wise a very insulated car,...a very RAW feeling which.....promotes driving confidence and feeling.
Banging through the gears proves FAR more DIRECT and does seem to direct more energy to the wheels.
On some late night after the wife goes to sleep back roads I found this modification to REALLY come into its own. The transition from trail braking to power on feels like you cut out a full BLINK( or in the cinematography world, 5 frames) as now it feels very confidence inspiring to come in hot , on the brakes HARD, and as you go from brake back to gas the rear end feels more connected and or as though you are enabling the differential to perform better. I think THAT is where this part shines. SImply put there is less movement in those critical moments where you need the parts under the car and around the diff to be "ON" and ready to transition.
Whiteline offers a COMPLETE bushing replacement option coming soon and that I would imagine has MORE NVH than this so thats for sure for VERY committed track day guys/girls.
My rating on this mod is a 9.5 out of 10. I love it.
Our first track event is in a few weeks so I will give an update then.
Myles Williams
Racecomp Engineering Founder.
