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Racecomp Engineering · 01-28-2013, 11:37 PM

History

JUst after we drove the pre-production car exactly 50 weeks ago(Feb 2012) I told one of my guys at RCE " man a shorter final drive would bring that car to life". A year later with 184 whp(158 baseline), 2650 curb weight and a decent amount of suspension mods we installed the Cusco 4.556 final drive gear.

Stock is 4.10. Stock theoretical top speed at 7400 rpm is 168mph. Sure if you have a turbocharged or supercharged FRS/BRZ you will hit that,but most of the "full exhaust and intake crowd" wont hit that not even down hill. The theoretical topspeed with the 4.55 final drive is 148 mph at 7400 rpm. While thats not a speed I regularly hit while on the way to pick up my son....it does mean that corner exit speeds at my local track WILL be up and the motor will be be in a part of the power band that is FAR more willing to rev to redline than before.

So yes I committed to NOT turbo charging my car a month ago. Instead I wanted to take a different path. wanted a 2550lb car, shorter gears, as close to 250 CRANK power (adding headers and carbon drive shaft)and a LOT of suspension and brakes. I wanted this because this is a track "day" car. Drive it to the track , have fun, drive it home. Its NOT going to be a time Attack car, nor a drag car, nor a "bagged" show car. So by now I'm sure I lost MOST of people who started reading this.

So probably whats left are the functional people who might like this approach. This isnt the first time we did this. My old 16valve ITA Golf had a modified 4K box with a rally bolt kit in it. My 944 turbo had a IMSA Firestone Firehawk 944S2 trans in it that was shimmed up to 85% and a shorter final drive. That car hit almost redline at the end of the straight at Summit Point(155mph). The 280Z I had fresh out of high school had a different rear end in it as well. In each case the "geared" cars always had an advantage. Was it the fastest ? NOPE. There's always someone with massive power and in a track setting that means there's always going to be someone who can NOT get that POWER ........to the ground !

Impressions

If I had to guess what this feels like in WHP gain, I'd say 11-15 hp. I base that off of the way the car felt after getting the overpipe back done and tuned. The car for CERTAIN accelerates faster thru the gears. IN EACH GEAR....the response is MUCH improved. 6th gear feels like the old 5th. 4th gear is BRUTAL now. 2nd gear in the rain when going straight, breaks the tires loose at 1500 rpm ! ( I'm on Michelin Pilot Supersports too). 6th gear at 70mph is 3450 rpm. When I go to accelerate no downshift is needed to get a BRISK response. Going back to 5th at that speed means I am sitting at 4600 rpm and thats where my tune REALLY starts to make power. So 4th ( in the rain tonight meant some correction was needed to keep things straight at yes.....80+ mph) really ROCKS !

Hardware

This was a Cusco kit. In the Cusco box is a final drive kit with 3 pieces, ring, pinion, and a install sleeve. The funny thing is the instructions for this actually say " Toyota motor corporation" on it. The parts are Toyota factory parts. In some ways that VERY reassuring actually. I mean you KNOW you are installing factory parts. It tells you all the shims you will need in order to shim the final drive tolerance. I bought all 22 because each car will be different. We only use 1 so that means you will have 21 left over. In this case IAG will reuse these on the next one they do. ( we don't do transmission work so we took this to our closest and most trusted RCE installer in the area IAG performance).

I am told that the way to do this on the cheap is buy a junk yard IS300 or IS250( Limited slip version) rear end which already has this 4.556 final drive in it WITH a differential too. This allows you to swap the entire rear end and presto ! Not sure what these cost at junk yards.

Installation

Be prepared for a 7hr install. I had done my homework on this and STILL was stressed over how it would turn out. So the day of the first install it snowed. The next attempt it snowed also. Then a week later today...it was sleet and freezing rain this morning. I had a roll back on stand by as I was determined to get it done ! I would suggest doing other suspension mods while the rear end is out. Do some differential inserts and access to the rear camber bushings is a little better. Same for some other bushings.

Conclusion

While I haven't tracked the car yet the initial impressions are VERY good. Does it feel like I did a turbo? NO, not at all. Is it a solid modification? YES. Will most do it? NO. Most will spend TONS of money getting their NA car dyno-ed and dyno-ed and dyno-ed until it makes like 205 whp. And thats fine. Its just not for me. I want it to handle very well and have adequate power, lower weight and make full use of its power out of corners. this addition I think...will enable me to do just that. This mod REALLY changes the feeling of the car. Like most reviews....as corny as it sounds....."this is how the car should have come from the factory".

01-28-2013, 11:37 PM	#1
Racecomp Engineering Join Date: Nov 2011 Drives: 2016 BRZ, 2012 Paris Di2 & 2018 STI Location: Severn, MD Posts: 5,403 Thanks: 3,418 Thanked 7,241 Times in 2,962 Posts Mentioned: 303 Post(s) Tagged: 9 Thread(s)	CUSCO 4.55 FINAL DRIVE installed. History JUst after we drove the pre-production car exactly 50 weeks ago(Feb 2012) I told one of my guys at RCE " man a shorter final drive would bring that car to life". A year later with 184 whp(158 baseline), 2650 curb weight and a decent amount of suspension mods we installed the Cusco 4.556 final drive gear. Stock is 4.10. Stock theoretical top speed at 7400 rpm is 168mph. Sure if you have a turbocharged or supercharged FRS/BRZ you will hit that,but most of the "full exhaust and intake crowd" wont hit that not even down hill. The theoretical topspeed with the 4.55 final drive is 148 mph at 7400 rpm. While thats not a speed I regularly hit while on the way to pick up my son....it does mean that corner exit speeds at my local track WILL be up and the motor will be be in a part of the power band that is FAR more willing to rev to redline than before. So yes I committed to NOT turbo charging my car a month ago. Instead I wanted to take a different path. wanted a 2550lb car, shorter gears, as close to 250 CRANK power (adding headers and carbon drive shaft)and a LOT of suspension and brakes. I wanted this because this is a track "day" car. Drive it to the track , have fun, drive it home. Its NOT going to be a time Attack car, nor a drag car, nor a "bagged" show car. So by now I'm sure I lost MOST of people who started reading this. So probably whats left are the functional people who might like this approach. This isnt the first time we did this. My old 16valve ITA Golf had a modified 4K box with a rally bolt kit in it. My 944 turbo had a IMSA Firestone Firehawk 944S2 trans in it that was shimmed up to 85% and a shorter final drive. That car hit almost redline at the end of the straight at Summit Point(155mph). The 280Z I had fresh out of high school had a different rear end in it as well. In each case the "geared" cars always had an advantage. Was it the fastest ? NOPE. There's always someone with massive power and in a track setting that means there's always going to be someone who can NOT get that POWER ........to the ground ! Impressions If I had to guess what this feels like in WHP gain, I'd say 11-15 hp. I base that off of the way the car felt after getting the overpipe back done and tuned. The car for CERTAIN accelerates faster thru the gears. IN EACH GEAR....the response is MUCH improved. 6th gear feels like the old 5th. 4th gear is BRUTAL now. 2nd gear in the rain when going straight, breaks the tires loose at 1500 rpm ! ( I'm on Michelin Pilot Supersports too). 6th gear at 70mph is 3450 rpm. When I go to accelerate no downshift is needed to get a BRISK response. Going back to 5th at that speed means I am sitting at 4600 rpm and thats where my tune REALLY starts to make power. So 4th ( in the rain tonight meant some correction was needed to keep things straight at yes.....80+ mph) really ROCKS ! Hardware This was a Cusco kit. In the Cusco box is a final drive kit with 3 pieces, ring, pinion, and a install sleeve. The funny thing is the instructions for this actually say " Toyota motor corporation" on it. The parts are Toyota factory parts. In some ways that VERY reassuring actually. I mean you KNOW you are installing factory parts. It tells you all the shims you will need in order to shim the final drive tolerance. I bought all 22 because each car will be different. We only use 1 so that means you will have 21 left over. In this case IAG will reuse these on the next one they do. ( we don't do transmission work so we took this to our closest and most trusted RCE installer in the area IAG performance). I am told that the way to do this on the cheap is buy a junk yard IS300 or IS250( Limited slip version) rear end which already has this 4.556 final drive in it WITH a differential too. This allows you to swap the entire rear end and presto ! Not sure what these cost at junk yards. Installation Be prepared for a 7hr install. I had done my homework on this and STILL was stressed over how it would turn out. So the day of the first install it snowed. The next attempt it snowed also. Then a week later today...it was sleet and freezing rain this morning. I had a roll back on stand by as I was determined to get it done ! I would suggest doing other suspension mods while the rear end is out. Do some differential inserts and access to the rear camber bushings is a little better. Same for some other bushings. Conclusion While I haven't tracked the car yet the initial impressions are VERY good. Does it feel like I did a turbo? NO, not at all. Is it a solid modification? YES. Will most do it? NO. Most will spend TONS of money getting their NA car dyno-ed and dyno-ed and dyno-ed until it makes like 205 whp. And thats fine. Its just not for me. I want it to handle very well and have adequate power, lower weight and make full use of its power out of corners. this addition I think...will enable me to do just that. This mod REALLY changes the feeling of the car. Like most reviews....as corny as it sounds....."this is how the car should have come from the factory".