| the native 3.69 ratio to a 4.1 ratio presumably after considerable time having been spent in the experience with the 3.69 setup. I have always run the NA 4.08 diff over the span now of nearly 13 years time. 11 of those years being with a TT'd engine ranging through stock turbos, GT28R, and now with my "tweaked out discos" - GT28RS w/ 10-blade 79-trim turbine. Current setup achieves 1bar of boost by ~3250 RPM, which is ~250RPM earlier than a stage 5 TTZ with stock turbos. =) Stage5 TTZ @ 410RWHP
 My Z:
 When you say the new gearing ratio has diminished the "punch" of the stock turbos, is this observation referring to the experience felt in the lower gears, such as 1st and 2nd ONLY? It makes a lot of sense that this would occur - going to a lower gear ratio at the differential will reduce the peak vehicle speed attained at the top of each gear - in effect, you will "top out" in each gear at a lower speed. This will give the impression that you are accelerating quicker because your experience in the seat is so closely tied to what your hands and feet are doing. However, the increased rate of acceleration through a gear will decrease the amount of time spent in any gear, which will change the relationship between the boost pressure response relative to engine RPM. This effect actually works against the total power output of the engine over its full operating range of engine RPM and all 5 gearing ratios within the trans. The turbos take time to spool up and the 4.1 gearing allows the engine to accelerate the car quicker but to a lower peak speed. The engine is directly coupled to the driveline so if the car accelerates to its peak velocity for a given gear in shorter time, this also means the engine reaches its rev limit in shorter time. Fire your Z up and let her reach operating temp. While in neutral, stab the throttle wide open and hold it just until she hits the rev limiter, noting the peak boost pressure achieved in the process. You'll quickly realize that virtually zero positive manifold pressure was achieved. This is simply because the engine was able to increase in rpm to its limit far quicker than the turbos could get spooled. Now if you stab the throttle to redline and let her bounce off the limiter several times, you will note that the turbos will produce several psi of boost. Going to the 4.1 gear set has an analogous effect on the turbocharger spoolup as the example above. The faster the engine can rev up to its limit, the less time the turbos have to get spooled. Going to the 4.1 diff gearing reduces the peak vehicle speed of each gearing ratio offered by the trans. While it may feel quicker because you are rowing faster, you may not actually be accelerating to higher speeds in less time. In applications where a broad range of vehicle speed is required, going to the 4.1 ratio may result in more gear shifting events; you may find that in certain circumstances, you only need gears 1-4 with the 3.69 diff but with the 4.1 gearing you will have to use 1-5. Each time a shift is required, there is no power being delivered to the wheels during that process. The questions are how does the effect of increasing wheel torque with the 4.1 ratio compete with the decreased spoolup response? If the 4.1 ratio's increased torque outweighs the drawback of boost response, how does the increased torque compete with the need to use an additional gear? What effect does shortening the gearing with the 4.1 ratio have on the total energy delivered to the rear wheels over the timespan of accelerating through all 5 available gears? What beneficial effect does going to the 4.1 ratio have in a rolling start drag race? What effect on traction does the 4.1's increased wheel torque have? Keep in mind, the more you have to row through the gears, the less time you spend putting power to the wheels. You may put more torque to the wheels with the 4.1 gearing per trans gear, but each gear covers less increase in vehicle speed and less time for the turbos to get spooled. From my experience with the 4.08 diff, I actually am inclined to believe it would be in my best interest to go to a taller diff gearing. It will spread the gears out so I can cover a larger range of speed per gear, it will reduce the torque at the rear wheels which will likely allow the tires to grab traction in 2nd gear (even at 14psi in 2nd gear I will blow the tires loose with the 4.08 gearing), and the primary benefit is that it will also allow the turbos to spool up earlier relative to engine RPM in all of the gears, thus producing more total power to the wheels than the 4.08 ratio over an identical timespan of acceleration......... Just a few things to consider..... =)
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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That is an interesting observation. You have changed from - 
