Originally Posted by GoingTooFast
Let me do the math for you using the above formula:
7450 rpm (BRZ's rev limiter) * k (const.) = 59.2 mph
x rpm (rpm @ 40.0 mph) * k (const.) = 40.0 mph
x = (40.0 mph * 7450 rpm) / 59.2 mph = 5033 rpm
This means that at 40 mph in 2nd gear you don't even benefit of the Toyobaru's engine full potential because you haven't reached engine's max. torque yet which only appears at 6400 rpm.
@ 6400 rpm the speed has already increased to (40.0 mph * 6400 rpm) / 5033 rpm = 50.9 mph
So, you get the best useful window ONLY over 1050 rpm (7450 - 6400) with a max. speed variation of 8.3 mph before you need to shift up.
I must reckon I was wrong and you were right about downshifting into 2nd @40 mph and get the best of the Toyobaru's engine.
Looking at the FA20 engine torque curve one can see that it's pretty flat around engine's max. torque from just under 5000 to 7000 rpm
, thus it has a much wider usable power band than that I've mentioned: