New Chapter in my quest to find out if a six speed gearbox is any good on the RX-7, and its not looking the way i thought it would.
The numbers are run and the graphs displayed. Since this is a beta, i'll cut to the chase:
It turns out, with the software setup the way i have, the 5 speed is faster than the 6 speed
As you can see, the 5'box is superior in acceleration and top speed. If you count the gear-changes, represented as "bumps" of no acceleration, the two units are equal (the ghost is 6 speed) only through a tiny portion of 4th gear. Remember this is with equal final drive ratios.
So what happened? Well i think i've narrowed it down to two, possibly 3 good reasons.
Reason 1 (Possibly): Engine curve
I may have picked a curve which is too "short", i.e. there is some data missing for higher rpms. The curve I've used, which had the advantage of being very smooth, may not suit the 6 speed very well. However there is no mathematical way to prove that more rpms will close the performance gap, if anything it should move the two curves further up together. There could be a slight acceleration gain from being able to shift later in the power band and drop less revs with the gears being so close together.
Reason 2 (Definitely): Tires
I have issues against this type of tire simulation. There are too many variables like tire wear and temperature which are not considered when calculating the coefficient of friction (mu).
For example: My friend Alessandro recently installed a TD06 SL2 18G turbo on his S15. For legal reasons (and a little drifting) he's running 235/40 17 tires all round. His car is outputting far more power than the RX7 in my simulation, and it wheelspins through all of first, second and a little bit through third gear. In this software, my virtual 285hp RX7 with 265/35 18 tires wheelspins through all of first and second gear when accelerating, with the 5 speed gearbox wheel-spinning less than the 6 speed in second gear.
In total, the 5 speed lights up the tires for 75m vs the 6 speed's 71m upto 108 km/h ! ).
The software can be configured to use different mu values, however the default setting is already 0.9. Slick tires can exceed 1.0, however these quoted figures represent only a "static" value.
In reality, tire grip (as we all now) varies considerably. It would be reasonable to assume that in a situation like the one represented i.e. a drag race, the tires would be hot and considerably stickier than their "indicated" value. More grip can favour the shorter geared six speed as it would allow it to put more power to the ground before exceeding the tire limit.
Reason 3 (Probably): Final drive too short?
My choice to use a 4.1 final drive ratio (same as the stock 5 speed manual) may have backfired. After all, the 5 speed gearbox is designed specifically with that ratio in mind. It could be possible that by just slotting in a 6 speed and keeping the stock differential, all I am effectively doing is adding a gear between 4th and 5th, thereby hampering performance more than adding to it. Research is needed on the longest final drive available for the RX-7. Perhaps by using a six speed and a longer final drive there can be benefits, but so far I've proven that swapping gearboxes and using the stock final drive
does not work.
Stay tuned for Beta 2
Oh hai! I has reads your posts nao ^_^