SIX SPEED??????????????????????????

the fd needs a FIVE SPEED.

5th gear is ridiculous. 4th is one to one and 5th is .72? so if you shift at 7000 you end up in 5th at 5040 rpm. check out the hp and tq on a reasonable modded rotary at 5000 rpm.

i changed 5th gear to .832 and hit 5th at 5824.

the shorter 5th makes the car twice as responsive to drive on the highway. i also get over 20 mpg on the highway..... of course i don't really care about mpg. i am into mph.

howard coleman

 

I've also put shorter RZ tranny for my Blk FD.

 

look at the 6 speed's gear ratios, and the old mazda comp box, you'll find the rx8 has a granny gear 1st, but 2-6 are almost the same as the racing trans from 79...

how come everyone thinks a 6 speeds gotta have some crazy overdrive?

the rx8 box is actually shorter than the fd box. if you put the rx8 tranny into the fd your cruise rpms will GO UP

 

You guys do know that those 6psds shorten the gears, so you run through them faster. The same reason the miata has shorter gears. Its not so much to get better highway mileage (its already a 4banger) but to make it quicker and keep it in its powerband (which has already been stated way earlier in this thread).

So instead of having a 5spd that tops out at something like 200mph, you have a 6spd that tops out at 180 (id probably crap myself if i went that fast anyways). You get through the gears faster, and on tracks (I guess it does depend on the track though) having a shorter gearbox might result in placing you in a much better spot in your powerband through some of the turns (say, at 5k instead of 4k)

 

The 6 speed tranny is only good for 350WHP...

 

We have turbos. We have a fairly broad powerband. Like howard said, to improve this setup for performance, the answer is not to add an even higher gear - the answer is to bring 5th down into a usable range.

You want a shorter gearbox, change the diff. Even with a short 5th and a big reduction in back, you're not going to redline in 5th.

Dave

 

So what happens if you put a big single on and lose your broad powerband? Then it would be usefull to have 6 short gears over 5 long gears? Again, half the reason to do such a swap is to get you through the gears quicker (which can also be done with a lower final drive) but also keep the car in high rpms as much as possible to prevent exiting the turn to low in the rpm range or way too high in a lower gear.


Im not trying to prove why someone should get it (I honostly think its a waste of money) but there's some arguments Ive read in this thread that have been...well...I guess I expect the FD community to be a little smarter about the topic, especialy before commenting.

 

Gear ratio info:

99+ Miata 6-speed 1st 3.76:1 2nd 2.269:1 3rd 1.645:1 4th 1.257:1 5th 1:1 and 6th 0.843:1

RX8 6-speed 1st 3.760 2nd 2.269 3rd 1.645 4th 1.187 5th 1.000 6th 0.843

1993-95 TT (US) 1st 3.483:1 2nd 2.015:1 3rd 1.391:1 4th 1:1 5th.719:1

RZ and Spirit R have 5th gear 0.762
Bathurst R has 5th 0.806

 

RX8 final - 4.44

FD3S 5sp m - 4.10
FD3S 4SP Auto - 4.33

Miata 6sp - 4.10

 

so if fd's fifth gear is .719 and the n/a is .711, that'd be about right for what i want.
i usually don't dump the clutch going into 5th, so i'm not worried about it breaking... now if it would only fit???

anyone ever try that?

 

I think you ment FD3S 4SP Auto - 3.90? I wish they had 4.33s. I would guess getting ahold of them would be easier.

 

Sorry about that, you are right.. 4SP auto is 3.90

 

I like this guy!!

 

Not exactly true look at any dyno chart there is nothing flat about the power curve at all until fuel cut. Yes it produces better then average torque many naturally aspirated rotary, or a four banger, but it's right in line with a six. With the 99 spec twins and not really happy with the power until after the transition say 5500 rpm. From that point on the car has violent acceleration, but I don't think the power would be particularly great for anything but straight line driving. The fluctuating power band would make it difficult to get the most of the car on a winding track.

On the other hand once you redline 1st gear you can pretty much keep the core of the sweet spot all the way to topend. So like just like any other low displacement engine you can't make power without the revs.

 

If a person is driving in a situation where this *really* matters, then they would want a tranny with entirely replaceable gear pairs. That way you can ensure you exit each corner at whatever RPM you want.

Besides, if you run the numbers, 8k shifts on an FD tranny result in a drop just below 6k. If a single turbo can't span that, then why would single turbos and 5 speeds been predominant for years?

Not to mention the disadvantages: it weighs more, it's one more shift per straightaway.

But the bottom line remains that Miata/ RX-8 transmissions are hopelessly weak for any serious RX-7.

What did you expect from a 4-year-old thread asking about Miata and RX-8 drivetrains?

Dave