jimlab

If "power" at the wheels is what determines the rate of acceleration, and power doesn't drop off in higher gears... why does the rate of acceleration drop off in higher gears?

turbojeff

iTrader: (30)

Are you suggesting we can change the HP of any motor/engine by changing the gearing? I know we can optimize gearing to take advantage of it's power curve.

What would happen to lost engine "power" if you drew a control volume around the drivetrain, where would it go?

jimlab

No, I'm suggesting that torque at the axles determines the rate of acceleration and torque at the axles falls off as gearing decreases... it was a rhetorical question.

turbojeff

iTrader: (30)

Torque at the axles coupled with axle rpm = power.

Snook

iTrader: (12)

I was never aware that anyone ever had problems with the fd transmission. If its properly oiled and not abused I don't see why it can't take any power you throw at it. Should the 400rw+ daily driver 7 guys be worried?

rotorbrain

nope, not at all. . . just another rotary world attempt at over-engineering the rx-7 setup. . .

paul

Erdin

Help me out with the ratios im not to good with that side of things. There gears are higher would that not mean that you would have harder acceleration at a given Rev or is it that the revs would go up for a given speed. I don’t understand help me out.

1st 3.827:1
2nd 2.360:1
3rd 1.685:1
4th 1.312:1
5th 1.000:1
6th 0.793:1

Ours:
1st 3.483:1
2nd 2.015:1
3rd 1.391:1
4th 1.000:1
5th 0.719:1

turbojeff

iTrader: (30)

The Supra gears are numerically higher, but have a "shorter" ratio. They offer more multiplication of engine torque. If you had the same diff gears in both cars the Supra would need to shift before the FD.

Erdin

would a 3.9 final drive in the diff help out at all.

jimlab

that depends on what your goal is. 3.90s behind the Supra 6-speed would still give you more torque multiplication in every gear, and add another gear in the higher speed ranges. It would also drop 70 mph in 6th gear to ~2,930 rpm (stock tire) vs. ~2,790 for 5th with the FD 5-speed, which would help with highway mileage.

Supra 6-speed with 3.90s
1st - 3.827:1 (14.93:1 final drive)
2nd - 2.360:1 (9.20:1)
3rd - 1.685:1 (6.57:1)
4th - 1.312:1 (5.12:1)
5th - 1.000:1 (3.90:1)
6th - 0.793:1 (3.09:1)

FD 5-speed with 4.10s
1st - 3.483:1 (14.28:1 final drive)
2nd - 2.015:1 (8.26:1)
3rd - 1.391:1 (5.70:1)
4th - 1.000:1 (4.10:1)
5th - 0.719:1 (2.95:1)

The question is, would it be worth the cost and effort? The answer is a resounding "**** no". A set of 4.30 gears in the FD's differential would do about the same thing with far less hassle.

FD 5-speed with 4.30s
1st - 3.483:1 (14.98:1 final drive)
2nd - 2.015:1 (8.66:1)
3rd - 1.391:1 (5.98:1)
4th - 1.000:1 (4.30:1)
5th - 0.719:1 (3.09:1)

Erdin

I mainly wanted it for the strength of the box to use for drag racing because its one of the easer and cheaper gear boxes to find in the uk that can take 500rwhp+ but after reading every thing about the ratios iam starting to think twice about it.

ruos

iTrader: (1)

An ideal box is one that keeps the engine within the torque curve where it produces more force.
A 6 gear box is more of a vanity, or a marketing strategy.


Or, throw a CAGS solenoid to force it to fourth and high five the EPA like Chevy's Vette. Of course, you'll need good low-end torque to pull the car in fouth.

jimlab

Especially with a 3.42:1 ring and pinion.

Erdin

Ok just found out that I was wrong it’s the 5 speed supra TT that they do a adaptor for and not the six speed so has any body got any details of the ratios for the 5 speed we could look at.

Would be greatly appreciated

Erdin

Rhode_Dog

The 5 speed? Thats from the MKIII supra right?

Erdin

Ok these are the ratios from the 5 speed what do you think
1st 3.30:1
2nd 1.95:1
3rd 1.34:1
4th 1.00:1
5th 0.75:1
Rev 3.20:1

jimlab

Not much different than the stock 5-speed.

1st - 3.48:1
2nd - 2.02:1
3rd - 1.39:1
4th - 1.00:1
5th - 0.72:1

rpm_pwr

Well that's gotta put that one to bed. Why would you bother? Also the 5 speed supra box is weaker than the stock FD box so you're nuts going that way too.

Erdin

No this one is the R154 from Toyota 3.L Turbo 7M-gtm its a heavy duty one i was speaking to one of the shops in Australia and the guy said that they used it on their 750rwhp rotary. so if that is true then its stronger then standard rx box and cheaper then the after market one's, and the ratios dont seem all that bad the only thing is its hard to come by.

cmartinp28

erdin.... how much power are exactly looking at? unless your name is vosko, its pretty hard to ruin an fd transmission. tranny brace helps a lot too

rpm_pwr

Yes I know I've smashed one into little pieces
There are lots of people down here that have smashed those boxes with a lot less power than that. I really suggest you drive a car with one before getting it fitted:
-They're a pig of a box. Notchy, baulky badly gated
-They're HEAVY
-You have to be brutal with them
Sadly, a lot of people sell W57/8's as R154's too, which are fragile crap with all of the same failings. Yes, some people reckon they're stronger, but the top drag teams down here don't bother with them and generally have a horror story to tell you about them. For serious power, nobody is using a Japanese box.

DaGOATCorollaGTS

Has no one thought of taking a look at the RX-8 6 speed in the FD?

Ive heard all this talk of supra missions and none of the RX8. Im Curious.

dgeesaman

iTrader: (7)

It's a Miata transmission, too weak. Do some background reading before suggesting something like that again, noob.

Erdin

So which one would you go for and also is there any way to tell the deferent’s between the W57/8's and the R154.

Thanks

Erdin