6 speed gearset for ST165/185/205

[wagonist]

For the guys asking for the price...
really don't know how much it will be... but we will know soon:
next monday I'll take them my gearbox, and they'll start working on it.

Will they be able to give an idea then?

Other thing I know is that the more we will be in the GB, the cheaper it will be!
So I'm even, indirectly, replying to the guys discussing of the ratios, because you have to understand that:

1. The most important thing is that we have to be many in the GB!
Because if we won't be many, ther will NOT be any GB of any gearset!

2. So the gearset's ratios HAVE to meet the most consent.
Which are the ratios that will get the more consent ?
Who will be happy to buy this gearset ?
Let's think about it...

I don't think a normal road user will buy it, because he will have no need of it.
I think that a better than stock gearset will be bought by sporty mountain drivers, occasionally or not track drivers, rally drivers, drag racers.

Why wouldn't a normal road user buy it? If it's usable on the road, then why not?

So I thought about a better spaced ratios for any of the above situations.

What do fast road/mountain/rally drivers need ?
Longer than stock 1st for hairpin bends
Shorter than stock 2nd for hairpin bends
Less gap between the gears

What do track drivers need ?
Less gap between the gears to have always good power to come out of the turns

What do drag racers need ?
To tell the thruth, really don't know ! I'm not a drag racer... I imagine a good gap between the gears, and maybe more top end ?

Sporty mountain road & track use would be very similar. The aim is to have the car at the right rev range when driving through & exiting a corner.
Even drag racing would be aimed to keep the car on boost, just aiming to reach the redline of a gear just after you cross the line. but this depends on a lot of factors like power, tyres, suspension setup. And despite that, after 400m, you'd still be only doing 200km/h. Cuts and Justen might be able to give a better answer to this as my car is factory unmodded yet & i haven't drag raced it yet either.

But please also consider that just changing the Final Drive to the 3.933, you'll get more gap and top speed:

I'd seriously suggest staying away from changing final drive ratios. This then requires a rear diff change as well then.

As for your target market:
90% of the people who've replied on here would use their car as their daily transport.
For the applications you've described, I see no reason to not have a tall top gear for cruising, there's not really any places where in a racing (or spirited driving) application that 5th wouldn't be tall enough as these engines have a wide enough rev range.
It probably is even possible to just modify 1st to 4th, give a taller 5th, and not worry about the headache of the 6th gear. My 2nd gear is good from 20km/h to 110km/h, my 5th from 70km/h to whatever it'll do without the JDM speed limiter. It's not like these engines have no torque once their on boost.

Rally drivers are not going to be interested in the gearset you've described because it is too tall. Most rally cars I know of hit the rev limiter in top gear at around 200km/h. And there are other gearbox options for them anyway.

[JustenGT8]

I'd seriously suggest staying away from changing final drive ratios. This then requires a rear diff change as well then.

No it doesn't Steve

[Spectre]

Id like a nice tall cruising 6th gear to bring down the revs while cruising @ 100km/h+

[wagonist]

No it doesn't Steve

I'm confused.
Maybe we're thinking of different things. Isn't the final drive the diff ratio?

[Joshstix]

The final drive is the front diff ratio. This is what drives the transfer case to drive the tailshaft and rear diff. If the stock rear diff is say 3.5:1 then the transfer case is 1:3.5 in terms of how it drives the tailshaft in relation to the drive it is recieving from the front diff.

Basically the same output that turns the front wheels also turns the input to the transfer case and the stock transfer case and rear diff are configured to drive the rear wheels at the same speed as the front wheels. So no matter what front diff ratio you run if you are running a matched transfer case and rear diff the rear wheels will be 1:1 to the frront wheels.

[wagonist]

Still a bit confused
What I'm used to (admitted Subaru, but until this current car they're the only thing I'd had that was 4wd):
Gearset drives a transfer shaft
this then drive the transfer case (centre diff)
this then drives the front & rear diffs

From your description Josh, this is what I understand:
the gearset drives the front diff (same as FWD) & also a transfer shaft to the transfer case (this is the final drive).

Which is a little different to what I saw when I borrowed Mos's GT4 box with unbolted transfer case a couple of years ago.
What I thought I saw:
gear set drives transfer shaft (instead of diff in FWD box)*
transfer shaft drives transfer case
which then drives tailshaft & also another transfer shaft back to the front diff
If * is the final drive, then yes I can see that this could be changed without causing changes anywhere else.

[Fodder]

I've often dreamt of a 6 speed, but don't think I'd be able to afford it any time too soon!

[terryo]

i have built numerous special close and wide ratio boxes for race & rally Gt4's. I have all the ratio data.
there are 2 basic choices for a 6 speed, narrow the 1-4 gears and fit 5 in there, or pack out the 5th section and fit 2 in there. the latter would be the easiest choice, but the selector mechanism would be much more difficult.
narrowing the gears inside the cases is what was done in the RAV4 V6 boxes, and they are already giving problems. with custom gear making, special steels etc, that might be OK however.
whatever you do, you have got to get 1st gear correct for the application. in most cases, we chase about 3.0:1. much lower than this (like 3.4 or so), and 1st gear becomes useless in a serious performance engines, as all you get is wheelspin, and not very far before you have to change gear.
personally, for circuit work, I like to have as tall a 1st gear as I can have, cause that gets you further before the all important change to 2nd. keep the 1-2 gap small.
in a road car, that is not quite so important, and you often need a low 1st gear for the occassional hill start etc.
i doubt a single gear set would suit all possible users.
My circuit race car has a 7 speed gearbox (4 conventional plus 3 overdrive). for each track, we know what ratios are needed and we select which overdrives to use so we can get fast shifts between the conventional gear and the overdrive (which is switched electrically and faster than a conventional change), for example, on long flowing tracks like Phillip Island, apart from the start, you really only need 3 widely spaced gears (2, 3, 4) , but on short winding/tight tracks like Warwick, you need 4 gears, but packed much closer together , 2, 2 o/d, 3, 3 o/d. In this case, the overdrive is a 18% change between the base ratios.

[w0n0matic]

i'd love a 6 speed for my mr2

[Wolf_Tm250]

I'm confused.
Maybe we're thinking of different things. Isn't the final drive the diff ratio?

Final drive, on our boxes, is the CENTER diff ratio..
so changing it you don't need to change anything else...

[Wolf_Tm250]

The only reason i am suggesting to do some computer analysis on the ratios is that you will be able to see the results before you even build the box, or at least be given an indication that you are on the right track.

The aim ratio change for the 5/6 speed boxes that i have presented are from a circuit racing book (cant remember the name - but can get it if you need it). Whie i dont understand the minor differences in the different applications you have chosen (fast road, mountain, circuit, drag), i would think that all have the same objective and that is to accelerate as fast as possible, whether that be to the next corner or not. Now i know that the fast road/mountain ones will have less time for this and having a gear change at the wrong time will really ruin a time but its very hard to estimate ratios for this compared to selecting them for a circuit where everything is in comparison relatively fixed.

One more thing i want to add is that in my analysis, i found that getting the perfect ratios would sometimes lead to faster acceleration, even if you have an extra gear change. When comparing a 5 and 6 speed and if you take that both gearboxes have the same top speed, the only time the 5 speed was ahead was when the 6 speed needed to change which only led to a small percentage of the total run where the 5 speed had the advantage.

Either way you decide to go selecting ratios, it isnt very hard or time comsuming to do some analysis and i would like to help any way i can. Like i said, i can modify the spreadsheed to show anything you want and although right now it is configured to do a 1/4 mile run, i can select any start speed (exit speed from a corner for instance) and for a prescribed distance (entry to next corner) give you the final speed and total time (including time breakdown per gear to see if its lost in the gearchanges).

Sorry big zop, I appreciate your help, but I still think you're not understanding the point...

we have NOT to choose correct ratios for a GIVEN car, with a GIVEN power curve, racing in a GIVEN track or in a GIVEN drag race...
in this case I would be with you, searching and changing ratios according to what is gonna give us the best performance.

BUT we are in a TOTALLY different scenario:
many DIFFERENT cars, with DIFFERENT power curves, in DIFFERENT tracks or situations!
So completely unuseful to try to calculate something, because you have NO fixed/given data.
What we know, and this is the only thing common in all our cars, is that the 1st gear is too short.
And what we also know is that shorter gears can let us choose the correct gear almost in EVERY situation: you can choose the shorter or the next longer one because you would have ONLY 1700/1400 rpm gap between them.


For example, look at the ST205 graph:


With the stock ST205 box, if you have to run a 135 kmh turn, in 3rd gear you'll be with engine at 6300,almost at the end of the power curve... while in 4th gear you'll be only at 4500 rpm... too long gear !



Look now at the ipothetical 6 speed mid#2 in the same situations:


In 135 kmh turns you can choose to be in 4th gear at 5800 rpm OR EVEN in 5th gear at 4700 rpm.

There is nothing more to say... a shorter gapped gearset will always let you have the engine at a good rpm.

Graham Bell in his book says:
"A car with a set of nicely spaced cogs is always much more enjoyable to drive.
Ideally, in a road car, we want 5 close ratio gears for performance, plus a big overdrive top gear for effortless cruising.
The Subaru Liberty, like the Impreza WRX, has an unacceptably large gap, over 29%, in the vital 3rd to 4th step.
The other, though, are all a little under 24%.
This is what we want, anything wider 25% is too big"

[terryo]

there is no point in selecting a 6th gear ratio that will not allow the engine to perform, otherwise you spend you whole life changing from 6th back to 5th., or even lower, just to cruise past someone on the highway . This is what happens with my IS200 6 speed lexus. That will jsut kill any suppsoed economy gain of a tall 6th gear.
For 3SGTE's, engines, I suggest needs to be at 2200rpm or greater as it negligible torque below that point, especially if it has the common mods like big exhaust. If it has a big turbo etc, then that needs to go up to more like 2600.
Assuming the final drive (diff) ratio remains constant, then real advantage of a gear kit will be taller 1st gear, and closer packed intermediates.

[jonathan yee]

agree with terryo.

like on my mini, i had a cooper's' gear set which made the 1st nice and long, second was almost skipable but not quite. made it a much more fun car to drive etc.(only 4cogbox tho)

so yeh everyone agrees on the long 1st, 6th for me i wouldnt care if it's the same as the current 5th(mr2sw20) or only minimally taller and then space all the gears evenly in between.


i mean how many tracks are you gonna revout your current 5th? and i'd hope noone hear would be doin it on the road.

and anyone with the power levels to rev out in 5th on the curcuit somehow i dont think will give a crap about fuel economy.

so 6th gear will need to keep the eng's revs where its efficient.

[Gimpster]

Just saw this thread posted over on MR2oc.com.

I'm not sure about other Toyota cars, but the frame rail on our MKII MR2's (yaya.. whatever you call it) is pretty tight by the cover. How much higher do you think this will get? Let me put it this way, I had to replace my 5th shift fork not too long ago ... required dropping the transmission down from the car until the crank pulley was sitting on the other rail.

I'd give you exact clearances, but I'm too cozy inside to jack it up in Winter

Not trying to throw a wrench in it for MR2 owners, but just something to keep in mind for the "dreamers".

Exactly, now the 5th is outside, so we'll have to make a deeper 5th gear cover to add the 6th gear...

[wagonist]

there is no point in selecting a 6th gear ratio that will not allow the engine to perform, otherwise you spend you whole life changing from 6th back to 5th., or even lower, just to cruise past someone on the highway . This is what happens with my IS200 6 speed lexus. That will jsut kill any suppsoed economy gain of a tall 6th gear.
For 3SGTE's, engines, I suggest needs to be at 2200rpm or greater as it negligible torque below that point, especially if it has the common mods like big exhaust. If it has a big turbo etc, then that needs to go up to more like 2600.
Assuming the final drive (diff) ratio remains constant, then real advantage of a gear kit will be taller 1st gear, and closer packed intermediates.

I've got no prob with changing down the gears. I do it anyway to overtake.
Don't forget your 1G-FE is down 70kW on a 3S-GTE (114kW vs my 191kW), along with the comparable drop in torque. My car is already producing boost at 2600rpm, and will pull from 1500rpm. Though, as you've pointed out, mine is completely stock. I would've thought a freer flowing exhaust would help spool up because of the reduced back pressure

When was the last time you went for a really long highway drive (ie between capitals)?
The roads are mostly flat at the same speed for many hours on end. On most rural country roads you don't even need to acclerate to overtake.