Technical Hybrid/Close Ratio Gearbox

[RS-1989]

Right, I've had a thought about a Hybrid/Close ratio gearbox for the rally car. I've heard people talking about the 6 speed being better at keeping the engine 'alive' and a nice mod for the Cinq. But obviously because of the longer box you lose a little of the lock and I'm not keen on that TBH. So a thought I had was putting the first 5 gears and the Final Drive from the 6 speed into a 5 speed casing.

Now looking at a few threads on here the ratios from 2nd to 5th are the same between the 2 boxes jest the first is shorter on the 6 speed and the final drive is 4.9:1 instead of 3.8:1. So, has anybody had these 2 boxes apart and compared them? Do people think its possible? If no one has done it, I will be probably giving it a go at some time when I get a job and that.

My thinking is it will give a great rally/quick accelerating box.

Thanks
Sion

 

[fingers99]

Unsure -- the 5 speed box from an Abarth Sei would give lower gearing.

 

[clock34]

abarth box adds 500-750rpm. had it in mine but tbh i think your looking for more. 60mph in 5th was 3550rpm.

 

[RS-1989]

This is a good point, I think the final drive ratio on them is 4.01:1 or something along those lines, which of course is better and would give better acceleration. But only thing I think with this is they would be harder to come by.

From looking on ePER (I know its not the best way of comparing parts etc) some of the bearings and seals are the same, but its just more of a thing of the 1st gear fitting onto the input/output shaft. From other gearbox experience final drives are usually alot more interchangeable, so I'm hopeing the same can be said about these boxes.

 

[clock34]

i have a buggered one here. was whinning under load. probably scrap as its been left with the selector and cups off in the rain but if its anything to you its free if collected.
(not a sales ad)


other than that i think a 6 speed is the only waay. i dont really understand box's tbh, where is the final drive located? near the diff id imagine, if so its more than likely a 6speed fd would fit in a 5 but wouldnt the speedo worm be out. (if bothered)

 

[craigb244]

Ill put it simple... swapping bits from and between boxes (even more so for the 6 speed) is not possible without £££££
the input shaft is one peice with the gears machined onto it (other then the 6 speed the gear IS bolted onto the end BUT the shaft is longer so parts are not swappable (altho you could have the 6th speed change (think overdrive) by having two gears machined.



so the answer is simply... the gear ratios fiat offer on the verious models are what we are stuck with.... no mix and matching between boxes.


there is one option... punto speed gear box.
this does not have gears. only a belt and two pulleys/cones. its a constantly variable transmission that is servo controlled by an ecu. if you can fit this box and figure out how to crack/code the ecu you can then choose ANY gear ratios you want (with even more precision then a normal box) as many gears as you want

 

[craigb244]

other than that i think a 6 speed is the only waay. i dont really understand box's tbh, where is the final drive located? near the diff id imagine, if so its more than likely a 6speed fd would fit in a 5 but wouldnt the speedo worm be out. (if bothered)

the speedo worm is the same on all fire boxes. same as the speedo drive (if fitted) as its on the diff its not effected by gear ratios.

 

[whitz]

lightening the gearbox would make it a bit more fun



looks ££££ to me

Ash

 

[craigb244]

looks like it would weaken them a lot. and cant imagine there been much gain at bet you couldnt even detect a gain from that on the best dyno out there.

 

[rallycinq]

To confirm what Craig was on about.

When I discovered my 6 spd had a bonded, not bolted crown wheel we looked at fitting a 5 spd bolt on crown wheel, but the 6spd pinion wouldn't allow and we couldbn't put the 5spd pinion into the 6 spd box.

Cheers

D

 

[RS-1989]

Hmm I see, so basically its a lost cause without going for bespoke shafts/gears/final drive then. Was just a thought because from what I could see from ePER, the actual gears came off the shafts and I was hoping Fiat (with cost in mind obviously) would have just made the shafts longer to fit the extra gear, so different gears for different ratios could have been fitted to them. Obviously not.

Ah well back to the drawing board

Thanks
Sion

 

[rallycinq]

Some of the gears are seperate, they have to be there are only two shafts so need to be disconnected from their hunbs while other gears are driving.

The gears need to be in matched pairs, thats where the problems start.

Most road vehicle manufacturers have the gears machined in solid at some point.

With a wee bit of work I am sure one of these can be made to fit.

http://www.sadev-tm.com/en/#

Cheers

D

 

[craigb244]

To confirm what Craig was on about.

When I discovered my 6 spd had a bonded, not bolted crown wheel we looked at fitting a 5 spd bolt on crown wheel, but the 6spd pinion wouldn't allow and we couldbn't put the 5spd pinion into the 6 spd box.

Cheers

D

same issue i had but opposite.
couldnt find a bolted crown wheel 5speed but got a shiny new 6 speed box with a bolted crown.

I stripped the box (along side the 5 speed) with the hope of fitting the gears onto the 6speed shafts (because the final drive was different and i prefer 5speed box but needed a bolted crown wheel)
after getting it all apart it is obvious switching parts is impossible.

 

[Todger182]

Thats a pain, would it be possible to have a straight cut drive made up or is that out of the question due to the limited ways of modifying?

Dogbox style gear changes would be nice .

Thanks

 

[rallycinq]

Thats a pain, would it be possible to have a straight cut drive made up or is that out of the question due to the limited ways of modifying?

Dogbox style gear changes would be nice .

Thanks

Check out the STC

http://www.sadev-tm.com/en/#

Cheers

D

 

[Brooky]

Thats a pain, would it be possible to have a straight cut drive made up or is that out of the question due to the limited ways of modifying?

Dogbox style gear changes would be nice .

Thanks

I'd take a straight cut final drive for the LSD if you get a batch sorted

 

[Todger182]

It's something i'm considering after these next few mods are done .

Thanks

 

[craigb244]

It's something i'm considering after these next few mods are done .

Thanks

why? your never going to produce enough power to need a straight cut final drive!
the final drive is plenty strong... think about it this way... its the same box used on cars weighing easily twice the weight of the cinq.

even with slicks and an ATB diff you will find the drive shafts fail before any gear box component does

 

[whitz]

my MJet panda uses these gearbox's just with a much higher gear ratio so im sure it can handle what ever you can throw at it from these engines


Ash

 

[craigb244]

exactly I know of no one who run any modified fire boxes not even fiat used them on there rally cars (the most they did with the drive train is the shafts as i mentioned)

having a striaght cut final made means you need a crown wheel made along with a whole shaft that all the gears/selectors run on... I recon it would cos at least 2k to have it made.
A lot of money for a gearbox that will sound like someone emptying a machine gun in your engine bay and been only useful for pub talk