Technical Please help ID my gearbox

[Benjammo]

I've got a 6 speed punto box from a mk2 punto 1.2 sporting that i was going to stick on my seicento, still may if i can find the time.

I've read alot about doing this on here and aparantly theres more than one, does any one know if theres any codes, id numbers or any other ways of identifying which box i have?

 

[arseofbox]

I've got a 6 speed punto box from a mk2 punto 1.2 sporting that i was going to stick on my seicento, still may if i can find the time.

I've read alot about doing this on here and aparantly theres more than one, does any one know if theres any codes, id numbers or any other ways of identifying which box i have?

Theres loads of little codes on the castings - mainly part numbers on ePER.

The Gearbox should be a C514 on that model but could be a C513. Look for a number that follows the long part number thats common to most housing parts and that should give a reasonable indication to which box you got!

 

[Benjammo]

thanks mate i've had a look around and i've hound the number c514.5.13, along with some random long numbers again starting with c154513, i'm confidant that its a c514, anyone know what the final drive ratio this box has and the stadard seicento sporting mpi box? is it going to be worth changing?

 

[jug]

its definately worth changing, you'll gain acceleration and top speed, difficult to believe i know but its true, wait and see.

the mk2 box uses much longer ratios that the mk1 6 speed, that is because the mk2 has an engine that isnt as weak as a retarded ant.

the final drive is 4.071
1st gear ratio 3.545
2nd gear ratio 2.158
3rd gear ratio 1.480
4th gear ratio 1.121
5th gear ratio 0.921
6th gear ratio 0.766

do the maths and you'll see its a good choice for a sei sporting, maybe a bit long geared, but so is the standard box imo. a better choice would be scrapping the 1.1 engine.

 

[Smiler121]

Been struggling to find specific mention of Mpi Sei ratios, but I think I read somewhere the FD fitted was different depending on wheel size (13" vs 14") that was chosen when it came out of the factory? (I'm not certain).

If in an Mpi Sei we have the same gearbox ratios as other Seicento Sportings then...

Just adding some gear ratio's for the Seicento (thanks to a Polish workshop manual and the Abarth I used to own):-

1108cc Sporting
1 3.909
2 2.158
3 1.345
4 0.974
5 0.766
R 3.818
FD 3.867

1108cc Sporting Abarth(pre-facelift)
1 3.909
2 2.158
3 1.345
4 0.974
5 0.766
R 3.818
FD 4.071

A lower number final drive will give more miles per rev.

IF the figures jug quoted are the correct match for your GB, my Sei was originally fitted with 13" wheels so using these figures I believe that after fitting this box I'd see a longer 1st gear (higher top speed in 1st) but as the ratio in 6th is the same as my 5th I'd get a lower maximum top speed.

Given the other final drive option (for 14" wheels) is 4.071 then the Maximum top speed would be the same in 6th as it was in 5th before the change.

 

[Smiler121]

its definately worth changing, you'll gain acceleration and top speed, difficult to believe i know but its true, wait and see.

Given my calculations I don't get how this can be true?

Acceleration maybe by being able to better manage the revs & stay in the peak torque/power range but at these ratios I don't see how the top speed can be more?

 

[jug]

6 speed 4.071*0.766=3.1184

sei sporting 3.867*0.766=2.9621


at any rpm the 6 speed will be doing more turns of the road wheels, so unless your rpm is limited by the longer gear you will have a higher top speed. on a light car with a fairly slow top speed the chance of the power limiting the rpm you can achieve in top gear is very small, in my experience you can always hit the same rpm unless the gear is significantly longer.

my data doesnt show that the abarth FD exists, however assuming that was true, then the top speed would be the same. i didnt know about the abarth FD so i did not consider it.

 

[Benjammo]

thanks for that, i think i've got the answer i need, as soon as my head stops spining from the numbers and maths, i'll try and decide if its going to be worth fiting it and paying the extra insurance.

 

[Smiler121]

Are the formulae in this handy calculator I found somewhere else on the site & then substituted the figures into wrong then?

Although the results aren't claiming to be accurate reflection of my car, they use the same method to calculate both lots therefore discounting wind resistance & actual power output I believe they should give a comparison assuming all other factors stay the same & that the formulae used aren't flawed?

 

[Derv drinker]

A bit of alongshot, but Fiat groups Fiat power train website may be able to identify the gearbox for you as they are listed with a little picture and some info about clutch size mating etc.

 

[jug]

Are the formulae in this handy calculator I found somewhere else on the site & then substituted the figures into wrong then?

i cant see anything wrong with them, but i cant see why so many variables need to be considered in such a simple comparison where the only variables are gear ratio and final drive.

 

[Smiler121]

I'm confused!!! The spreadsheets show that the 6Speed would have a lower theoretical top speed?

we've figured that it depends what you are after & if the ratios are the ones Jug quoted then using the spreadsheet I attached I still think it'll be lower top speed & slightly longer 1st gear.

I think it is important to work out for certain which GB it is though 'cos one of the boxes had a FD figure of 4.923 (were 15" wheels ever an option on any of the donor cars?) which would absolutely MURDER the top end speed & make all the gears really short.

The following is from somewhere else on the site...

Well i can tell you the 6speed is no good for what your trying to do, it will infact lower the top end as its a close ratio box. I was thinking about putting one on my turbo cinq but having driven a punto with the 6 speed box its defo a no no.

To be honest mate, the revs at 4250 is no biggy, you still get good mpg, if its noise your bothered by invest in some sound deadening and plaster the inside of the car in it.

 

[jug]

i think you're getting confused between the mk1 6 speed and the mk2 6 speed. the mk1 had very short ratio that are a bad idea (but were needed for the crap engie at the time), and many people have found out the hard way that this isnt a good box to use, but the mk2 6 speed is compeltely different. i drive a mk2 punto sporting almost every day and at 4000rpm in 6th it does nearly 100mph. assuming you stick it on a sei or cinq using the same size tyre (185/55/15) then the same would be true. since the sei and cinq use smaller tyres you effectively shorten the actual length so speed would be slightly less, but you're only talking a few percent less, it wont be 75mph as the excel sheet suggests, what size tyre is assumed in that calc?

 

[Smiler121]

Both comparisons were done using the same wheel & tyre size of 175/50/13 which is what is on my car.

The figures shown for a 5 speed of 80mph in 5th @ 4000rpm, & 6 speed 75mph in 6th @ 4000rpm. With your size tyre of 185/55/15 it suggests a real world 87.81mph @ 4000rpm which sounds entirely plausible For .

It is important to bear in mind speedo inaccuracy as I've seen my needle go off the clock (just over 125Mph) when hitting the rev limiter in 5th on a long "private" road & it is only a Sei 1108 Mpi on 13" wheels.

 

[BAJ]

so is it worth fitting a 6 speed box or not ??

and how hard is it to do ??