1.2 Ti Gearbox

[Marlow Sud]

Hi guys,
I hate to be greedy but I need another one.
The first one is in the 1.5SC now thanks.

The Trofeo has a very low final drive for hill climbing and I need a good 1.2Ti gearbox please.

Any help much appreciated.

Brgds
Simon

[PETROLHEAD]

Could you perhaps build a hybrid box of what you already have in the car with a taller final drive simon?

[alfasuddriver]

My friend has one Simon

[Veesix75]

Simon

As per the post from Chris (from sunny climbs) re gear ratios - some of the later series 3 gearboxes have the same final drive as a the 1200ti so depending on your ratios you might be able to change just the diff?

the best box I had for racing was a hybrid of 16v gears, 1200ti gears and 1200ti diff.

[Marlow Sud]

Hi Guys,

Great advice.
Can anyone advise what maximum speed I should be allowing for on the fastest sections of the circuits in an Alfasud?
ie: when do you hit the aerodynamic wall? 115mph?

Brgds,
Simon

[KevJTD]

i have a couple of 1.2 ti 'boxes simon. can let tom have a look over one or both if you'd like, condition unknown at the moment.

[KevJTD]

Hi Guys,

Great advice.
Can anyone advise what maximum speed I should be allowing for on the fastest sections of the circuits in an Alfasud?
ie: when do you hit the aerodynamic wall? 115mph?

Brgds,
Simon

my sud with the 1.7 16V engine, 1.2 ti box, 195/50 r15 tyres was perfect on gearing around cadwell really. 5th was a useable gear but never got near rev limiter (7,200rpm) in 5th.
don't underestimate the difference you'd gain by going up tyre sizes. much cheaper than changing diff ratios.
speak to tom/bryan first though. there is a sweet spot to be had, going bigger than 15's isn't a good idea i'm told

[Veesix75]

Simon, the only curcuit I ever hit max revs in 5th is Snetterton in its old format down the back straight.

The modified cars like Bryan's and Teds would be different.

With a 1200ti box I only use 5th twice at Cadwell, main straight and back straight, and neither is flat out in 5th. This on 13 inch rims.

At Donnington I use 5th twice, back straight and start finish. If I was braver perhaps craner curves.

I'd prioritise acceleration over top speed. On the rollers the sprint was doing 110mph or so flat out in 4th, so I reckon 120mph in 5th on the longer circuits. You need to get the speed quickly.

On your Trofeo rims, Perhaps go for a 1200 ti as best option initially if you can get one, then look at hybrids later ? Plus, I'd stick to 13inch rims to keep the period look...

[Marlow Sud]

i have a couple of 1.2 ti 'boxes simon. can let tom have a look over one or both if you'd like, condition unknown at the moment.

Hi Kev JTD,
Thanks very much. The selection of ratios is more complex than I thought. I have an excel sheet with all the various ratios, engine speed, tyre circumference etc that I need to study.
I will get back to you if I may.
All the best,
Simon

[Marlow Sud]

Simon, the only curcuit I ever hit max revs in 5th is Snetterton in its old format down the back straight.

The modified cars like Bryan's and Teds would be different.

With a 1200ti box I only use 5th twice at Cadwell, main straight and back straight, and neither is flat out in 5th. This on 13 inch rims.

At Donnington I use 5th twice, back straight and start finish. If I was braver perhaps craner curves.

Hi Tim,
Thanks for the info. What RPM are you revving to? And what is the circumference of your tyres?
That would be really helpful.
Tom advised me to put a chalk mark on the front tyre and the ground and push the car forward one revolution and measure the distance travelled.
Brgds,
Simon

I'd prioritise acceleration over top speed. On the rollers the sprint was doing 110mph or so flat out in 4th, so I reckon 120mph in 5th on the longer circuits. You need to get the speed quickly.

On your Trofeo rims, Perhaps go for a 1200 ti as best option initially if you can get one, then look at hybrids later ? Plus, I'd stick to 13inch rims to keep the period look...

[Veesix75]

Simon

I'm using 185/60/13 toyo r888 tyres - check their site I think it gives a diameter and / or circumference

I was using 7600rpm

My previous 33 racer using 6800rpm showed 102 mph on the rollers in 4th using 185/55/14 r888 (or I think they were 55' might have been 60 profile).

Both with a 1200ti box

Old fashioned I know, but the Haynes manual has all the Sud ratios , I'm sure Shrew once posted a link to a site that did all the calculations for you. I also have a formula for doing it scribbled down some where that is really simple to use. I'll try and find it.

[Veesix75]

Found it already

When I used it to calculate a sud 1.2 box @ 6000rpm on 13 inch wheels and 70 profile tyres gave 102mph in 5th, I reckon that's pretty close, and the equation works because a slightly higher ratio box worked out at 108 mph using the same equation.

MPH = (RPM * TD * 3.142) / (GR * 1050)

Where

MPH = speaks for itself
RPM = same as above
TD = Wheel AND Tyre Diameter (actual measurement, not guess based on nominal tyre size)
3.142 is the value of Pie (the mathematical one, not steak and kidney....)
GR = gear ratio multiplied by final drive (so you'll need to know each cog ratio and the diff value)
1050 = just a constant value, not sure where/why it is derived from

Or try this from Bryan

http://www.gearboxman.co.uk/inforatios.html

[Marlow Sud]

Hi Tim,
Your tyre circumference is 1.735 according to a website. Mine is 1.665 measured. My gearbox seems to be closer ratios than the 1.2Ti in that 5th is not an overdrive.

At 7600rpm your speeds are
34, 58, 83, 107, 128 with a 1.2Ti box

My speeds at the minute at 7600 are
31, 46, 59, 71, 83

If I use a 1.2Ti final drive at 7600 I get
40, 59, 76, 92, 107

If I use a complete 1.2Ti box at 7600 I get
32, 56, 80, 103, 123

If I use a 1.5Ti final drive at 7600 I get
43, 62, 81, 97, 113
Brgds
Simon

[Veesix75]

That bottom option looks like it could be ok on the twisty circuits, a close 4th and 5th isn't a bad thing.

I think I use 5th once at brands Indy

If your tyre was the same as mine, what would you get on the 1.5ti final drive?

What profile and width are your tyres?

The calculation clearly works, because you worked out 107mph at 7600 in 4th for my car, and I checked the rollers readout and it actually showed 108.2 mph at 7800rpm. That's a close enough match to trust it.

I won't be using 7800rpm again...!

[Spacenut]

This is from my spreadsheet...

TRANSMISSION RATIOS

Early 1350/1500 Early 1200/1300 Post 1982 1500 Sprint/Veloce

1st 3.545 4.545 3.75 3.545
2nd 2.062 2.062 2.05 2.048
3rd 1.452 1.434 1.387 1.452
4th 1.114 1.115 1.027 1.114
5th 0.921 0.931 0.825 0.897
REVERSE 3.091 3.091 3.091 3.091
FINAL DRIVE 3.889 4.11 4.11 3.889

Mr Haynes supplied these ratios too. I need a 1.2 Ti gearbox more than most, as I use 15" rims with 205/60 boots to fill out the wheel arches. Acceleration with my old '78 1.5 Ti box (3.889 final drive) was fairly decent, my most recent box (post '82 1.5) had pretty poor acceleration, theoretical top speed in 5th @5,800 rpm was 125 mph. It did help me attain average fuel consumption figures of 44 mpg though

My new 1.2 Ti gearbox should yield 111 mph in 5th at the same rpm. That's equivalent to a 13" wheels and tyres on a Green Cloverleaf. Looking forward to getting some more spritely acceleration out of the Green Machine!

Lauren

[Marlow Sud]

That bottom option looks like it could be ok on the twisty circuits, a close 4th and 5th isn't a bad thing.

I think I use 5th once at brands Indy

If your tyre was the same as mine, what would you get on the 1.5ti final drive?

What profile and width are your tyres?

The calculation clearly works, because you worked out 107mph at 7600 in 4th for my car, and I checked the rollers readout and it actually showed 108.2 mph at 7800rpm. That's a close enough match to trust it.

I won't be using 7800rpm again...!

Hi Tim,

At 7600rpm with 1.5ti final drive and your tyres: 44,65,84, 101,117.
My tyres are 235/45/13
My max power is at 7500rpm and max revs are 8700.

All the best,
Simon

[Marlow Sud]

This is from my spreadsheet...

TRANSMISSION RATIOS

Early 1350/1500 Early 1200/1300 Post 1982 1500 Sprint/Veloce

1st 3.545 4.545 3.75 3.545
2nd 2.062 2.062 2.05 2.048
3rd 1.452 1.434 1.387 1.452
4th 1.114 1.115 1.027 1.114
5th 0.921 0.931 0.825 0.897
REVERSE 3.091 3.091 3.091 3.091
FINAL DRIVE 3.889 4.11 4.11 3.889

Mr Haynes supplied these ratios too. I need a 1.2 Ti gearbox more than most, as I use 15" rims with 205/60 boots to fill out the wheel arches. Acceleration with my old '78 1.5 Ti box (3.889 final drive) was fairly decent, my most recent box (post '82 1.5) had pretty poor acceleration, theoretical top speed in 5th @5,800 rpm was 125 mph. It did help me attain average fuel consumption figures of 44 mpg though

My new 1.2 Ti gearbox should yield 111 mph in 5th at the same rpm. That's equivalent to a 13" wheels and tyres on a Green Cloverleaf. Looking forward to getting some more spritely acceleration out of the Green Machine!

Lauren

Hi Lauren,
Thanks for the info.
Have you still got your post 82 1.5 gearbox?
All the best,
Simon

[Spacenut]

Hi Lauren,
Thanks for the info.
Have you still got your post 82 1.5 gearbox?
All the best,
Simon

Yes I have. PM sent!

Lauren

[Marlow Sud]

Thanks Lauren.

Just to confirm to the thread, the gearbox I am after has a 39/11 final drive and comes from a post 82 1.3SC, 1.5SC, 1.3Ti or 1.5Ti.

All the best,
Simon

[PETROLHEAD]

Hi Simon

I opened up some of my hopefuls this morning, but it seems i have the uk stock of 9/35 sud/sprint boxes!

i have a couple more to assess yet, but before i do, do you need an inboard brake cased box or not fussed?

[Marlow Sud]

Hi Shrew,
Thanks for doing that. I have been all round the houses with engine speeds, final drive ratios and different 13in tyres to get all the options.
I have taken some expert advice and been told about the risk of over-gearing.
The final advice is to use a pre-82 1.5TI final drive 3.88 with my gear set.
One of these gearboxes was sent over with the car and is ready to go.
I will publish my spreadsheet for everyone to use and populate with their own ratios if they want.
Thanks to all for help and input.
Brgds,
Simon