Original Stratos stradale, Dino or 246 GT speedometer fitting to Hawk

[Rene]

Hi.
I have just picked up a set of refurbished revcounter and speedo from Roberto.

The ratio on the speedo itself is 1:1 according to Roberto, but I am not sure how this will work with the 164 V6 5 speed gearbox so I get the correct readout on the dial.
Roberto has offered to calibrate it so it is correct, but he is not sure either....

The TB15 270/45VR15 rear wheels should have a rolling distanse of 1,9625 m a turn, so 51 times should be about 100 meters and it would be possible to count turns on the cable.

In my head, one turn of the wheels should also make one turn of the diff, making it a locked 1:1 readout no matter the wheel size beeing 10" or 20", but what do I know and it should not matter if the crownwheel and pinion is changed for lower top speed / higher aceleration and a new LSD is now in the gearbox?
So it should be a matter of getting the correct pickupgear for the cable end on the diff or calibrate the speedo to the turns of the cable on a given distance?
But please correct me if I am wrong I have never done this before.

I guess someone here has done this allready and any input will be much appriciated.

Regards

René

[ChrisCar6]

The speedo cable output on the Alfa box is driven by the output side of the differential, so is fixed to the wheels rotation. If the rolling diameter of the wheel/tyre combo you are using is the same as the original Alfa fitment, then the speedo output will be correct. Mine appears accurate with my 578mm diameter 886 revs per mile tyres.
Original Alfa seems to be a 195/65 x 15" giving a 635 diameter which should make mine over read significantly!

[Rene]

Thanks Chris.

Good to hear I am not completly lost
The TB15S 270/45VR15 have 625 mm diameter, so that means around + 8% different to your tires but only - 1,5% off from the Original Alfa 195/65 x 15".
So should be 1,5 % more exact than the stock Alfa then. And there are always a built in error on the safe side of the speedlimit, that is probably why you get a accurate reading.

In Norway we drive by the speedlimit + VAT, witch is 25% and usually that is fine with the built in errors of the speedo + error at the police radar.

My concern was that the ratios inside the speedometer of the original Alfa and the original Stratos stradale, Dino or 246 GT speedometer was not the same.

What kind of speedo do you have in your car?

Regards

René

[ChrisCar6]

It's a Fiat one, don't know what from.

[Rene]

Hmmmm....

The the original Stratos stradale had a 250 km/t dial, but the most used Fiat speedo i think has 220 km/t, that was in my car too...

No one with a Veglia borletti 250 km/t dial and a Alfa V6 5 speed gearbox that can shed light on the issiue?

Regards

René

[Guy Mayers]

Hi Rene, most of the Fiat speedos I've had have a marking on the case that says 1 Giro = 1 Meter. I've currently got a 250kph speedo from a Fiat Dino Coupe in the car, attached to the Alfa gearbox and running 345s on the back. I think it's pretty accurate, pottering down the motorway and comparing it to the Sat Nav display and they're very close.
Hope that helps!

Guy

[Rene]

Thanks Guy.

Just what I needed to hear....
A strait swap then....

Regards

René

[Guy Mayers]

Hope so Rene - just sourced a 60mm Veglia Borletti speedo to replace the Dino one when I "improve" the Gp4 dash. It's TINY! The gauge has the 1 Giro to 1 Meter marking and the scale reads to 160 kmph. I've sourced a gearbox that converts this to 160mph and will get a new face to replace the existing one that reads 250kmph. Sounds complicated but it's not. The real problem I have is setting up a mechanical drive for a rev counter..... I'll get there in the end!

Cheers

Guy

[Rene]

Good luck Guy.
Will keep you posted on the swap, witch should take place in the spring, as the car will hybernate in the UK untill March / April.
No point taking her home to the salt and snow....

Have a nice weekend.

Regards

René