Gear Ration Spreadsheet

[LukeC]

Someone else will have to chime in. t depends on your application.

I have niether done it myself or driven one. Vin Sharp at pace will be more than glad to talk to you about it.

[John A Pucak]

The gear ratios in my group s race car are
1.  2.875
2.  1.72
3.  1.25
4.  1.04
5.   .88
Good for 206 kph.

[Paul Newby]

PTP, I started out with a standard Twin Spark box. With the 4.1 final drive and the 0.79 fifth gear I would only get into fifth gear after the start finish line at Phillip Island! It was pretty much useless.

My box has 1st and 2nd ratio from the Twin Spark box, 3rd and 4th from an early Alfetta box I had lying around and 5th gear is actually the Twin Spark 4th gear, which Vin machined on. The 4.3 diff came out an early South African Alfetta 1.6 but I'm pretty sure that 1.8 Giuliettas and I think late 2.0 GTVs had the 4.3 diff as standard. Now 5th gear is a lot more usable.

This is probably the ultimate affordable solution. I understand you can source Colotti straight cut close ratio gearsets from Italy but they are mega expensive.

[PTP]

Yeah, mine has 4.3s, which mean around 6000-6500rpm in 5th at the end of the straight at PI (I think, I was busy looking through the apex, not at the tacho), which is pretty good. A slightly shorter 5th with the rest the same ratios would be ok, but taller first and second, and shorter 5th would be best. But worth $6K plus? Doubt it.

[PTP]

The gear ratios in my group s race car are
1.  2.875
2.  1.72
3.  1.25
4.  1.04
5.   .88
Good for 206 kph.

I can find the origins of 1-3, but are 4 & 5 custom gears?

[carlo rossi]

are all isostatic ratios the same or did this change as well

[John A Pucak]

Gear set
3rd late series Alfetta
4th early series Alfetta
5th .88 Billett

[PTP]

That's a cool idea. Would be better still if it was also welded.

[Duk]

That's a cool idea. Would be better still if it was also welded.

You'd want to seriously know what you're doing to weld heat treated/heat treatable alloy steel and expect it to continue doing a job like this.
Assuming that the welding process didn't cause distortion in the part, which it would, a welded area has to be considered as a cast area. So any forging process that has gone into the parent metal is ultimately undone. Shot peening after welding would be a good idea, but can't replicate the effects of proper forging.

[PTP]

To be honest, the 3rd to 4th gear ratio spread isn't really the issue with these cars. It's the 1st and 2nd ratios, and for racing probably the 5th gear too.

[Bjurman]

To be honest, the 3rd to 4th gear ratio spread isn't really the issue with these cars. It's the 1st and 2nd ratios, and for racing probably the 5th gear too.

Hi  Here in Sweden we race some with the 116 gearbox..

The problem we got is that the 5th gear is to long..
so I do use to take the
3 gear from the early  Alfetta 1:35  and the
4th gear from  Bacci Romano 1:15
the stock 4th  in 5th       0:94 or the Alfetta 4th 1:02

Weldin is not any problem ..
/ Hans