Changing the Gearbox (ratios)

During my first test-drives, I discovered that the gearing of the beetle gearbox is a litle low for this Alfa engine. I can rev the engine very long in each gear, I can rev to 50 km/h in second gear easily for example. It isn’t a real problem, I now have the choice to drive very steady and quiet at low revs, or rev it up high and make the engine scream.
But I am having cooling problems, this might be caused by this low gearing. Because the waterpump pully is sized that way that it will give the coolant enough flow at certain revs. A certain speed is coupled to a certain rev count and that should give amount X of cooling air in gear Y. But, the beetle gearing is lower than that of the Alfa Romeo 33. At least, in my beetle, because it is a “S” model with 1600 engine and the lower geared gearbox.

The next beautiful tables are courtesy of Custom and Speed Parts.

This is the rev-speed table of my beetle’s gearbox with 175/70 15 tires fitted:

And this is the table of the Alfa Romeo 33 1.4 i.e.:
(NOTE: this is the gearbox of the 1.4 Alfa, the 1.5 and 1.7 Alfa 33 has a different (lower) differential value, namely 3.888)

You’ll have to compare the 4th gear of the beetle with 5th gear of the Alfa. As you can see there is about 10 km/h difference per rev number! Quite a lot. This means the waterpump is turning at a lower speed with the beetle gearbox than the Alfa gearbox at a given speed. This, while, the engine is working harder to turn that lower gear. That doesn’t sound good.

I don’t know how much impact this all has to the cooling system. But I have an AM gearbox lying around in my garage, which will give me these gear ratios:

Again, compare 5th Alfa gear with 4th beetle gear. These numbers are much closer to the Alfa gearing!
Maybe I will give this gearbox a try, it will probably improve acceleration a lot!


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