Let's put a wee diesel in a ruby- now what rear end ratios?

[A Spooky Ghost]

I've had the thought for awhile now about using a mini Kubota diesel.  As fate would have it, I found a d950. Temporarily installed in a old big mower.

Has a claimed 21hp, at 40ftlb torque. Max 3000 rpm.

So it seems, with a rear end ratio of 5.12 my safe max speed could only be 40mph...

That's not enough!   So does anyone know of some custom rear ratios, that could fit the factory diff.

Or this a find another whole axle thing?

[Ivor Hawkins]

Finding an axle that narrow in the States, with the correct ratio would be a challenge, I would go for a little three cylinder petrol (gas) engine and keep all the standard running gear.

Is your original engine scrap?

[A Spooky Ghost]

Yeah mine needs everything. I thought a mini diesel would be interesting.

[jpsmit]

could you grab a rear axle from a Kei truck or a side by side?

[FrogPond]

Suzuki Samurai rear housings have an offset carrier. If you use two short-side axles and shorten one side, you end up with a track of ~44" and a centered carrier. There are many ratios available for them. Standard was 3.73. They are 5 on 5 1/2 and can be drilled for other bolt patterns. 
What transmission are you going to use ? Mike

[Howard Wright]

Hi Spooky

The lowest ratio Austin made was 4.4 (9 to 40 teeth in Bill Williams Special building book), although I think these are really rare. 4.89 (9 to 44 teeth) is the most common ratio on most axles up to about 1932? Thereafter 5.25 was the norm. So at 3000 revs you’ll be struggling to get more than 47 mph.

Cheers

Howard

[A Spooky Ghost]

Hmm, never thought about a kei truck, or samurai axle.

I had thought about a Ford Model A axle. It's a perfect ratio, but would require some serious modification.

If I can make a adapter plate, I'm leaning towards using the factory 4 spd.

[Alan]

Why not keep the Austin axle and put in an additional 1:2 gearbox so the propshaft turns at twice the speed of the engine.

[A Spooky Ghost]

Not a bad idea.

Model A ford's have a aftermarket overdrive unit, in the torque tube. Now to find one used...

[Colin Morgan]

Hi Spooky

The lowest ratio Austin made was 4.4 (9 to 40 teeth in Bill Williams Special building book), although I think these are really rare. 4.89 (9 to 44 teeth) is the most common ratio on most axles up to about 1932?  Thereafter 5.25 was the norm.  So at 3000 revs you’ll be struggling to get more than 47 mph.

Cheers

Howard

There's one offered on ebay at the moment... courtesy of Mr Betts.