In the Mallock racer it's got a Hewland Mk9 heavy duty gearbox in the back. With the engine I'm going to build for it, I'm going to be very torque limited as to how much power I can feed through it, as they are only good for about 150 ft-lbs to 160ft-lbs. The engine I want to use is capable of a fair bit more than that and I'd like to use it if possible.
Apparently the weak part is the casing, between the gearset and diff housing.
Any tips on how to make them stronger? For those unfamiliar with them they are a basic VW beetle-type gearbox casing.



I posted this on another forum and had one guy say ...
"We fed 500hp through ours for hundreds of hillclimbs and only broke a crownwheel when we tried launch control. And that was with a car that weighed 550 + kgs and had 14 inch wide tyres of the softest compound. I'd personally choose something else to worry about.."

Well, the simplest thing to do is to take your housing into a foundry and use it as a pattern to cast a new one out of cast steel. That should handle 3 times the torque. (you can't actually use it as a pattern because of expansion, and the machining will cost a bomb).

However, that's a few thousand bucks, and scores about 3/10 for elegance.

So what we need is an exo skeleton for the current housing. The load case is pretty simple. You are trying to control the mesh of the pinion and crown. (To put this into context, controlling this is the MAJOR cause of diff inefficiency, and noise). SO draw some diagrams showing the forces on each bearing of interest and you might come up with a bright idea. I'm thinking triangular side plates.

If my name was Goran I'd build a cube out of 3/8 steel that picks up off the flanges, and then do some interesting experiments to find out how much I could cut away.

On the other hand I am sure we have many tame FEAers on this forum who need the chance to show off, so if you come up with some accurate dimensions you might get some useful help.

Ta Greg, I'll have to look at that.
I'm missing out on a good 100hp by limiting the torque.

How long will it last? Is it feasible to change it regularly?

Even at 150/160 lb/ft they are marginal - it is not just the case - CWP and gears suffer as well.
There is an after market 'Rino' case available ex USA that would fix the case problem.

You really need an FT or FG gearbox and even then around 220 lb/ft is about the limit.

For $213 I'd start here.

http://www2.cip1.com/ProductDetails.asp?Pr...081%2D301%2D513

These come from the Type 2 VW camper. Still in production in Brazil.

Keeping the suspension loads out of the gearbox will help. A goog strength tie across both the top and bottom of the side plates will also help even more.

Good luck



Charlie

Thanks very much chaps. The Rino case looks like a good start, as well as some bracing here and there.
I'll be using a Motec M400 on the engine and it'll have boost-per-gear so I can turn the power down in the lower gears, then increase it up to 5th gear, that should help as well.

This one also looks good ->
http://www.autocraftengines.com/product8.htm
A removable bell housing which is desirable as well.

silly boy !
should have kept the live axle

Remember if you use a VW case you have to get it machined to take the Hewland reverse idler gear. Easily done by any good machine shop. You can also get from some Hewland specialists a double width first gear. Originally for Hillclimbs but they will help with your bigger power output.

Absolutely!

Couldn't agree more...