MGB How much Torque can a standard MGB gearbox handle?

[al1978]

I am supercharging my MBG and am wondering if my gearbox will be able to handle it. I will probably be getting about 180 horsepower max not sure on torque. what sort of power can these box's handle?

 

[jlaird]

Well guess they hold it for the racer guys except they seem to use a lot of rear axles.

 

[Dave Russell]

Re: How much Torque can a standard MGB gearbox han

The "racer guys" usually don't use supercharging. The differences are illustrated as follows.

Going by these formulas,
HP = (Torque X RPM)/5252
and
Torque = (HP X 5252)/RPM

You can see that as rpm increases torque decreases for a given horsepower output.

Since street supercharging gives an engine considerably more torque at a lower rpm, & torque is the limiting factor on gear box strength, it's anybodys guess how well the gear box will hold up. Probably OK if you don't drive it at the max all of the time.

As an illustration, a stock engine that develops 90 HP at 5500 rpm would likely have a maximum torque of100 lb/ft at 4000 rpm.

Assume a conventional race engine that develops 180 HP at 6500 rpm & maximum torque of 140 lb/ft at 5500 rpm or 147 HP at 5500 rpm. Much of the horsepower gain comes from increasing the rpm at which maximum torque occurs.

If the supercharged engine develops 180 HP at 5500 rpm, & 160 hp at 4000 rpm, the torque would be 210 lb/ft at 4000. The supercharged engine would develop 50% more torque than the conventionally modified engine, & 210% more torque than the stock engine.

The above numbers are for illustration only. You can work out the numbers for your setup.
D
Edit:
Remember that more torque = more cylindr pressure = more stress on head gaskets = more stress on crankshafts = more stress on rods, pistons, & bearings. Not just the gear box,U joints & axles. Engine life will be shorter. Engines purpose built for supercharging have the strength of all these components increased.
D

 

[jlaird]

Re: How much Torque can a standard MGB gearbox han

And that of course is why they use so many rear axles.

 

[Deleted member 3577]

Re: How much Torque can a standard MGB gearbox han

4 speed boxes are pretty darn strong & I don't think you'll have any problems.

Don't know what kind of rubber you are planning on running or the type of clutch your going to be using.
(I'd use the heavy duty MGB pressure plate rather than a Tilton)
Keep an eye on your U joints.

So far as the rear end goes.....No problem there either.
(The MGB uses stronger axles than the Spridget)

 

[Steve_S]

Re: How much Torque can a standard MGB gearbox han

Gearbox should be fine. If you have an overdrive fitted, you better be careful with it.