Eaton M62

[davidt]

Acquired an Eaton M62 Supercharger and going to fit it to my M20 engine I need the diameter of a crankshaft pulley that will give a low boost any ideas

[appletree]

Whats "low" boost? the next size charger up the M90 would be a better choice if you could get one.

Would have thought somthing around 140mm would get a middle sort of boost -7psi maybe but i cant find the boost and RPM graphs at the minute

[davidt]

Thanks for reply,I was thinking more like 3- 4 psi to start with.

[GeoffBob]

David, M20B?? What displacement engine?

Eaton superchargers are essentially fixed volume pumps. That is to say, for every rotation of the pump-shaft the pump displaces a fixed volume of air. Hence, the amount of "boost" produced by the pump is determined, indirectly, by the ratio of the pump displacement to the engine displacement.

The Eaton M62 displaces 1.0 litre of air per rotation of its input shaft. I'll assume for the moment you are running an M20B25 engine, which displaces 1.25 litre of air per rotation of the crank. Hence, you will require a pulley on the Eaton M62 that has a diameter 1/1.25 times smaller than the crank pulley, just so that the Eaton can pump the same amount of air as is being combusted by the engine (boost = 0). To achieve a boost of say 3-4 psi (call it 1/4 a bar on top of 1 bar atmospheric pressure) will require that you make the pump pulley 25% faster again.

So if your crank pulley is 100mm, you'll need an 80mm pump pulley to break even (0 bar boost), and a ~64mm pump pulley to make 0.25 bar boost on an M20B25 engine. To put it another way, you will require a pulley ratio of ~1.56.

For a 140mm diameter crank pulley you'd need a 90mm diameter pump pulley. Or, for a 100mm diameter pump pulley you'll need a ~155mm diameter crank pulley.

BTW, the above ignores the effects of adiabatic heating of the air as it passes through the pump, which I won't go into here.

Furthermore. The term "boost" really doesn't apply to a roots type pump (such as the Eaton). You are not interested in how much "boost" you can make since your engine doesn't combust "boost" to make it's wheels turn. What you're really interested in, ultimately, is the mass (how many kg's) of air your supercharger can pump into your engine without the engine becoming damaged.

For more info, see my thread here

[davidt]

GeoffBob, Thanks Very much for the info, yes the engine is 2.5