Sizing a gas motor to replace an electric

[cjf12]

How do you go about getting the right size gas engine to replace an electric one? I have a 2 hp 220 volt single phase I want to replace to run a 3040 gast and a 3 phase 2 hp to be replaced to run a d60 leybold vacuum pump. Found a site describing torque vs hp and seemed a little much. I am assuming there is a rule of thumb such as 1 hp elec. needs 2 or 3 hp gas? Any recommendations

[tuckermtn]

How do you go about getting the right size gas engine to replace an electric one? I have a 2 hp 220 volt single phase I want to replace to run a 3040 gast and a 3 phase 2 hp to be replaced to run a d60 leybold vacuum pump. Found a site describing torque vs hp and seemed a little much. I am assuming there is a rule of thumb such as 1 hp elec. needs 2 or 3 hp gas? Any recommendations

I would suggest a 5.5 hp honda for both of them. not sure of sprocket/pully sizing. Think the GAST pumps run pretty high RPMs?

[Rossell's Sugar Camp]

It depends what rpms the engine will need to be ran at. My 6.5 HP Briggs and Stratton has to run at or below 2500 rpm. It does not produce much power until around the 3000 range which is powerband. If you go by the rating on the side of the engine you'd better be running the engine at powerband. I have a 6.5 hp briggs and Stratton replacing a half hp motor and at 2500 rpm it does pretty well. down around 2000 it really struggles. but at 3000 there is nothing going to stop it. The most important thing is to size your pulleys such that the engine will be putting out 3000 rpm or so and the piece of equipment be matched for this. unless you want to oversize the engine like I did.

Bottom line....
For your situation I would either use the 5.5 hp Honda or a 6.5 hp briggs & Stratton. making sure they run at 3000 rpm with the ratio on the pullleys to the equipment. It is a fairly easy calculation and im sure many traders know how to do it.