Hi,Is there a way to calculate hp for a gasoline driven power unit when switching from an electric one?? Trying to find the formula to convert. Thanks,Joe

P.S.Thanks for your help on posting Bud.

I always heard you should figure the electric motor HP and use 1.5 times that for a Gas Engine.
This web site says Twice the Elecric HP for a Gas Engine.
http://www.surpluscenter.com/Hydraulic.htm
Look at the Note on the Fill in the Blank Calculator about half way down the site.

Bud,thanks for your quick response.That's exactly what I needed.Poppa....

The 1.5 or 2x the HP method is okay but the best way to do this is to actually calculate the torque required by the pump Torque = CIR x PSI / 2pi
Then go looking for gas engine torque curve information.
Then just pick an engine that produces 15% more gross torque at that RPM than you will need.
15% more because you should not operate an air-cooled small gasoline engine at 100% of it's rated power, they are designed for 85% continuous operation.

Example - you have a pump that runs at 3,600rpm with an electric motor and produces 4gpm and the system operates at 2,000psi.
This meant you likely had a 5hp electric motor.

Since your 4gpm pump operating at 3,600rpm displaces .25666 CIR we can calculate the torque it requires and come up with .25666 x 2,000 / 6.28 and we get 81.74 in-lbs or 6.8ft-lbs. Go shopping for an engine that puts out 8ft-lbs of torque or more at 3,600rpm and you have a winner. It also guarantees you won't have more engine than you need (expense and fuel use) or less than you need.
The problem with the 1.5 or 2x the electric motor guesstimate is if you are operating at a different RPM. Small gas engines IDLE around 1,750rpm and there is no way that a 10hp engine at idle is going to put out the torque that a 5hp electric motor has available at 1750rpm. That is why I use the torque calculation method.

Good info fpda31 it's A Keeper for sure. I think I've read or heard this before but never had to use it so it went by the wayside,

Well, that 5 HP electric motor is putting out 15 ft-lbs at 1750 RPM. A 9 HP Honda GX270 puts out 5 HP at 2000 RPM, and probably around 13 ft-lbs at that RPM. There's no reason to believe a 10 HP diesel wouldn't be putting out the same torque or more than a 5 HP electric at 1750 RPM.

Thanks guys,youv'e been most helpful.Poppa...