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cc to HP conversion

12417 Views 19 Replies 9 Participants Last post by  Glenn M
Hi Folks,

Looking at a Generac GP 3250 generator for emergency power use. It has a 207cc engine. Googled "convert cc to HP" and came up with "15-17 cc = 1HP. Doing the math, 207/15=13.8 HP? I had a 5500 Watt Homelite with a 12 HP engine. So, a 3250 watt generator with a 13.8 HP engine?

Is the above mentioned conversion applicable for small gas engines or am I missing something? I know that Generac is a good machine, but that much overkill?

Thanks for your time,

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on a side note, i have to say that i don't agree with the part about generac being a good machine. if you can find one at a decent price look for a honda genny. to put it in the perspective of tractors, a generac is a box store unit while a honda is a medium duty dealer unit. they have their usefulness, you just have to know what you are getting and what you need it for.
keep in mind tha tif you need to use a portable genny for a week you better have a lot of gas and a lot of OIL on hand. you have to change the oil in them every 25 hours of run time, just like a lawn mower! that means 1x a day if you it continuous.

what we did during our ice storm of '94 was run the genny long enough to keep the fridge and freezer cold, then shut it down. if they are full they will stay cold a while. a deep freeze if left closed and rather fully stocked should stay below freezing for 16 hours or more, a fridge usually about 8.

for optimal fuel usage you don't want more than about 50% of rated load on the genny. the more electrical load you run, the more gas you will use per hour.

also, if you plan on running electronics off the generator i highly recommend getting a good UPS. power the UPS from the genny and the electronics from the ups. you can potentially fry them them if you don't.
that is what the UPS is for, it cleans up the AC. some will not run off generators at all they stay on battery!

i run a $100,000.00 paging terminal and network off a honda 5kw generator. we had to change out 1 ups becuase it did not like the AC the genny was doing and it would switch to battery and never try to run off power. the smarter the UPS, the more likely this is to happen!

local E-911 put in a new tower site a few years back and bought a 4 cabinet UPS with 84 batteries in it. it will run the site for 4 hours or more by itself. the old genny they installed has a mechanical governor and the output changes from 58hz to 61 hz regularly. the UPS would think the commercial power was too dirty and switch straight to battery! they ended up havign to put an electronic governor on the genny to solve the issue.
cheap UPS are actually more likely to work since they are not as ticky about the power. the best UPS i ever had on one was a little 240w tripplite, no smart sense or anyting on it.
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