Abby’s Guide > Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) > Discussions > HP questions
Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions |
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trouts2
Location: Marlboro MA
Joined: Dec 8, 2007
Points: 1328
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HP questions
Original Message Feb 16, 2012 10:50 am |
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Jrtrebor: “trouts2 - I agree, Bumping up the RPM on these engines does seem to be the only difference I've been able to find that explains the increase in HP.”
I’ve been curious about the hp ratings on similar engines for years. Very puzzling.
SO: Looking for feedback on hp production to see if I have things right.
Relative mostly to 4-7hp HSK and R*Tec two stroke engines with varying hp ratings. It’s looking like they get their hp boost from rpm changes but I’m wondering about the mix of a few things like gas, muffler and throughput.
What effects will various things have questions like the following scenarios: CARB/GAS MODS: If more gas is added but the governor fixed at 3600 no change in hp will happen or if any extremely slight. The added gas with the same air will make the engine run a little faster but being governor limited won’t make much difference. Possibly it could make a bit more powerful chamber explosion and add some torque when running up to rpm 3600 max but being governor limited at 3600 no significant change in hp. A carb change or bowl nut change without upping the governor will not do much. T/F?
BETTER ASPERATION: Similar to gas. If the intake or exhaust flow are improved the combustions will be more efficient the engine could see a very modest improvement in torque because of the improved combustions and the engine will spin up faster and more efficiently to 3600. If still governor limited the intake or especially exhaust change will only get you to 3600 in a better and efficient way with a tiny improvement in torque or hp due to governor limit. MUFFLER CHANGE: Same as better asperation. Thinking here of just a slightly better muffler not a “tuned pipes” type change.
Real hp changes would happen for the following while still 3600 limited:
Larger bore, long stroke, tighter head, port change i.e. all pretty big physical changes. Generally speaking no real change in hp will take place on an engine without big part mods. Most changes without changing the governor to allow faster spinning will have only insignificant effects on hp or torque. Given a well built engine with wide latitude in aspiration and gas flow, governor changes will easily bump hp. I’m now thinking the HSK850 and R*Tec are engines with wide latitude. Borat, you ran your engine to rpm max and it made me wonder if gas might have been the limit like if you go there then gave it slight choke it might have spun a bit higher. ?? It’s looking like all along from 4-7 hp for the HSK850 and 4-6.5 for the R*Tec that only governor changes were responsible for the walking up of hp. At least that's what I've been thinking until JRT posted his crank differences.
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jrtrebor
Location: Michigan - 3 hours north of Chicago on the lake
Joined: Feb 10, 2010
Points: 539
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Re: HP questions
Reply #3 Feb 17, 2012 8:59 pm |
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I would agree, engine specs as they refer to each other regarding changes in RPM, HP, and torque are never linear. The truth is we don't really know what the actual Specs are for any engine. We only know what they tell us they are. You might like to read what it said in the B & S Operator manual for the Model 084100, 084200, and 084300 engines. TECHNICAL INFORMATION
Engine power rating information.
The gross power rating for individual gas engine models is labeled in
accordance with SAE (society of automotive engineers) code J1940
(small engine power & torque rating procedure), and rating performance has been obtained and
corrected in accordance with SAE 1995 (revision 2002-05). Torque vales are derived at 3060 RPM
horsepower values are derived at 3600 RPM Actual gross engine power will be lower and is
affected by, among other things, ambient operating conditions and engine to engine variability.
Given both the wide array of products on which engines are placed and the varity of enviromental
issues applicable to operating the equipment, the gas engine will not develop the
rated gross power when used in a given piece of power equipment
(actual "on site" or net power). this difference is due to a variety of factors including
but not limited to, accessories (air cleaners, exhaust, charging, cooling, carburetors, fuel pump, etc),
application limitations, ambient operating conditions (temperature, humidity, altitude),
and engine-to-engine variability. Due to manufacturing and capacity limitations
Briggs and Stratton may substitute an engine of higher rated power for this Series engine
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