Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I know that there had been some previous discussion about B&S engines of the same displacement with different power ratings.  Being an owner of the 305 cc engine also known as the 120000 series, my curiosity has been piqued.  From what I've gathered, the 305 cc displacement is offered in power ratings from 9 to 11 horse power.  It's available as the Intek, Intek I/C, Powerbuilt, Intek Snow and Intek Snow Max.  Correct me if I missed any.  Having some time on my hands, I pulled up a copy of the service manuals for the 9.5 h.p. model (20A414) and the 11 h.p. model (20E414).  I compared parts that I though would have an effect on power output.  Things like crankshafts, pistons, connecting rods, valves, head gaskets, carburetors (including jets, gaskets and spacers.  Other than some variation of crankshafts within the same power groups for both the 9.5 and the 11 h.p. which do not particularly differentiate between power groups, there is no difference in the part numbers.  So, if all parts are interchangeable within all three power groups, what is the secret to the difference in power? 

Someone had mentioned that B&S plan to use carburetor restrictor plates on future engines.  Not sure if that would work.  Restrictor plates are used to restrict flow from the carburetor to the combustion chamber.  This in turn reduces rpm.  If an engine is designed to produce maximum power at 3600 rpm, the restrictor plate would reduce maximum rpm.  So, if an eleven h.p. engine makes max. power at 3600 rpm, the 10 h.p.  would be reduced by approx. 10% and the 9 h.p. by approx. 20%.  That would equate to the 10 h.p. machine achieving max. h.p. at 3200 rpm and the 9 h.p. achieving max. h.p. at 2880 rpm. 

 Maybe I'm wrong here.  If so, I would appreciate any enlightenment that can be provided.  Nonetheless, if anyone can explain the difference in power output from the same engine, I'd like to here what you have to say. 

I think you answered your own question. Since the engines all have the same displacement and if all the parts that affect horsepower are interchangeable then they can only have the same compression ratio and torque. Short of using exotic fuels that pretty much leaves rpm as the variable. I could be wrong though.

Honda HS928 TCD - If you lived where I live you'd have one too

Sorry for the italics I have no idea why the post came out that way.

borat,    jusy wondering did u compare all the  parts like flywheel, cyl head,  ignition coil, valve seats. intake/exhust ports maybe they change timing with different flywheels? just a thought , l think in the old days they mostly just changed fuel like the 3.5 to 4.0 B&S.

 l'm thinking the rpm idea is very intresting, it would certianly make it easy for them to change hp of the engines and make more money, all they would have to do is change the governor springs, it would be nice to see the hp/tq bar graphs, that should tell you exactly where those number sit. intresting for sure hopefully u find something out be nice to know

good luck keep us posted

Gelid wrote:
You probably pressed <Ctrl> I instead of <Shift> I when you first typed the sentence. You can always edit it. the other way to turn italics on and off is to click on the "I" button. Some browsers use the <Ctrl> I combination for their own uses so it doesn't always work.

  one  word   "  MARKETING".   this is the onlt difference.  some manufactureres onyl want a 5hp on there equipment.   guys thinks there getting more for the money if it say 6.5  or  6.75 hp  its alla 5hp block  12 series briggs verticals

There's been ongoing discussion over the past year or so about the HP ratings that manufacturers' have on the engines. The consensis is that they are lying by playing games with the conditions that the engines are running under. I.E. the RPM at which the engine is being measured at. There was even a class action lawsuit about it in the US. I believe that may be one of the reasons they are shifting toward the near useless specification of cubic inches or cc's of displacement.

This topic also begs the opposite question: why are engines with different displacements rated the same HP value depending on manufacturer or, even more boggling, depending if a machine is rated domestic use or professional use? I have used a wide range of snowblowers since the 1970's and have noticed that professional machines seem to be underrated . By this I mean that for a given HP rating professional-grade machines appear quite stronger than equivalent HP "domestic" ones. I vaguely thought it may have to do with more efficient design but I'm not sure.

niper99 wrote:

Yeah I didn't go part for part but I did look at pretty much everything that would have an effect on rpms, breathing and compression.   I cannot fathom why their model line-up is so convoluted.  Particularly when there is so much commonality between the engines.  One would think that a complicated catalog that B&S use would be a burden for them to manage.  There's got to be a simpler system. 

Does anyone know if the governor is set to the same RPM across the lineup?

I believe that all of their utility engines are rated at 3600 rpm as are most other brands.