OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines hp calculation

Hi all,
Does anyone know how to calculate hp/cc of a Briggs Stratton engine with the model type and code numbers? I know how to date it but not rate it.
The numbers are modle: 121702 type: 0191001 code: 90091357
By the way it has the 1� shaft so I assume it�s over 5 hp?
Thanks allot
Regards jay

The first one or two digits in the model number are the displacement in cubic inches. There are roughly 16.4 cc per cubic inch so if your 12 cubic inch B&S is exactly 12, it is about 197 cc. The output shaft size depends on the engine size rather than output, and B&S tends to have more than one output rating for each engine size anyway, depending on what maximum engine speed they have decided on (and that is likely to be higher for horizontal crankshafts than for vertical crankshafts). For example, in the 1970s the 9 cubic inch (148 cc) vertical-crankshaft engines were 3.5 hp and ran up to 3,600 rpm. Then B&S derated them by fitting a different carburetor, and set the maximum engine speed to 3,000 rpm; since then the 9 cubic inch engines have had less than 3 hp and B&S pretty much stopped talking about their horsepower. I don't think you can assume that your engine has any more than 4 hp, and it may have a bit less.

Below is the information that you require which will show as a stick post in future for all members, here is a link CLICK HERE .

G'day,
Thanks allot Bruce and grumpy, that chart is very interesting.
Just for future reference 1 cubic inch is equivalent to 16.387064 cubic centimetres. so 12 cubic inch is 196.64 cc
Regards Jay

Jay,

The problem with the size of the bore you can not be acurate with the hp as it also depends on the size of the jet in the carby etc. I have seen a few engines which are the same but different hp ratings.

Hi all,
Thanks Bruce. I just wanted to get a feel if it was suitable to replace an old 5hp Briggs on an old rear engine victa ride on. I know that the mid 80's 5hp Briggs were totally different from the newer junk. I think from memory it was 195 cc so 197cc can�t be too underpowered (although the 12.5 Briggs that�s in 300 pieces strewn across the shed would suit better!)
Soon I will have to order a gasket set (sump, breather and carby) and a set of rings for it. I have located them in the shop but haven�t added it up yet.
Regards jay

Jay click HERE for some more information regarding model numbers to HP rating.

thanks allot bruce, another one for the garage wall!

So the 121702 is 3.5 hp, which is quite a step down from 5 hp. However it will almost certainly have considerably more torque than the 9 cubic inch 3.5 hp engines.