Briggs 2.50 HP confusion

[creia]

Sooooooo.... What makes this a 2.5HP?

Shorter connecting rod. If you take the longer connecting rod (and crankshaft) out of a 3HP and install it into the 2.5HP, you'll have yourself a 3HP.
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The rod and crank are identical to a 3HP on this 2.5HP. I have already taken the 2.5HP apart and compared the rod and crank side-by-side to one of my 3HP engines.
Michael

[Merkava_4]

Couldn't be - longer con rod with more throw on crank would change the stroke spec - as noted originally, both the 2.5 and the 3 HP have a 1.75" stroke, and stroke would be a function of the crank's throw... putting a longer rod in without changing throw would result in the piston poking through the head... and using a longer rod with shorter throw results in shorter stroke... Both engines also have the same displacement (8 CID) - What changes the HP output will be the same as what changes the Torque spec - Reducing the amount of air/fuel the engine is able to draw in, and altering its top no load governed speed.

My bad. I'm going from a 2.0HP to 3.0HP. Not 2.5HP.

The engine is a very old 1968 model 60100. I took the crankshaft, connecting rod, and piston out of an 80200 engine and put it in the 60100.
Same exact bore size, but the 3.0HP engine had a crank with a longer throw. That tells me the crankcases are identical.

I installed a Magnetron ignition coil kit and a chrome ring kit that consisted of 8 piston rings total. The cylinder bore was only worn .001.
Still have the engine today. It's sitting on a McLane edger. It burns cleaner than a new engine does. Great little engine.

[creia]

I checked the ipl. The 80100 has the same bore / stroke as the 80200 and the 80300. All have the same cylinder head and camshaft. Carb is different on all three models. I checked the torque charts that are published in the 1970 Engine Spec Catalog.

The 80100 has 4 ft lbs torque or slightly higher at 2700 - 3100 rpm. In 1970, the list price for this engine was $57.70.

The 80200 has 4.6 ft lbs torque or slightly higher at 3000 - 3300 rpm. This has the pulsa jet.

The 80300 has 4.6 ft lbs torque at 3000 -3200 rpm. This has the 2 piece flo jet.

A comment in the 1977 engine spec catalog indicated the 80100 was discontinued in 1977.

Thank you bluemower.
I am convinced that the ONLY reason this engine is rated at 2.5 HP is due to the smalle venturi on the "Vacu-jet" carb. Both the "Pulsa-Jet" and "Flo-Jet" carbs have the larger venturi.
Michael