Originally Posted by mapbike
Good one Baird, I think my Dell must be kinfolks with your HP.....LOL!
First let me say I'm NOT a pro at this stuff, but I do have some experience building engines stock and modified.
HP is good but HP alone isn't what gets you moving, it's more about the torque produced by an engine that gets things moving rather than just HP.
Example: A 3.5HP Briggs engine on a mini bike with a centrifical clutch that has 10T driving a 60T sprocket mounted to a 13" wheel/tire, this set up will take off and go pretty good even with a 200lb fella on it and will hit around 30MPH ungoverned.
Now take one of those 4.2HP 2 smoker GP460 or a 4HP modified CAG and put it on that same mini bike set up the same way and you will find that you will not be going anywhere fast, do they have the HP rating yes, do they have the torque? NO
The briggs developes it's HP rating @ around 3600 RPM's and the GP460 or Cag gets it rating at probably 3 times that.
I said all this to say nope HP isnt all it takes.
From: Measure Twice
I have an old 70's era Briggs model type 808202 0430 and I am not sure of the HP or Brake HP (Torque) or even the displacement. But it looks like the size of a similar 3hp more modern Briggs by size I figure. See 3 pics and one with a side by side of my old Briggs and a new one that on an edger the store listed as 3 Horsepower, but Briggs Mfr does only list on the engine as 148CC and 4.75 Foot Pounds of Torque SAE. Also the pic early on of the sort of dropping the engine in for mock up.... still finishing the off road bike now... no pedals.... looking to get State approved OHV sticker for State, Federal, and Private parks that have OHV facilities.
Just as a word of caution, but I guess many already know is as the engine displacement goes up the power can and does many times does go up and not linearly. That is good though ..... better weight to HP or Brake HP ratio!
I suppose someone here knows or I contact Briggs directly or go to a shop and see if they have old records for model type numbers to get that info.
Anyway I saw many times engines that have listed HP at different values maybe as a typo from the seller and differing from the mfr. In any case displacement is probably what I would be looking for to see if the cost for an engine is worth the cost or to make a comparison to another even regardless of cost.
Then comes the new labeling for small HP Briggs and there are no listing even online for HP, only Torque. I guess no problem there should be a way to convert values. The HP is more of a power rating over a longer period of time and Brake HP (Torque) a more immediate measurement if I think I got it right?
The reason I read for Briggs to have small, I think somewhere under 10 hp or so listed as Torque and not HP for the power measure was something to do with a more relevant measure for the application that small engines have.
The thing is that for a long time I always knew about Brake HP (Torque), but really paid no mind to it since I knew of small engine 4 stroke for mini bike and motorized bikes, I was making evaluation of what I saw for this application in HP rating power, and I had apples and apples to compare.
Now with Torque only to see on new small Briggs engines, I have now apples and oranges, so I guess I can do a conversion to make evaluations work for me. If you know the exact application then if they are the same, then you can try doing an accurate conversion and make a good evaluation.
I tried a few formulas and had a bit of a difference in them so I have a little bit of a dilemma.
What is something that I got out of this by serendipity was that I had a couple of engines and think I know more of why the act as they do.
Beside the many Briggs I have had, were Clinton and Tecumseh engines brand for around 3 to 4 HP ratings. I remember that the later two brands with similar HP rating as it were then, I found pulling the rope starter recoil the feel of the piston to go from compression to power stroke before the engine caught, was a feel that if did not like to stay at top dead center for nearly as long as the Briggs engine.
It could have been that the Briggs engine was a bit more leaking at the valves and lapping was no longer the answer, the valves and seat needed the angles on both restored by cutting. I did that recently with a few Briggs and it helped a way lot. But if it was true that there was a difference in the piston throw from top dead center to bottom dead center, then maybe I have something here.
But to the point I heard somewhere that the Clinton engines were very powerful, but what I think what was meant was that it was that they had short piston throw and that equates to more Horsepower for greater speed, but less Torque (Brake Horsepower).
The opposite with greater Torque and like gearing down the Briggs or any other engine regardless of brand that uses a longer piston throw, up to a point gets more hill climbing ability without gearing down as much comparably. I think of it as a gearing down without the uses of toothed gears. It is mechanical advantage by leverage, no gears though. This maybe not too extreme but does account for maybe the feel in the feel of the rope starter cord pull.
All this seems that if you desire to climb hills as a trade off with less speed, you might not need to gear down as much later with actual toothed gears or pulleys later to get to the drive wheel.
Of course if you afford to have a Torque Converter then I guess if you want to go fast and have torque at low speeds, you may I think want an engine with a short piston throw and let the torque converter get the low gear when it finds it is necessary. The infinitely variable transmission!