Can anyone add some values to this, along with what it is? People ask for this conversion a lot and depending on what I get, I may be able to come up with formulas that have small errors. cc hp rpm 1.76 0.27 17000 3.5 3.45 42600 9.95 1.9 16000 32 2.2 10000 50 4.2 7000 125 28 14000 2998 920 19200 28000 1400 4000 71500 3500 2800 25498000 108920 102 I need practice with fitting formulas to data. TIA

I think there is much more to the formula than the three values you are using. The grind on the cam, the shape of the piston head, the compression ratio, the valve size , the carburetor fuel and air flows, the type of fuel, the ambient temp, the altitude of operation, all have and effect.

That's the beauty of stat formulas; they summarize. In return you get some error in the values predicted by the regression formula. For a small range (not what I've shown) in cc values and using many values you can get pretty decent accuracy. Grainger publishes comprehensive specs for their engines so I guess I should look there first.

I don't know if this helps or hurts your quest, but this did get discussed about 5 years ago, here is the link. http://www.houserepairtalk.com/f11/ft-lbs-cc-equivalents-4119/ Hopefully it has gotten a better answer.

Thanks. I'll start with the cc/cu.in vs. hp specs on my lawnmower, leafblower, chainsaw and string trimmer and proceed cautiously from there. While using various Excel functions to reduce these data and hone my data reduction techniques, it would also be good If I come up with some useful answers.

I've got a new take on this. First I did just lawnmower engines, then just leaf blower engines, then both, none of these using zero cc = zero hp. My chainsaw and string trimmer did not post hp values. Then I repeated, using zero cc = zero hp, which makes sense based on the physics. The max percent error, 3 ea. lawnmowers, no zero, was 8.3 and with zero, it was 8.4. The no zero formula is hp = cc x 0.01875 + 0.475 for the range 148 to 188 cc and 3 to 4 hp, and 1/0.01875 is incrementally 53 cc/hp. The max percent error, 5 ea. leaf blowers, no zero, was 8.2 and with zero, it was 8.2. The no zero formula is hp = 27 x cc for the range 0.95 to 1.1 hp and 27 cc, and 27 cc/hp. The max percent error, 8 ea. lawnmowers + leaf blowers, no zero, was 8.4 and with zero, it was 17. The no zero formula is hp = cc x 0.01854 + 0.509 for the range 27 to 188 cc and 0.95 to 4 hp, and is incrementally 54 cc/hp. Therefore, cc = (hp - 0.509)/0.01854 With this formula, a 100 cc engine should put out 1.854 + 0.509 = 2.4 hp, + 8.4%, - 8.2%. There's a big gap between the 0.95 and 4 hp, so if anyone has some other values, the formula above can be made more comprehensive (with possibly larger errors). And, for some reason, using zero makes the errors worse.

Here's that word again...Assuming with just the "motors-CC's "all the carbs are the same....Now add in your other carbs, and your turbos or govorners....still same cc's but different Hp. I think that is why a formula is hard to come by. Variables everywhere.But maybe still able to be narrowed down. I won't pretend I understand your formula, however, if you have not already included this in your theory, http://en.wikipedia.org/wiki/Horsepower

If you plot a graph, lawnmowers seem to be in a class by themselves, so for only things that people carry with their hands, e.g., leaf blowers, chain saws and string trimmers, hp = (cc x 0.09966)-1.6430 with about 10cc/hp. Max error is +10%, -15%, with avg. error lower. No theory, just fitting a straight line to samples picked from the Web. Plotting the values makes outliers obvious so I removed them. cc hp ratio calc'dhp.% error device 27 0.95 28 1.05 .....10.3....leaf blower 27 0.95 28 1.05 10.3 leaf blower 27 0.95 28 1.05 10.3 leaf blower 36 1.9 19 1.97 3.9 chain saw 66 4.9 13 4.92 0.5 chain saw 29 1.4 21 1.25 -10.9 string trimmer 25 1 25 0.85 -15.2 string trimmer 75 5.9 13 5.79 -1.8 chain saw 32 1.6 20 1.57 -2.1 chain saw 50 3.2 16 3.36 5.0 chain saw 27 1.1 25 1.05 -4.8 leaf blower 27 1.1 25 1.05 -4.8 leaf blower

That's what I started with. It shows 1 to 42 cc/hp and my straight line formula had terrible errors using it. Maybe some kind of exponential formula would work better with it. 1 hp per cubic inch (16.4 cc) was supposed to be the holy grail of car engines in the 60s but some of these manage to exceed this.

I can do the straw-into-gold thing but The Big Gold Interests bought the patent and shelved the technology.