DIY Home Improvement, Remodeling & Repair Forum > cc/hp/rpm

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12-26-2012, 05:48 PM
Wuzzat?
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cc/hp/rpm

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

12-26-2012, 07:31 PM
JoeD
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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.

12-27-2012, 02:57 PM
Wuzzat?
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Quote:
 Originally Posted by JoeD 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.

Last edited by Wuzzat?; 12-27-2012 at 03:01 PM.

12-28-2012, 08:03 AM
inspectorD
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Well

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/f...ivalents-4119/
Hopefully it has gotten a better answer.
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12-28-2012, 11:44 AM
Wuzzat?
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Quote:
 Originally Posted by inspectorD 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/f...ivalents-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.

12-28-2012, 01:55 PM
Wuzzat?
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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.

Last edited by Wuzzat?; 12-28-2012 at 01:59 PM.

12-28-2012, 04:04 PM
inspectorD
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ok

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
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12-28-2012, 04:36 PM
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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
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

Last edited by Wuzzat?; 12-28-2012 at 04:46 PM.

12-28-2012, 04:43 PM
nealtw
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I don't know if it will help but I found this list.
http://www.simetric.co.uk/si_cc2hp_data.htm

12-28-2012, 08:15 PM
Wuzzat?
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Quote:
 Originally Posted by nealtw I don't know if it will help but I found this list. http://www.simetric.co.uk/si_cc2hp_data.htm
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.

Last edited by Wuzzat?; 12-28-2012 at 08:32 PM.