Thread: Convert cc to hp ?

1. Convert cc to hp ?

I think this comes under the 'measurement' forum....

So does anyone know how to convert cubic centimeters (cc) into horsepower (hp) ?

I know its not a direct conversion but Im sure it can be done. Anyone know the formula or even an approximate conversion?

2. Is that some kind of trick Irish question
Or post in the Apple & Oranges Forum
Al.

3. Originally Posted by diarmaid
I think this comes under the 'measurement' forum....

So does anyone know how to convert cubic centimeters (cc) into horsepower (hp) ?

I know its not a direct conversion but Im sure it can be done. Anyone know the formula or even an approximate conversion?
I have a two cylinder overhead valve Honda engine with a capacity of 640 cc that develops 23 HP so one conversion factor is 1 HP for every 27.826086cc.

But really this conversion has no more meaning than my using 6 decimal places.

What are you really looking for?

4. lol.....unfortunately not!

The problem I have is that I have seen an engine in a similar application to what I want to use one for and it is just shown as 50hp. No info on engine type or bore capacity.

I want to initially use a 125cc engine and I need to know how far short of this approx hp rating its going to fall so I can allow for the space and weight increases of a bigger engine in the future.

5. Thanks Geof. That does help a little bit. At least I have a general basis figure to work from. Right now I dont need to be exact. Although the 49hp engine I saw was a lot smaller physically than an average 1.2litre 4 stroke so Im going to have to check it out some more.

6. Originally Posted by diarmaid
lol.....unfortunately not!

the problem I have is that I have seen an engine in a similar application to what I want to use one for and it is just shown as 40hp.

I want to initially use a 125cc engine and I need to know how far short of this approx hp rating its going to fall so I can allow for the space and weight increases of a bigger engine in the future.
Clearly 40hp needs 1113.0434 cc and 125 cc can produce 4.5 hp.

Actually this type of crude calculation does have some validity when you are comparing engines of similar type, i.e. carburetted versus carburetted or fuel injection versus fuel injection with similar compression ratios.

7. Originally Posted by diarmaid
Thanks Geof. That does help a little bit. At least I have a general basis figure to work from. Right now I dont need to be exact. Although the 49hp engine I saw was a lot smaller physically than an average 1.2litre 4 stroke so Im going to have to check it out some more.

I should also have included same rpm range although that is more or less implicit in 'same type'. Just don't try to compare a Formula 1 engine with a Vespa scooter.

8. torque and rpm can do it,

P=TN/63000 T= in*lb T'= oz*in N= RPM P= HP

P=TN/9550 T= N*m N= RPM P= KW

Jon

9. Originally Posted by diarmaid
Although the 49hp engine I saw was a lot smaller physically than an average 1.2litre 4 stroke so Im going to have to check it out some more.
I remember way back when in the UK they imposed a limit for motor cycle riders with learners licence to 250cc, British 250cc were not that powerfull, so the Japanese produced a 250cc with the performance almost equal to the older 500cc.
Al.

10. THe formulae posted in reply #8 are merely ways to convert find power when you have torque and rpm. The other formulae simply converts hp into KW. These won't predict power output potential.

Essentially there is NOT a reliable way to convert engine displacement into output power potential. Why? Much more than displacement effects power output potential.

Easiest way to illustrate the displacement versus power output potential is to look at a 350cid Chevy engine.

A production version of the engine was provided at power levels from 295 to nearly 370hp. In racing trim, the engine can produce upwards of 700hp assuming normal aspiration.

Why so much difference?

It all has to do to the changes you can make to the induction system, exhaust systems, heads and valvetrain as well as bore vs stroke relationships to make the engine ingest more air and thus burn more fuel to make more power under a particular set of situations.

If you want a "thumb rule", almost any literate engine builder can make 1hp per cid of displacement without any effort whatsoever. Sharper ones can make 1.5hp /cid. It takes a real good, professional one to make 2hp/cid.

If you can make much more than 2.35hp/cid (normally aspirated and w/o nitrous or other power adders) and the engine lives, you can make a VERY good living building engines for race teams in the Southeast USA

Now, when you start adding nitrous, nitro fuel and/or turbo charging or supercharging, it is easy to double the numbers posted above, albeit with disproportionate reductions in life expectancies of the engines.

11. From NC "If you want a "thumb rule", almost any literate engine builder can make 1hp per cid of displacement without any effort whatsoever. Sharper ones can make 1.5hp /cid. It takes a real good, professional one to make 2hp/cid.".

Obviously Honda, at .5889hp/cid, do not even make it up to the literate level.

12. I've found out how another small engine I was looking at got 118hp from such a small size. They used a rotary engine. Thats ok, I'll look into that route. Thanks all.

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