[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?

[Al_The_Man]

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

[Geof]

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?

[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 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.

[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.

[Geof]

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.

[Geof]

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.

[JFettig]

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

[Al_The_Man]

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. :violin:
Al.

[NC Cams]

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.

[Geof]

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.

[diarmaid]

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.

[NC Cams]

23 hp in 640 cc is only 23hp in 39.055/cid which I'd concur is pretty lame for anybody

OR

the engine was tuned for some other purpose than to make absolute maximum HP.

Or

that is the power output at a certain design operating RPM and the engine is governed NOT to reach max power or RPM.

100hp per liter has been a benchmark of reasonability for production engines for quite some time. That equates to 1.6387hp/cid.

That's only 589.9hp from a 350 Chevy.

[Geof]

.....that is the power output at a certain design operating RPM and the engine is governed NOT to reach max power or RPM.

Little industrial engine that I repowered my mini Case digger with. I think they are deliberately derated.

Which serves to demonstrate that a simple cc to hp conversion is a bit useless unless your precision is of the order of 1 +/- 1

[fkaCarel]

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

I have to defend Honda. They were literate a long time ago.
In 1966 they had a 2-cilinder 50cc (bore/stroke: 35.5 * 25.1). Specified power: 11.8Kw/ 16hp at 21500rpm, which makes 320hp/ltr. In development was a 50cc 3 cilinder which was targeted at 18,4kw/ 25hp at 25000rpm. 500hp/ltr.

[diarmaid]

I'd like to get my hands on one of those 50cc/16hp Honda engines. Any idea of the make/model or if an equivalent is in production nowadays?

[fkaCarel]

Consider them unobtainable. They are handmade jewelry. Search for 250cc 6-cilinder replica's. $500000 each.

[Geof]

I have to defend Honda. They were literate a long time ago.
In 1966 they had a 2-cilinder 50cc (bore/stroke: 35.5 * 25.1). Specified power: 11.8Kw/ 16hp at 21500rpm, which makes 320hp/ltr. In development was a 50cc 3 cilinder which was targeted at 18,4kw/ 25hp at 25000rpm. 500hp/ltr.

My Case digger would really smoke the ground with one of these installed

[Al_The_Man]

Did you specify what you are looking for 2 stroke? 4 stroke? Single cylinder? etc.
The smallest 1cyl. I can think of industrially is the Weed Wacker type 50cc 2 stroke.
Honda make a 4 stroke cc? for their Generator systems.
Al.

[NC Cams]

Not really Geoff

You my have an engine with a power rating at 2500 rpm which is the governed speed. If you ran it ungoverned, it might make 0.9hp per cid or more at a higher RPM

The 5hp Briggs and Stratton engines used on go karts make 5hp at 3600. But if you rev them to 6 or 7k, they put out nearly 8.

Rated power point and absolute max power output from the same engine might be both viable and totally different.

If I recall correctly, the Turbocharged 1800cc F1 engines were putting out nearly 1000hp.

Anyway, the examples cited clearly shows that you simply can NOT multiply displacement by some magic factor and predict the power output of ANY engine.