How do you convert liters into horsepower?

Question

How do you convert liters into horsepower?

Answer 1

The formula for determining the horsepower for a particular engine requires more information than the displacement of the engine.

The three things you need are displacement (engine size, or the swept volume of all pistons in one Otto cycle -- 2 revolutions), rpms, and Brake Mean Effective Pressure (BMEP -- the peak pressure in the cylinder).

The factors that affect BMEP are many, but as one wag explained it, they boil down to "adenoids, indigestion, and constipation" (intake restriction, combustion inefficiency, and exhaust back pressure).

The first of those factors is affected in turn by such things as the shape and length of the intake manifold, whether the engine is throttled (most engines) or direct injected, the number and size of valves, and of course, whether the intake charge is under pressure (supercharged).

The second depends on valve timing and lift, combustion chamber shape, fuel mixture, fuel/air stratification, and the temperature of the incoming charge, among other things.

the third also varies with valve size and number, timing and lift, the shape and angle of the exhaust ports, exhaust manifold shape, and the way in which the various individual exhaust manifolds connect to the exhaust collector (4 into one, etc.).

If you get into 2-strokes, you have a whole different formula, and individual exhaust pipes with expansion chambers to take advantage of acoustic charging come into play.

I always give the example of the original Honda S2000 and BMW M Roadster.  Each was rated at 240 hp but the Honda was a 2.0 liter and the BMW was a 3.2 liter.  The biggest difference was that the Honda's power peak was at 8,300 rpms (redline at 9,000) while the BMW's was at 6000 rpms.  Of course the Honda only put out 153 lb-ft of torque at a lofty 7,500 rpm while the Beemer came in with 235 at 3800.

Answer 2

You can't. Engine size has zero to do with horsepower. I could have a 302 (4.9) that makes 225hp, and I could have another 302 (4.9) that makes 150hp... and there is. In the Mustangs the 302 got 225hp, and in say a low line thunderbird with a 302, it only makes 150hp. Also, I could have a turbo 1.6 that makes 1000hp if I built it strong enough.

Answer 3

You can't.

Best you can say is more engine capacity (measured in liters), gives you more HP, everything else being equal.

But there are other ways of increasing HP without increasing capacity, such as a turbo, higher compression, more valves, etc.