What determines, in a car's engine, the amount of horsepower produced?

Question

For example the Mitsubishi Eclipse has a 3.8 liter engine, but only produces 260 horsepower. On the other hand you have the Infiniti G37 with a 3.7 liter engine that produces 330 horsepower? Why the difference?

What would be the point of making such a big engine with so little horsepower?

Answer 1

The amount of fuel being pumped into the intake, the density of the air (colder air is denser and provides more horsepower), the type of intake manifold (long or short runners), the bore of the cylinder and length of stroke of the crank/piston, the length and size of the exhaust/headers before the collector, the restriction of the exhaust (catalytic converter and muffler), the type of oil you use (regular or synthetic), the engine can be balanced, the intake and exhaust ports can be ported and polished... and so on with numerous little things that can be done to increase horsepower.

Answer 2

Lots of factors - let's start with bore, stroke, length of time valves are open , how far down the valves can go into the cylinder (letting in more fuel vapor), any mods such as less restrictive exhaust, variable valve timing which keeps valves open longer at low engine speeds, turbo or supercharging and the simple fact that as years go by engineers find more sophisticated ways to extract more horsepower from engines.  In 1985, Chrysler needed a turbo to get 145 horsepower from a 2.2 4 cylinder, now with 16 valves in a 4 cylinder you can get 140 horsepower WITHOUT a turbo.  Just goes to show you.

Answer 3

Cause they can. Efficiency, dooood!

Answer 4

HP is a function of torque and engine speed.  Torque is just force x distance.

One of the limiting factors is money.  Lots of money gets you lightweight materials and variable intakes and exhaust which help the engine breath better at all speeds.  The Infinity engine is probably much more expensive than your Mitsubishi engine.

Answer 5

Putting it in very simple terms.

A number of "features" makes an engine be more powerful than other. at the end of the day the HP comes from the ability of "breathing" of ingesting air. A bigger engine "eats" more air but also other features like compression (turbo) or flow (bigger ports/valves, etc.) will increase the HP.

Answer 6

I wont answer the first parts because you already deleted the other question (same question).

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>What would be the point of making such a big engine with so little horsepower?

260 HP is NOT so little power. In 185, the Trans Ams had just 145 HP and tons of torque.  Just because other cars comes with MORE HP, it doesn't mean 260 is not a lot.  It is what you do with it that makes a difference.

As some old timers about HP.

Good Luck...