How does one calculate Horse Power or (Brake Horse Power)

[The Stigenator]

Given:

Bore
Stroke
Compression Ratio
<Edit>
Also we can/cannot be given the displacement.
</Edit>

is there anything else needed? A forumla would help tonnes.

 

[ElFenix]

ummm... no...

BHp is british horse power
its different from SAE Net.
HP is usually tested on a dyno.
its a function of the rate energy is released from fuel. so in addition you would need RPM as well. but thats just going to be an optimum number even then, and would have little to no bearing on real life autos.

 

BHP is NOT British horsepower,It's Brake horsepower.

You are confusing BTU,British Thermal Units.

There is a formula but I can't seem to find it in my Toyota Tech manuals at the moment

Before 1971 Horsepower was measured SAE Gross=At the crankshaft,no accessories
After 1971 Horsepower SAE NET,all accessories connected and operating

 

[The Stigenator]

actually BHP is Brake Horse Power. Not British Horse Power.
Anyway I had seen somewhere a long time back to calcaulate it without RPM (since RPM is rotation of engine speed on the crank).

I think it went something like HP = Bore*Stroke / Compression

Bore * Stroke = Volume at max.
Compression ration should be from volume max by compression.

But I need a good answer.

 

[Pacfanweb]

You cannot accurately calculate HP from just bore/stroke/compression. You need to know what the heads flow, cam specs, etc. I'll look around and find the formula.

<<Also we can/cannot be given the displacement>>

If you have bore and stroke, you have the displacement.

 

[The Stigenator]

true with bore*stroke you are given displacement. Sometimes they dont give exact decimals. Its rounded off. They dont build a 1.8 liter engine to be exactly 1800cc's. Its like 1770cc's. They claim 1800cc's. On top the displacement they sometimes quote is rounded off. So in actual readings the 1770cc's would be 1769.55

 

[The Stigenator]

additional values to be considered:

Octane ratings (hp goes up or down depending on octane and knocking)
Fuel/Air ratio set at 50% each

 

[yakko]

I use a calculator.

 

[Pacfanweb]

Ok, there is a rough formula that uses compression, displacement, and max rpm to estimate HP. I just can't find it anywhere.


Also:
Horsepower= Torque X RPM/5252


Hope that helps.

 

[Zenmervolt]

1 HP = 1 FT*LB/second

One horsepower is the power needed to lift one pound a vertical distance of one foot in one second. Brake horsepower only has to do with where the horsepower is measured, a car's drivetrain &quot;eats&quot; some of the horsepower that the engine generates. Engines used to be tested with no accessories running at all, even the alternator and water pump were externally driven I believe. That was Gross Horsepower. Net Horsepower (for SAE at least) is the average of five engines with all accessories attached and running. Both Gross and Net are taken at the flywheel. Brake Horsepower is much more accurate as it measures the horsepower available after all the frictional losses in the drivetrain.

Zenmervolt

 

[Tominator]

That is correct...

The ONLY way to measure Horsepower is on a Dynometer. Horsepower is the relation of torque and resistance.