This video showcases a naturally-aspirated 2.7 L Honda K-series engine that revs up to 10,000 RPM and claims to produce 500 hp.
I understand that this is for a motorcycle FWD drag racing application, but a specific power output of 185 hp/l seems high for an engine that doesn't employ forced induction.
Using the equation presented in this answer, I'm calculating an effective compression ratio of roughly 17:1, which is scarcely believable.
What is going on here? Am I missing something?
This article has further details:
To keep the reciprocating weight as low as possible, which enables this engine to scream to 10,400 rpm, the forged Wiseco pistons weigh just 260 grams and are supported by a set of 340 gram aluminum GRP “Pro Stock” connecting rods — producing some serious cylinder pressure with a 16:1 compression ratio.
So:
Assuming 16 bar effective working pressure, I get 502 hp with these updated numbers:
Effective power = engine displacement
× effective working pressure
× engine speed
/ 2
= ( 2.7 / 1000 ) m^3
× ( 16 × 1e5 ) Pa
× ( 10,400 / 60 ) 1/s
/ 2
= 374,400 W
= 502 hp
Side note
For regular unleaded octane, a 16:1 compression ratio is usually a recipe for auto-ignition/detonation. It seems that the reason this engine can afford such a high CR is because it is intended to be used with detonation-resistant race fuel. From the same article:
And a 70/71.5 mm Kinsler induction system pulls air in through a set of CNC ITBs before injecting the required Q16, Methanol or similar race gas.
It is not unusual to see motorcycle engines with specific outputs of 185 hp/l. Look at the Suzuki GSXR1000R, Honda CBR1000R, BMW S1000RR etc which all exceed 185 hp/l. The horsepower figure alone does not tell the whole story since HP is a product of RPM. Engines for this sort of application typically sacrifice peak torque and torque spread for gains at high rpm.
