# 500 hp from a naturally-aspirated Honda K-24?

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?

• what fuel is it burning? – Steve Matthews Apr 10 '17 at 12:28
• I have no clue. – Zaid Apr 10 '17 at 12:35
• could be the key to how much power it's making. – Steve Matthews Apr 10 '17 at 12:59
• It could be. I do think that 16:1 is a very high CR to support regular unleaded fuel. – Zaid Apr 10 '17 at 13:26
• Reading the article it says Q16 or methanol as fuel.... – Solar Mike Apr 10 '17 at 14:44

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:

• the engine can rev up to 10,400 RPM
• compression ratio is 16:1

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.

• My question isn't so much about the specific power output as it is about why the numbers don't make sense for this K24 engine. For example, the specs for your GSXR1000R show that it's compression ratio is 13.2:1, redline is at 14,500 RPM and it's a 1.0 L engine. Assuming sea level ambient conditions (and ram-air effect), these values give a theoretical 214 hp, so their claimed max power of 200 hp is believable. What I can't fathom is how this K24 makes 500 hp from 2.7 L at 10,000 RPM - it would require an unusually high CR to achieve that, or some means to increase intake charge pressure – Zaid Apr 10 '17 at 10:39
• I think this is believable. the engine makes 500 hp @ 10,000 RPM so it makes 262 ft.lb of torque @ 10,000 rpm = (500 / 10000) * 5252. 262 is not an excessive amount of torques for a n/a 2.7L – r.anderson Apr 10 '17 at 10:47
• As usual with performance Honda VTEC engines - it is the RPM which makes the power not the torque – r.anderson Apr 10 '17 at 10:52
• I found hard data. See my answer – Zaid Apr 10 '17 at 11:30