bigger engine??

[Speedline]

Let's calculate some 300hp at 9.000rpm on the mentioned Honda engine.

For 300hp at 8.000rpm you need a whopping 265Nm (57Nm or 27% more then standard!) which is almost impossible to reach without extensive tuning of all engine subsystems. At higher rpm the torque figure goes down;

For 300hp or 221kW at 9.000rpm you need 235Nm.

235 x 2 x pi x 150 (rpm in Hz) equals 221.000W or 221kW/ 300hp.

The standard engine delivers 208Nm at 7.500rpm in Euro spec. You need to extract another 27Nm 1.500rpm higher up the power band.

This is not impossible but is difficult and as mentioned is only possible with different camshaft profile (more lift, more overlap), higher compression ratio and perhaps some head and port work including bigger valves. I do not have experience with these kind of Honda engines; I base my opinion on more conventional engines which almost always need the mentioned combination of mods for high specific outputs/ high rpm operation.

These conventional engines which are not equipped with variable valve timing and lift will show a(n enormous) lack of torque down the rev range with the high lift cams due to slow airspeed in the manifolds. Thus with any engine it's probably a better idea to tune the engine in the daily drive powerband. And that's mid range or the rpm band between best torque and best hp.

At 9.000rpm mean piston speed of the 84mm stroke Honda engine is 25.2meters per second which is very very high. With this mean piston speed engine life will be greatly reduced. For endurance racing it's probably a better idea to tune the engine to max out at 8.500rpm for longevity.

I think the 270-280hp at the crank with extensive mods by tuners like Mugen are a more realistic figure. 300hp is not impossible but the cost to build and tune an effective 300hp engine is staggering.

Just my 2 cents.