Sunday, July 15, 2007

Torque and HP for the umpteenth time

I don't know why supposedly intelligent gear-heads would state that "HP sells cars and torque wins races."

If this were true, F1 cars would have turbo-diesel engines and 40 speed gearboxes.

Perhaps the misunderstanding arises from the failure to understand the importance of the width of the power band and gearing. For race applications, you want as much torque to be developed as late as possible, for as long as possible. Why? Simply because horsepower is a function of both torque and RPM. So a high torque value at a high RPM will yield a higher HP figure. And if it's broad enough, you can make use of gearing to produce the desired torque at wheels.

Radical SR8LM

Radical Motorsports announced the Radical SR8LM on 1 July, a 2.8L normally-aspirated motor producing 455 bhp with a rev limit of 10,500 RPM.

"Gotcha!" I hear you say. "Didn't you previously have a blog entry that stated 300 whp from a normally-aspirated 2.4L is improbable in the local context? So how do you explain a 2.8L engine doing almost 100 bhp more?"

Let's do the math.

Since Radical doesn't post up the power graph, let's assume peak power of 455 bhp is achieved at 10,000 RPM. This would yield a torque of 239 lb-ft at that engine speed. 2.8L is 171 cubic inches, so BMEP is 211 psi. Well within reason. By the way, Radical suggests an engine rebuild interval of 30 hours. This engine is not meant to be driven daily.

So logic prevails. I stick with what was stated previously and would require a lot more convincing that a daily-driven, locally built and tuned 2.4L normally aspirated engine revving to just 8000 RPM is capable of 300 whp.