Roll The Corner In A Higher Gear

rslifkin said:

Wait a minute, de-tuning the top end to flatten the curve without doing anything to add power down low can't possibly add area under the curve.  It might make the engine a bit smoother to drive, but it shouldn't make the car faster (unless it's just dramatically easier to drive) and won't improve acceleration in a high gear.  The logic of de-rating power (and getting a resulting flatter curve) to meet class rules makes sense, but this wouldn't help you anywhere else. 

I said "the area under the curve is much higher than a normal 240 rwhp power curve".  What I mean by that is that if you compare the chart above to something that makes a peak power of 240 without any detuning (a stock S52, for example), you wind up with much more area using the detuned S54.

But yes, clearly it is not as high as you'd get with the full power tune on the S54.

He's not gaining area under the curve. If I was implying it earlier, it's because I was considering the use case of using a turbocharger to fatten up the bottom end of the curve.

He simply chose a highly capable engine (with great bottom end power delivery), and cut power up top. Because the starting point was excellent (because it's the best I6 ever produced by anybody in the history of ever), then his power curve should be optimal for his class, versus some naturally aspirated engine that peaks at 245 horsepower after climbing up some sort of traditional, uncapped power curve.

Edit: I was typing at the same time as codrus.

rslifkin said:

Wait a minute, de-tuning the top end to flatten the curve without doing anything to add power down low can't possibly add area under the curve.  It might make the engine a bit smoother to drive, but it shouldn't make the car faster (unless it's just dramatically easier to drive) and won't improve acceleration in a high gear.  The logic of de-rating power (and getting a resulting flatter curve) to meet class rules makes sense, but this wouldn't help you anywhere else. 

No one recommended de-tuning unless the rules require it. In an ideal world, you could bring the curve up to make it flat which would be the most area under the curve. For a given peak hp though, flat is best. 

Assuming engine(s) making the same hp and going through the same efficiency drivetrain, or just making the same hp at the wheels... If the vehicle speed is the same and the rpm are different, then they will necessarily have gear ratio torque multipliers exactly offsetting their different engine torque to give them the exact same torque to the tires.

So it doesn't matter if it's 2 totally different engines (S2000 vs Viper @240hp) in the same weight cars or the same car with a flat hp curve in different gears, as long as the speed and hp are the same the acceleration will be the same in that moment.

However, as soon as the speed is different, all bets are off. The scenario putting more torque to the tire at any given moment in time will have the stronger force accelerating it.

Using our edge case example of the flat hp car, which is certainly the best case scenario for a hp limited application but only there, acceleration still falls off with the dropping torque curve as speed (and rpm) rise in a single gear... It just does so exactly equally to the gear ratio multiplication of torque difference that would be require for any different engine speed at that given 'different' vehicle speed. Which goes back to it no mattering which gear you're in as long as you're somewhere in that rpm band. Think of it akin to a CVT output at that point.

To get the same (acceleration) force at higher speed (greater distance in the same time) is doing more work in that time, which is the definition of more power. So acceleration being the same throughout a speed (and rpm) range in a single gear (and ignoring aero effects) would instead come from a flat torque curve.

Put me down firmly on the 'higher gear if you can manage it' side. 

A friend of mine is a Michelin performance tire engineer, and many years ago (gulp - close to 40 years now. LOL) he taught me about being smooth and carrying speed more into and through a corner in higher gears, and he was 100% right. I picked up 2 seconds a lap by going through a couple of faster corners in a higher gear, and actually didn't work as hard behind the wheel. Not only was it easier on the driver, it turned out to be better on the car, too - clutch, trans, brakes, fuel, and even tires. 

The big thing for me was taking the leap of faith in getting away from the 'safety' downshifts I was doing to feel more in control of the car's weight distribution and traction with larger deltas in decel and accel, and trusting my eyes, butt, and hands, to balance the car at a higher rate of speed and be very smooth about it. This really helped with lower power cars such as Showroom Stock B and C cars that I raced in my early days - but also still applies to the (much) higher power stuff I'm currently driving, such as my Gen V Viper. 

- Bill C 

In reply to BillCuttitta :

I ran a SSC Miata in the late 90s and rolling through in a higher those was so key to going fast. My joke was that if you're truly on the limit, once you turn into the corner, you should be a passenger all the way to the exit.

This all made sense to me because I was road racing a 125cc GP bike before switching to cars. You had to ride like an animal and corner speed was everything.

As for turning in at a speed one believes is to fast does indeed take some level of faith. 

One additional psychological effect is that, at least for me, the car doesn't feel as fast when it's in a higher gear.  Less noise and clamor from the engine helps me to overcome that reptile brain that's screaming "too fast, too fast!" in the back of my head. :)

In reply to codrus (Forum Supporter) :

A add on to that is when you scrub speed in the higher gear it registers instantaneously.

In the Datsun scrubbing speed when the motor is turn 8K doesn't seem that bad as the motor is still revving it's guts out.  Do that at 5800 RPM and it just sounds bad.

I sense the outline of a neat GRM article brewing here. The concensus seems to strongly favor the higher-is-better scenario (even though I think you're all wrong!). Make that the hypothesis, and test it? Maybe grab a couple different cars to represent the scenarios we have here? At the very least, it's been a fun question to ponder.

In reply to confuZion3 :

I also suspect it will also vary, maybe it's faster to use the higher gear in most cars but not all.