Power

OK, here's another bombshell: every single one of my fastest runs at each event, without fail - I mean every single fastest run had one specific thing in common with every other single fastest run.

Are you ready for this? It'll shock you to your core.

It had the highest average throttle position.

Every single one.

Now at first, this may not seem all that surprising - Hey! More throttle makes you go faster! Sheer genius! - but think it through for a second.

This is another way of saying that the fastest run of a given event for a given car had the highest average amount of delivered horsepower - getting power to the ground makes you go faster.

So here's one of the real secrets: my car was capable of putting 100% of its power to the ground at any given point in time without wheelspin. That's up to 350 actual delivered wheel horsepower, at will, with no side effects other than some understeer (and sometimes, given that the thrust vector of the front wheels was off-axis, you could drive through this)

That, more so than any other single factor, was the reason why the car was as fast as it was: you could slap the throttle open at will, and the car would go - and go - and go - and it would never spin out, or light up tires and slow down, or do anything else otherwise untoward save maybe adopt a larger turn radius than you wanted.

This let me do all kinds of crazy things: most notably, I could dive in on the inside of a corner, chop all that distance off the entrance to the corner, slow down enough to minimum-radius the turn, and stand on the gas at the apex (actually, a little bit earlier to account for turbo lag) and still make the same exit speed as a car that took the corner wider to carry speed through it.

Think of it this way: I was running the same tires as the M3s - exact same size. I was a little heavier, but my wider front track and better front suspension (double A-arm vice McStrut) meant peak lateral G was about the same. How you get to peak G is a function of turn radius and total speed: make the turn radius smaller and the speed you can carry at peak G drops. But the tradeoff is that you are covering less distance; even though my apex speed was slower than the M3s, I have beat them to the apex by taking the shorter line. Then, because I can accelerate so much harder out of the hole, I can catch up to their exit speed for a net gain on time.

I tried this over and over again at test sessions, trying the classical line vice my minimum distance/maximum power line, and minimum distance won almost every single time. Autocross courses are just too short and too slow for carrying more speed on entry and apex to make up the difference IF you are capable of hammering out of the corner at full song and have enough power to make up the difference.

This almost certainly doesn't work at higher speeds where aero losses means that you need huge differences in power to be able to make up the difference. It also works better on slippery surfaces than it does on sticky surfaces (where slippery surfaces means the ability of your competition to put power down is being impaired) and it is most definitely NOT a panacea (the skinny M3 track width paid them huge dividends in slaloms, where my wide track width punished the hell out of me in slaloms. Any course with a decent-sized, close-set slalom would just murder me relative to the M3s)

I get a HUGE kick out of the people who like to sniff and stick their noses up in the air over my "point and shoot" driving style. That was a dead giveaway that they didn't understand what was actually going on. Put me in a Viper or C5, and after a spin to remind me that big HP RWDs cannot be smacked to WOT at will, I'd adopt a similar driving style to everybody else - 'cause that's what works in that type of car.

Anyway, the major point here is that anything you can do that delivers more power to the ground WILL make you faster. This is THE reason why the C5 Z06 is so fast (it has a lot of power and it is very good at putting it down) and why the Kumho V710 worked so well on the C5 (it gave up a little transient response to the Hoosier A3S04, but its forward bite was just so much better that the increase in delivered power more than made up for whatever might have been lost to slower response.

There are, however, a couple of caveats:

The first is that it has to be the right kind of power - by which I mean that peak power alone does not tell the whole story. What you want is the largest amount of area under the power curve in the RPM range in which you operate. For an autocross car, this means a power curve that is as close to flat as you can possibly make it - which in turn implies more low-end torque.

OK, another quick aside: horsepower and torque are the exact same thing - the HP curve is mathematically derived from the torque curve, so the one implies the other. All the Internet flame wars over torque vice horsepower are utter wastes of time, because they are talking about two aspects of the same thing. The key here is that the thing that determines the rate of acceleration of the car is the delivered horsepower, and to maximize acceleration you want the highest possible average HP in the operating RPM range of the engine. Biasing the torque curve lower in the RPM range tends to flatten the power curve at the expense of peak HP, and biasing the torque curve later in the RPM range tends to make the power curve "peakier" but delivers a higher peak HP value.

If you are a drag racer or road racer, you go for peak HP and then regear the transmission to move the operating RPM range to bracket the HP peak - and you go faster because you have the highest average delivered HP in the RPM range. Autocrossers can't afford the time spent shifting all the time, so they are better served by wide and flat power curves. Big displacement engines or forced induction are ideal for autocrossers; high-strung, high-revving peaky motors are not. Had I stayed in the sport, my next motor iteration was going to be a 2.4l stroker with a faster-spooling ball-bearing turbo.

When you look at the dyno plot for my motor, you see a nearly flat power curve centered on the RPM histograms for the average course. That is no accident.

Caveat number two is that more power makes the driver's life more difficult. The world happens much faster, there's less time to react, and you wind up needing more driver inputs - and every driver input is an opportunity to screw up - and when you are moving faster, the penalties for screwing up are much larger. In a low powered car, a given turn may be flat-out - just a steering input required. In a medium-powered car, that same turn might be a lift - a steering input, and a throttle input. In a high-powered car, that same turn might need braking to negotiate the turn - a throttle input, a braking input, and a steering input - and because he is going faster, he has less time to get more done. Keep cranking up the power, and eventually everybody runs out of talent: low power driven right usually trumps high power done poorly.

Nowhere is this more apparent than in a car that has a gross excess of power relative to grip. If you can get wheelspin at 20% throttle, all you've done is make the car more difficult to drive with absolutely no payoff. This is a common mistake amongst those with more money than experience.

So then, build and drive strategies:

  • AWD: Big power - you can use more than any other car on similar tires. Sort out the diffs so you can got WOT at will. Drive diamond lines to win on minimum distance corner entrances and big power on exit.
  • FWD: Power doesn't help you as much, as weight transfer is working against you and it gets worse with more power. Use an LSD to squeak out what delivered power you can, and drive momentum-maintainence lines.
  • RWD: Build as much power as you can hook up; any more than that is a waste and makes life more difficult. Rig the throttle such that you get lots of pedal travel early for relatively little throttle plate travel - this will make the car less sensitive at tip-in and a whole lot easier to drive. Drive a semi-diamond line; give up the minimum distance you have to on entry to retain full exit speed.