17. What is heal-toe shifting and why does it help?
It’s really all about rev-matching to decrease driveline shock, especially if you’re also braking hard. (Imagine yanking on the parking brake while turning and you’ll get the picture.) While it’s typically considered a performance driving practice, we actually try to practice it daily since rev-matching also decreases stress and wear and tear on the clutch and entire driveline.
So how do you choreograph it?
- Lift your right foot from the throttle and press the brake
- Clutch in with your left
- While still braking, roll the side of you right foot (or use your heel if more comfortable) and blip the throttle to bring the engine up to the rpm necessary to match the engine to the speed of your tires
- Downshift the trans
- Release the clutch and rotate your right foot off the gas simultaneously
- Continue trail braking through corner as much as necessary (usually up to the apex)
- Foot on the gas to accelerate out of corner
18. Quick vs. Fast: Are they interchangeable?
These two words often get used interchangeably, but they’re really two different things. Quick is a measure of time; fast is a measure of speed. They’re also both a bit relative depending on what is being referenced. For example, 190 mph in a street car is fast, and so is a top speed of 415 mph across the Bonneville Salt Flats. On the quarter-mile cars with low elapsed times, 9.50s for example, are quick.
That also explains why quick cars aren’t necessarily fast, and fast cars aren’t necessarily quick; a car geared to run over 200 mph won’t accelerate as quickly as one geared to cover the quarter-mile as rapidly as possible.
19. Does cutting a coil spring increase its rate?
In a word, yes. Things get tricky in springs with differing wire diameters or inside diameters, but in the case of standard consistent coil springs like found in vintage cars, the rate of a spring is determined by the amount of steel used. Simply stated, rate is the amount of weight required to deflect a spring 1 inch. Assuming a set group of parameters, the longer the wire is, the lower the spring rate. As the wire gets shorter (as when cutting coils) the spring rate increases correspondingly. For complete explanations, check out the spring gurus at Eaton Detroit Springs (www.eatonsprings.com). So yes, you will increase rate by cutting a spring. Even time, however, can’t do the opposite. Coil springs never lose their rate. Even if it sags and loses its load height, the spring’s rate is still the same as when it was new.
20. How do I get the best mpg?
This can be a tricky question since many variables can be thrown into the equation, but assuming a nice flat road with little elevation change the maximum mpg per rpm is at the lowest possible rpm with the lightest throttle pressure in the highest possible gear that does not lug the engine. That’s true for any gear, though the obvious problem is that you may not be traveling at the speed you’d like. Without changing gearing or overall tire diameter, cruising rpm versus vehicle speed is a constant, so part of the consideration therefore becomes how fast you want/need to drive and how do you maximize that condition.
At that point it all becomes about driving habits and keeping the load light on the engine. Driving in Sixth at low rpm isn’t efficient if you’ve got your foot halfway to the floor to accelerate. You’ve heard this before: slow acceleration, light and steady pedal pressure. The easiest and most foolproof way to keep yourself in the zone that will return the best mpg for your particular car is still the good old manifold vacuum gauge. At full throttle, the gauge will read 0 Hg, but could be as high as 24 Hg when coasting. The key is to train yourself to drive in a manner that keeps the vacuum pressure as high as possible because the higher and more consistent you can keep the vacuum, the leaner and less voluminous the fuel mixture being burnt, and in turn, the better the mileage. Typically, this is in the 10-17Hg range for engines with stock to moderate cams.
All that being said, the ideal scenario for theoretical max fuel economy is to have the very smallest engine displacement possible that can overcome weight, rolling resistance, and aerodynamic drag at the target speed with uncambered airflow that minimizes pumping losses from a partially closed throttle blade and restrictive exhaust. That’s the theory behind variable displacement cylinder deactivation: make a larger engine cruising inefficiently effectively smaller and open up the throttle to maintain required power.