We took a trip to Lodi, California, to visit Kevin Sittner, owner of Precision Machines, to talk cars. Kevin has been around cars since he can remember and has always had a thing for early Fords. His shop focuses on the build and preparation of street, autocross, road course, and even some drag cars. The cars he builds are products of years of track experience, and they don't flaunt the newest shiniest parts unless they meet his standards. He builds cars that work, period. We asked him what are the most important things to consider when building a car for autocross and road racing, and what we can do to our street cars to make them perform their best. His answers cover performance upgrades, safety items, and preparation for the event.
The first thing to ask yourself is: Where do you want to race? Do you want to join your local SCCA autocross group? Is a faster road course more your style? Are you looking to move up to the fastest groups? The answers will dictate how much work you're in for.
Safety Equipment
Even if this is your first autocross in your mom's base-model beater, safety equipment should be the highest priority. Aside from factory or better seat belts, every car should have a fire extinguisher. You should never count on a corner worker to be close enough with a functioning fire extinguisher. Luckily, a mounted fire extinguisher in the cockpit looks cool and will be hugely impressive to your friends. As you get into the faster and more serious levels of racing, you will need to add more safety equipment. A four-point rollbar would be the first addition, as it provides a place to mount racing harnesses, and adds more strength to the chassis. A full-out race car can have more weight in bars than sheetmetal to conform to the rules set by the sanctioning body or organization. These upper level racers will also have a fire system more advanced than a fire extinguisher. They have a system that's composed of brake-line sized metal tubing all throughout the cab, trunk, and engine bay that emits a colorless Halon gas that interrupts the fire. This stuff doesn't make a big mess like a fire extinguisher does and doesn't require the driver to even get out of the seat.
Older cars don't have much lateral support for the driver. This makes negotiating technical turns difficult and unsafe. Swapping the factory vinyl bucket for a fixed-back race seat with provisions for a five-point harness will give you better lap/course times and is safer in the event of an accident. When shopping for belts, look for an FIA certification that is good for five years rather than the two for SFI.
Safety Attire
All of the safety gear here isn't always required, but there are some minimum requirements. A beginner's track day is at least going to require a DOT- or Snell-approved helmet, long-sleeved top, long pants, and closed-toed shoes. It's always acceptable and recommended to wear more safety items than required. You may find that driving shoes and gloves actually make you a better driver. Sittner always chooses red gloves because they are more easily visible when trying to communicate with other track personnel or other drivers. The firesuit and neck brace are required in the pro groups, but should be worn if available. Like the cab-mounted fire extinguisher, it makes you look really cool.
Corner Weight
Having the right balance front to back and left to right is crucial to performance at the track. A car with a 50/50 front-to-rear weight distribution will be more neutral than one that is nose- or tail-heavy. Neutral is when a car doesn't have a tendency to oversteer or understeer. It's common procedure to corner weigh the car before tuning with different spring rates, shock valving, sway bar settings, and suspension alignment adjustments.
You can adjust the way weight is distributed by relocating weight and adjusting the height of each corner of the car. Keep in mind the driver's weight needs to be in the car and may need adjusting (fewer hamburgers). The battery is commonly relocated to the back because most American Muscle cars are nose-heavy from the factory. Any item whose location isn't critical can be used to balance the weight. Coilovers make adjusting height very easy and shims can be used on stock-style suspensions to tip the car in any direction.
Alignment
First off, never take your car to a tire shop for an alignment. The data they have is based on old technology, old tires, and is not for performance driving. Even a spirited street car needs more attention than they will give it. An acceptable specification to them for camber may be between +2 and -1 degrees. The car will do crazy things when the alignment is far out from the desired specifications. Every car and suspension manufacturer is different, but as a baseline, figure a sport street car should have between -0.5 and -0.7 degrees negative camber, 2.5 – 3.5 degrees positive caster, and between 0.0625 and 0.250 degrees toe in. The same car set up for a road course would benefit from -2 to -3 degrees negative camber for a better footprint during extreme cornering. A street car would feel twitchy over uneven pavement and would wear tires faster with this type of setup. The caster would need to be as positive as possible to create straight-line stability and improved turn in. A street car will ride nicely with maximum caster but will experience a decreased turning radius, something that's important on the street, but not at the track. A track car will have much better turn in with 0.125 to 0.375 toe out, something that would be uncomfortable on the street and will scrub enough to actually handicap a lower-powered car's acceleration. Autocross cars get very similar suspension treatment though they are usually stiffer in the rear to promote oversteer, an important tool for getting around a tight course.
Tires
Tires are the most important change you can make to your car, so choose the right ones. Sittner's favorite tires are the Hoosier R6 for road course and the A6 for autocross. These tires may be nearly identical, but have different characteristics. The R6 is a slow-wearing and slow-warm-up tire that's designed to keep grip over long periods of track time. The A6 however, is designed to heat up quickly, but will lose its grip in a couple minutes. That makes the A6 perfect for autocross and even for qualifying at a road course where you only need a couple laps of grip. They both have a tread wear rating of 40. The lower this number, the softer the compound.
If you're planning on driving the car to the track with the same tires for the session, Kevin recommends the Nitto NTO1. It's a 200-treadwear tire that has grooves designed to tolerate water. It's a great tire to keep around for a track day that gets rained on. Many classes have tire requirements either by tread wear or vintage. Goodyear makes a vintage tire legal for nostalgic racing, but it shouldn't be used instead of a modern tire when you have the option.
To get the most performance out of whichever tire you choose, you need to cycle it once before the event. Run the tire for a lap or two then remove them from the car to cure overnight. This will extend the life of the tires. A brand-new tire will never run better than its second heat cycle, but if it's not left to cure after the first, it will wear at an increased rate.
Tire pressure is just as important as tire choice. There's no magic number that will work for every car, but there are signs. You will be able to look at wear onto the sidewall of your tire to determine if you need to add or remove pressure. If there is wear too far down the sidewall, increase pressure, if it doesn't reach the edge of the flat contact portion of the tire, decrease pressure. It will take some experimentation, but people at the track are usually quick to help out another racer if you need advice. Adjusting tire pressures can both improve the contact patch and overall grip, as well as change the oversteer/understeer balance of the vehicle.
Balance
A car with a decent amount of power is going to cross the 100-mph mark on any road course, so all of your rotating parts better be in balance. Imagine the frustration of getting your new slicks on your car and finding out on the first straight that they are horribly out of balance. Wheels are the first thing we think of to balance, but there other parts that can cause a distracting or even damaging shake. The wrong flywheel, misbalanced driveshaft, or bad rotors can wreck your track day. The most sneaky of shaking issues comes from excessive axle runout. Kevin takes all of his customers' axles and runs them on the lathe to verify their flatness. It only takes a couple minutes to remove the studs and turn the axle. Here you can see what a 0.025-inch cut off the face of an axle looks like. The most runout you should have is 0.005-inch so you can see how far off this axle was. It wasn't until 0.030-inch that the cutting bit touched the whole face.
Once-Over
You've seen the videos on YouTube of wheels and other major parts falling off at the worst of times. This is almost always due to poor maintenance or too many people working on the same car. The best place to look over a car is on a lift, but tall jackstands will do the job. You should put a wrench on every single bolt and nut from major suspension components to electric fuel pump mounting hardware. Cars experience a lot of vibrations and things may loosen over time. Spending an hour looking it over before each road course or autocross event can save you a tow home. Preventative measures include using locking nuts and safety wire, but factory hardware can only be checked. This is a good time to pump some grease into all zerk fittings and inspect every component for damage or wear. Whether it is you or someone else, assign this task to one person, or have two people go over the car separately so there's no question if everything was done.
Rollerize Your Engine
Being an engine is hard work, and nothing takes the load off like replacing as many metal-to-metal contacts with their roller counterparts. The easiest and cheapest thing to do is to get rid of those stamped rockers from the factory and replace them with roller-tipped rocker arms. This is an opportunity to reduce friction at the valve end and increase performance with a higher-than-stock ratio. Swapping from a flat-tappet to roller camshaft, be it mechanical or hydraulic, can dramatically improve performance and durability. Despite the higher spring rates, roller lifters reduce wear on the camshaft. Roller cams are billet steel rather than cast, giving them their higher price and longer life. Flat-tappet cams have the potential to fail in even the first hour of runtime. The engine oils being sold today don't have the same components like zinc and ash that helped protect non-roller components. For those who are weary of the maintenance of solid lifter cams, today's top manufactures have anti-pump-up hydraulic lifters that can rev up to 7,200 rpm.
The roller theme can be applied to the bearings as well. If you're starting from scratch, you can over-bore the cam journals to accept roller bearings. Anything you can do to relieve the engine of friction is helpful. In the same way, lightening rotating parts lessens engine load and allows more power to get to the ground. It also allows the engine to accelerate and decelerate faster. On big tracks, downshifting is an important part of slowing down and the faster the engine slows down the better.
Clutch Choice
A clutch's material has huge impact on the driveability and holding power. The most street friendly material, organic, doesn't have the holding power that a more aggressive material might. The tradeoff is that a more aggressive material may not be traffic friendly. Many companies like McLeod design clutches to have maximum holding power with the least amount of pedal pressure, which makes them great for a street/track application. A street car with 500 horsepower or less can easily get away with a Kevlar or Kevlar/organic combination disc that will be smooth on the street and tough on the track. Higher output cars or ones that will see more track than anything might use a sintered-iron disc. This material is not intended for street use, but can tolerate a lunch run or two as long as there's no stop and go. It's prone to chatter if overheated, but is right at home on the track.
Brakes
No amount of horsepower in the world is going to help you around a tight autocross track or short road course. Brakes, however, represent an area where overkill is OK. Choosing a caliper with enough clamping power to exceed your skill level can save you from yourself. Rotor choice isn't as obvious. Though the look of drilled and slotted rotors may be appealing, no track or autocross champ will tell you that drilled rotors are a good idea. They have a high failure rate due to cracking around the holes. Slotted rotors, on the other hand, are extremely helpful. The slots are not to remove heat, but rather to let gasses produced by the pads escape. Without the slots, the pad can kickback from the pressure. The thickness, veins, and diameter of the rotor are what determine its cooling ability. The vents between the front and back rotor face take in air from the center and push it through the rotor and out the perimeter. A cheap way to help cool the brakes even more is to route ducting from the front or underside of the car to the brakes as close to the center as possible.
Brake pad material varies from street to track. Street pads (lower pad pictured) are designed for quiet operation and long life more than anything else. A race pad is designed for maximum grip in extreme heat and nothing else. The materials for race pads (upper pad pictured) may need to be heated up to work properly and shouldn't be used on the street in many cases. Any brake pad change should be done in conjunction with a rotor resurface or at least a scuff. The brake pads will not grip properly if they are put to a shiny rotor surface. A brake-in or “bedding” procedure should also be performed at each pad change as well. This consists of three or four medium stops in a row, a cool down cruise, and six or seven aggressive stops.
The brakes should be given a quick bleed before each event to clear any air bubbles that hinder braking performance. Old brake fluid can have a low boiling point and could have absorbed water. Anything in the brake lines besides brake fluid can make the brakes soft and unpredictable. A good flush is a good idea if you're not sure what the condition of the fluid is. Brake fluid prices are all over the place but you don't need the most expensive stuff. Sittner has had a lot of success with Ford's Motorcraft brake fluid, as it has one of the highest boiling points available. It's inexpensive and readily available.
Tech Inspection
You may think you're safe and ready to run at the track or autocross venue, but a tech inspection can catch you off guard unless you're prepared. Every organization has some sort of tech inspection to keep you and your fellow enthusiasts safe. It's wise to print out the tech sheet provided by each organization and perform a tech inspection on your own prior to the event. This will help ensure there's nothing left unknown. This is a sample from the Northern California Shelby Club, a group Sittner works with frequently. They provide a pre-technical inspection form for this very reason, to make sure everyone is prepared for the track. A tech inspector will always check your car for a rigid seat mount and acceptable brake pedal pressure if nothing else.
Pack Like a Boy Scout
A good track-day kit can save you a lot of time and frustration at the track. The bare minimum items are pictured here and include a jack, jackstands, air tank, tire pressure gauges, ½-inch cordless impact gun and spare battery, torque wrench, flashlight, battery jumper, drill, and basic tool set.
Your car isn't the only thing that will be put to the test at the track. Driver error is the number one cause of accidents and it's often due to fatigue. There's a certain buzz and excitement that comes with a track or autocross event that tends to remove the idea of eating and drinking from your mind. Proper hydration should start the night before and needs to continue through the event day. Pack high-protein snacks, water, and drinks like Gatorade to keep your energy up. A hydrated and fueled person is less likely to make mistakes behind the wheel.
Fluid Control
Road racing is hot. Unlike drag racing and even autocrossing to some extent, road racing needs extreme focus on keeping things cool. Every car has an engine coolant temperature gauge from the factory, but oil temperature is even more important. The first thing to do is install a temperature gauge, and more than likely the information on the gauge will prompt the addition of an oil cooler. Plumbing is easy and could save your engine.
To keep the coolant temperature under control, you need a quality radiator, properly fitting shroud, high-flow fan, and a radiator cap that works. Every pound increase in the cooling system lowers engine temperatures but can also spring leaks. A 7psi cap may work great on street, but a well-built cooling system can support 24 psi of pressure. These caps need to be checked occasionally because they do fail just like thermostats. Many racers use a restrictor plate that fits in the thermostat location and limits the water flow through the thermostat housing. The idea is to remove the potential failure of a thermostat while keeping water from over circulating.
Race cars are not allowed to use traditional coolant because if it leaks onto the track, it can be a major hazard and is difficult to clean up. Coolant is very slippery, but distilled water with additives like Water Wetter is not. They don't have the corrosion protection that coolant does, but race car engines aren't left unopened for very long so that's not as much of a concern as on a street car. Non-competitive track days and autocross events won't have a no-coolant requirement.
Adding Strength
Rollbars are great for safety and performance. The flex in a car's chassis changes so much about how the car handles. You may see something as small as a strut tower brace to help keep things square, but every race car will have something. A full rollcage like the one pictured will give maximum rigidity, but for a street car it's pretty intrusive. Kevin welds the seams on the front-end sheetmetal and incorporates this custom plate to remove flex at the base of the tower. These are things that don't have any downsides, which makes them great for street cars too.