In the late 1970s the cost of
racing began to rise in a way that made it less and less affordable for the those racers who did not come endowed with their own
trust fund. In the early days of
road racing, people raced their street cars. Of course they also wanted to make said street cars faster, and began to
modify them. The thing is, the further out one goes out on the modification path, the less streetable a
race car becomes. Particularly if you want to win. In fact, in most classes winning precludes having a car that could be driven regularly on the street. Which means racers not only needed a car, they needed a
truck and trailer to get the car to and from the track. The
Sports Car Club of America heard its members griping about costs and decided to do something about it. So they created the preparation category
Showroom Stock to provide the lowest possible costs for racers. All you had to do was buy an econobox, say a
Ford Pinto or a
Datsun 610, bolt in a
roll cage and the required driver restraints then take it racing. Since it was stock in every imaginable way, the car was remained completely streetable, emissions neutral, and ran readily on pump gas. You could drive it to the store, to work, to school and to the track. The number and the cage might even get you noticed.
That's really all it took to go racing. But there's a key problem with the racing, in that racing inherently involves competition. People who like to race, like to win, even if it's only beating their buddy. There are a lot of subtle things one can do to prepare a racing car for competition. The first step is a really careful alignment on all four wheels with an eye toward maximizing the cars handling. Subtle adjustments in camber, caster and toe can have a significant effect on how a race car handles. For example, maximizing negative camber (meaning the bottom of the wheel is outside the top of the wheel relative to the center of the car) maximizes tire contact patch during cornering (see weight transfer). Toe can affect how quickly the car turns in. Second, one can tune the engine for maximum performance, particularly at higher RPM. In older cars with a mechanical distributor and ignition points the gains can be significant.
But even that isn't enough for some people. in the SCCA Showroom Stock B and C and National classes, which means the top drivers are eligible to compete in The Runoffs, the amateur national road racing championship of the United States. (As some Canadian racers participate, North America might be the real title though Canada has its own sanctioning body). The Runoffs are serious. The cars listed above can be a lot of fun and even win at the regional level. But I know a guy who had a top regional SSB car and had supposedly slower SSC cars blow by him on the back straight. What gives?
Money.
Showroom stock is intended to be really cheap racing. One way the SCCA did that was to ban all engine modifications. All of them. The only thing you can do is tune the motor, and really with modern electronic controls even that is difficult. In showroom stock, the ROMs must remain stock. If you find yourself on the podium at the Runoffs, your car will be torn down to verify this. The guys in the Tech shed will download your engine software to check it against factory settings. All internal parts will be weighed, measured, parts numbers checked plus a check for machine marks that would come naturally were your engine blueprinted and balanced.
But there's this little thing known as tolerances. Nothing in the mass market is made to absolute perfection. The only way you get perfection is through hand assembly. And you have to throw away a lot of parts that really have nothing wrong with them. Ferarri does this, but how many of you drive a Ferarri? Some pistons are slightly larger than others. One cylinder head may have a slightly smaller combustion chamber than the one next to it. One may flow slightly better than its brother. In SCCA category Improved Touring where a blueprinted engine is legal, these matters are adjusted by a machine shop. It costs a few thousand dollars to have your motor torn down and reassembled with anal retentive care, but as a rule it's one of of the cheaper things a racer can do, as a blueprinted and balanced engine both makes more power and is more reliable than its dead stock equivalent.
But that would leave machine marks. And if you pick parts at the high end of the manufacturing bell curve those little differences can add up to a big deal. A friend of mine once sat through a presentation from an auto manufacturer stating that a perfectly innocent racer could, by mere chance end up with a new, dead-stock V-8 with a 12.5 to 1 compression ratio. Even though the factory spec line was an already high 10.5 to 1 (hint: higher compression ratios produce more power).
So here's how you build a competitive showroom stock engine, say for a Dodge Neon. Order four engines. Order an additional forty pistons, rods and sets of intake and exhaust valves. Order five or six additional camshafts. Measure and weigh each and every one of them. Take the best head, the hottest dead stock cam, the lightest and smoothest matching set of valves, the four lightest pistons and rods (making sure they all weigh exactly the same) and best crank. Put each head on the flow bench. Then assemble one engine. Put it on a dynomometer and test each engine computer and fuel injection system. Keep the set that produces the most power.
Congratulations. You have just spent $20,000 building a dead stock engine for your Showroom Stock C Dodge Neon. Instead of the factory specified 132 horsepower, your Neon probably produces something in area of 160 horsepower, a significant advantage. Torque will also be up. You will annihilate the guy with a real stock motor sitting next to you. In fact, you might even sell him one of the motors you didn't choose. And if you win The Runoffs the tech shed will not see even one machine mark on any of your parts, because this motor really could have come from the factory exactly this way had the stars aligned in Pisces with Jupiter in the seventh house.
That's how you build a competitive showroom stock motor.
Of course if you raced said Neon in the regional class Improved Touring A you could have put on a set of headers, had the engine blueprinted and balanced, done a bit of port work and for $4,000 come up with a motor making even more power, with equal reliability. Of course everyone else would have the same level of prep. But hey, you wanted to win, didn't you? BTW, the vehicle specification line for said V-8 engine lists the stock compression ratio. For some reason the comp board didn't buy the idea of a dead stock 12.5 to 1 motor. Wonder why?
After reading this you may ask why someone would race showroom stock anyway? The answer is the cars are dead nuts reliable. If you treat one with respect there's almost no at track finagling to do with the motor. They start every time. In some other category specifications, that isn't true at all. They're also somewhat cheaper then a competitive car in any other national class besides spec racer ford. There are lots of ways to spend money racing.
In case you're interested, Ferarri doesn't do its engines this way either. They adjust tolerances using an in-house machine shop, because it's a lot cheaper to do it that way than to throw out 90% of your parts. And just as good.