It's a fact worth visiting again. Mismatch an engine's basic components and you can expect mismatched results
Tales From The WorkshopWhether you build your own engines or rely upon someone else for that service, parts-selection mistakes can be costly ... both on and off the track. An engine, any engine, is a "system" of parts that require integration to maximize power and minimize costs. Determining and following some reasonably simple guidelines can help address both these issues.
Torque or horsepower?It's an age-old discussion, and you have some choices. But in the end, you'll likely discover that torque creates acceleration and horsepower boosts speed. At the risk of an absolute statement, in the vast majority of cases, torque helps win races unless track conditions create situations where acceleration is less important than speed. So choose parts that build torque, and make certain they are designed to operate in relatively the same range of rpm.
Identifying a range of RPMThis is important. Torque curves aren't "flat," so you can expect certain segments of rpm to exhibit higher and lower amounts of power output than others. Not surprisingly, this is because engine components and their performance can vary with engine speed. Therefore, before selecting and combining parts, determine (as best you can) a specific range of rpm in which you want to achieve optimum torque. You might call this your "target" rpm range, ultimately becoming the span of rpm in which parts selection/function will be targeted.
To help make the job easier, some parts manufacturers identify the range of rpm in which they've designed their components to be the most efficient. And if they haven't, ask why. At the time you're selecting parts, it's pretty safe to assume the builder of the parts knows more about his parts than the buyer. Pre-purchase information is far less costly than post-purchase information ... especially if you bought parts and discovered they weren't the correct ones.
Additionally, once you've determined minimum and maximum rpm points, there are further on-track benefits from zeroing in on engine speeds within the pre-determined range. Let's say you've decided a range of 3,500-7,500 is the spread. But within this range, you determine that off-the-corner acceleration (torque) from 3,500-5,500 is more important than passing rpm from 5,500-7,500. In this case, it might be worthwhile to choose a header system dimensioned to be the most effective at a lower rpm than the intake system ... as an example.
Major components that affect torque performance No single component will determine an engine's overall torque (or volumetric efficiency) performance characteristics, particularly as it relates to peak values. However, the selection of intake and exhaust systems (design and dimensions) will strongly influence the shape of a given torque curve.
In previous Circle Track tech stories, many of the factors that affect torque output have been discussed, most notably intake manifolds and headers. Worth remembering is the fact each of these systems can be "tuned" within different ranges of rpm. For example, if you are faced with developing torque over a broader (rather than narrower) span of engine speed, selecting an intake manifold that helps build torque at higher (or lower) rpm than the exhaust tends to widen the torque "band." As the required range of torque output narrows, these two systems can be tuned (via dimensional selection) closer to the same range.
Once chosen, each of these two systems can be further tuned (carburetor spacers, header collectors, etc.) as steps toward refining a given engine's torque curve within the pre-selected range. In fact, it is by these methods that changes in tracks and track conditions can be addressed, in much the same way you'd alter spark timing, fuel delivery, and gearing for the reasons each of these are part of the "tuning" process.