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Basics of High Performance - Steps To Power

The Basics Of High Performance

Photography by From the Car Craft Archives

For the carbureted crowd, this leads us right to the age-old debate over single-plane versus dual-plane. Back in the '70s, some of the aftermarket intake manifold manufacturers tried to bridge the gap between the two by creating street-oriented single-plane intakes, but in recent years, the better option for the street/strip small-block set seems to be track-oriented dual-planes. That may sound like an oxymoron of sorts, but manifolds like Edelbrock's Performer RPM series offer the benefits of low-end power and smooth low-rpm operation typically associated with dual-planes with the added advantage of high-rpm flow characteristics to keep performance engines happy all the way to 6,500 rpm. Dyno testing has shown time and again that these designs work, and the most recent addition of the Edelbrock Air-Gap design, for example, separates the intake runners from the manifold's floor to keep heat from the engine's crankcase away from the intake charge like single-plane intakes have been doing for years.

Of course, the RPM series can only go so far, so when it comes time for a truly healthy engine that will see regular track use, a good high-rise single-plane still makes sense. Modern single-plane intakes are able to support the high-flow capabilities of modern performance cylinder heads, and often minimize the sacrifices to the low-end normally associated with these designs. It seems that 600-plus-hp engines are no longer that uncommon, and while much of this can be attributed to modern cylinder head port technology, a good deal of credit should also go to the intake manifolds that support those killer heads.

We can't ignore fuel-injected performance cars, since this has been the norm from Detroit for nearly 20 years. Plus, the level of performance from late-model cars running engines like GM's LS1 is astounding, particularly when you consider how streetable most can remain. Again, the aftermarket has stepped up to offer improved manifolds for most popular EFI applications, eliminating a major obstacle to ultra-high-performance EFI engines. In fact, there are so many offerings for some of the most popular applications that builders of cars like the 5.0L Mustang have to make careful choices in much the same way carbureted builders do to ensure that they don't over or under do it. The long runners of intake manifolds found on 5.0L Mustangs and TPI Chevys are made that way to take advantage of ram tuning. The length of the runners is specifically sized to coincide with cam timing to take advantage of intake charge pulses so that low-end torque is enhanced. However, these same longer runners usually sacrifice upper-rpm performance. Larger runners often boost output, but short-runner, box-plenum intakes on otherwise stock engines can make for sluggish low-end performance. As usual, the "bigger is better" approach is not advisable for stock or mild engines. Typically, a stock or mild EFI engine that originally had long runners will benefit from a manifold with similar-length runners that feature a larger cross-sectional area for increased flow while maintaining low-rpm velocity. Once you upgrade your heads and cam, you may be ready for something more serious.

For those running carbs, the choices are vast. However, just as with most aspects of your engine, the biggest, baddest aftermarket piece is not going to be the one for your mildly tweaked street cruiser. Stock two-barrel carbs are like running at part-throttle with a real induction setup, and the myths about superior fuel economy have long been proven erroneous. A well-tuned four-barrel will increase performance and economy, but selecting the right carb and setting it up properly seem to be elusive to many novice rodders.

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