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Basics of High Performance - Steps To Power

The Basics Of High Performance

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Mild small-blocks really don't need much more than 600-625 cfm. If you have plans for a bigger cam, better heads, and maybe more compression, you might step up to a bigger carb, but be realistic. Your stock 350 will run with a 750 double-pumper, but it might be happier with a 650-cfm carb. Even the larger carb's idle circuit will most likely be rich to the point that no amount of fiddling with the mixture adjustment screws will get it right. An experienced carb wizard could remedy this, but why go through the hassle when what you really need is a smaller unit? Generally, the classic "double-pumper" mechanical secondary carbs are not necessary, nor advisable, for mild small-blocks with automatic transmissions and stock torque converters. You'll just be dumping extra fuel that your engine can't use.

Instead, select from the array of carbs in the 625-to-650-cfm range that use vacuum-actuated secondaries, and start reading up on carb tuning. You may not need to turn a single adjustment screw, but it pays to know what you're dealing with and how to use it.

By the way, if your car already has a four-barrel, or you can get your hands on a factory-type setup to install, don't assume that original equipment can't offer solid performance. Factory quads like the Quadrajet, Thermoquad, and earlier Carter AFB models can all be tuned to support stout street engines.

Ignition systems have come a long way since the early days of the musclecar, and many of the factory electronic systems from the mid-'70s are still in favor today. There really isn't any reason to be running breaker points any longer, since they limit the output of the ignition system and require frequent maintenance. Most of the engines we deal with can be retrofitted with a factory-style electronic system from a later model, often using brand-new components either from the OE manufacturer or the aftermarket. A sound alternative is available in the form of electronic conversion kits that can fit into original breaker-point distributors, such as those from Pertronix, Crane, and M&H Electric. The retrofit kits should not be seen as a compromise, as testing has proven their competence. The only possible problem may lie with prior wear to the bushings in the stock distributor.

The quality of your tune-up parts is still a critical issue, even with a strong ignition, and the most commonly faulty element is the spark-plug wires. Even on late-model vehicles where spark plugs seem to last indefinitely, plug wires still deteriorate with use and time. Even a brand-new set of carbon-core resistance wires suffer from high internal resistance. This means less voltage and current at the spark plug and a weaker spark. Resistance testing with an ohmmeter usually reveals the true capabilities of plug wires-look for no more than 100 to 200 ohms per foot as a standard. The best wires are the spiral-wound plug wires from companies like ACCEL, Crane, Moroso, MSD, Taylor, and many others. These are the only plug wires you should consider.

Once you're running electronic ignition through sound equipment, you may want to consider another upgrade to some form of ignition system booster, such as the capacitive discharge units offered by Crane, Jacobs, Mallory, MSD, Pertronix, and others. Some of these companies offer the additional benefit of multi-spark discharge below 3,000 rpm. This means that for every firing of each cylinder, there are actually several sparks to ensure that the mixture lights off completely. Note that while these systems offer real advantages, stock engines won't show as much benefit as more highly modified engines. It all comes back to cylinder pressure. However, once you enter the realm of power-adders, like nitrous and forced induction, a high-output ignition becomes a requirement.

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