Boosting Your Horsepower - Gettin’ Air

Understanding the finer points of larger throttle bodies, boost and cold air.

Richard Holdener Sep 23, 2013 0 Comment(s)
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For the power hungry, the only thing better than a modified LS engine is a supercharged LS motor. Nothing wakes up a Gen 3 or Gen 4 small-block like a little boost. As cool and powerful as the supercharger kits are, they are only the beginning. You see, a supercharger is only as good as its induction system. Nothing kills the power potential of a supercharger faster than a restrictive throttle body, mass airflow (MAF), or air intake system.

How much power is a throttle body, MAF, or air intake upgrade worth? Not surprisingly, the power gains offered by the flow restriction inherent in the stock inlet system depend on the modified power output. Technically speaking, the more powerful the engine, the more restrictive the stock components become. This should not come as a big surprise, since the factory inlet system and throttle body were never designed for these elevated power levels. The system GM designed to support 426 hp on a stock Camaro LS3 has no business on a supercharged motor making 600 or more horsepower.

Have you ever read a dyno test on a throttle body that offered no power gains? How about one that offered 10 hp, 20 hp or even 30 hp? Just how much is a simple component like a throttle body (or air intake system) worth? The question seems simple enough, but the answer is somewhat less so. Power gains seem to range from as little as zero horsepower to as much as 25-30. Why such a broad range? Is the testing flawed or otherwise biased? In point of fact, we have seen throttle body upgrades that netted over 60 hp on a Kenne Bell supercharged application. The key to the power gains offered by a throttle body upgrade is the application. In reality, the question is not so much can a throttle body swap net a sizable jump in power, but rather does such an upgrade always results in said gains? The quick and dirty answer to that question is a resounding no, but the reason behind it is certainly worth a closer look.

In its simplest form, the throttle body is nothing more than an air valve. There is no magic to the workings of a throttle body, though there is some magic to maximizing the flow rate through it. A given opening will flow a certain amount of air, but radiused entries, thin throttle blades and the elimination of hardware in the air stream all combine to further increase the airflow of a given bore size. It stands to reason that a 90mm throttle body should outflow a 80mm throttle body, but it is possible for a well-designed 80mm throttle body to outflow a poorly designed 90mm unit. Back in the early days of the L98 small-blocks, we marveled at the ability to upgrade the factory throttle bodies to dual 58mm units. Modern LS3 motors are equipped with massive 90mm throttle bodies flowing over 1,100 cfm, but even these monstrosities are not enough to support a high-horsepower, supercharged application.

1306 Super Charged 2/17

It stands to reason that a larger throttle body will outflow a smaller version (assuming equal design quality), but now we can take a look at why the installation of a larger throttle body may or may not improve power. According to testing performed at Kenne Bell, the stock ’10-up Camaro SS 90mm throttle body flows 1,147 cfm. From testing on the airflow bench and DynoJet, we know the formula to convert hp from airflow. Using the formula that 1 hp requires roughly 1.5 cfm, we see that this stock throttle body might support as much as 765 hp—way more than the factory-rated 426 hp. The first obstacle in terms of power production is the fact that the throttle body is not the only component in the induction system. The flow rate of the throttle body is only as good as the supporting components. In the case of the Camaro, the flow rate of the complete induction system is only 964 cfm, a significant drop from the 1,147 cfm offered by the throttle body alone. According to our formula, the stock air intake system is capable of supporting 643 hp, considerably more than the stock power output, but things quickly go south once you add a supercharger.

Before going on, it is imperative that we backtrack a bit on our power/airflow formula. We indicated that it takes roughly 1.5 cfm to make 1 horsepower, correct? While this calculation has been proven accurate time and time again, it is by no means an absolute. Just because the induction system flows 964 cfm, doesn’t mean that it is only capable of supporting 643 hp, or that there won’t be any power losses up to that point. The formula is a rough estimation, but our testing has shown that even at lower power levels, the components in question start posing a restriction. The level of restriction and associated power losses increase with the power level. The throttle body or air intake system doesn’t all of a sudden become a restriction; it is a little restrictive at lower power levels, becoming more restrictive at higher power levels. Just because the component flows enough to support 650 hp, 700 hp, or even 800 hp doesn’t mean there aren’t additional power gains to be had below these points. On a positive displacement supercharged application, maximum airflow on the inlet side is the key.

An obvious factor when it comes to the power gains offered by the throttle body or air intake is engine combination. From a most basic standpoint, the higher the power output of the test engine, the larger the throttle body required. Upgrading a throttle body already capable of supporting 765 hp with a larger version capable of supporting 1,000 hp on a 425hp motor will have predictable results.

The 765hp throttle body is already oversized for the application, so there is no need to upgrade on the normally aspirated motor. This is especially critical on supercharged applications, where elevated power levels are more commonplace. While 600 hp, normally aspirated Camaro motors are less common, supercharged LS3s exceeding 600 hp are everywhere.

It should be noted that throttle body sizing and maximum flow is less critical on a blow-through (centrifugal supercharger and turbo) application than a draw-through (positive displacement, like Roots- or Screw-type). Pressurizing the air before the throttle body artificially increases the flow rate of the throttle body. Obviously it is best to eliminate any pressure differential caused by the throttle body, but a stock throttle body will be less of a hindrance on a blow-through than a draw-through.

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