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ITB The Way It Should Be

A Look Into The World Of Individual Throttle Bodies, And Why They Are...Well...Awesome!

If for no other reason, our shared desire for "the next best thing" is what gives the sport compact culture a more progressive and dynamic quality than any other in the world of automotive customization. Fueled by rapid technological advancements among OEMs, and complemented by a proportionately growing aftermarket, today's tuners are able to develop more efficient methods of realizing their goals than ever before. Accomplishments that were cutting edge only a few years ago are all but commonplace, thanks to the readiness of tuners to embrace new technologies. Sport FWD drag racers need to run consistent 9-second passes to stay competitive, while all-motor, in-line four's routinely reach the traps in less time than their turbocharged brethren three times as powerful. AWD consumer sedans regularly break circuit track records long held by purpose-built RWD roadsters, some even besting open-wheel, multimillion-dollar race machines (think AMS). And if your daily driven street car isn't producing three times the power, or accelerating to highway speed in half the time it was originally intended to-forget gaining any respect on the streets. Still, however surefooted our advancements seem to be, every step forward is built on countless steps back, as it seems the very same enthusiasm that allows tuners to master their goals prompts some to make hasty mistakes that bring hard-shaken misconceptions for all to overcome.

In the performance end of the sport compact world, almost every new technology (or adaptation of an old technology) is met with a lingering air of fear and uncertainty, no matter how beneficial it may eventually prove to be. A decade ago, tuners were reluctant to turbocharge their rides, fearing the same disastrous outcomes met by a few DIY-ers who were eager to increase power without first properly learning how to. Likewise some stubborn Honda B-series tuners who unsuccessfully rushed into K-series projects wrote the engine off as garbage, initially giving it a bad reputation. While the efforts of others eventually shed light into the darkness, disproving once golden rules of: "Turbocharging will blow up your engine," and "K20s are weak," tuners could have realized an even more rapid evolution of their sport had initial efforts been better planned beforehand.

Individual throttle bodies (ITBs) seem to be one such technological adaptation that remains a fearful mystery to many SpoCom enthusiasts. Despite a rich history of success among potent racing teams and consumer OEMs alike, sport compact tuners are slow to embrace ITBs, influenced in big part by well-circulated misconceptions and negative experiences a few have had with them. In reality, with proper tuning, ITBs have proven beneficial in almost every arena applicable to sport compact performance, yet rumors that they aren't streetable, are only useful for top-end power, won't pass emissions testing and destroy fuel mileage are repeated in conversation add nauseam-to the point that many tuners wouldn't give them another thought.

Nissan's Skyline GT-R and Pulsar GTI-R, BMW's M coupes, Toyota's 20-valve 4AG engine and McLaren's F1, not to mention modern fuel injected sportbikes and almost every winning F1 car in the past quarter century, all have one thing in common-none uses a single-throttle, intake manifold found in most consumer cars; they all breathe through ITBs. Whether used in a turbocharged or naturally aspirated application, with four, six, eight or more cylinders, ITBs simply work. In the average piston engine, each cylinder gets its own of every necessary component-spark plug, fuel injector, intake and exhaust port(s) and intake and exhaust manifold runner-except a throttle body. It doesn't make much sense, until you consider the inclusion of a single-throttle manifold from an OEM perspective: "Individual throttles are a very expensive feature," explains Lance Hayward, of British Columbia-based ITB manufacturer Hayward Performance. "Single-throttle, plenum manifolds get the job done on most consumer applications, but can never optimize (an induction) system's full potential, especially for naturally-aspirated cars."

As Lance explains, air is most efficiently introduced to an engine through a straight, unobstructed path into the cylinders, along a "port-centerline"-something a single-throttle, plenum manifold can't offer. "ITBs allow each cylinder to aspirate equally, and in the most efficient way possible," he explains. "In a conventional plenum manifold, some cylinders are farther from the throttle than others, thus air has to travel different distances and along different paths to reach the cylinders." Aftermarket exhaust manifold companies always tout the benefits of "equal length runners" in the exhaust, so why not in the intake too?

As Lance points out, another problem inherent to the conventional single-throttle manifold in naturally aspirated applications is the pumping loss each cylinder incurs while 'pulling' air into combustion. "Collectively, ITBs offer a larger throttle area than would be practical to use in a single-throttle application," he explains. "So air can flow more easily through each throttle without having to be stretched through a smaller, shared single throttle, when 'pulled' into the engine."

Additionally, ITBs allow the user to custom-tailor power and torque production characteristics. Just as air most efficiently travels into an engine along a port-centerline, it is 'pulled' into an engine at the most efficient velocity through the smallest sufficient opening, at a specifically decreasing cross-sectional area. Without a lecture in fluid dynamics, this means that in custom applications, runners of ITB systems can be changed in length and width to maximize efficiency in power production for the desired part of the powerband, and to better complement the engine's intake ports. The ITB's horn-shaped runner design allows the desired cross-sectional area to be better realized than a plenum manifold could-very important to naturally aspirated engines.

Improvements in flow with ITBs also allow the addition of much more aggressive cams than can be used in conventional manifold situations. "Our ITB kits have made gains of as much as 40 whp to an otherwise stock S2000's mid-range, with over 20 whp top-end, and as much as 70 whp with cams," explains Lance. Forced-induction tuning experts, RB Motorsports, also know well of the advantages ITBs have in allowing the use of larger cams. "The reason that Nissan went with ITBs for the Skyline GT-R was so they could get the car to idle correctly with large duration cams," explains RB's Sean Morris. "With a common plenum there is a lot of reversion and crossover between cylinders."

An additional, well-documented advantage ITBs offer over the conventional single-throttle plenum manifold design, and possibly the most attractive to OEMs, is increased throttle response. A conventional manifold comes under vacuum when the throttle plate closes, and as Sean explains, "When the throttle opens again, the manifold needs to refill with air before the cylinders can. The area for vacuum to accumulate between a throttle and cylinder in an ITB situation is far smaller, which leads to quicker throttle response." Despite all apparent benefits, ITBs do have a particular drawback for forced-induction engines: The individual throttles can disrupt airflow in high-horsepower applications, if placed too close to the head. "The stock GT-R throttle blade and support is about 5mm thick," explains Sean, "but it creates a rough path about 5mm above and below itself, disrupting airflow and fuel atomization at high pressure. This is why a lot of the big power builds use a large single throttle manifold with a plenum."

Some mid-'80s Formula 1 teams actually fielded cars with turbocharged engines that combined ITBs near the port entrance, and a plenum-style single throttle to fine-tune manifold pressure and throttle response. After the organization's turbocharging ban in 1989, most F1 cars retained the use of ITBs for their tuning latitude and increased throttle response, but with a unique twist; in contrast to many production ITB designs that put the fuel injector in the runner between the throttle and head ports, F1 research teams found they could make significantly more power by placing the fuel injector outside the intake runner altogether for it to spray fuel through the throttle and into the engine. With the injector placed away from the throttle a bit, F1 researchers found airflow could be less obstructed and fuel could further expand on its way into the cylinders, dropping intake temperatures and mixing more minutely with the charge-a discovery the sportbike manufacturers were quick to adopt.

Another, more recent, fan of this stand-off injector placement technique is Honda all-motor champ Bisi Ezerioha. When his all-motor single-cam Insight dragger hit a plateau last season at about the 9.6-second quarter-mile range, Bisi decided that a switch from gasoline to methanol was necessary to stay competitive. The only problem was that the dual Weber carbs he was previously running wouldn't be able to keep up with the added flow demands meth required; Bisi decided to take a page from the F1 book and switch to electronic fuel injection, by way of Kinsler ITBs and a combination of stand-off and in-runner injectors. "The stand-offs come online as secondaries," he explains, "their small size, increased fuel pressure and out-board mounting position really atomize the fuel and cool down the charge. The difference in power was very noticeable." Bisi is quick to point out that while stand-off injector placement is optimum for performance, he wouldn't recommend a top-feed-only setup on the street, since a backfire and/or reversion backflow at camshaft overlap could cause an engine compartment fire. Still, the gears of the one-time street racer turned as we talked, "But if they were tuned secondary to in-line injectors, and only engaged at high rpm with an ideal EMS like an AEM, then the safety concerns can be eradicated. But of course, the tuner is a key component to this equation."

Our conversation with Bisi brought another consideration to mind-the importance of using ITBs as part of a fully built head package. He agreed with what Lance Hayward explained previously: that ITBs really only support the head. They provide ideal flow into the head, to allow for aggressive cams, complementary porting and greater latitude in cam timing, so the head can make the most power. And Bisi reminds that a fully built head package doesn't stop with the head. "Tuners often run into the problem of having an exhaust that can't keep up with their intake (when tuning ITBs)," he explains, "and a big part of this is in the header and exhaust design. To reach full potential, these components have to be custom-built to complement the head the same way as the ITBs and their runners are." "There's no one header that's going to suit everyone," Bisi cautions. "That's why we only recommend and manufacture custom-made and tested components."

Of course, there needs to be special care taken in properly and effectively using ITBs, especially on a street-driven car. First of all, most of the rumors cited in the introduction of this article are, according to Lance, "Total BS." On the claim that ITBs aren't streetable and reduce fuel efficiency, he clarifies, "ITBs flow more air. More air needs more fuel. More air and fuel make more power." He continues, "How much of that air and fuel you use depends on your foot; if you drive more aggressively in a fast car, you're going to use more fuel, but don't blame it on the ITBs!" Lance's tuning with ITBs have proven gains throughout the entire powerband; ITBs being widely incorporated among OEMs and circuit track racers for their boost in usuable, low-end power attests their streetability, if part of a properly-built, tuned setup. And with new ITB kits we've seen planned to pass California smog, we're doubtful they'll have a hard time passing any state's emissions testing.

But their design does allow for one weak link when applied to many modern sport compacts. Their lack of a unified area for vacuum to accumulate can wreak havoc on brake boosters, MAP sensors, mechanical fuel pressure regulators, etc., which rely on a constant vacuum source to function properly. Fortunately, most ITB kits on the market make use of a common vacuum-accumulating "rail" or "tree" to eliminate these problems. In other instances, some tuning solutions allow for certain sensors to be bypassed, such as throttle position metering versus rpm instead of MAP for N/A applications and the same setup with the addition of boost metering in forced induction instances.

Far and wide, the reason ITBs have such a bad rep is because of widely shared horror stories from inexperienced tuners. "If you throw untuned, ITBs on a stock motor that wasn't designed for them, you're gonna have problems," explains Denis Howell, of Youngwood, Pa-based Hybridynamics. "Even if everything does work, mechanically, the powerband will be a mess. ITB's aren't a starting point for any build; everything else should be modified to work with them." Over the past year, Denis has encountered few opportunities to hone his ITB tuning skills, but has nonetheless been able to extract 266 whp and 199 lb-ft torque from Mark Schuessler's, K24-powered yellow EG. "A year ago, this car making just over 230 whp with the Euro Accord manifold," explains Denis, "Once we got the ITBs on and sorted out, and switched the cams, we picked up 36 whp top-end and more than 40 whp throughout the mid-range." Schuessler adds, "And we still have some room to go; now that we've come this far, we can port the head a little, make a few other changes and re-tune for good." The street-going dragger has made consistent low 11-second passes in practice, and with the additional power Mark expects to find at next tune, should be firmly planted in the 10's.

Genuine as their improvements may be, ITBs are very much in their infancy relative to the majority of sport compact platforms. Experience racing and building OEM ITB-equipped vehicles over the years has given much knowledge for aftermarket designers to build on, yet enthusiasts remain cautious to bite. The scarcity of these aftermarket conversions keeps ITB cost/benefit ratios a little high for most. A quick look at one of the leading S2000 ITB kits and a recommended pair of cams shows a dollar/horsepower rate of 55:1 at best, while a leading turbo kit weighs in at just 41:1, and boasts CARB certification and potential for more power. The numbers for more popular Honda B- and K-series kits are even farther apart; an ITB kit's dollar/horsepower rate remains about double the price of a similarly powerful all-inclusive turbo kit. Of course, ITBs are today's "something different"-and likewise, we all want it (or at least would give it a try for the right price). Our bet is that once knowledge is shared among tuners of the best way to use them, ITBs won't be such a thing of mystery; prices will fall and they'll gradually become less scary, albeit less "cool." At least, until the next new thing gets abused enough to take its place in the shadows.

Bisimoto Genuine as their improvements may be, ITBs are very much in their infancy relative to the majority of sport compact platforms. E
British Columbia
RB Motorsports
15110 East Nelson Unit C
City of Industry
CA  91744
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