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 K20.org, 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.