It's crunchtime, ladies and gentlemen. After gathering hard information on the exact amount of airbox pressure present at speed in various ram-air-equipped sportbikes, via Pi Research's System 3 data-acquisition system, the time has come to strap these bikes to the dyno and see how much additional power is really available. This is where Sport Rider finally answers the question of whether all this ram-air horsepower hype is a measurable performance increase or nothing more than advertising smoke and mirrors.
We took the ram air data, seven current sportbikes and the Pi data-acquisition system to Two Brothers Racing in Santa Ana, California (www.twobros.com), where proprietor Craig Erion would run the bikes on his Factory EC997a Eddy Current dyno. The Eddy Current dyno was chosen because of its ability to hold a steady rpm; this made it a lot easier to set the correct airbox pressure, compared with the common Dynojet dynos that can only make a complete run through the rpm range. With the Pi System 3, measuring the airbox pressure at speed for the first segment of our ram air test was a simple task. And its sophisticated software permits the user to view the pressure data in real time using a laptop computer. This gave us the chance to set the pressure on the dyno to the same parameters derived from the previous top-speed test.
Our biggest obstacle to completing this experiment was figuring out a way to force enough air into each of the airboxes to simulate the pressure encountered at speed while running on a dynamometer. There is an incredible amount of wind energy at 150 mph. If you've ever popped up out of the bubble while braking for Turn One at Daytona, or even stuck your hand out of a car's window while traveling faster than 130 mph, you know what we mean. We required more than a fan setup that ran up huge cfm (cubic feet per minute) numbers. It would need to supply that volume at pressures above ambient, requiring a large, high-horsepower fan and the necessary ducting-not something readily obtained without spending huge amounts of money, nor easily built and mounted in the limited space and time we had available. Several fan options were tried but none could provide the amount of pressure we needed.
The setup we finally used may seem a bit unorthodox but it definitely gave us the necessary amount of wind energy and pressure. A pair of huge 185 cfm portable air compressors normally used with jackhammers were employed, and the requisite three-quarter-inch hoses directed the airflow. For the smaller bikes, we only needed to direct one compressor hose at a distance from the ram-air inlet to get the necessary pressure. The larger bikes, however, required us to use both hoses and, in some cases, seal up one side of the ram-air inlet while force-feeding the other.It should be noted that Eddy Current dynos typically give horsepower readings 15-20 percent lower than the more common Dynojet dyno readings. We started each run at 7000 rpm (both with and without ram-air assist), since we figured all of our top-speed data was gathered using full throttle and anything less than 7000 rpm in top gear would offer inconsequential ram-air pressure/data. Also, although many will argue that using air compressors brings up the issues of heat (compressing air raises its temperature) and moisture (compressing air also condenses the moisture in that portion of air), these graphs are basically relative in nature and the increase in air temperature and the amount of moisture condensation present were negligible.
Unfortunately, two bikes that were present during the top-speed data sessions had to be returned before we could begin the dyno sessions. Both the Kawasaki ZX-7R and ZX-9R are missing from these tests. However, we did manage to procure a Honda CBR600F4 and Kawasaki ZX-6R to take their places.
On each of the dyno graphs, the bold lines represent ram-air-assisted readings-solid for horsepower, dotted lines for torque. As we stated in "Ram Air Test: Part One" in our October issue, the results will definitely surprise you.
YAMAHA YZF-R6: Here is obvious proof that ram air works on smaller-displacement engines. Ram air helps the R6 hold its peak power higher and longer (12,000-14,000 rpm), and the torque curve is higher and flatter as well. This isn't just an incremental increase on top, either. We're talking about an average difference of five horsepower through the midrange and a far more usable power spread. The ram-air assisted reading would probably be higher at 13,000 rpm, but we were unable to generate the required airbox pressure on that particular run at that point. To give a relative reference, without ram air the Yamaha registered -11mb. Again, remember the lower peak-horsepower reading of 84.4 is due to the Eddy Current dyno.
SUZUKI TL1000R: It was difficult to determine what the average peak pressure was in the Suzuki TL-R's airbox (check out its graph in "Ram Air: Part One," October '99), so we decided to stick with 12mb. Although we were skeptical at first, it's fairly apparent ram air works on V-twins, too. The horsepower and torque curves are well above their non-ram-air counterparts, with a seven horsepower bump at 10,000 rpm. It should be noted that the sealing on the Suzuki ram-air components (specifically where the ducts route into the airbox) is less than satisfactory. We encountered substantial leakage and estimate that peak pressure might be higher if the connection points had a more effective seal. The non-ram-aired TL-R registered -19mb for relative comparison purposes.
SUZUKI GSX-R750: The GSX-R750 is another case where ram air helps the engine hold its peak power higher and longer. The dip at 10,000 rpm on the ram-air graph is the result of a pressure glitch. We had a problem getting the correct mb setting at that rpm, in addition to a persistent exhaust-gasket leak. Note the power peak builds earlier and carries much farther compared with the non-ram-air graph. The GSX-R also suffered from leakage around the airbox/ram-air ducts. Again, overall peak pressure could be higher if the componentry had a better seal. Without ram air, the GSX-R drained the airbox to the tune of -11mb.
HONDA CBR600F4: You'll note that besides the dip in the ram-air-assisted chart at 10,000 rpm, the Honda F4's graph also registers below the non-ram-air graph at 7000 rpm. This was due to the difficulty in getting the engine to run cleanly at that rpm. The float-bowl vents (which pressurize the float bowls so fuel continues to run through the jets when the airbox is above ambient pressure) are positioned just abreast of the ram-air inlets, initially making it difficult to aim the compressed airstream to obtain the same pressure for both the airbox and float bowls. Check out the peak power curve, though; where the non-ram-air F4 is signing off, the ram-air F4 continues to build right up to the rev limiter.
HONDA CBR1100XX: Well what would you rather have-115 horsepower or 122 horsepower? The CBR-XX obviously reacts well to ram-air induction. The horsepower and torque curves literally mimic the non-ram-air graphs, only with a five to seven horsepower increase and three to five additional foot-pounds of torque. It should be noted the Honda XX's ram-air system is one of the most efficient on the market, showing immediate power gains well before the 7000-rpm starting mark and posting high-pressure readings during our top-speed test. For comparative purposes, the CBR-XX's pressure reading without ram-air assist at full-throttle/top rpm was -8mb.
SUZUKI GSX1300R HAYABUSA:Even though the Hayabusa posted median pressure numbers during our top-speed test and didn't build pressure beyond ambient until 145 mph, it's apparent that any internal-combustion motor benefits from ram-air induction. The reason the power curve is tailing off a bit around 9500 rpm is because the Suzuki's mondo engine was basically beginning to require more air than we could feed it at that point. It was the only motorcycle we ram-air-dynoed that left both compressors gasping for breath. And again, the Hayabusa suffered from leakage around the airbox/ram-air duct junctions, which possibly prevented it from posting higher numbers.
KAWASAKI ZX-6R:After witnessing the high-pressure readings garnered by both Kawasakis during our top-speed tests in the first session, we were anxious to see what another ZX-R could do on the dyno. Unfortunately, we ran into a problem. As the revs started to climb beyond 10,000 rpm, we couldn't get the Kawasaki to run cleanly. It was obvious the float-bowl vents weren't getting the same airstream pressure as the airbox during our dyno runs. Without ram air, the ZX-6R ran perfectly and posted excellent power numbers. No matter what we tried, we couldn't get our simulated pressurization to work with the Kawasaki's ram-air system properly. It was frustrating. If we would have had more time to fabricate ducting that enshrouded the ram-air inlets, we're confident our ram-air simulation would've worked. Still, the ZX-6R shows the initial signs of definite power gains up to 10,000 rpm. And judging by the excellent graphs drawn from our top-speed tests of the 7R and 9R, it's a sure bet the ZX-6R would have set the pace as far as showcasing the benefits of ram-air induction.
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This story originally appeared in the December '99 issue of Sport Rider.