Steve Turner
Former Editor, 5.0 Mustang & Super Fords
July 15, 2011

If there's one thing we've learned over our years of testing speed parts, it's that positive-displacement superchargers hate inlet restriction.

Over the course of its development, Project Vapor Trail has worn a number of different inlet combinations as it climbed the ladder to higher and higher boost levels. It was practically born with the standard 113mm FRPP kit (PN M-9603-M54SC; $350) and TVS, and from there it moved up to a Ford GT inlet tube and 123mm Cobra Jet (PN M-9600-CJ; $665.95) mass air housing. This gradual increase in inlet tube and mass-air-housing diameter helped maximize the growing boost built with the additions of an FRPP/Innovators West overdrive balancer, and VMP Tuning's inlet elbow and dual 72mm throttle body. With these free-flowing parts maximizing the FRPP TVS, PVT was building over 18 pounds of boost and surpassed 700 rwhp in ideal conditions.

"The 123mm and 127mm are significantly larger in size than the 113mm. The 113mm is capable of metering enough air for a car making well into the 600s at the tire," Justin Starkey of VMP Tuning explained. "Over 700 rwhp though, and you need a larger housing to reduce restriction and increase mass air sensor range. With the larger housings, the factory mass air sensor is capable of measuring over 100 lb/min of air. That puts you into the 800-plus-rwhp area."

Obviously the combo was working, but there was just one problem. The GT tube is obviously free flowing, but it's not exactly a clean, direct fit on a GT500; perhaps more importantly for me, it's not carbon fiber. As such, when our friends at JLT Performance released a one-piece, all-carbon 127mm CAI (PN CFCAI127-GT500-07; $449), it was a must-have addition for PVT. Not only is it larger, but it offers a much cleaner presentation.

Of course, we couldn't just throw it on and drive away. It would require a bit of tuning, so we headed over the VMP Tuning to have the combo refined with SCT software and test it against PVT's prior configurations.

On the Dyno

"When tuning for larger intakes, start with your stock mass air transfer function, or whatever you had before that is known to be accurate, and do the math. If your new mass air housing has roughly 20 percent more area, then you use that as the starting point for your tune by multiplying the current transfer function by 1.2," Justin said of the tuning process. "From there, you fine-tune the transfer function based on feedback from a wideband O2 sensor."

As you can see, the 123mm only bested the 113mm by 1.08 hp and 6.63 lb-ft at the peaks on the graph, but looking at the charted data you can see it's far better from 2,000 rpm through 5,000 rpm, but the 113mm managed to hang in there from 5,500 to 6,000 rpm. Obviously the graph has more data points, but the chart allows a snapshot of what's going on across the curve.

Adding the JLT Big Air 127mm raised the peak numbers by 6.17 hp and 4.39 lb-ft. You can see that moving the inlet progressively larger added boost to the equation, but interestingly, moving to the 127mm was like moving to a short-runner intake manifold. It gave up a little down low but thundered from 5,000 rpm up. Of course, if you compare the 127 to the more attainable 113mm, the Big Air is better across the board.

It's worth noting that the temp in the dyno room crept up from 88 to 92 degrees during our testing. We'll have to revisit this combo in the winter and see how the glory numbers stack up with the new combination.

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