Steve Turner
Former Editor, 5.0 Mustang & Super Fords
September 1, 2010

Devoted followers of the 5.0&SF gospel know that since it was born two years ago (time flies) Project Vapor Trail, an '08 Shelby GT500, has seen a constant string of modifications. The goal has long been to create a mild-mannered but ultra-powerful 'Stang that looks great.

In our last installment, PVT reached my arbitrary goal of surpassing 700 rear-wheel horsepower through the stock exhaust manifolds. The exact numbers were 706 hp and 701 lb-ft of torque, which is serious business for a street car burning wholesale-club 93-octane fuel. Our admiration goes out to Justin Starkey at VMP Tuning for the tuning and inlet science that allowed the goal to see fruition. However, if you read the story, you know that we attained this goal in idyllic Florida-in-January conditions. Once the weather warms up and gets wet, PVT will certainly slide back into the upper 600s.

While we all know that cooler, denser air creates more horsepower, you might not know that the GT500's engine management will start reeling in timing to protect the boosted engine from detonation when things get toasty. Safe is good, but a hot engine with less timing is no recipe for maximum horsepower.

"To give you an idea of where we are starting, stock spark (for '07-'09) is in the mid-teens at average temps. Depending on boost level, an aftermarket tune will have spark in the 20s (same goes for 2010s).

"The 2010 has slightly less aggressive ACT retards," Justin said. "This is part of why stock cars vary so much in power output. If you were to dyno one on a super-cold day, its possible that the PCM will add timing and you'll run over 20 degrees of spark. On the flip side, if it's hot enough outside and the car is heat-soaked, spark can go down into the single-digit range.

"When you're in the middle of a timing curve, 1 degree is roughly equal to 10 rwhp (the laws of diminishing returns apply here). So you can see how these approximately 10-degree timing swings result in stock GT500s making as low as 390 rwhp or as much as 480 rwhp."

"I am often asked by customers considering boost upgrades whether they must upgrade the heat exchanger. The best way to look at it is the factory system was designed for factory boost (and the in-block intercooler is quite good). Factory systems are generally over-engineered alittle bit and tolerate small increases in boost," Justin adds. "For a street car that sees only short blasts of WOT for a few seconds at a time, the factory cooling system will work fine. However, for the same street car that sits in traffic with no airflow over the intercooler, there will be a big improvement in felt power when everything is kept cool with a fan-cooled heat exchanger."

In order to ensure that the power doesn't slide back even further due to blower heat soak, I opted to upgrade the car's heat exchanger yet again. Having had good success with Afco's standard dual-pass heat exchanger, I was excited to try out the company's new twin-fan unit.

While things were apart, it was an ideal time to install some Samco silicone hoses from Blue Collar Performance as well. So, I packed up PVT and headed over to VMP Tuning in Deltona, Florida, to document Justin Starkey performing the install.

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