Details are important—from the date of your parents’ anniversary to the day your credit card payment is due and the color of your girlfriend’s eyes. And when it comes to building cars, they’re what separate a merely good one from a benchmark car.
After nearly 20 years of building groundbreaking Pro Touring cars and developing Chevrolet’s performance vehicles, Mark Stielow knows more than most how the little things contribute to the big picture.
“You can drop in a big engine and throw on big wheels and a coilover suspension and you’ll get the look right for the street, but there’s so much more to building this kind of car if you want it to perform on the track,” he says.
For his latest Camaro project, dubbed Gunner, Stielow is drawing on the experience of previous builds such as Jackass, Red Devil, Mayhem, and Hellfire to push it to the next level of capability, durability, and aesthetics. The mostly original Fathom Green exterior will be left alone, while a 650-horsepower LT4 crate engine will provide the thrust, channeled through Detroit Speed Inc.-infused chassis and suspension systems.
Although the engine choice is new, the chassis and suspension setup is familiar territory, and that’s where experience drives the details. He’s been around the block—and cones—more than a few times with similar setups so Gunner offers the opportunity to refine the formula in myriad small yet significant ways. The oil reservoir for the dry-sump system, for example, has been expanded and a transmission fluid overflow tank added.
“The expanded oil tank’s extra capacity helps keep the oil under control on the track, and we’ve designed the addition to ensure it provides the necessary aeration as the oil circulates through it,” says Matt Gurjack, the owner of Sled Alley, which is handling the bulk of the car’s fabrication work, including the modified tanks. “And we added the transmission overflow tank based on Mark’s experience with the Jackass car. Under really hard use, it would push fluid out of the vent tube. This new overflow tank will take care of that.”
Most Pro Touring-style street cars won’t need that level of powertrain support, but Stielow works his cars like rented mules on hot summer days, at tracks all over the country, so that kind of capability is a must for consistent, trouble-free performance. His cars are typically supercharged, too, which adds more underhood heat to the equation.
Additionally, many of the small details have a large influence on weight distribution and the vehicle’s overall mass. That oil tank is located in a custom pocket created within the passenger side of the firewall, moving approximately 40 pounds (including the oil, tank and related lines) toward the middle of the car and offsetting the driver’s weight.
“The more you run them, the more you learn,” says Stielow. “There’s something new with every build that leverages the experience of the previous cars, so we make them that much better the next time around.”
It’s some of the fine details, then, that we’re highlighting in photos with this installment of Stielow’s latest project. They include the aforementioned oil tank mods, as well as adapting a conventional, hydraulically operated power steering system to an engine drive system that was designed without it, and even some of the bodywork details that eliminate some of the sheetmetal wrinkles while preserving the original paintwork.
In the end, it will all look seamless. That’s the plan and it’s all in the details.
1. The exterior of the Camaro won’t be painted, but that doesn’t mean it didn’t need some attention. The front valance had taken a hit and required straightening. The catch here, however, was smoothing it without breaking the 48-year-old paint. Sled Alley’s solution involved using the conventional hammer-and-dolly method but with an old T-shirt wrapped around the hammer to prevent its edges from digging into the paint.
2. The left-front fender also required a little sheetmetal straightening using the same method, performed here by Matt Gurjack. The T-shirts, he says, don’t last long under the continual hits with the hammer, meaning they’ve got to be replaced often. The results are worth it, as the original paint looks untouched after he’s worked it.
3. Crafting the aluminum air intake tube was a surprisingly detailed project. Besides routing it from the throttle body to the custom filter housing inside the left-front fender, it had to be flared seamlessly from 4 to 5 inches in diameter. That involved welding a 4-inch corner section to 4-inch straight tube, followed by making a series of pie cuts in the tube to flare it out roughly to the diameter of a 5-inch tube. When the length and proper clocking of the intake was determined, it was all tacked together for the final metalwork. With a supercharged engine, the inlet flow needs to offer the lowest possible restriction.
4. The intake tube flows into the filter at the front fender. A custom bracket was made to fit the contours of the inner fender and serve as a closeout panel to separate the filter element from hot underhood air. And while the filter housing itself is a tight fit within the fender, it’s designed for relatively easy removal.
5. A look through the front of the Camaro shows just how large the AEM air filter is—and just how much room it absorbs. With 650 horsepower on tap from the supercharged LT4 crate engine, it will process every ounce of atmosphere it can draw through the filter.
6. The filter was so large that clearance was a factor between it and the headlamp housing. Along with the housing itself, the rearward protrusion of the headlamp bulb and wiring harness had to be taken into account. It was a very tight fit, but all the measurements suggest adequate clearance when the front end of the car is reassembled.
7. Here’s the final mockup of the intake tube, showing the masterfully metalworked aluminum. Remember, it started out as three separate pieces. Note, too, the insertion of the mounting pad for the mass airflow sensor. This is exactly what we mean by the finer details of a project. Once it’s powdercoated, it will blend in with the rest of the underhood details, but it represents approximately 20 hours of craftsmanship.
8. One of the significant head scratchers of the project involved the power steering system. Because the factory applications of the LT4 don’t include it in their drive systems—the Corvette Z06 and Camaro ZL1 employ electric power steering—adding a hydraulic-based system was a challenge. Mark Stielow started with a CTS-V power steering pump and pulley from Turn One and a modified mounting bracket. Once installed, however, the outer edge of the power steering pulley was uncomfortably close to the front suspension’s upper A-arm. A little flexing of the engine mounts, especially when cornering, and there would be a serious chance for disaster.
9. By eliminating an idler pulley in the accessory drive system, lowering the power steering bracket and using a slightly shorter belt, the power steering pulley was pulled about 1.5 inches closer to the engine, providing more than enough clearance between it and the front suspension. Moving the power steering pump inward also necessitated moving the belt tensioner in about an inch, requiring entirely new brackets to relocate the tensioner and add a mount for the power steering pump. Drive Junky offers a good system for wet-sump LT4 setups, but this is a dry-sump application and as of this writing, there is not yet a bolt-on aftermarket solution.
10. A home for the Chevrolet Performance E92 engine controller was found in the front corner of the right-front fender, which required a custom-fabbed mounting bracket. Besides the position providing easy access, it is away from major heat sources, and the crate engine wiring harness can be plugged in with modifications to lengthen it.
11. Another item that required some space in the front of the Camaro was the A/C system’s receiver/drier, mounted with another Sled Alley-fabricated bracket. By the way, do you know the difference between an A/C accumulator and receiver/drier? Both trap moisture and regulate the amount of refrigerant that enters the system, but the receiver/drier is used on systems with a thermal expansion valve, while an accumulator is used typically on OEM systems with an orifice tube. The receiver/drier also separates gas from liquid, so the liquid doesn’t damage the compressor.
12. The front of the Detroit Speed subframe was used as the mounting point for the intercooling system’s electric water pump. It’s a Chevrolet Performance part (PN 22901367), which is recommended for use with the LT4 crate engine.
13. More space on the subframe was made for an ABS pump. Stielow has adapted antilock brakes to several of his Pro Touring Camaros, but it’s not an easy task. Modern four-channel systems rely on yaw and pitch sensors in addition to the wheel sensors, which makes tuning tricky if the vehicle’s overall mass and weight distribution differs significantly from the vehicle originally designed for the system. And it can be difficult to separate the ABS’ function from the electronic stability control system software that most antilock systems are designed to complement. Using a Detroit Speed subframe/suspension system brings OE-quality SKF wheel bearings with built-in wheel-speed sensors. Detroit Speed also offers a system that enables SKF wheel bearings to be used with a Strange rear axlehousing or similar. For this project, Stielow is using a 2007 Corvette Z06 ABS module, which requires special calibrations, but the best bet for a tunable system is the Bosch M4 ABS system.
14. Look closely here at the rear corner of the engine compartment and you’ll see a removable panel was cut into the backside of the inner fender (arrow). It will provide access to the dry-sump oiling system’s reservoir and other related components, which are mounted essentially inside the firewall, without the need to remove the right-front fender.
15. Another detail that adds up while subtracting weight on the Camaro is a set of billet aluminum hood hinges from Eddie Motorsports. With small gas struts rather than the springs of the OE stamped steel hinges, these modern replacements weigh less than half of the originals. It also takes weight off the nose-heavy front end.
16. Because the supercharged engine doesn’t make great vacuum—and no vacuum under boost—the braking system will get some assistance with this vacuum pump, which found a home on the firewall, near the master cylinder. It’s a GM part (PN 20939309) used on the Chevy Equinox/GMC Terrain and Cadillac SRX among others, and is readily available through sources such as gmpartsnow.com.
17. The oil tank for the dry-sump system started off as a Peterson 2-gallon tank that was expanded to hold an additional 4 quarts, while ensuring adequate aeration. To achieve that, holes were drilled at the top and bottom of the tank to provide circulation through the added chamber. That allows the oil to maintain the proper aerating circulation from top to bottom. Note the fittings at the top of the tank, too. They were cut off, re-clocked and re-welded for clearance within the Camaro’s firewall. Detail, details …
18. For crankcase ventilation, a Mann+Hummel ProVent 100 diesel-based engine oil/air separator removes oil from the blowby gases, reducing crankcase pressure in the supercharged engine, helping it produce more vacuum, and therefore reduce oil consumption and the tendency for oil to be pushed through the crankcase breather system. With a one-way check valve, its use requires a drain back to the dry-sump tank below the oil level, while the vent itself must be mounted above the oil level.
19. Finally, the oil tank is also home to a custom-fabricated overflow tube for the transmission. On previous cars he’s built, Stielow noticed trans fluid pushing out of the vent tube in high-rpm conditions. This simple solution will capture the fluid and return it to the transmission, where it belongs.
20. With much of the fabrication details finished, they’re all stripped off as the custom brackets, mounts, and other components are readied for powdercoating. The same thing goes for the front subframe. From here, the engine will be removed so the subframe can be unbolted and sent out for powdercoating. The next steps will involve putting it all back together.
21. Stielow’s Gunner Camaro will soon move from Sled Alley back to his home shop for the installation and wiring of the engine, as well as the rest of the car’s assembly. Much progress has been made, but there is still a long way to go before Gunner takes aim at the racetrack.
Photos: Barry Kluczyk