Riders on the Storm

Rear Mounted Turbos from Squires Turbo Systems

Bob Mehlhoff Dec 23, 2004 0 Comment(s)

When we first saw the STS turbocharger mounted near the rear axle of a fourth-gen F-body, we had some hesitation. After all, turbos have always been located in the engine compartment where they can build up enough heat to cook a pizza while consuming precious under-hood real estate. But then one of the freethinkers from the office said, "Why not mount it in the rear?" and we scrambled for answers.

Just about that time, Rick Squires of STS Turbo Systems threw us the keys to one of his pressurized Firebirds equipped with one of his new patented turbo kits and told us to take it for a rip. We couldn't find an open stretch of industrial L.A. road quick enough and we couldn't believe the rush. Nail the throttle of an LS1 that inhales through one of STS's turbos and you'll feel like you're traveling at fast-forward-video speed down the asphalt. After we got back to the building and pulled our faces back into place, we had to learn more about these butt-mounted hair driers.

Squires always loved the sensational power a turbo produced, but didn't like the high-underhood heat, packaging restraints, and additional front-end weight a traditional turbo location brings with it. He decided to mock up a system that mounted the turbo under the car away from the engine heat. The solution was to install the blower where the muffler once lived and from there, plumb the intake tubing up to the engine to provide the boost, while the 38mm wastegate bleeds unneeded exhaust to control the boost pressure. The turbo would serve double-duty to muffle the exhaust sound and to provide a deep and throaty note.

Since these systems are uniquely designed to function at the rear of the vehicle, it operates without any noticeable lag and will produce full boost below 3,000 rpm. This is because the intake-tubing volume is about the same size as most traditional turbos that are front-mounted with an intercooler. The system is a true bolt-on kit that can usually be installed in an afternoon. In an F-body, the intake tubing is routed under the car on the driver's side. The tubing's exposure to ambient air alongside the car also serves to cool the charge. Tests have shown that turbo outlet temps with 5-psi boost measured 175 degrees F (at the rear of the car) and dropped to 115 degrees F at the intake discharge up front. The pressure drop was 1/4 to 3/4 psi. The bottom line is that the intake tube acts as an intercooler, dropping the rear-mounted turbo temp (which is already lower than engine compartment installations) about 50 percent and with a very small drop in psi.

To lubricate the turbocharger, Squires designed a system that taps into the engine's pressurized oiling system (above the oil filter). The pressurized oil travels through 12 feet of tubing back to the turbocharger. From the turbocharger, an electric oil pump removes the oil and pushes the lube forward to the engine and into a fitting in the center of the oil cap, where it drops back into the crankcase. Each time the lube travels up and back through the tubing it is cooled by ambient air.

The result is that you can realize huge horsepower and torque gains after a single day's work. The STS Turbo kit keeps your car stock in appearance, while retaining its original drivability. And oh yes, in most cases your fuel economy will stay the same or improve (in most cases, fuel economy improves 2-3 mpg). That is, of course, if you can keep from mashing the fun pedal.

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The STS Turbo System comes as a ready to bolt-on kit and the typical installation takes about an afternoon. The kit includes a Garrett turbo, TiAL wastegate, HPC-coated tubing, an oiling system, and everything else needed to install the turbo. Since the turbo is mounted at the rear of the car, there is no added heat build-up and the system is cooled from fresh ambient air, which creates denser exhaust molecules to propel the turbo's turbine wheel more efficiently. The turbo also serves to provide a deep, throaty exhaust sound in place of the muffler.

With the unit placed behind the rear axle, there is improved weight transfer, thus better traction, and turbo temps are reduced about 500 degrees F compared to a traditional engine compartment installation. As such, the need for a turbo-timer that allows the engine to run after shut off to cool the turbo and avoid oil and bearing damage is eliminated.

The K&N filter element ensures a clean supply of air and serves to shed most all water, even in a wet environment. To keep mud and sand from the air filter, STS recommends installing a K&N pre-charger (nylon) sock over it, which is simple to clean.

The intake tube, which runs up the driver's side of the car, displaces an internal volume that closely matches most front-mounted turbo systems installed with intercoolers. In simpler terms, a large compressor (the turbo) fills a small volume (the intake tube) in about 0.05 seconds with the STS Turbo system, resulting in very minimal lag.

On this LS1 system, the mass air flow (MAF) sensor is located in front of the engine above the intake tube. All of the STS tubing is HPC-coated for long service in all types of environments.

At the front of the rear axle, this STS pump scavenges oil from the turbo and feeds it into a length of tubing that travels up and into the new oil cap. The benefits of this are that the air around the tubing serves to cool the oil (both up and back) and since the oil is fed directly into the oil cap, there is no need to drill a hole in the engine's oil pan as with most other systems. The STS patented oiling system provides "wet-start" oiling to ensure instant lubrication at start-up.

The oil used to lube the turbo is sourced just above the oil filter.

This 38mm wastegate is a TiAL unit and maintains a predetermined boost level (typically 5-6 psi). The wastegate controls the speed of the turbo by limiting the amount of exhaust to the turbine.

Under the hood of this '95 F-body you'll only find an LT1 engine, and the intake tubing from the rear-mounted STS turbo. Because the turbo is mounted behind the axle, the underhood temperatures are lower.

STS Turbos ensures the quality of all of their kits by building them in-house at their facility in Orem, Utah. Kits are also available for many late-model Chevy and GM trucks and one is being readied for the GTO as well. There are also kits for Toyota and Dodge Ram 1500 Hemi pickups.

STS recommends that all vehicles are tuned and wideband tested to ensure safe air/fuel mixtures, especially on LS1 applications because the high compression ratio (10.1:1) makes it necessary to tune before running even 5 psi of boost. For more tuning information STS recommends contacting www.nelsonperformance.com or www.ststurbo.com.

The installation has a clean and well-engineered appearance. On Camaros and Firebirds, the factory fuel tank heat shield does an excellent job of blocking the heat of the turbo from the tank. STS products are sold through authorized dealers. To find an STS power dealer dealer near you call 1.866.WE.TURBO (866.938.8726) and press option 2.

The Truth is in the Numbers
STS makes kits for LT1 and LS1 Camaros. STS stresses that tuning is critical for all of its kits. For LS1 tuning information, STS recommends and sells Nelson Performance Programming.

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