How does rear mount turbo work

STEP 2 After much discussion with STS regarding the application and installation, they recommended a pair of their 67mm T4 turbos, which are good for around hp each. Turbosmart manufactures many ancillaries for STS and supplied the STS-branded wastegates, blow-off valve, silicone hose, oil line and boost reference line.

The only thing missing is the actual pipe, which is supplied with specific-fit kits. STEP 3 Positioning the scrolls is always a complicated packaging exercise. They can face in any direction as long as the exhaust gasses enter up into the turbine housing. Note the standard T4 turbo mount.

Compared to fabricating a set of one-off extractors, this is a fairly straightforward undertaking. STEP 5 Rather than completely welding each join until the whole job is completed, Les just solidly tacks each section as he goes.

STEP 6 Things are beginning to take shape. To get the best flow possible and to ensure there are no repeals reductions in cross-sectional area in any of the bends, Fat Pipes used 3. STEP 7 Cutting and welding each section of pipe to form nice flowing symmetrical contours is the most time-consuming part of the job and is an art form in itself.

Compare the dump pipes here to the pair of large mufflers in other images. STEP 8 The last part of the rear section to be fabricated is the ducting and mounting flange for the dual 38mm wastegates. STS suggests that the optimum position for the wastegates is in the bend right before the turbo, as this is the point of maximum flow. The wastegates control turbine speed which in turn controls boost pressure by bleeding off exhaust pressure to the atmosphere.

Finally, it prevents other parts of your engine—fuel lines, wiring, intake, cooling system - from being exposed to the significant amount of heat generated by a furiously-spinning turbo.

There are some compromises associated with a remote mount turbocharger. Given that a turbo is driven by engine exhaust gases, which spin the turbine and compress the air that is then fed back into the engine intake, the farther the air has to travel in that cycle, the more lag there's going to be between stepping on the accelerator and making usable boost.

There's also the cooling of exhaust gases and decrease pulse size once it reaches the turbine's fins, which makes a turbo's operation much less efficient than when installed closer to the header. Because of this, it can be more difficult to use a rear-mount turbo on a small displacement engine, where the lack of torque can make lag a frustrating issue at lower rpm. There ways to tune around this, but it requires a strong knowledge of how to properly plumb the diameter of the tubing involved, which given the rarity of these installations usually means finding a specialist willing to work out all the kinks.

In general, basic kits that offer low boost are simple enough to install and use with high-torque, large-displacement motors, but anything else is going require more than a little expertise. A few other things complicate a remote-mount turbo installation.

Finding room for the turbochargers is only half the battle - you'll also need to make sure there's space to run the tubing as well, and that it doesn't pass too close to suspension components or hang too low underneath the vehicle, where it risks being scraped or damaged. Then there's oiling the turbocharger, which will require an additional pump and line as well as typically a secondary oil reservoir that's nearby to the turbine.

Given that rear mount turbochargers are more complex to install, less efficient than those located closer to the engine, and not usually suited for small-displacement engines, are there any compelling reasons to go this route? Frankly, the strongest argument for a remote turbocharger is necessity. If you don't have space up front, and absolutely want to run boost, then it's really your only option.

As a rear-mount turbo requires a much longer intake piping system than a traditionally mounted turbo, there is increased turbo lag and pressure drop. A traditionally mounted turbo has the advantage of pressurizing a smaller volume of piping, thus offering quicker response and more efficient pressurization.

To run most efficiently, turbo-heated air needs to be circulated through an intercooler system before entering the engine. As rear-mount turbos' piping is long and in the ambient air of the vehicle's underside, an intercooler system is not necessary, for the charged air is cooled enough by the time it reaches the intake manifold. Again, the downside of this setup is turbo lag, as the air takes much longer to reach the throttle body from a rear-mounted turbocharger.

Traditionally mounted turbos have the benefit of being bolted directly to the engine, thus allowing easy access to engine oil. Rear-mount turbos require a more extensive system of oil and coolant lining.