Subaru Impreza EJ25 WRX & STI Twin Scroll Header / Rotated Up-pipe
Full-Race’s legendary STI/WRX Twinscroll header/rotated up-pipe is the proven solution for fast spool on Subaru’s EJ engine configuration. Designed to optimize performance for a stock and built EJ engines, this up pipe uses a dual wastegate configuration for maximum kinetic pulse energy. Fits almost any Twinscroll T4 turbo (S200SX, S300SX, S400SX, GTX30R, GTX35R, GTX40R, GTX42R) and compatible for LHD chassis ONLY at this time.
Utilizing ideal cylinder pairing and the proper implementation of twinscroll technology, huge increases at the low end, midrange and top end can be realized, all while minimizing spool time and improving throttle response. Proven to make substantial horsepower and torque gains, the twinscroll rotated kit is the best performing AND the most versatile subaru turbokit we’ve ever developed. The Full-Race WRX/STI exhaust manifold is the last manifold your Subaru will ever need!
Full-Race Twin-Scroll Manifold features:
- Thick wall stainless steel construction
- Precision robotic TIG welding
- 1 year warranty for the original purchaser
- The OEM Subaru triple layer steel gasket is strongly recommended. There are other less expensive options available, but this is the best because it has a built-in crush ring and is steel so it will not deteriorate. The Subaru part number for the exhaust gaskets is PN # 14038 AA 000. Torque properly to factory specifications.
- Not Compatible With 2.0L Oil Pan. Requires 2.5L Oil Pan and Pick Up. Contact Rep For More Info
- Coatings highly recommended for Subaru applications; the main benefit of high grade coatings, which header wrap does not acheive, is the coatings will stop any oxidation or corrosion of the base material. In a subaru application where the header is under the engine and susceptible to the elements, the coatings are a huge benefit to improving the longevity and durability of the header – particularly at the flanges, welds and the runner areas. Additionally, if you were to use only the header wrap, that wrap can hold moisture close to the metal and force oxidation. With a coating you can use wrap on top of the coating for maximum protection from heat and corrosion. A coated header/up pipe PLUS header wrap on top of that coating is what we run on the cars built here at Full-Race.
About Twin Scroll:
- Twin scroll turbo system design addresses many of the shortcomings of single scroll turbo systems by separating those cylinders whose exhaust gas pulses interfere with each other. Similar in concept to pairing cylinders on race headers for N/A engines, twin scroll design pairs cylinders to one side of the turbine inlet so that the kinetic energy from the exhaust gases is recovered more efficiently by the turbine. For example, if a four-cylinder engineï¿½s firing sequence is 1-3-4-2, cylinder 1 is ending its expansion stroke and opening its exhaust valves while cylinder 2 still has its exhaust valves open (while in its overlap period, where both the intake and exhaust valves are partially open at the same time). In a single scroll AKA undivided manifold, the exhaust gas pressure pulse from cylinder 1 is therefore going to interfere with cylinder 2ï¿½s ability to expel its exhaust gases, rather than delivering it undisturbed to the turboï¿½s turbine the way a twin-scroll system allows.
- The result of the superior scavenging effect from a twin scroll design is better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbochargerï¿½s turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side while drawing out the last of the low-pressure exhaust gases, helping pack each cylinder with a denser and purer air charge. As we all know, a denser and purer air charge means stronger combustion and more power… but the benefits of twin scroll design donï¿½t end there. With its greater volumetric efficiency and stronger scavenging effect, higher ignition delay can be used, which helps keep peak combustion temperature in the cylinders down. Since cooler cylinder temperatures and lower exhaust gas temperatures allows for a leaner air/fuel ratio, twin scroll turbo design has been shown to increase turbine efficiency by 7-8 percent (faster spool, quicker response) and result in fuel efficiency improvements as high as 5 percent. It is wise to size the turbine housing A/R larger than the single scroll turbine A/R typically used!
- Subaru Impreza Sti MY12, 2.5 engine, complete Full Race T4 turbokit with intercooler and BW 8375, 1000cc injector, at 21psi on 98oct fuel:
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