High Power GC8 Impreza – Torque Developments derestricts monster Impreza GC8
When can less, be more? During the course of re-mapping Simon North’s Subaru 22B engined Impreza GC8 TDi’s technicians noticed that they were approaching the point of diminishing power returns far earlier than they would have expected. Crucially the Impreza’s entire turbo system was having to work extremely hard, with high boost levels to achieve the power output. Clearly something was amiss with the turbo exhaust manifold and system configuration on the car, which was installed by another tuner.
TDI’s technicians, lead by Operations and Technical Director Sam Borgman soon established that by half way through a dyno run, there was a back pressure build up (over 160kpaA) in the main exhaust system post turbine, which was causing a gas flow restriction.
Ideally, post turbine back pressure should be absolute zero (O kpaA) or in other words a complete vacuum, but reality this isn’t possible, but TDI embarked on designing and producing a new exhaust system which aimed to get as close to this figure as possible.
Pleasingly, a post full power run on TDI’s Roto Test hub dyno revealed that Simon North’s Subaru Impreza’s exhaust back pressure now peaked at a mere 108kpaA, compared to an ambient pressure of 102kpaA.
Because exhaust manifold pressure for a given intake manifold pressure is now significantly reduced, there’s an increase in the pressure delta across the cylinder head. The Impreza’s exhaust gas temperature (EGT) readings are also significantly reduced, and as you might expect torque production is massively increased.
The results of all this exhaust development and the simultaneous fitment of a superior exhaust manifold design has been a large jump in the Impreza’s torque and power figures. “It’s as if the hand brake has been released in terms of engine efficiency,” says TDI’s Sam Borgman.
On TDi’s Roto Test hub dyno, Simon’s Impreza (which uses a large ‘twisted’ GT40 turbo, MoTec M800 ECU and Cosworth intake plenum,) produced a mighty 557bhp @ 6870rpm, allied to 454 lb.ft of torque at 5590rpm.
So what difference has this made to Simon North’s Impreza GC8 in reality? Prior to TDi’s work on the Subaru Impreza the best standing quarter mile time down the Santa Pod drag strip was 10.6 seconds. Crucially, this was achieved running a full 2.5 bar of boost and nitrous oxide injection. Last Sunday Simon matched that time on the unprepared concrete surface at Elvington airfield running just 1.8 bar of boost and no nitrous oxide injection.
By correctly identifying and resolving the parasitic pumping losses caused by the poor exhaust design on the EJ22 engine, TDi’s technicians have produced an ideal outcome – less boost, less engine stress, more power and more proven performance from Simon’s monster Impreza GC8. Proof positive that with the knowledge and facilities at TDi, less really is more!
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