Project Toyota Supra MKIV: Part 6 – 800whp Build Update


PHR did exceptionally well with the fitment of their exhaust manifold, using every last millimeter they could to get the most out the exhaust bends for maximum flow.  Check out how close we are to the fender here.

While the wraps and coatings will do wonders to keep under-hood temps at bay, MKC still heat-shielded the ABS components as an added precaution, given their close proximity to the manifold.

Our twin 46mm Precision Turbo wastegates are installed and waiting to make some noise.  The PHR-supplied dump tubes were also a perfect fit.

The cool thing about running a dual, open-dump wastegate setup as opposed to one is, not only do you get better boost control, you actually get reduced back pressure and, thus, increased flow.  The area of a 3.5in tube opening is 9.62 square inches, while a 4.0in tube is 12.57 square inches.  In case you thought calculating the difference would be merely as simply as dividing 4 by 3.5 (for an increase of 14%), the area difference is actually nearly 31% greater in terms of flow, as you can see by dividing 12.57 by 9.62.

The wastegates add to the overall exhaust pipe volume when dumping atmospherically.  But when wastegates are routed back into the exhaust (for quieter operation under boost), the flow numbers don’t change, and we stay with 12.57 and 9.62 for 4in and 3.5in, respectively.  However, with twin 46mm gates dumping atmospherically we’re adding 5.15 square inches when the gates open up for a total of 14.77 square inches with the 3.5in downpipe.  That’s a 17.5% increase in flow over a 4.0in exhaust system with a re-circulated dump pipe! 

Previously, this car was running a 3.5in full exhaust with a larger, 60mm open wastegate.  It made over 760whp at 29 PSI on pump 93 octane with a spray of methanol.  That exhaust’s total area with wastegate was 14.0 square inches.  This means our new exhaust setup should flow 5.5% better.  But let’s not forget this is turbo-back—it isn’t taking into account our larger PHR manifold, our reworked cylinder head, or even our larger intercooler core (more on that next time).  And hey, what about that crazy Hypertune intake manifold with 90mm throttle body (providing 91% more volume over the stock 65mm throttle body).  If you couldn't tell already, we’re very excited to see the results!


Behind exhaust runner #6, MKC was able to utilize more Thermotec hose protectors by shielding a heater line here.

Previously, this coolant neck had two lines that circulated through the factory twin-turbo setup.  For years, the male ends were rubber-capped so it’s nice to see them properly welded shut.  MKC went even further by giving it a chrome finish to match the rest of our engine.  The coolant temp sensor you see here goes to a SPA Technique Oil/Water digital twin-temp gauge in the dash.

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