The Toyota Supra Mark 5 has captured the hearts of enthusiasts worldwide, carrying the torch of its legendary predecessors. For those looking to push the boundaries of performance, lessons from past Supra generations, like the iconic MKIV, offer invaluable insights. This exploration delves into a turbo upgrade journey on a MKIV Supra, highlighting key aspects relevant to achieving peak performance in your modern Toyota Supra Mark 5.
Alt text: Precision Turbo GEN2 PT6870 CEA turbocharger installed on Toyota Supra MKIV engine, showcasing a high-performance upgrade for enhanced horsepower and torque.
Recently, a GEN2 PT6870 CEA turbocharger was installed, marking a significant step in enhancing engine output. Before pushing the limits further, a routine check of vital components is crucial. Spark plugs, often an indicator of engine health, were inspected. NGK BKR9EIX spark plugs, after 1.5 years of service, showed minimal wear, demonstrating their resilience under demanding conditions.
Alt text: Close-up of NGK BKR9EIX iridium spark plugs removed from a Toyota Supra MKIV engine, displaying their condition after extended use and highlighting the importance of regular spark plug inspection in performance vehicles.
To ensure optimal performance with the new Precision Turbo, a fresh set of NGK BKR9EIX iridium plugs was installed. Prior to this upgrade, a compression check was performed on the engine, built by Four Rings Performance. After two years of running a PT6766 CEA turbo at a 700-750+ WHP level (around 23-27 PSI), the engine displayed impressive compression readings: 134, 130, 129, 127, 128, 128 PSI across cylinders 1-6 respectively. This minimal variance, just 5% across all cylinders, and a mere 1.5% excluding cylinder #1, speaks volumes about the engine’s robust construction and sustained health under high stress.
A common oversight during spark plug replacement, especially with pre-gapped iridium plugs like the NGK BKR9EIX, is verifying the gap. These plugs come pre-gapped by NGK at 0.030-in, which was wider than the previous 0.018-in gap used in this setup. At boost levels exceeding 20 PSI, the wider gap led to engine stumble and hindered acceleration.
Alt text: Mechanic adjusting the gap of a new NGK BKR9EIX iridium spark plug for a Toyota Supra MKIV engine, emphasizing the critical step of proper spark plug gapping for optimal engine performance and boost handling.
Correcting the spark plug gap to approximately 0.020-in resolved the issue. Subsequent road testing on private roads at 30 PSI demonstrated the transformative power of the GEN2 PT6870 CEA turbo. The car exhibited phenomenal acceleration, becoming a true “rocket,” demanding careful throttle control, especially without traction control engaged.
Comparing the spool-up characteristics of the GEN2 PT6870 CEA with a 1.00 AR divided housing to the previous PT6766 CEA with a 1.15 AR divided housing revealed a slightly laggier response. However, above 4000 RPM in third and fourth gears, the new turbocharger delivers rapid acceleration. For everyday drivability, the GEN2 PT6870 performs admirably, even at highway speeds. In sixth gear, it produces 5 PSI at a mere 2800 RPM, showcasing impressive spool for a high-flow turbo on a 3.0-liter engine.
While the new turbo delivers enhanced performance, there’s a subtle trade-off in sound. The distinct whine of the PT6766 is slightly less pronounced with the PT6870. The PT6766’s sound profile was reminiscent of the favored PT71-GTQ journal bearing turbo.
Future plans include fine-tuning the AEM Infinity’s traction control system and obtaining new dyno figures at Modified by KC’s Dynojet 424x. These developments promise further refinement of this high-performance build.
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SOURCES:
MODIFIED BY KC PRECISION TURBO AND ENGINE PTP TURBO BLANKETS SPARKPLUGS.COM SWAIN TECH COATINGS
