Turbo lag is easy to talk about and harder to quantify, so we put it on the dyno. Starting at 1,000 RPM and going wide open to a 320-horsepower target, the stock L5P variable geometry turbo reached that mark in 2.9 seconds. The larger non-variable-geometry wastegated turbo took 4.3 seconds. That gap is the lag you feel on the street. The variable geometry unit also smooths the turbo RPM curve as the engine accelerates, which helps response in the lower RPM range. If you want to run the larger wastegated turbo on an L5P or a similar engine, converter calibration becomes part of the fix so the engine can move through the low-speed range and get the turbine working sooner.
The test addresses a common concern with larger, non-variable-geometry turbochargers: turbo lag. Rather than judging response by feel, the team developed a dyno test that measures how quickly the engine can build power during a simulated real-world acceleration event.
The test simulates a wide-open-throttle acceleration through a gear. The engine begins at approximately 1,000 RPM and 50 horsepower, representing a low-speed cruising condition.
From there, full throttle is applied and the test measures how long it takes the engine to reach 320 horsepower.
With the stock variable-geometry turbocharger, the engine accelerated from the starting condition to 320 horsepower in 2.9 seconds.
That provides the baseline for comparing the response of the larger turbocharger.
With the larger non-variable-geometry turbocharger, the same 320-horsepower target took 4.3 seconds to reach.
Under identical test conditions, the larger fixed-geometry turbo therefore required significantly more time to produce the requested power.
That additional response time is turbo lag.
Instead of describing lag subjectively, the dyno test quantifies it. The larger non-VG turbo took 1.4 seconds longer than the stock variable-geometry turbo to accelerate the engine from the same low-power starting point to 320 horsepower.
For a street-driven L5P or similar application, the recommendation is to loosen the torque converter calibration.
Allowing the engine to move more quickly through the lower RPM range helps it get onto the turbine sooner, bringing the larger turbocharger into its effective operating range more quickly and reducing the lag experienced during acceleration.
