| I would say that for a street car with 2" inlet turbos it is generally NOT a good idea to upgrade from 2" to 2.5" piping, here's why: 1.) There will be an increase in turbo lag with larger pipes. There is simply more air volume that needs to be moved and larger pipes take the turbos longer to 'fill up'. This lag will be more noticeable at part throttle under dynamic driving conditions. A dyno chart from a 4th gear full-throttle pull won't demonstrate this, which is why a lot of tuners incorrectly talk about this being a 'lag-free' upgrade. 2.) An increase in post-compressor/plenum air volume moves the surge limit of the compressor to a higher-flow area of the compressor map. This will increase the likelihood of compressor stall (bad) and/or surge (very bad). But what's a compressor map, surge limit and compressor stall? (for a good time, type that into a google search) Compressor maps are data provided by the turbo manufacturer to indicate the pressure and airflow characteristics of a specific turbo. These measurements are made on a standardized test-bench in a lab setting using an electric heat source, not attached to an engine.
When installed in vehicle, the characteristics of the intake system change the compressor map of the turbo. Increasing volume downstream of the compressor (i.e. 2.5" pipes) moves the surge-limit to the right, meaning the compressor will go into surge/stall at a higher airflow. Not good. Compressor stall, according to wikipedia:
"is a local disruption of the airflow in the compressor of a gas turbine or turbocharger. A stall that results in the complete disruption of the airflow through the compressor is referred to as a compressor surge. The severity of the phenomenon ranges from a momentary power drop barely registered by the engine instruments to a complete loss of compression in case of a surge, requiring adjustments in the fuel flow to recover normal operation. "
Long story short, with 2.5" pipes on a 2" inlet turbo, your car will require higher RPM to spool up to the same boost level, and will be laggier on throttle transients, especially at part throttle. The trade-off is that you get a bit more power at full-throttle.
- Sam |
06:55:14 10/02/20
