We had a chance to install/tune 2 different GT-R's with the billet aluminum Forge actuator kits. Many of you have asked which spring you should run, and we now have some good data to share with everyone.
If you are running an external boost controller, such as the HKS EVC 6, here are the SUSTAINED "BASE" boost pressures you will see with the boost controller turn off. We run 1-2mm of preload. The biggest benefit to running an external boost controller, is the ability to switch to different boost levels on the fly, without having to stop and reflash the ECU. We create one calibration that covers all boost levels for a given type of fuel.
Stock Actuator: 8psi
Forge Actuator Blue Spring: 12psi
Forge Actuator Red Spring: 15psi
The Forge actuator allows for higher boost levels, less boost tamper, and more power, but we are still reaching the limits of the stock turbocharger and injectors. We are just touching 100% duty cycle at about 18psi sustained boost, which delivers about 525whp on our dyno (baseline stock is 390-400whp).
Upgrading to larger injectors is very straightforward, and we have calibrations for different sized injectors. But for those that want significantly more power, a turbo upgrade is the next logical step.
The OEM turbos are rated at about 30 lb/min worth of air each, so in THEORY, we should see 600bhp out of them. We are seeing about 525whp wich puts us slightly beyond their theoretical max airflow. Remember, the presssure or PSI is not the deciding factor in power production....rather...it's the volume of air usually measured in lb/min that determines airflow power potential. The turbo upgrades on the market, from what we have been told, flow roughly 40 lb/min worth of airflow, which would give a theoretical maximum power of 800bhp.
We also noted that air inlet temps reached 120F after 4-5 consecutive runs, pointing towards the definate need for high capacity intercoolers.
One final point, is that many dynos read very differently, so please use my numbers in the context in which they are stated. I don't want to get into a dyno numbers debate in this thread.
Edited by Sharif@Forged, 25 April 2009 - 03:40 PM.