We had a conversation with a high level Porsche® 918 Engineer, we were discussing engine control strategies and a lot of interesting things were learned and validated. Take a look at our study of the 991 RS on the dyno to understand a bit more about this. Historically the engine was controlled reactively as in a sensor reads something abnormal and the car reacts to it after the event (knock sensor detects unstable combustion and the car pulls ignition timing for example). With increased emissions control required, Porsche® had to change their strategy for the 2014 and up vehicles. Porsche® has built engine models into the engine controller so that they can predict outcomes before they occur and look at sensor readings before the combustion events (like intake air tempearature, air pressure, ambient conditions, coolant temps etc...) and predict what would likely occur and change the engine parameters based on this.
So incase your dynoing your car with uncontrolled, hot intake air temps or at the track on a hot day and notice the power is down, now you know why...
Below is what the engineer told us...
Porsche's® Engine Management strategies are now proactive not re active. As soon as one parameter starts to go out of the designed limits the engine power is immediately pulled back in a sequential fashion so the driver does not feel any immediate loss of power. This is done by Cam timing, throttle plate position and Ignition timing. The ignition is done per cylinder up to a certain stage then per bank,(in the case of the 918) if large changes are required. Along with cam timing and throttle plate changes, this degradation of power is not felt as a sudden loss of power but a more gradual loss, so car performance does not suffer in the minds of the driver.
Air temp is a huge factor. With smaller packaging and lighter cars to meet fuel mileage etc, the engine inlet temps suffer quickly due to air duct entry’s etc. As soon as the air temp rises, the cam timing is changed along with the throttle plate position. This is to limit the air mass as fueling cannot be added to help lower air temps. This is because the fueling is already pulsed to keep the cat working correctly, so additional fuel added to control the air temp is an emissions problem. In the case of air temp, cam timing is changed per camshaft per bank, the throttle is closed and the fuel timing is adjusted to suit the new overlap period to ensure the Cat still gets fueled to stay alive.
They cannot see any detonation as the CEL is a major issue for servicing etc, so strategies are in place to limit the possibility of any detonation. If the engine does see major detonation, then it goes into limp mode.
In the case of the 918, the shift point in the trans are also adjusted to suit the engines drop in power output.
So air temp is a huge factor in performance now. Because they cannot add fuel to cool the charge as the fuel is in the cylinder after the hot air has entered, the other parts of the engine are adjusted to control any detonation. With so many changes happening at once and continuing to change, the driver doesn’t feel a sudden loss in power. This is done on purpose, otherwise no one would buy a Porsche®.
Would like to make a review of the products as well as the customer service of Jamie in particular.
Summary - High quality products paired with superb customer service - highly recommended!
Just a brief background on the car:
2007 997.1 GT3RS
Car has about 35000 miles and I intend to keep it for a long time to come. Decided to install the harmonic damper, although the harmonic issues are supposed to be less problematic in the 3.6 cars - would like to have peace of mind and if in future I were to consider upping the capacity - there will be less worry.
Ordering / Payment / Delivery process - Jamie is prompt in answering all questions and no pushy at all. Tried to tempt me for the long race headers - but its no go in my country due to the strict regulations here. Jamie kept me updated on the built process of the airbox and shipped both items once the airbox is ready.
Installing the harmonic damper pulley - no issues at all.
Carbon Airbox (dual cone / single inlet) - nicely made and came in a sturdy wooden box (no worry about delivery damage). Noticed no cutout to accommodate the engine compartment fan. After initial installation - upon test closure of the engine lid, realised that the engine compartment fan will interfere with the airbox preventing closure of the engine lid. Messaged Jamie - who told me there were no interference issues with the other 997.1RS he had. He suggested cutting the support spacer on the lower part of the airbox. Tried that - still having issues with interference. Jamie was in the process of ordering an aftermarket low profile fan for me when he realised that there are 2 stock OEM fans. The newer ones are lower in profile and eliminated the interference issue.
He promptly order the new fan and had it shipped to me after he received the fan (fan was not available locally).
After installing the new fan & with the lower spacer height (by 1cm) - there was no interference - but I noticed that the rubber piece that seals the airbox from the intake opening is not flushed with the airbox. Returning to the original spacer height made the seal flush but had a little intereference with the connector of the fan which can be resolved with a file within a few mins (non-consequential part).
Subjectively car feels smoother and more torquey. Having only driven the car in city traffic so far after the installation, I can feel the car being smoother and just generally nicer even in the lower rpm ranges 2.5-4.5k rpm. Haven't have much chances to go beyond that to make even a subjective opinion.
I usually drive the car in the non-sports mode (exhaust valve closed) in city traffic - as I like the intake / mechanical noise over the exhaust noise. In the 2.5k - 4K rpm range - the intake noise is definitely a little louder and more melodious. My wife described it as "the car sounds different in different gears". All in all - it made the car more enjoyable to drive even at mundane speeds. Hopefully the change is even better in the upper rpm ranges. ~ HerShann - Singapore: 997 GT3 Carbon Airbox, Harmonic Damper