Alex
Good questions on a fascinating topic. If you start from: why did Porsche MS commission Secan (aerospace company supplier to Airbus) to build the intercoolers for the 993GT2 race cars to enable them to race with a reliable and maintainable ~630hp when (especially now days) loads of tuners can get 600/700/800 hp using far cheaper intercoolers….
Looking at the 997tt specifically, there are many “tuners” offering their intercoolers which “support” up to 800hp yet RS Tuning say that you can only have 680+hp if you use the 15K Euro Secan units….
Who is wrong and who is right ?
RS Tuning produce engines which carry on making their power under race conditions ie when things are VERY hot, this is not the same as a car built for a 1 mile drag race where the IAT (inlet air temperature) can be kept to within limits for the duration of a ~20 second run.
For road cars RS tuning stuff could be considered overkill but their philosophy is in fact the same as Porsche’s has always been with their road engines hence the myth that Porsche’s always have more hp than advertised, they don’t its just that their hp will still be there on a track day when your TVR, Ford, Merc or whatever will have wilted in the heat.
What actually happens using modern ECUs when the IAT goes up is that the ECU retards the timing in stages which reduces the power, this starts at around 32degC IAT and maximum retard is around 70DegC also the boost will be reduced to bring the IAT back , by 80 DegC the boost may be at 85% of its maximum (for a given rpm in DIN conditions) so at 80DegC 1.2bar at 600rpm will become 1 bar and the timing will be reduced by ~6 degrees , if the IAT carries on going up then the ignition will be cut….
So a more efficient intercooler keeps the ECU using the best possible timing map and boost levels……
The Secan is the gold standard, nothing to date tested has come close and you will notice if you review what is on offer that there is lots of talk of flow rates and end tank efficiency, increased core volume etc but nothing about real cooling performance – IMO the stuff out there for the 997tt which can be had under 3K Euro is at best slightly better than stock but some of the aftermarket units are so heavy and thick that for sure IMO they would heat soak very badly if used for a track day for example.
Getting back to your question, the 997GT2 does run very high IATs as stock, it has the high 1.4bar boost at the top end which despite the cooling effect of the expansion manifold (I’ve heard the number 15DegC reduction banded around) still is on the limit of the stock units. Obviously the stock units work well enough to produce the 530PS enabling a 204mph top speed but any ECU tuning is going to trip the IAT over what the stock intercoolers can handle, the effect of which is probably not noticeable (in terms of acceleration) unless the car is tracked, maxed out, used in very high ambient temps.
My plan is to have RS Tuning fit their 600PS kit and optimise the ECU for the additional “ceiling” provided by the better intercoolers…. In raw numbers terms this may mean an additional 10PS DIN on the 600 but practically speaking it means that the 600PS will be there under all conditions….
-- Apologies in advance to Fritz for bad/inaccurate terminology 
2009 997 GT2 RS Tuning 542PS/736NM
so the real time say through 5th gear is whatever it takes to go from ~130 to 170mph........
