An interesting thread was started on the PCGB Forum recently concerning the tuning of the 944 models. Whilst it was suggested that the 944 Turbo can be quickly and easily tuned with some eBay sourced chips, some Wastegate shims and a boost valve; the general consensus was that tuning a car (not just a 944 Turbo) sometimes requires a little more up front investment to deliver the best value in the longer term.
The manufacturer (in this case Porsche), makes a considerable investment into ensuring the car can reliably deliver the quoted power output in such a way that the car is user friendly, reasonable on fuel and will not out perform any other more expensive models in its range (that are marketed as having higher performance). This usually means that (especially on Turbo cars) there is some margin for performance enhancement.
The 944 Turbo 250bhp model is a very popular choice for those wanting to achieve a 300bhp sports car without compromising reliability and without making a sizeable investment in after market tuning products (compared to the value and/or purchase price of the car).
Whilst the suggestion made in the first paragraph could be applied for little more than £200 (assuming DIY fitment) – that comparatively little investment could seem insignificant compared to the cost of a blown head gasket or, worse still, a melted piston (through the AFR being too lean and/or detonation occurring). It may achieve 300bhp – but it is unlikely to do so without compromising the operating parameters of the engine – the results of which can be avoided with a more considered approach.
Poor tuning can result in catastrophic engine damage. It is always wise to consider a sensible and proven approach to reliably achieve your objectives. The most popular kit we sell to reliably achieve 300bhp (+/- 10bhp) is the ProMAX Level 2 kit. Using this kit will deliver the power enhancements reliably ensuring that your engine will not be compromised (as in the opening example) and will continue to operate with a safe AFR (Air Fuel Ratio) and no detonation. Taking the same approach with other components (that do a similar job) will work also. If you have your Level 2 kit fitted by ProMAX Motorsport you can also be sure that everything is 100% correct with your car (compression, fluid & coolant levels and electronics). We also recommend a pressure test for the turbo boost circuit to make sure that none of your valuable boost pressure will be leaked when running the Level 2 kit.
So what about AFR and detonation? Why do these things matter? AFR (Air Fuel Ratio) is important because if the AFR is incorrect, it will result in either: poor performance, excessive fuel consumption or possible engine damage. The optimum AFR for petrol is 14.7:1. The AFR will vary from this under certain conditions and it may be desirable to have a richer AFR (a lower value) under hard acceleration (especially with forced induction). Optimum AFR is where the fuel / air mixture burns almost completely with no residue or other remaining reactants (air & fuel). The optimum burn ratio is called the stoichiometric ratio. The AFR for Methanol (as a comparative example) is 6.4:1.
Detonation (also called knocking) occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle (contrast this with Pre-Ignition which is where the combustion starts before the spark plug fires). The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. This is why a knock monitor can be very useful and is also why most turbocharged engines have knock sensors to instruct the ECU to retard ignition and suppress boost (where so controlled) when detonation conditions are detected.
The tuning approach for turbocharged cars is very specialized and careful consideration must always be given to cooling, air ingestion and the release of exhaust gases. As the boost increases; these aspects become more of a challenge and I’ll discuss these in a future blog. Andrew S