Ok, upgrading/tuning your normally aspirated Saab.
May I be as bold as to say that most bolt on bits will give little or nothing; you buy something from your local autoparts store/tuning shack, you fit it, hey presto, your car is faster. A bit like a placebo effect? Take the sugar pill and hey presto, you feel better?
Power requires the ability of an engine to take in air and mix it with fuel at the maximum possible for a given cubic capacity; the ability of an angine to do this is governed by 2 things:
1. Valve area
2. Fuel delivery
Though we shall see that even these are fundementally linked.
Valve area; your car is a comprimise between economy, reliability, longevity and ease of manufacture, so, Saab like any other car maker has carefully balanced these for what they believe is appropriate for the vehicle’s market need at the price point. You want more.
Have the valves/head gasflowed and the valves opened up, but, this will only give about 10% increase, why? Due to the overall efficiency of multivalve engines and the accuracy required to produce these heads there’s little extra to be gained [unlike old style 8-12 valve engines which can gain upto 20% more power with big valves and flowing] the manufacturers have already done a “stage 1” tuning job on the head from the foundry! Never the less a good head job is the starting point.
Cams: these lumps of metal regulate the opening and closing of the valves; you can have the cam profile modified for longer opening duration or open further [these can of course can be combined] allowing the valves to let more air [therefore fuel] in and exhuast gas out.
Ultimately it is this capacity to burn fuel that produces power there’s no magic involved, simple physics, that is all, the more air and fuel in, the more power out.
So, bearing in mind how important the head/valves, cams and fuel delivery capacity are in regulating the power output how do these magic bolt on bits increase power significantly? They don’t…
…much of the modifications improving airflow [in or out] are restricted by the airflow at the valves, so any changes elsewhere will not be fully realised until these are also increased.
Chipping: changing the ECU perameters on your N/A will do little as the manufacturers nailed the car down well to begin with for legal emmission reasons. You want more power from your chip? Then you’ll want it to allow more fuel through combined with a raised rev. Limit. Will the engine withstand this increase in spinning speed under load? You’ll find out. So it’ll need to be lightened and balanced, ‘blue print’ is the phrase. Seriously expensive but gives ultimate throttle response.
So to recap, gas flowed head & cams will give at best 10% each, but the power gains do not compound. The lambda sensor will make the ECU increase fuel accordingly so chipping is not necessary [unless it is old and due replacement] so a chip only offers gains with more engine revolutions.
Funky air filters, tidy exhuasts, wierd fuel regulators and suchlike will at best give a 1-5bhp increase on your Saab as they offer no real improvement in airflow at the critical point. Good servicing and diligent maintenance will give more power than a shiney bit from the internet.
Turbocharging; bearing in mind all the above, and, how important airflow is [a turbo is a crude HVLP compressor when all said and done] then all the above is valid for turbo cars too, right?
