It's nice to see how owners are beginning to enjoy modifying their M96/7 cars to increase their enjoyment while protecting their longevity. It is clearly starting to provide a lot of interest as well.
Information about power and torque figures are always going to be subjected to variables that can confuse results, however it is a fact that EU legislation has changed the way manufacturers rate their engines and this has altered comparisons between older and newer cars.
The practice of elevating power outputs in some models in the Porsche range and down rating others to rank then in the preferred order between 911's and other models has gone on for years (mainly started with the 924S) and as a result we find older models of the M96/7 usually produce less than claimed in standard form with newer models closer to what we find.
Power outputs recorded from braked inertia runs don't usually follow the same graph plots as the manufacturers versions either and so between all the various different methods of testing engines and manufacturers claims and EU regulations the picture has become extremely confused and variable.
What is probably better to consider is the differences changes can make after modifications rather than trying to link them to other claimed figures and results.
Torque is what accelerates a car (and rear wheel torque at that) and not BHP which only benefits performance if the gearing exploits changes in the maximum torque range. Gearing down a car built to max at over 170 mph (that you will probably never use or experience) will always increase rear wheel torque from the same engine output but if you cannot gear down the final drive, it is better to exploit the range of gearing you are stuck with and as the cars are overgeared from standard - the best way to do this is to increase the mid-range torque, which increasing the capacity does beautifully.
These engines are built to do this anyway (for the same reasons) and variable cam timing and valve lift enable the engine to breath a lot of air at peak revs while trapping more at the bottom to mid range and overall increase the torque you experience when accelerating through the gears.
As a result - increasing the capacity has a bigger affect on the amount the mid-range increases than the top end so an oversized engine by say 9% might increase the mid range torque by nearer 15% but the top end by nearer the capacity increase (because at those revs the engine is reaching its breathing limit).
This increase in torque also makes the cars more responsive and easier to drive especially coming out of corners.
But there is much more that can be done to increase performance. Acceleration is proportional to torque/resistance so increasing torque has the same effect as reducing weight and the two together double the benefit.
Inlet and exhaust systems that increase air flow at the top end will also increase top end power but may slightly reduce that mid-range torque making it necessary to spend a lot more money for minimal increases in overall performance. The increase in capacity combined with weight reduction is therefore a very cost effective way to get a lot more performance than chasing revs and top end air flow especially if the engine needs a rebuild anyway.
Lots more on this topic is available in a long technical report on our oversized engines from our Sharon on
[email protected] but it requires a lot of stamina and some technical knowledge to get through it all, a few days to cover it fully, a few whiskeys to recover from it - and is not for the faint hearted. It will however explain a lot for those interested enough to work through it slowly enough to understand the difficult issues covered because they have been mis-represented for so long many no longer understand the subject as they could.
Baz