Making the 911 that Porsche were too sensible to consider

Most people have a good understanding of the history of the 996 - it was launched with a development of the water cooled flat six from the Boxster, pushed to 3.4 litres, but the decision was taken to install a water cooled evolution of the older air-cooled motor to create a high performance version that would be called the GT3. The same engine also appeared in the turbo, and the Porsche Cup cars (with changes appropriate to each, of course).

Slightly less well known is the X51 Powerkit, a comprehensive upgrade package for the M96 engine that was created when Porsche was evaluating whether the M96 had what it took to be the base engine and the high performance version.

For the 996.1 this kit was extremely comprehensive, encompassing an additional oil scavenge pump, heavily revised sump, X51 specific heads, pistons, cams, valves, a whole new cast aluminium intake (instead of the stock plastic unit) and much larger diameter exhaust manifolds, an additional central radiator and a revision to the DME to manage all the changes. This wasn't a red badge and a tweak to the map - the engine was gone through from top to bottom and almost every system was revised or enhanced.

And, of course - it wasn't enough. The decision was made that the Mezger was the way forward and the rest was history.

The X51 kit continued to be offered, but with each subsequent iteration it was less comprehensive, and whilst certainly more than a trim level it was never as comprehensive as it was in its original form.

Over the years the M96 has become the butt of many jokes, the chocolate engine, the engine Porsche wanted to forget, and with the move to the 9A1 architecture it largely was.

I have to admit though, I liked it - characterful, makes a great noise with a sports exhaust, plenty of shove low down but some real zing in the upper reaches of the rev range. I had bought my 996 on 60,000 miles, and decided that I was going to run the engine through a prophylactic Hartech rebuild before it hit 100,000 in order to preserve all the things I liked, but remove the weaknesses that were well known to bedevil the M96 (and some that were less well known, but still needed to be engineered out).

Around this time Matt Falks had the engine in his very well known 996 C4 rebuilt, in his case by Autofarm, and pushed to 3.7 litres.

He was good enough to publish some estimated power power and torque plots for his revised engine, and it was clear that the new unit had more horsepower and torque- both delivered lower down in the rev-range.

This was clearly a strong indication that when I got my engine rebuilt I should swap from the 96mm bore to the 100mm bore in order to take my 3.4 to (the obviously much more desirable) 3.7.

But, why stop there? It occurred to me that if one were to add the X51 kit to the 3.7 then it's higher lift cams, flowed heads and increased rev limit might create a unit that continued making power when standard 3.7's were already changing gear, an engine that potentially answered the question "what if Porsche didn't choose the Mezger?"

I started to put together a wish-list for my new engine, a list that could be summarised in two key points: remove the weaknesses of the M96 and add drama in the form of revs and power.

First, the weaknesses.