Making the 911 that Porsche were too sensible to consider

I'd never thought of using anyone other than Hartech to rebuild the engine - their knowledge of the M96 is unparalleled, and Baz Hart is an extremely talented engineer and (rather helpfully) a very nice chap. I spent ages on the phone with both Baz and Grant, and their willingness to share their knowledge really made this project possible. Hartech race the M96 engines and have developed fixes which address the weaknesses exposed by both road and track use - incredibly useful empirical knowledge of the engine, won the hard way.

Now, the M96 has an intermediate shaft that runs beneath the crank and transfers power to the cams via chains, and the oil pump via a 50mm hexagonal key. It's got an oil fed plain bearing at the oil pump end, and at the other a sealed bearing - the infamous IMS bearing. This is the beté noire of the M96 according to Porsche folklore, and it's said to be simply a matter of time before it destroys every engine in which it is found.

This isn't quite true, and anyway for the new engine we'd use the final development of the IMSB from the M97 - a much larger bearing than used in the 996 versions, so large in fact that it can't be installed or removed without splitting the engine cases.

Next on the list was crank flex- the construction of the M96 is such that the crank has a marked cantilever from the final main bearing to the flywheel, and this, when combined with vigorous use of the clutch and revs can flex the crankshaft, leading to rapid wear of the main bearings, leaking Rear Main Seals (RMS) and - in extremis - snapped crankshafts. Hartech offer an EN40B crankshaft (which a good friend who joined me in the project chose for his engine, more on this in due course) and also they can machine the engine case and install an additional bearing just behind the flywheel which constrains the degree to which the crank can flex, and essentially removes this problem.

Now, I was determined to spin the engine past 8,000 rpm - I wanted fuel cut at ~8,500. This meant we had to look at the valve train, and by this point a chap from 911UK who has an incredible knowledge of racing engines had offered his assistance. We quickly identified the tappet chest as a weak link, for numerous reasons.

For one, it was cheap crap - a weak casting with the bare minimum of material required, and was known to suffer from hydraulic fracturing in normal road use. As new camshaft blanks were not available for the M96 we'd also need to re-grind stock ones, hence would have a smaller base-circle, which would mean that the tappets would ride higher in their bores, and would need both more support and the oiling hole position changing.

It was clear that we needed a new tappet chest, as we simply couldn't modify the existing one to meet our requirements. By this point I'd managed to infect another chap from 911UK with my obsession, and he'd decided to build not one but two engines to our new "X51 Cup" specification, and very rapidly it became apparent that without his input we'd have got nowhere fast.

We ran a stock tappet chest through a scanner, creating a highly detailed (and enormous) digital image of it. My partner then created a CAD model from the digital image, and in consultation with the engine designer we created a new tappet chest that addressed the weaknesses of the OEM one. I emailed Richard Brunning (of Bad Obsession Motorsport fame) and asked if he had a recommendation for a machine shop that could do the work - step forward Specialist Engineering, who created this prototype for us: