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16 valve 3 Litre Turbo
- Thread starter Diver944
- Start date
Barry Hart
New member
The 2.5 block is what you see machined, with an upper and lower coolant inlet. The old cast in liner tubes have been jig bored away exposing the outer and lower crankcase faces. You will notice that the cylinders have flanges half way up that seperates the flow from each inlet so we can alter the head flow to reduce temperature differentials (keep it cooler).
They are cylinders really - not liners - so the top part does not fit inside anything (except that it is a precise fit in the three machined outer diameters so it cannot move anywhere - i.e. is stabilised throughout its height. Liners inside tubes made from other materials are not good for structural stability, size variation, thermal dissipation and stiffness - not as good that is as a single cylinder (rather like a motorcycle cylinder with the fins machined off sitting inside a water jacket). The lower portion is a precision slide in fit.
I have used nikasil on cast aluminium cylinders for over 35 years with no problems (see buyers guide section on older motorcycle racing engines). nikasil keys better to a cast alloy surface than either a smooth machines steel or dural surface. We have manufactured similar cylinders to repair Boxsters and 996 and 997 engines for about 6 or 7 years with no problems at all (again photos on the buyers guide).
The alloy cylinder expands like the original block so runs with small initial clearances like a standard engine (unlike steel which I would expect to need bigger cold clearances of about 1 thou (.024mm) or more.
The alloy cylinder transfers heat better and so the surface of the piston/oil/bore interface is actually cooler.
The pattern we have made for the bare cylinder castings will also make a cylinder to repair any 2.5, 2.7 or 3 litre engine (and will soon be in stock). If the former deep block 1- then the lower flange sits on the lower deck face and if the latter shallow block then that is machined off and the upper flange rests on it.
I have made it large enough to accept a bigger bore but am not sure how far to go as this time I am looking for more of a top end racing engine than an improved road turbo and everything you do to increase capacity lowers the peak torque revs (because the same air/exhaust flow is reached at lower revs and there is a limit to how much you can open the ports out without making the cast cylinder head walls too thin).
Sorry - no time for any more now.
Baz
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