Hello;

There is not much information in any of th Porsche Literature about the internals of the 996 motor.

Does anyone know the dimensions of the Intake and Exhaust valves? Do these differ between the 3.4, 3.6 and GT3 motors?

What are the differenced (other than displacement) of the 986 motor versus the 996 motors? Does the Boxster motor have differnt cylinder heads (i.e. are the cams interchangable and is the Valve train the same (springs, followers etc.)

Porsche has always made such a engineering marvel o developing the engines, but there is not much information in print or on the Web.

Regards

Franz

 

Best source of information is to order the "Information Technik" books from Porsche related to each model introduction. You can get these at <a href="http://www.myporsche.com" target="_blank">MyPorsche.com</a>. These books have engine drawings and complete descriptions of the engine systems, dimensions and valve timing, however details of port and valve dimensions are lacking.

The 996 and 986 engines are very similar and share the same basic block (cylinders and bottom end) and cylinder head castings. This engine is designed for volume production at low cost and to maximize sharing of parts between 911 and Boxster. The major differences between variants are in the bore and stroke which determine displacement. There are other detail differences in the port and valve sizes, camshaft timing and timing control, induction system etc. which change the horsepower between the 996 and 986. The 986 and 996 engines probably cost about the same to build though, despite these differences IMHO. These engines are NOT equipped with a dry sump oiling system. The non-replaceable cylinders are cast into the crankcase using the so called "Lokasil" method of casting a high silicon cylinder liner into the block.

The Turbo, GT2 and now defunct GT3's normally aspirated engine on the other hand is a COMPLETELY different engine. The normal 996 engine described above will apparently not support performance increases or racing use. The Turbo/GT2/GT3 engine is very similar to a 962 racing engine, really a water cooled variant of the air cooled 911 engine. The GT1 and Porsche Supercup engines are also based on this engine. The crankcase is the same crankcase as the early aircooled 911/964/993 engine with it's true dry sump oiling system, ie the oil is pumped out of the engine to a separate tank for de-aeration and to supply a constant flow under extremes of braking and cornering. The replaceable cylinders fit into the crankcase just as the aircooled cylinders do on an aircooled 911 but all 3 cylinders each side are covered with a water jacket. The cylinders are Nikasil lined as first introduced on the 917 Porsche and used for all high pefromance Porsches since. The water cooled DOHC cylinder head is completely different than the SOHC early 911's with 4 valves per cylinder and here one cylinder head covers 3 cylinders rather having than individual heads for each cylinder. This is a wonderful engine, suitable for racing use, I wish for it's $25,300 premium over the Boxster that the 911 was based on this engine (not to mention the Turbo/GT2/GT3's superior G50 based gearbox).