By Jay Coates
PORSCHE 9A1 ENGINE
This article is intended to provide a brief, technical description of the Porsche 9a1 engine. Its design is robust and advanced.
Main Differences from Predecessor M96 & M97 One of the main differences from the predecessors M96 & M97 is that the 9a1 engine has no IMS bearing or shaft. The timing chains on 9a1 engine are located on the front of engine for both banks as well as a small chain to drive the oil pump. Because of this configuration the chains are longer and the timing chain speed is faster. The engine block in the 9a1 engine is a monolithic-alusil (alloy material commonly used in sleeveless engine blocks, mostly used by German auto manufactures) with integral cylinders. Its weakness is that it is not very forgiving to overheating and cannot be welded; however, its design is robust and powerful. The 9a1 has 8 main bearings as opposed to 7 on the M96 & M97 engine. The crankshaft of the 9a1 is forged and nitro-carburized heat treated with a .015 depth (as opposed to the M96 & M97 has heat treating of .003). The crankshaft has 12 counterweights and 63mm main bearing journals. Number 2,4,6 main bearing journals are grooved to supply oil;
the rest are smooth. All timing chains and the oil pump drive run off the front of the crankshaft. There is no crankshaft carrier in the 9a1 engine. The main bearings are built into the block. The engine block has a closed deck design as opposed to the open deck of the M96 & M97. Just to note, the closed deck design is more robust; however, comes with higher coolant temperatures and higher oil temps under heavy load.
Pistons in the 9a1 are forged. The top ring land on the piston is hard anodized to handle the increased pressure due to the DFI (Direct Fuel Injection). On the bottom of the pistons are oil squirters for cooling. The compression ratio of the engine is 12.0:1. The oiling system on the 9a1 is an integral dry sump with 4 scavenger pumps. Oil pressure is controlled by the DME (Digital Motor Electronics) on demand. The DME recognizes combustion and responds with the correct oil pressure. The returning oil coming out of the scavenge pumps will be foamy and needs to de-aerate, which is done directly out of oil of the pump in anti-foam swirl pots.
HEADS/CAMSHAFT The 9a1 heads are die-cast (not sand cast), which is a good method of limiting and/or eliminating porosity issues and maintains more exact tolerances since the metal is forced into the die under high pressure; however, as a result they cannot be welded. There is no lifter carrier in the heads. The lifter bores are integral to the head. All 9a1s are variocam plus. The camshaft has hardly any duration but has huge lift and ramp speed. The camshafts are shorter on B2 because the fuel pump drives off bank 1. There are stronger cam caps, stronger gears (2014+ have module cam lobes like a 904 or a 4 cam Carrera). There is 5 mm more valve lift on 911 9a1 as opposed to the 9a1 Boxster and Cayman. Valves are bi-metallic with a 6mm stem and dual valve springs. Valve guides are short 31.75 mm or 1.25” long and made of manganese (Mn). The head gasket is a multilayer steel, coated with heat resistant plastic. Thermal heat transfer is good. There are coolant stabilizers to maintain and even coolant flow balance in the engine block. The water pump is a closed impeller, pretty much overkill but nice to have. DIRECT FUEL INJECTION
Fuel is injected directly into the combustion chamber under extremely high pressure (between 1400-1740 psi). Fuel pressure can only be checked using Porsche Scan Tool (PIWIS or equivalent tool). As previously noted, the fuel pump is driven off the front of the engine B1, exhaust cam. Advantages of DFI are that engines can have a higher compression ratio and run leaner mixtures. The stratified fuel charge does not require long idle periods to warm up the engine. CONCLUSION Best thing to do is go buy one, start the car and drive. Keep the RPMs under 3k until the engine warms up, which does not take long. Note: slow drives at low RPM are an unhealthy diet for this engine. Burn good fuel and drive hard. That is what this engine needs and loves.