Cylinder head is based on M30 cylinder head with exceptions:
- Special exhaust manifold studs
- Nimonic exhaust valves and seats
- Unique intake valves and seats
- Injectors 300cc or +50% on intake manifold
Head shares most parts from M30 engines including:
- Camshaft 264 degrees (M30B35)
- Rocker arms and shafts
- Valve guides and springs
- Camshaft gear, chain and tensioner
- Headgasket (M30B35)
Nimonic valves are for wear resistance in turbo engine. They have good qualities in extreme temperatures. Basically matching M30 head can be used with lesser lifespan. M106 turbo heads are later casting having smaller water channels for improved rigidness. Casting number should be similar to 1288086 with “TURBO” or “K” on intake side. Intake ports are not polished and have rough finish. When resurfacing head more than once, thicker 2mm head gasket may be needed. With resurfaced head piston to valve clearance can be verified with modeling clay.
Original turbo heads are hard to come by, if one is available consider buying it. Always check head for hairline cracks, usually spotted between exhaust valve seat and water channel. Turbo head delivers advantage on durability over stock M30 head, exhaust valves make a difference. There are many turbo’ed stock M30 engines running successfully with high boost levels. Though long-term durability is not usually part of discussion there. According to Ireland Engineering aftermarket stainless steel valves with dual valve springs work well in low boost turbo engine.
Exhaust manifold is a two piece log style shape and very different to NA engines. Special grade fasteners, K27 turbo charger, external wastegate and special gas-filled gaskets are used. Manifold can be fixed to M30 head with retapping threads, notice deeper bores. It is not unusual to have cracks on turbo side of manifold. Also wastegate can seize and misbehave, this is solved with soaking in thin oil until free. All manifold gaskets except wastegate pipe metal gasket can be reused. Exhaust manifold should be retorqued to head after break-in, torque as in assembly.
Dual valve springs are fitted from factory on late M30B34 heads. These 1288086 casting heads can be spotted at least on last model years of E28 5-series engines. Dual springs are for better valvetrain harmonics, 745i turbo engine power peaks at low 4900rpm having not so great benefits. These heads also share 264-degree camshaft with turbo engines, only exhaust manifold side needs attention before drop in replacement. If rebuilding head with unknown history, check head gasket surface with crack-proof spray not to waste effort and time on broken part.