Retro 1. Mk11 engine specifications
This is the first in a series of retrospective posts dealing with the development of a BMW R100 ‘airhead’ motor (Race motor Mk11) leading up to a record breaking run at the 2018 DLRA speed week at Lake Gairdner in outback South Australia.
We’ll start the series with the final engine specs then go back and look at how some of these were achieved.
Donor bike: 1993 BMW R100LT horizontally opposed twin ‘boxer’ engine.
1. Top end
Chamber shape: hemispherical
Displacement: 980cc (stock)
Bore: 94mm (Stock)
Stroke: 70.6mm (stock)
Compression ratio: 12:1
Valves: OHV, 2 per cylinder
Valve actuation: pushrod via 1.39 ratio stock rockers
Inlet valve diameter: 46mm stainless steel
Exhaust Valve diameter: 38mm stainless steel
Springs: Dual race springs with titanium retainers and stock collets
Pushrods: Custom Skrunkwerks dual tapered aluminium alloy
Lifters: lightweight lifters from Wank Germany
Spark plugs: 1 per cyclinder
Pistons: shortskirt, high compression from Moorespeed. Reduced compression height to suit longer conrods.
Conrods: 15mm longer than stock from Moorespeed.
Fuel mixture delivery: 1 x 40mm Lectron carburettor per cylinder.
Inlet tract and ports: Custom Skrunkwerks Design
Exhaust: 2 into 2 Custom Skrunkwerks design
2. Short Block
Crank: Stock. Rebalanced for pistons and rods.
Cam: Schleicher 340
Cam sprocket: Adjustable from Nova Racing
Oil pump: Low volume from Moorespeed.
Ignition: Ignitech programmable. Silent hektik Inductive pickup on crank. Total loss system (alternator removed). 2 x PVL single post coils.
Clutch: Heavy duty Sachs diaphram spring with K75 pressure plate.
Sump: Extension from Motoren Israel with screw-on filter and provision for oil cooler.
Oil cooler: From 2005 Triumph Bonneville plumbed into Motoren Israel sump extension
Crankcase ventilation: Custom Skrunkwerks design slash tube to exhaust sytem.
Power: 90rwhp @ 8200 rpm (approx 100hp at the crank)
Torque: 65 ftLbs @5900 rpm
As measured on a Dynojet dyno in full inertia mode with SAE J1349 correction applied.
So there you have it, the bare bones. Stay tuned for Retro 2. where we look at what was done to increase compression ratio.