Ilmor Engineering, the firm made famous for its work with Indy Cars and Formula One, as well as Triumph Motorcycles and Harley Davidson plus GM, Honda and Mercedes have built an engine that will make you think for a bit, it’s a 700cc, 3 cylinder, 130 horsepower turbocharged 5 stroke. Did they say 5 stroke?

The 2 outboard cylinders are the high pressure (HP) fired cylinders while the center low pressure (LP) cylinder makes extra use of the exhaust gases. The point of this design is to enable the expansion and compression strokes to be decoupled. The effective expansion ratio is 14.5:1, almost diesel territory, converting the maximum thermal energy into work. The compression ratio can be reduced, delaying knock, without a decrease in performance. The extra expansion stroke of the LP cylinder is, effectively, the 5th stroke.

Fuel consumption and emissions levels are similar to that of current diesel engines, without the serious problem of particulate and NOx emissions which plague diesels.

Fuel consumption is decreased by 10% over conventional 4 stroke operation. The entire engine is built using conventional technology, no new manufacturing technology or processes are needed.

This is more than a computer model, the running prototype is being dyno tested with a second development engine planned for in-vehicle testing.

Just when you think the internal combustion engine has pretty well emptied the bag of tricks, a little creative thinking comes along and gets higher fuel efficiency and lower weight than equivalent engines by adding another stroke to the process. So now we have 2, 4, 5 and even 6 strokes. Very impressive engineering, I like it.

Link: Ilmor Engineering

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