Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Improving a 3-cyl two-stroke car-engine

JohnAh · 07-09-2012, 05:22 PM

I have a long-term project based on a 1974 Saab 96 that I will start by converting it to a 1964. This means I will install an 850cc three-cylinder two-stroke that is far from an efficient engine. But all improvements are relative and I look forward both to drive a nice vintage two-stroker and try to do my best to save every drop of fuel.

I practise eco-driving with some success on my present family car that is a 1974 Saab 96, but this car have a 1600cc four-stroke V4 engine. All Saab 96 have a freewheel that allows the engine to idle as soon as the throttle pedal is released. This feature combined with a driving-style as if the brakes were out of order save a lot of fuel. Before my saabs I had a tiny Fiat 127 that I drove over 4000 km after ripping out two of it´s four pistons (and saving 15% fuel).

But let´s return to the two-strokers now! I suppose there are few eco-drivers who have experience from driving a car with this type of engine so perhaps I will have to answer all questions myself...

So what can be different from an ordinary four-stroke car engine? First of all, a two-stroker is less fuel efficient and it also consumes a lot of oil mixed in the fuel for lubrication. (yes, the treees and birds will cry) I also guess that a TT-engine have a narrower band for it´s best efficiency.

My point of view is that an engine (regardless of type) that gives more power/torque than what´s needed for the wanted cruising speed is forced to run less efficient. The best way to overcome this is to let the engine work harder for shorter periods and then be shut off until it´s needed again. With the freewheel in the Saab transmission this is much easier to put in cycles than with an ordinary transmission.

A secondary benefit for a two-stroke may be improved lubrication when the engine doesn´t need to run so much with part-load. When less fuel is sucked through a two-stroker it also sees less oil.

I think a lot about the exhaust system. Adding an expansion chamber type exhaus is a well known way to improve performance/power but I suppose it may also improve fuel efficiency at a certain engine speed.

Any thoughts?

07-09-2012, 05:22 PM	#1 (permalink)
JohnAh EcoModding Apprentice Join Date: May 2012 Location: Vallentuna, Sweden Posts: 129 Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4 90 day: 52.77 mpg (US) Thanks: 17 Thanked 55 Times in 30 Posts	Improving a 3-cyl two-stroke car-engine I have a long-term project based on a 1974 Saab 96 that I will start by converting it to a 1964. This means I will install an 850cc three-cylinder two-stroke that is far from an efficient engine. But all improvements are relative and I look forward both to drive a nice vintage two-stroker and try to do my best to save every drop of fuel. I practise eco-driving with some success on my present family car that is a 1974 Saab 96, but this car have a 1600cc four-stroke V4 engine. All Saab 96 have a freewheel that allows the engine to idle as soon as the throttle pedal is released. This feature combined with a driving-style as if the brakes were out of order save a lot of fuel. Before my saabs I had a tiny Fiat 127 that I drove over 4000 km after ripping out two of it´s four pistons (and saving 15% fuel). But let´s return to the two-strokers now! I suppose there are few eco-drivers who have experience from driving a car with this type of engine so perhaps I will have to answer all questions myself... So what can be different from an ordinary four-stroke car engine? First of all, a two-stroker is less fuel efficient and it also consumes a lot of oil mixed in the fuel for lubrication. (yes, the treees and birds will cry) I also guess that a TT-engine have a narrower band for it´s best efficiency. My point of view is that an engine (regardless of type) that gives more power/torque than what´s needed for the wanted cruising speed is forced to run less efficient. The best way to overcome this is to let the engine work harder for shorter periods and then be shut off until it´s needed again. With the freewheel in the Saab transmission this is much easier to put in cycles than with an ordinary transmission. A secondary benefit for a two-stroke may be improved lubrication when the engine doesn´t need to run so much with part-load. When less fuel is sucked through a two-stroker it also sees less oil. I think a lot about the exhaust system. Adding an expansion chamber type exhaus is a well known way to improve performance/power but I suppose it may also improve fuel efficiency at a certain engine speed. Any thoughts?