Improving a 3-cyl two-stroke car-engine

[JohnAh]

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?

[DIMS]

Cleanest Running Two Stroke Ever

[JohnAh]

Fantastic! May be a bit too fantastic for a vintage engine that is quite sensitive though... I don´t dare to experiment with the fuel/oil ratio. But the ammount of oil is not the whole story for a two-stroker. Oil is money, but so is fuel! I hope "on/off driving" can save some fuel. Perhaps tuning the exhaust can do more, but that´s a quite complicated thing to do. Fitting three huge zuccinis under the hood and connecting them to a long pipe is difficult.

In the end I will most likely replace the TT for a small diesel but I definitely have to see how much I can improve the TT first and it´s still a long way before my project car is ready for the streets.

[Grant-53]

Talk to someone familiar with racing 2 stroke motorcycles about porting mechanisms.

[Frank Lee]

HUGE strides in 2 stroke fuel efficiency, emissions, and power have been made by the snowmobile manufacturers mainly via EFI and guillotine valved exhaust ports...

I am interested in your 2 piston delete! (New thread please!)

The +15% is as expected... how did you deal with balance, plugging crank oil holes, power, vibes, etc.?

[JohnAh]

Frank, I have a weak feeling that I may have written something about my crazy Fiat experiment earlier so I have to search the forum before I create a new thread for it.
Meanwhile, here is my webpage (mainly in Swedish but with lot of photos and some videos):
Projektblogg - Fiat 127 engine downsizing

(my webserver may appear to be offline due to IP-changes that I hope to be corrected within a few hours from this post)

Update: The URL above seems to work now.
Update 2: I found my thread about the "engine split":
http://ecomodder.com/forum/showthrea...lly-21753.html

Nothing new have happened in the thread nor the concept. I´m still thinking about trying the "engine split" on a Saab 96 (actually Ford) V4 engine but my two-stroke project feels a lot more interesting now and my Saab 96 family car runs a bit too well now for such a brutal experiment. (have to consider the WAF) ;-D

[Frank Lee]

You are correct! I found them- can't believe it slipped my mind!

[jamiec]

Hi johnAh this is very interesting as i also have two cars that have 3 cylinder two stroke engines in them of 539cc these are suzuki carry vans. I just got a spare engine and want to make improvements for power and economy. I have spoken with a motor bike mechenic that used to race bikes years ago about getting him to make 3 separate expansion chambers so i can have each cylinder optimized for differant rpm ranges to broaden the power band. These engines have a seperate oil tank and a pump that sends oil to the crank shaft and to the cylinders.


Cheers Jamie

[JohnAh]

jamiec, what´s the name of your Suzuki models? It looks like a quite modern engine on your photo. How much power can it deliver? The old Saab 3-cyl TT is 750 or 850cc and gives out about 35-50hp depending on version.

Two-strokers have survived long in small two-wheelers and in boats. I talked to a friend who´s an offshore racing boat driver just a few days ago. His V6 engine is definitely modern with air-assisted fuel injection and separate oil injection. Such an engine is said to consume 20-30% less fuel than a traditional carburetted two-stroker. I guess this is not very far from a four-stroke. When it comes to care about the enviroment such an engine still consumes 2-4% oil so it´s still beaten by four-strokers on that point.

The fuel is injected at high pressure with addition of compressed air AFTER both the transfers and the exhaust ports are closed by the piston. This makes sure not a single drop of fuel is lost during the cylinder scavenge. Without the separate injection of oil this method of injecting fuel would be impossible.

Since it´s a marine engine the exhaust is arranged the usual way through the propeller hub but since it´s a fast-going boat the propeller hub is above the water surface at high speed to reduce drag. I don´t know how a V6 handles the exhaust pulses but I have read somewhere that a 3-cyl with a short exhaust manifold will do well without expansion chambers at low and medium speed, perhaps even more efficient since it "follows" the engine speed better than a tuned resonator. At least I think so...

[JohnAh]

An engine with working separate oil injection is probably a good platform for experiment with direct fuel injection like the marine V6 I described above. By delaying the fuel injection until the compression have just begun I suppose a two-stroke could be similar in efficiency compared to a four-stroke. -Lubrication oil consumption excluded.

I guess it may be recipie for disaster to experiment with separate oil injection from scratch, at least without a similar engine with such a system to look at. Or is it perhaps quite simpe? -Just install oil injectors at strategic points found on another engine and calibrate the oil pump to give the same ammount of oil as drawn by the fuel. This means the engine will consume exactly twice the normal ammount of oil during the calibration. In the end only piston wear can tell...