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2 Stroke V8

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2 Stroke V8

Old 17th Aug 2015, 13:06
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2 Stroke V8

Could think of some interesting applications for this baby

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Old 17th Aug 2015, 13:10
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It's an Evinrude boat motor.You wouldn't last long if you had your window down in the garage while starting/warming it up,with all that smoke !

http://www.engineswapdepot.com/?p=5141
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Old 17th Aug 2015, 15:01
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Oh, thought you you meant the Detroit Diesel two-strokes with Roots blower and turbochargers I had the dubious pleasure of having as auxiliary engines/generators on a gas carrier.
Probably as reliable as the thing in the video.
Per
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Old 17th Aug 2015, 15:34
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Could think of some interesting applications for this baby
Such as blowing lots of oily blue smoke up me keks!
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Old 17th Aug 2015, 15:48
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Sounds a bit like my old Jawa 90.
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Old 17th Aug 2015, 17:45
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I have no doubt somebody lurking around this thread could enlighten us about the intricacies of 2 stroke exhaust design. I am mystified, and would appreciate a resource.

The fabrication skill required for this particular set is really impressive.
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Old 17th Aug 2015, 17:50
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Pretty good explanation here:
https://en.wikipedia.org/wiki/Expansion_chamber
I have an Evinrude, (good old Viking name that) two stroke E-tec outboard, a marvel of power, packaging and electronically controlled emissions.
Reliability, no so much.
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Old 17th Aug 2015, 18:03
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Tuned Pipes

421Dog, Two stroke exhausts are designed to create a pressure wave which allows the burnt gas to exit the exhaust port easily, whilst the reflected pressure wave stops the incoming fuel/air mix from following it, for the period that both the exhaust and transfer port are uncovered simultaneously. As a result, large ports and overlaps are possible for maximum gas flow and power.

The downside is that the optimum conditions only exist within a narrowish power band (minimum to maximum rpm at which the pipe works as intended) and inefficent running occurs outside these speeds. For this reason, bikes with this type of exhaust often have a large number of gears to keep the engine within the optimum speed range.

https://en.wikipedia.org/wiki/Expansion_chamber

Looks like Ancient Mariner got there first!

Variations in the length, taper and diameter of the various segments of the pipe determine the ultimate power output and flexibility (width of power band) for the engine.

Each cylinder must have its own discrete exhaust, as joining them together creates unwanted interactions between the pressure waves and exiting gases.

Generally the pressure wave is supersonic, whilst the exhaust gases are subsonic.

All the curves and twists are simply due to packaging the expansion chamber into the engine bay (in the case pictured) or in a contour following fashion around the frame of a motorcycle. A straight pipe is as good, if not better.

Last edited by Mechta; 17th Aug 2015 at 18:17.
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Old 17th Aug 2015, 18:30
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This is why I love this site...

So that explains the beautiful stainless expansion chambers and stingers here and on motorcycles, but that all being said, how do all of those two stroke outboards, and 2 stroke truck diesels which terminate in a common exhaust and don't seem to have said expansion chambers function in their absence?

Are they just accepting the loss of potential efficiency?

Per, are you available for rent? I'd like to park you next to the fire, feed you whatever you'd like to eat and drink and listen to you expound about all the stuff you know. (my wife just got back from Norway and we're well stocked with minke whale and akvavit if you're so inclined)

I'd be happy to fix you up with as many warbird rides as you need.

Mechta, in the few iterations of modern automotive 2 cycles (Saab sonnets, etc) was a tuned exhaust employed? I've peeked under the hoods of a few, but don't remember the sweet TIG welds...

once again, thanks for the great information
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Old 17th Aug 2015, 20:04
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how do all of those two stroke outboards, and 2 stroke truck diesels which terminate in a common exhaust and don't seem to have said expansion chambers function in their absence?

Are they just accepting the loss of potential efficiency?
421dog, the applications you list all need flexibility of performance through the engine's rpm range that the tuned pipe doesn't give. In the case of the outboard, the pipes would get in the way and lose a lot of the convenience too, as this racing hydroplane demonstrates:



Two stroke truck engines, in the case of the opposed piston type anyway, have inlet and exhaust ports at opposites ends of the cylinder, so loss of the incoming charge isn't an issue. Also it is only air coming in as the fuel is injected directly into the cylinder and it is accepted that some will be lost out the exhaust port to ensure exhaust gases are fully purged.

It looks as though tuned pipes (expansion chambers) are used on two stroke SAABs, and what's more they use one pipe for three cylinders.

http://www.classicsaabracing.com/PDF...ample_0409.pdf

When you want max hp from a given engine, and can accept the loss of flexibility the pipe wins every time, as seen in this standard and piped chainsaw comparison:


Last edited by Mechta; 17th Aug 2015 at 20:16.
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Old 17th Aug 2015, 20:24
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Thank you.

The first time I put an aftermarket injection system on a V-8, O2 sensors made sense to me, but I have been stymied by 2 cycles despite having built quite a few modified midget racers with "built" 2 cycle motorcycle engines for others. (just chassis and assembly by me, engines [exhausts] and transmissions by others).

I'd be curious to read about those who elucidated the physics of these engines. It is much more complex relative to 4 strokes.
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Old 17th Aug 2015, 20:48
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421dog, although Mechta gave you a perfectly good answer, I'd be more than happy to take you up on your offer of "as many warbird rides as you need".
Add in the Akevitt and minke whale and I'm off. Should I bring some salted seal and real lutefisk?
I'm afraid my experience with two strokes are pretty much limited to marine diesel engines of the large, and slow-revving variety. Although the principle is the same for the smaller petrol ones, my fingers are not built for working on them. My spanner selection start at 24 mm.
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Old 17th Aug 2015, 21:06
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421Dog, Again Wikipedia is your friend: https://en.wikipedia.org/wiki/Two-stroke_engine

What always surprises me is how early many of the developments are. Schneurle porting which came in on model aircraft glow plug engines in the 1970s, was a 1926 invention. It gave a massive increase in power on the engines that had it (Does anyone else remember the OS 25 and 40 FSR engines?).

My own experience is at the other end of the scale to Per's. The smallest two stroke I've operated is the compression ignition Allbon Bambi at 0.15cc, and the smallest glowplug engine being the 0.16cc Cox Tee Dee .010 which splits your eardrums at 31,000rpm.

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Old 17th Aug 2015, 21:24
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Oh, thought you you meant the Detroit Diesel two-strokes with Roots blower and turbochargers I had the dubious pleasure of having as auxiliary engines/generators on a gas carrier.
Don't knock the fuel to noise converters, or top up the oil and check the fuel engines..

To be fair the Jimmy was the backbone of construction and road transport industry for eons.
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Old 17th Aug 2015, 21:27
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I used to like the sound of the Commer TS3 two stroke in the lorries used by the firm where I did my 'prenticeship.
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Old 17th Aug 2015, 21:28
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31000 rpm? We were at 120 rpm, or less. More mass, and just maybe a slightly longer stroke?
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Old 19th Aug 2015, 01:15
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More mass, and just maybe a slightly longer stroke
Yes nothing like a good long stroke and more mass, as long as its distributed correctly.
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Old 19th Aug 2015, 03:34
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421dog
Much of my racing was with 2-stroke engines, and as the others have mentioned the exhaust was everything. Getting the mixture right was a few percent horsepower, getting the exhaust right was ~30% horsepower (granted, you'd have to get it pretty seriously wrong to loose it all that 30%). There was a pretty serious tradeoff - you could get huge power but over a really narrow RPM range, or 'good' power over a relatively wide RPM range (and of course numerous options in between). Sometimes the difference between contesting for the win and being an also-ran was the pipe you chose.
Some engines we would vary the length of the header (we measured the distance between the piston and the first divergent cone of the exhaust) - 1/8" one way or the other could mean ~ a second/lap.
I used to get ~45 horsepower out of a 125cc 2-stroke, and some of the deep pocketed guys were getting north of 100 hp. out of a 250cc engine

Oh, and if a ride in a warbird is on offer, I'll spill my guts of pretty much everything I know that doesn't have a confidential or proprietary label on it. I'll even supply the beer .
Err, the beer would be after the warbird ride
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Old 20th Aug 2015, 11:04
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how do all of those two stroke outboards, and 2 stroke truck diesels which terminate in a common exhaust and don't seem to have said expansion chambers function in their absence?

Are they just accepting the loss of potential efficiency?
The Detroit Diesel 2 strokes are slightly different inasmuch as they are blown engines, so scavenging of exhaust gases is accomplished by the force fed air rather than a tuned exhaust system, hence the common manifold and stack a-la regular engines.

This from Wiki...
  • Intake begins when the piston is near the bottom dead center. Air is admitted to the cylinder through ports in the cylinder wall (there are no intake valves). All two-stroke Diesel engines require artificial aspiration to operate, and will either use a mechanically driven blower or a turbo-compressor to charge the cylinder with air. In the early phase of intake, the air charge is also used to force out any remaining combustion gases from the preceding power stroke, a process referred to as scavenging.
  • As the piston rises, the intake charge of air is compressed. Near top dead center, fuel is injected, resulting in combustion due to the charge's extremely high pressure and heat created by compression, which drives the piston downward. As the piston moves downward in the cylinder it will reach a point where the exhaust port is opened to expel the high-pressure combustion gasses. However, most current two-stroke diesel engines use top-mounted poppet valves and uniflow scavenging. Continued downward movement of the piston will expose the air intake ports in the cylinder wall, and the cycle will start again.
https://en.wikipedia.org/wiki/Two-stroke_diesel_engine
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Old 20th Aug 2015, 13:11
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For noise and smoke you want a https://en.wikipedia.org/wiki/Napier_Deltic as used by the Andrew, British Railways and the New York Fire Brigade in the SuperPumper
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