Had an interesting coversation with a co-worker over lunch. Need you guys to answer some questions:

1. When people refer to engines that are "Single Stroke", or "2-Stroke"; what exactly does that mean? Are they referring to the number of cylinders, or the number of cycles the engine goes through, or something entirely differnent. Need some details on this!

2. Given the answer to number 1 above -- how many "strokes" are the V-8's in our cars?

Need good answers from you car gurus so someone gets a free lunch!

Thanks!

 

Car engines are four stoke...I'm looking online for a good pictorial representation right now...

Okay, here's a great pic:



and here's a two-stroke:


Notice the location of the intake/exhaust valves in the two pictures, which facilitate to combustion/exhaust process according to the engine type.

Looks like others are already adding to the explanation, I'll let them handle it...

[Modified by Bohot, 3:30 PM 3/6/2002] :) :) :)


[Modified by Bohot, 3:39 PM 3/6/2002]

 

Motorcycles ( dirt bikes ), outboard motors and chainsaws are two strokes.
Cars are 4 strokes.

the two stroke cycle is
1. Intake/exhaust
2. Compression / power

The four stroke Otto cycle is;
1. Intake
2. compression
3. Power
4. exhaust

Each stroke is 1/2 of an engine revolution, so a two stoke fires once every rev while a four stroker fires every other rev.

Two strokes have twice the power, ( almost ) and have much simpler valves. But they are very dirty since they use the downward movement of the piston to pump air into the combustion chamber. They are also only lubricated by the little bit of oil mixed in with the gas...

 

gas engine in cars are allways 4 cycle, 4 stroke, if you will,....
piston goes down, intake, valves close, piston comes up..compression, plug fires, piston goes down, exhaust opens, piston comes up pushing exhaust out, exhause closes, intake opens, piston goes down for another cycle....
4 strokes for each firing...
2 cycle...every time piston is at top/cylinder, plug fires....valves are typically a reed type thing....flapper valves...located in a variety of places, oil has to be mixed with fuel/gasoline....in order to lube the cylinder rings and flapper valves...
2 cycle smokes like Pall Mall.....

GENE

 

Sorry but just too many comments flied into my pea brain, maturity just went out the window. :crazy:

 

Thanks. My last point of clarification:

When looking at the cranksaft with the #1 cylinder at TDC, when the engine has made ONE FULL REVOLUTION (gone all the way around 360 degrees) has that cylinder gone through all 4 strokes or just 2?

 

One stroke of any engine is 1/2 turn of crankshaft.
So normal car engines ( but not all ) are 4 strokers, meaning 1 explosion per 2 complete crankshaft revolutions.
2 stroker engines, like some bikes, most lawn-mowers have 1 explosion every 1 revolution of crankshaft, this making them very powerfull with relatively small size engines.
I haven't heard of 1 stroker engines ?
Strokes have nothing to do with the number of pistons .
Hope I didn't spoil this.
Gunther :seeya

 

The other thing with a 2 stroke is there is no valve train or cam. This allows for very high rpm and can sustain high rpm without to much problem. I have a V6 outboard and can run 5500 rpm all day without worry. The yare powerful but as said before very dirty engines. I went to the boat show this year and it is amazing how many 4 stroke outboards are being produced now. They are getting very high HP out of small 4 strokes now. i even have seen some of the motorcross teams now running 4 stroke motors in the 250cc class. Modern technology has come a long way.

 

There are four stroked running in motocross now because California anounced they would not allow the sale of 2 stoke engines anymore. The motocross circuit allowed four stroke engine with higher displacements to run in the 250cc class.

To clarify one point, dirt bikes have been available as both two stroke and four stroke for a long time. Also, there are many two stroke diesels on the road today.

 

I rev of the crank is just two strokes....
so at 600 rpm idle speed...the plug fires 5 times a second...
ten times the piston is at top of stroke per second...

so even at 6000 rpm's...firing is only 50 times a second...
in electronic terms, that's really slow....

GENE

 

I'll add my $0.02 on the 2 stroke cycle.

I'll use bohot's pic


Lets start at top dead center with a full charge of fuel/air.

Spark. The fuel mix burns and drives the piston down. As the piston goes down, it uncovers the exhaust port. Exhaust gasses flow out. It also uncovers the intake valve. So we have gasses rushing out the exhaust port and gasses rushing in the intake to take their place. The velocity of the exhaust gasses going out helps suck intake air/fuel in. (you can see how a turbo or supercharger would help by forcing the air mix in). BTW, there are reed valves in the intake and exhaust ports that are 1 way valves toprevent things from flowing the wrong way.

So exhaust rushes out, air/fuel flows in and the piston starts to move up. As it does, it closes off the intake port and the exhaust port. Then in what travel it has left on the way up, it compresses the air fuel mix and we're ready for another spark.

So the process is:
Bang!
Down
Up
Bang!
etc...

So EVERY time the pistong comes up, you get a compression and spark and power.

Contrast that to a 4 stroke cycle:
BANG!
Down (power)
Up (puhing exhaust gasses out)
Down (sucking new air/fuel in)
Up (compressing the new air/fuel)
BANG!

The 2 stroke is a more "power dense" engine since you get a power stroke EVERY time the piston comes up as opposed to every other time in a 4 stroke cycle engine.

Comprende? :)

Dave

 

A 4-stroke girl can handle 2 guys at a time. :conehead

 

I hope Jenny and Juliet don't see this.. :eek: :eek: :crazy:

:flag

 

Another thing about two-strokes:

Due to very minimal lubrication - only what is in the fuel - they do not live long lives.

 

You're right about these new 4-strokes Gordon. I have a 250cc 4-stroke MX bike that makes around 35 hp at 13,000 rpms! If my 427 could match that power-to-displacement ratio, it would make 1036 hp! :yesnod: What a ride...

-Joe

 

Just as an interesting sidebar, Saab made a V-4 two stroke that went into cars. I believe the Sonnet came with em.

 

An interesting point....2-stroke crotch rockets are a little bit easier to ride at the limit because the power is smooth and linear. A 4-stroke rocket is a bit harder because of the pulsation of the power, it has more of a tendency to want to break the rear tire loose. Think of it as riding a bike on a slippery surface...pedaling at constant speed, or crushing the pedal and then coasting a bit.

Conversely, 4-strokes seem to be superior in motocross due in part to the fact that the power pulses help to gain traction in the dirt. 2-strokes have more of a tendency to spin, while the 4-stroke is more apt to grab on one pulse, settle in, and then push out on the next.

 

Remember that Kawasaki 3 cylinder 2 stroke? I think it was 500 cc. Came out about the time Honda started producing the 4 cylinder 4 stroke 750.

As far as 2 stroke engines being dirty, when I was at Lake Tahoe a couple of years ago learned they had recently banned 2 stroke engines (including 2 stroke jet skis) from the lake. MJ

 

the motor oil/gas mix usaully causes harmful smog

 

I think I saw that video. :eek: Hey it was free from Adam and Eve, but we'll just let that be.