Here you go mate, a full analysis of 2 stroke v 4 stoke engines with some noise and my butt at the end.

A 4 stroke engine usually has a distributor that supplies a spark to the cylinder only when its piston is near TDC on the compression stroke, ie. one spark every two turns of the crank shaft. Some 4 stroke engines do away with the distributor and make sparks every turn of the crank. This means a spark happens in a cylinder that just has burnt gasses in it. This just means the spark plug wears out faster.

Most of what is written below on advantages and disadvantages of 2 strokes Vs 4 strokes is not actually correct! Take for example the lubrication issue of 2 stroke engines, sure small chainsaw engines may have the oil mixed with the fuel but this is not a direct result of the engine being a 2 stroke, this is just a result of someone designing a very simple engine. look at any large Caterpillar, or Detroit 2 stroke they have conventional oil sumps, oil pumps and full pressure fed lubrication systems and they are 2 stroke!!! also the argument about valves of 4 strokes Vs reeds and ports of 2 strokes is also incorrect. Sure some simple 2 strokes may use very privative systems to achieve the control of fuel/air mixture into the engine and exhaust out of the engine but again this is not a function of them being 2 stroke! I've worked on 2 stroke engines that feature poppet valves in the head (like a standard 4 stroke) - but they are definately 2 stroke - it's just that engines like this are not so much in the public eye - next time an ocean liner (ship) pulls into port check out its 2 stroke, turbo charged, direct injected diesel engine!! Finally the arguments of simplicity, weight, power to weight, and cost of manufacturing are not a funtion as such of 2 stroke Vs 4 stroke engines. The mistake of most of these commentaries is that they are comparing a simple chainsaw 2 stroke engine Vs a complex 4 stroke engine from a automobile - not a very fair comparision. As far as emmisions of 2 strokes - check out the Surrich/Orbital 2 stroke design that Mercury outboards are using - this is as clean burning as any 4 stroke.

The ONLY correct comparison below of 2 strokes Vs 4 strokes is that a 2 stroke can (in theory) produce twice the power of a 4 stroke for the same sized engine and the same revs.

As for the diagram [in the Snowmobiles episode of Scrapheap Challenge] - sure small 4 stroke engines do tend to "waste fire" the spark plug at the end of the exhaust stroke but this would not cause an explosion as depicted in the diagrams, but again here the idea of "waste firing"has noting to do with the 4 stroke cycle, rather it is a result of the simple design of a lawnmower motor. The diagrams should depict the inherant differances of a 2 stroke and 4 stroke engine. Hence one should show a firing every revolution and the other a firing every 2 revolutions.

TWO STROKE ENGINES - THE DISPUTED LIST
Advantages:
- Two-stroke engines do not have valves, simplifying their construction.
- Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost.
- Two-stroke engines are lighter, and cost less to manufacture.
- Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

Disadvantages:
- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas: burning about a gallon of oil every 1,000 miles.
- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.
- Two-stroke engines produce more pollution.
From:
-- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.
-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.

Why 4-stroke beats 2-stroke

First some explanation on how the 4-stroke engine works:
When the piston moves down fresh air and gas is sucked inside the cylinder from the carburettor. When the piston moves up again the valves are closed and the air is being compressed. When the piston reaches it's highest position the spark plug produces a spark that ignites the fumes and causes an explosion. Because of the power of the explosion the piston is pushed back. When the piston moves back up again the exhaust valve is open and the fumes are pushed out the cylinder. Now the whole process restarts (exactly after 4 strokes. That's why we call it a 4-stroke engine...Duh!).

The 2-stroke engine works a little different. It performs 2 strokes at the same time (twice) so after only 2 strokes the whole process restarts. A two stroke engine uses the space above and below the piston. Below the piston are fresh gasses, above the piston these gasses are ignited. Assume the piston is in the lowest position with fresh gasses in the cilinder above it. When the piston moves up, these gasses are compressed, but at the same time teh airpressure below the piston drops and fresh air is sucked inside. When the piston is in it's highest position the sparkplug ignites the gasses and the piston is pushed down. About halfway down a channel from the fresh gasses to the exhaust gasses opens and a channel to the exhaust. Because of airpressure differences the fresh gasses flow inside the cilinder pushing the exhaust fumes out. Now the process starts again. As you can see this only took 2 strokes.

But which one is better?!? Of coarse "we" 4-stroke people say 4-stroke, but do you know why?? Probably not, so I'll explain. First I'll name some of the advantages of the 2-stroke engine over the 4-stroke engine.

* When the engine is reving at 10000rpm the 2-stroke engine ignites gasses 10000 times per minute while 4-stroke engines ignite only half. So it should have twice as much power, right?
* The 2-stroke engine does have channels for air transport but the piston opens and closes the channels, in a 4-stroke engine there are seperate valves and a camshaft that do this. This means extra moving parts and a far more difficult cylinder head design. Because of this maintenance is more difficult.
* 2-stroke engines give more power. At 50cc races 2-stroke bikes can reach speeds of over 130km/h while 4-stroke bikes can hardly reach those speeds with 70cc!! The same applies to everyday use. When you remove some restrictors from a scooter it will go 80km/h. You won't reach these speeds with you're 4-stroke bike by just removing some restrictors.

What about the advantages of 4-stroke bikes? Are there any? OF COURSE! LOTS!!

* So what does a stock 2-stroke bike use? About 1 litre fuel per 35km. What does a stock 4-stroke bike use? About 1 litre fuel per 50km!
* 2-stroke bikes burn oil!! This absolutely doesn't give them more power and is of no use at all (for ignition purposes), all it does is clog up the exhaust and smell bad! So why they do it? They have to lubricate the cylinder and cylinder channels big time or the engine will be wrecked...
* Look at the cylinder(head) of both engines. Notice the HUGH cooling fins on the 2-stroke engine. Heck, some of them even have forced air cooling or even water cooling.Did you burn the fuel for heat!?! I don't think so! 2-stroke bikes waste much more energy on heat than a 4-stroke bike does so the 4-stroke engine is much more energy efficient.
* Did you read the part on how the 2-stroke engine works?? Did you notice fresh fumes are used to push out the exhaust fumes?? Of course these two gasses will mix in that process, so or fresh fumes are pushed out too or exhaust fumes stay in, either way, it's bad and it sucks.
* Ever tried to speed up a 2-stroke bike?? So fast that it could do speeds of over 100km/h. If you have you know you have to add lots of extra oil to the fuel and even than it's a big problem to keep the engine running for let's say a couple of months without mayor engine damage, wasted cilinders and screwed up pistons. Take a 4-stroke engine on the other hand and it will keep running fine for months and months and months... without extra oil The reason is that because of those channels in the cilinder it's much harder to keep it lubricated enough all the time. The 4-stroke engine doesn't have this problem because it has no channel in the cilinder.
* Have you ever drove on a Honda MT/MB or anything comparable with a fast cilinder? Did you notice it only had power between about 9000 to 12000 rpm?? Take a 4-stroke engine and it will have power from 1000 to 12000rpm. No problem! The reason is that such a 2-stroke cylinder has optimized airflow channels for that rpm range, outside that range the whole gas mixture gets screwed up big time. That's why those scooter engines always run at almost the same rpm. To optimize airflow, without that a 2-stroke engine looses a lot of it's power.
* Because of technical aspects the 2-stroke engine can only have it's intake channel open only half as long as the 4-stroke engine...What a pitty
* Listen to the sound of both engines...Doesn't need further explanation I suppose.

Yeah, yeah, I know, 2-stroke bikes with the same displacement are faster, but look at it in another way. A 50cc racing 2-stroke engine will use over a litre per 10km. Now take a 4-stroke engine that uses the same amount of fuel. I guess you would end up with a 90cc or even a 106cc with a 26mm carb or something. No try beating such a machine with that crappy 50cc racebike thing


And as promised....flames

That was really loud IRL!!!!

Flames are cool

Thanks for stopping this from being as popular as a poo sandwich ladies

THAT.

FUKKIN'.

ROCKED!






Any chances you guys will be in Italy in August '09 ???

mdiver said:

I enjoyed the info and learned something ~ so thank you

maybe that means I like poo sandwhiches

The very first bike I learned how to ride on was a RZ500. Loved the old kick start and loved how that thing took off. That bike was very cool.



My boyfriend at the time told me that the moment I got on it for the very first time and rode away immediately with no problems, was the very moment he fell in love with me.



Then it was a FZR.



Then my baby.

JustErin said:

Ok i am gonna spark up the 2 stroke and post it

is that shirt lavender???

roodboi said:

2 stroke heaven

roodboi said:

Yes.....and.....

JustErin said:

Mucho respect for the 500...they were great bikes and the power band was a joke

I don't know much about bikes, except that I love to ride on them...but the flames were pretty cool.

MoniGram said:

They are even more fun on the over run in to a 100mph corner.....my brother nearly shat himself the first time he followed me in to a corner and she did that back at him

My bike history




RG125, a bit morbid but i was borrowing up until i rebuilt this after a mate was killed on it.

Then i went to its big brother



Then my first 4 stroke was an RVF400



That was the first bike i rode on a track and got hooked, went and rebuilt one of these NC23



Until it looked like this



And we got sponsorship to run it in the UK 400 series. My brother killed it chasing my ass at Lydden and its currently being rebuilt

Had one of these for 400 racing after that

FZR 400



Then my baby



Raced this for a bit



And then went back to 2 stroke roots



My bro just got given a busted up RVF.....i wanna rebuild it
[Edited 8/21/08 12:35pm]

My bike history...


Honda Helix 250

everyone say "Wah waaahhhh..."




but you could fit a flat of pabst blue ribbon in the trunk so I was happy

oh yeah, I lost it in an arson attack at my place...




but some day, SOME DAY!!!

RenHoek said:

Keep the faith bro and every day thank the dude that burned that bitch

mdiver said:

its lovely...

roodboi said:

Fuck you Jason

mdiver said:

roodboi said:

Next time i will wear one of my pink or purple ones or maybe the one with blue pansies in the collar

mdiver said:

I fucking heart pansies...which says alot about my admiration for you...

mdiver said:

As i typed that Val says " funny thing is that he will think you are joking about owning those shirts.....but you are not"

roodboi said:

I will get a pic just for you

mdiver said:

dude, trust me, I have some really questionable shit hanging in my closet...stuff that would make your blue pansy shirt look like an Army uniform...

roodboi said:

We should have a "ghey off"

mdiver said:

phil, we're posting about our clothes...nobody in orgland is as ghey as we are right now...

roodboi said:

This thread was seriously manly till you showed up, i mean , even Erin got her testicles out

Yeah...

thanks fellas!

now you'll have to excuse me whilst I press and fold my pink polo shirts...