This question has been cropping up in my mind for a long time what why are 2 stroke (2C) engines more powerful than 4 stroke (4C) engines? What makes them more powerful? and if a 40 size trainer needs .46 2C engine you can use a .60 4C engine on it as well and I have seen 2C engines fly the planes much faster than 4C engines and aso the difference in weight, in sound, fuel efficiency and maintenance. I never used any 4C engine, so I don't have much idea about them but seen them being flown, they are kinda slow comparing 2C. I know 2C engine needs one cycle to complete a stroke where 4C engine needs 2. Pls clarify me and give your precious opinions and experiences.


Super Tigre
G-61 Ring

Type: 2-Stroke
Displacement: 0.610 cu. in.
Cylinders: 1
Low RPM: 2500
High RPM: 16500
HP: 1.750 bhp@16000 RPM
Weight: 19.96 oz.

Magnum
XL-61 RFS

Type: 4-Stroke
Displacement: 0.610 cu. in.
Cylinders: 1
Low RPM: 2000
High RPM: 12000
Weight: 15.50 oz.

Thanks in advance

Have safe flying

Mody

You already answered your own question. A 2 stroke engine running at 10,000 RPM has 10,000 combustion sequences. A 4 stroke engine would have only 5,000 combustion sequences. The 2 stroke is burning fuel at a faster rate and producing more power than an equivalent displacement 4 stroke.

Also, the 4 stroke has more moving parts and has more friction loss.

A rather simplistic answer but basically that is the difference in power between the two.

Thanks PipeMajor,

You clarified me more than what I knew. 4 Strokes engines also have to front cylinders where as 2 strokes don't have, why these 2 cylinders are always there in 4 strokes? May be I little naive but I want to learn


Mody

The 2 strokes are not necessarialy more powerful than a 4 stroke of the same displacement. They will only turn more RPM, they will not pull as large a prop, so, what are you after, screaming RPM, or thrust? Truthfully, thrust is where you live, unless you are into racing. For sport or scale flying, make mine a 4 stroke.

Bill, AMA 4720
WACO Brotherhood #1

I think you are referring to the tubes that carry the pushrods that operate the valves.
Valves cannot open and close very quickly so they limit the maximum revolutions on a 4 stroke. 2 strokes can rev more.

2 strokes are cheaper to buy and there is less to go wrong. Only buy a 4 stroke if noise is a problem , fuel economy is important or you do not like a large silencer hanging out of the model.
A plain bearing 2 stroke of a reliable make will give long service without much trouble.

4 strokes generally make a lot of torque so they can turn a larger propeller. They also have a wider power band. A 2 stroke may have to run at very high RPM to make much power but a 4 stroke will make a lot of torque even at lower RPM's. Is one better than the other? Yes and no. It really depends on the application. Personally, I will run a 4 stroke if at all possible. I find that they idle better, have better throttle response and are easier to tune. When their propped right and sized right for the plane they have more than enough power. I also think 4 strokes sound way cooler than a 2 stroke. The biggest downside in my opinion is that 4 strokes cost more.

Also, don't put too much stock into the HP ratings used in engine advertisements. They are some benchmark number taken at some RPM that you will never reach in real life. Use them as just a loose guide.

Regardless of whether you go with 2 or 4 stroke, buy a quality engine and you'll be just fine.

The reason for a two stroke having more specific power (power for a given capacity) has been already been given as been due to the fact that two stroke has a power stroke every cycle vs. every second stroke for four strokes.

Just to clarify some things on torque vs. power.

The formula to calculate power when you have the torque is
Power = Torque x angular speed
angular speed is the speed (rpm) of the motor. From this equation it can easily be seen how 2 stroke engines can get such high power figures when compared to a similar sized 4 stroke motor is because it revs so high to compensate for the low torque figure.

The most simplistic definition for torque and power in our rc case is
The higher the torque, the better the ability to turn a larger prop
The higher the power, the faster the engine can deliver the torque

To make a statement that one is better than the other if one looks at it purely from a torque or power point of view is very difficult (I would go as far as to say impossible). For starting out in the hobby I would definitely recommend two strokes because they are simply easier to run and maintain for a beginner (I know there are exceptions).

To get a good idea of how 2 strokes and 4 strokes work, this is a good page
[link]http://www.keveney.com/Engines.html[/link] to see how this type and a lot of other types work.

Lastly just to add one last comment to really confuse it all, although 4 strokes are definitely more fuel efficient than two strokes in radio control engines, the most fuel efficient engines in the world are large 2 stroke diesel engines.

Cheers
Pups

Another thing that needs to be understood is that the torque needed to turn a prop varies exponentially with the rpm. Double the rpm of a given prop and the torque needed to turn it quadruples. Because of this, it actually takes more torque to turn a 10x6 prop 15,000 rpm than it does to turn a 12x6 prop at 10,000 rpm. Not understanding this relationship leads to the common myth that four strokes make more torque than two strokes do. Without a tuned pipe, two strokes also have a broad power band.

The ironic thing is that as the horsepower race started with four strokes, fueled largely by the old F3A rules that allowed two strokes to be .61 cubic inches but allowed four strokes to be 1.2 cubic inches, four strokes became thirsty, and loud and really critical about prop sizes. Realizing that they have defeated the very purpose of four strokes, the rule has been changed to allow any engine or electric motor of any size as long as the plane stays under the 5 kilogram weight limit.

Here's a picture that shows just how quiet four strokes are. So quiet that mufflers aren't even needed.

Yes indeed, Your picture is the very definition of old time rock and roll. Now a days you can't sit behind that big "Quiet" engine.

Anyway to topic: Every engine has it's place and aplication. If you are saying that 4C engines fly slow than you are probably seeing them in 3D planes which are built light for high angle of attack manouvers. Speed kills 3D planes so they are propped accordingly with low pitch large diameter props. Speed planes tend to be propped with high pitch smaller diameter props and relly on peek RPM to create thrust Hense a 2C is a better choice due to peek RPM. However if propped for it a 4C in the right airframe can "go fast" I have a Saito 100 in a H9 Spitfire with a MAS 15x6 and it moves pretty good. If I went to a 14x8 I could probably add another 10-15 MPH to it... but I like pulling power

One thing that no one has mentioned yet is 4 strokes can become addictive... Believe me.. I started out with all 2 strokes, got one 4 stroke and now have 14 four strokes and 2 2strokes... If you appreciate the sound of a Harley sitting there idling you will love the 4 strokes.

First of all Thank you all very much for sparing your time in giving your precious experiences advices, I learned a lot, Yes one thing I must admit that the Idle of 4stroke is way better than 2 Stroke, and honestly speaking as one of our forum member said, that You would be Addicted to 4 Stroke, I feel no doubt about it, cos, I never saw any 4 stroke giving trouble, naturally Im waiting to buy one first 4 stroke for me. Here I wanna ask one more thing, which size is best to buy in 4 stroke, .46 or more than .61? as Im gonna have a 60 size trainer/advance plane like easy sport, which 4 stroke would go better with it.

Once again I say Thank you all, I really appreciate it.

I was referring right on top of carburator, 2 pipes coming down from the head of engine I think its head, I think those are front 2 valves, I still dont understand what they are


Mody

[link]http://science.howstuffworks.com/[/link]


Interesting site. You might find answers at.

Mildly tuned two strokes that are designed for low rpm use can and often do beat four strokes at their own game. That includes being quiet and good fuel economy. I had a Kadet Seniorita powered by a OS .40 FP. Using a 11x5 APC prop, the plane was so quiet that one of my neighbors thought I was flying an electric plane. This engine also sipped fuel and I had no problem getting 15 minute flights out of the plane's 6 ounce tank.

A lot of the noise that high performance two strokes get blamed for is actually coming from the propeller. Watch this video of this high performance electric plane to get an idea of just how much noise propellers make at high rpm's.

http://flyemfast.com/files/BestVen.wmv

I see this quoted quite often.

Yet if you go by the manufacturer's own prop range recommendation for any given identical displacement, the same prop sizes are suggested.

e.g. a 4 Stoke .50 has the same size recommended prop for a 2 stroke .50.

Given however that the 4S .50 is producing less specific power than the 2 stroke of the same size, relatively speaking you could say that it is indeed "swinging a bigger prop".... but this IMHO seems more of a marketing ploy.

... not that I dislike 4 strokers....

However in the sub 1.00 range it's hard to rationalize paying 300.00-400.00 for a 1.2 four stroke equivalent to a 80.00 .75 2 stroke engine, if the latter is reliable.... yeah they sound and idle nicely, but for the price difference in this range, is it really worth it?

There are all kinds of ways to compare things here.. It has been my experiance that the 4 stroke will swing the bigger end props at equal or better rpm then the 2 strokes.. When it fcomes to the smaller end of the range the 2 strokes shine... Thus torque for 4 strokes and speed for 2 strokes..
As for price I just purchased a couple Mag .91 4 stokes for 119.98 to my door.. Great running engines that will hold there own against most sport .91's... Comparing a Tower .75 to a Saito 1.00 is really going to two extemes...

I think it has a lot to do with how the 2 strokes are designed. My Jett .76L will turn the same 3-D prop faster than my 70 Surpass or .82 Saito.

ORIGINAL: armody

Here I wanna ask one more thing, which size is best to buy in 4 stroke, .46 or more than .61? as Im gonna have a 60 size trainer/advance plane like easy sport, which 4 stroke would go better with it.

Once again I say Thank you all, I really appreciate it.[/i]




LOL all yall are discussing 2C/4C and not even answering his question.

I think If you have a .60 trainer then you need something like an .75 4C

(personal observation) Why the heck you put a $300 4C on a trainer?

Got to agree with that one .. For a trainer keep it as simple as possible...
As for what size to go with 4 stroke it depends on how you want to fly and the brand engine you are buying... For instance with Saio you have quite a selection to choose from with very little penalty weight wise.. Very light powerful engines... For a .60 trainer I would be tempted to go with a Saito .91... This will more then power your trainer and will also give you an excellent 4 stroke for your next plane... These are expensixe and I prefer as much versatility out of them as I can get... Mostly depends on what you want to do now and where you are headed...

Ooh... yeah at that price I have no problems rationalizing it at all, heh... must get two.... who sells them for that?

...What language is that?

Thanks a lot psullivan for replying me my question. Well, other people did give me good information and knowledge as well. One point of you is right that why would I spend a lot on 4 stroke engine, well, the country I live in, which is Pakistan, here we have a lots of scrap come to use them in many metals, so in scrap we find a lot of engines come from many countries in the world, which are almost new, I would look for a 4 stroke engine for my 60 size otherwise, I already have HB .61 engine for that plane You guys won't believe how much I bought 2 engines, they are as good as new, in my country's currency they cost me Rupees. 600, which equivalent to US nearly $11[X(] would you believe that? Well, in future Im planning to move to Texas, USA, cos my wife belongs to Texas. The engines which come in scrap imported from all over the world its your luck to find good one, most of them are new but have dust, sand and other crappy stuff in it. One lucky guy got a JetCat turbine in that dont know what size is it, but I heard he got it for nearly US $200 to 250 Bucks, a real surprise but only luck counts and we have to spend their hours in order to find those engines. Anyway
once again thank you all very much for your replies, and support.

Have a great safe flying!!!

Mody

As It was discussed here as well, that the 4 strokes can turn larger size props, I have one more question honestly speaking I wanna increase my knowledge that if in 4 stroke we use larger size prop, ofcourse as it can turn larger size props, what would be the effect on speed? speed of the airplane would increase by using a larger size prop on 4 stroke or using little smaller size prop using 2 stroke engine with higher rpm? Higher torque would give more speed or higher rpm would give more speed to the plane?


Pls clarify me

Mody

its not all about the diamiter of the prop it also has to do with the pitch, I have 3 warbirds all powered by OS 91fs engines, on 2 of them I am spinning 14/9 3 blade props and there plenty fast I usually run at 1/2 to 2/3 throttle.
FYI when you are talking about prop sizes the first #14 is the diameter the second is the pitch, the pitch is the curve or angle of the blade the higher the pitch the more "bite" through the air you have 2st engines will labor with a prop that has too high of a pitch you don't need to have a high pitch prop for them because they are running at a higher RPM, the high torque 4st will spin a high pitch prop without laboring as much not having the the extra RPM's but having more torque on the low end of there range.