4 stroke debate
 

I did a search and found some very interesting information on the 4 stroke versus 2 stroke debate. Having studied 2 stroke and 4 stroke engines in college I really need to ask how some of the information came to being.The following points are generally considered standards of the industry.1) 4S engines are more efficient due to the intake charge not being diluted as much by exhaust gasses . 2) 2S engines make about 80% more power per cubic inch since it is firing on every down stroke. 3) Since 2S engines have no valves to hit the pistons at high speed they are generally more capable of high RPMs. 4) 4S engines are more complicated therefore have more things to go wrong. 5) 4s engines have(generally) more torque at lower RPMs and 2S engines have a more narrow power band placed at higher RPMs. I heard someone state that 4S engines are lighter for the same displacement and that makes no sense to me since the 2S has less parts therefore less weight. I welcome the ensuing debate.

RE: 4 stroke debate
 

What's to debate?

RE: 4 stroke debate
 

"Tastes like chicken", that still just slays me.LOL.

RE: 4 stroke debate
 

In the rc world 4c's are generally the same weight or lighter than the 2c counter parts. I am not sure why this is, i did read a thread a while back that explained it. Something to do with the lighter ring or cylinder or something like that. They most of the time, BUT not always, get better fuel economy. They most of the time, BUT no always, have better transition. They most of the time, BUT not always, can swing bigger props. A low ported 2c will compete with a 4c that is 30 displacement higher than it. That has been my experience with 4 cycles. Most 2c's are ported for high rpms and swing much smaller props at a much higher rpm.

Oh, and %80 more power is to much. I would expect about a 20-30% power gain over there 4c counterpart

RE: 4 stroke debate
 

....what's to debate ? :eek:

Internet myths flourish around here, and everywhere else. You can say almost anything,
and if you say it in a convincing manner.... some people will take it as Gospel....

....because they read it on the Internet. :eek:

Four stroke, and two stroke engines are like apples and oranges. Six of one, and a half
dozen of the other....take your choice. :)

FBD. :D

RE: 4 stroke debate
 

Making 80% more power is expected, 4S engines fire every other down stroke while 2S engines fire every down stroke. The reason they do not make 100% more power is due to mixing of the exhaust gasses in with the intake charge. Detroit diesels tried to fix this by putting exhaust valves in their 2S Detroit engines. If you are not getting this number with RC engines I would have to wonder why.

RE: 4 stroke debate
 

There are exceptions to every point you make. This subject has been hashed over here many more times than I care to remember. I have never understood why folks use the 4 vs 2 terminology and ask which is better??? Better for what? I take the opinion that there is no one type better for sport flying, some folks like the put-put-put, and others prefer RRRRRRrrrrrrrrrrrrrrrrr. Both engine types can be had with enough power to rip the wings off any plane. I personally like em both and am glad not to have just one choice, what do you prefer?

Mike

RE: 4 stroke debate
 

All I know is that the YS110 shows how much power can be pushed out of a 4C engine, its got about the same power as a 120 2C. Anyways, its all about technology ... F1 engines are LIMITED to 19K RPM and they are 4S. Prior to the ban on turbo charged F1 engines they were getting about 1,100 HP from a 1,300 cc engine. Also at the end of the turbo era they were about to generate 1HP/cc. If you are willing to pay you can get anything.

The ASP 180 2C is heavier than the ASP180 4C ... that is just engine alone, did not take into consideration the muffler of the 2C which is usually heavy. To each their own, some love 2C some love 4C. In the RC world, 2C means less maintenance and its easier to run. A 4C needs more attention and care but they do sound good in certain applications.

RE: 4 stroke debate
 

Of course there are many variables like bore and stroke dimensions and port size and shape affecting power. does anyone have dyno graph sheets posted for their engines? Certainly helps when choosing components in my racing engines.

RE: 4 stroke debate
 

....dyno graph sheets ???

....I don't have any.

RE: 4 stroke debate
 

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Our glow two-strokes, in modeldom, are exceptions to some of the rules that you learned in college.

In general purpose utility engines, four-strokes are nearly always heavier than equivalent two-strokes. However, front rotor, shaft induction two-strokes are an oddity that is specific to model applications. It is easy for a model glow two-stroke, or Diesel, to be considerably heavier than a model four-stroke glow or Diesel.

Why? Two factors come into play (probably more, now that I think of it).

As mentioned previously, shaft induction (front rotor) two-stroke glow engines have much heavier crankshafts than four-stroke glow engines. The added girth is there to accomodate a large intake pathway and to provide extra strength to accomodate the extra power being produced by such an engine. Also, the two-stroke's muffler must be larger in capacity in order to quiet the engine sufficiently. A four-stroke glow engine, while producing a much lower pitched exhaust note, is not perceived as being as loud as a two-stroke glow exhaust note.

There are two-stroke exceptions to the high rpm rule, just as their are exceptions for the four-stroke low rpm rule. Intended usage and design timing and porting have more to do with whether an engine is a screamer or a torquer. The 1972 Yamaha 360 Enduro was a torquer, not a screamer. The more recent four cylinder inline 250cc four-stroke Honda redlines at 17k rpm, not exactly a torquer, by anyone's standards.


Ed Cregger

RE: 4 stroke debate
 

????????

Do you have any for yours?

If so, please post them so we can see what one looks like for a model engine.

Mike

RE: 4 stroke debate
 

Dynos for planes? Not heard of it yet, we prefer to see prop and RPM numbers guess that is a good easy guide. Well in the RC car dyno tests they have made it clear that not all dynos are set to the same standards and that the test done is on one particular dyno only so the results will be more 'relative' than 'definitive'.

RE: 4 stroke debate
 

Engine manufacturers don't want modelers to be able to make objective, quantitative comparisons between various engines. The marketplace would collapse down to two manufacturers: the one who makes the most powerful engines and the one who makes the cheapest engines.

RE: 4 stroke debate
 

Jeff, you can safely say that two strokes have more HP because the numbers say that but on a plane FLYING Power counts and four strokes have as much or more of it than two strokes.

RE: 4 stroke debate
 

I miss William Robison!

RE: 4 stroke debate
 

I still don't think that is correct. I might be wrond, and maybe Edd, Flyboy, or hobbsy can elaborate on this but i believe that a 2c does not consuming twice as much gas every complete revolution as a 4c so it would be hard to get 80% more power out of a 2c.

RE: 4 stroke debate
 

I have yet to find a same displacement four stroke with the same power as a two stoke, though some may exist. However, the same weight four stroke will often have the same and sometimes more power than the same weight two stroke.

RE: 4 stroke debate
 

OK, ,,, Why? anybody.
Dyno tests are just a common tool to high performance, I think we should demand that manufacturers provide them. Heck I even have a program that estimates power output called Desktop Dyno, it is pretty accurate having built several engines and done comparisons. Believe me I know about all the variables! but even so you can get the "flavor" of a combination and see it on paper. Manufacturer "A" says his engine puts out 1.2 horsepower and man "B" says his puts out 1.1 horsepower with the same size engine, we everybody buys man "A" because his is more powerful. But if we had a dyno sheet we would find out that "A" only makes that figure at 15600rpm with a very low torque number while "B" puts out peak at 12500 with a very broad flat "useable" torque curve due to having a long stroke or whatever.

RE: 4 stroke debate
 

You are correct, the reason that two strokes do not get 100% power is not just because of exhaust gas mixing back into the fuel and air, but also that the effective volumetric efficiency is less, both of these reduce the amount of fuel and air that get into the cylinder so the fuel consuption is also less than the therotical max.

RE: 4 stroke debate
 

Prop RPM's will give us those numbers. There are plenty of HP/Thrust calculators out there the you imput prop pitch, length, and the tached rpm. Torque can be seen (but not measured) simply by how fast the engine transitions and how big of props it can turn. If engine A turns the same prop, on the same fuel, 500 rpms more the engine B than engine A is more powerful. The closest you can come to a dyno is the tach forum. Compare rpms and prop sizes of different engines and see wich ones fit your flying style.

RE: 4 stroke debate
 

Do you have a reference to the claim that 2 stroke engines make 80% more power over 4 strokes?

RE: 4 stroke debate
 

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We all miss Bill. :(


Ed Cregger

RE: 4 stroke debate
 

It was part of the subject material during engine studies when I attended college but I no longer have access to my books. (it was a long time ago).

RE: 4 stroke debate
 

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Yes, it gets very, very complicated. And, as Hobbsy pointed out, some times engines with less dyno peak horsepower can feel more powerful (four-strokes) than much more powerful two-strokes.

I once (1964) bought a 55 Chevy coupe with a 327 V-8. The car was beautiful, but it came with two ratty Rochester carbs (4-barrels) mounted on the engine. Because the carbs were shot, it didn't perform worth a hoot.

I borrowed a friend's two-barrel setup until I could get a big Carter AFB and the appropriate manifold. I was absolutely startled at the increase in low end torque with deuce on the engine. That lesson always stayed with me when it came to visualizing how various size carbs work on engines and the benefits/disadvantages that may accompany them. The principle learned was exactly the same for model engines, whether two or four-stroke.


Ed Cregger