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Old 07-31-2004, 07:04 PM   #1
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Default difference between 4 cycle and 2 cycle engine?

Kyosho is comming out with 4 cycle engine cars.
What is advantage of 4 cycle engine in terms of performance?
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Old 08-01-2004, 01:11 PM   #2
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If 4 cycle means 4 stroke the only advantage is in fuel consumption.
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Old 08-02-2004, 03:13 PM   #3
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don't feed him full of crap.

A 2-stroke, or 2-cycle fires once every 2 strokes of the piston, and has no valves, only ports.

and a 4-stroke, fires once every 4 strokes of the piston, the advantages, 4 stroke has a cooler running temperature, they are more durable and much more "torqish". they run at lower RPMs, and are smoother.

A 2-stroke will wind out alot quicker which gives it much quicker acceleration, but in the long run, a 4 stroke of the same size will have almost twice the top-end of the 2-cycle.

E-mail me if you need to know more.
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Old 08-03-2004, 07:47 AM   #4
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Before you go accusing me of blowing smoke up someones arse maybe you should check your facts mate. A 4 stroke having only 1 combustion cycle for every 4 strokes will make roughly half the power of an equilivently sized 2 stroke. Its just basic physics.

A 2 stroke will always out power a 4 stroke whereas the 4 stroke will have more torque. 2 combustion cycles vs 1 combustion cycle every 4 cycles.

Last edited by Adoika; 08-03-2004 at 08:01 AM.
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Old 08-03-2004, 08:03 AM   #5
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Quote:
Originally posted by Adoika
A 2-stroke will wind out alot quicker which gives it much quicker acceleration, but in the long run, a 4 stroke of the same size will have almost twice the top-end of the 2-cycle.
Uhhhhmm.... no...... that's BS. A 4 stroke has much more torque, which will accelerate out of a corner faster than a 2 stroke. RC Car Action has done a lot of tests on this in previous issues. Why do you thing airplanes use 4 strokes??? Torque....

On the other hand..... a 4 stroke will run out of leg on the top end- it has much heavier components to spin, and the RPM range is much narrower than a 2 stroke. Two strokes are running 42K+ rpm these days!! There is no 4 stroke that is going to match that RPM. Do the math, and tell me what will run FASTER on the top end.... assuming both engines are running through the same drivetrain. If the gear ratios are the same, and the 2 stroke will out RPM the four- the 2 stroke will be faster. I don't care if the 4 stroke has twice as much horsepower- if it's doing less RPM than a two stroke (geared with the same final drive) it will be slower- period.

It's simple physics......
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Old 08-03-2004, 02:47 PM   #6
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Quote:
Originally posted by Adoika
A 2 stroke will always out power a 4 stroke whereas the 4 stroke will have more torque. 2 combustion cycles vs 1 combustion cycle every 4 cycles.
let me tell ya somthing

torque=power
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Old 08-03-2004, 07:10 PM   #7
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yea...... torque = power, but we also are dealing with gear ratios here and RPM limits of each engine.

Use a simple rollout /speed calculator and we'll see the winner here.

With a 1.5 HP Nova Rossi 2 stroke- capable of 40K rpm, and a FINAL drive of 4.00:1, with 60mm tires, theoretical top speed would be= 70.275 mph.

Do the same math on a 3.0 HP 4 stroke capable of only 30K rpm and you get a top speed of 52.707 mph.

Horsepower matters, but the winner here is RPM and gearing.

check this site for a neat little top speed calculator- http://www.pbracing.com/info_rcgears.html.

Does it mention horsepower or torque?? No....

Need a math lesson?? just PM me........
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Old 08-03-2004, 07:31 PM   #8
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Torque does NOT equal power.

Power (W) = Torque (Nm) * rotationfrequency (2*pi*RPM/60)

A 2-stroke may get much higher RPM than a 4-stroke, but they have poor torque, especially at high RPM.

Comparing both types of engines with the same gearing is unfair to both. 4-stroke will have much better acceleration, 2-stroke will have much better topspeed. I think you will find both are reletively close in performance when you find different optimal gearing for each for a given track.
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Old 08-03-2004, 07:37 PM   #9
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how do I find out the gear box ratio???
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Old 08-03-2004, 08:08 PM   #10
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Quote:
Originally posted by KevinS


Torque does NOT equal power.

Power (W) = Torque (Nm) * rotationfrequency (2*pi*RPM/60)

A 2-stroke may get much higher RPM than a 4-stroke, but they have poor torque, especially at high RPM.

Comparing both types of engines with the same gearing is unfair to both. 4-stroke will have much better acceleration, 2-stroke will have much better topspeed. I think you will find both are reletively close in performance when you find different optimal gearing for each for a given track.
What I was stating is that, as torque increases so does horsepower. torque is the numerator in your equation, so yes, it makes sense that more torque= more horsepower. heres the simpler version of the same equation for the mathematically challenged....

Horsepower= (Torque*RPM)/ 5252

from many runs on a real engine dyno, it's amazing how the HP and torque values cross at 5,252 RPM... always...

I also stated earlier that the 4 stroke would accelerate better, and the 2 stroke would have better top speed- with the same gearing. I don't think there are any factory kits that could be geared right for a 4 stroke using available off the shelf parts.

I think we are on the same page here, but others...... I'm not so sure
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Old 08-03-2004, 08:45 PM   #11
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Has anyone seen 4 stroke engine V-ONE-RRR or FW-05R run?
Anyone from japan?
Check out the japanese kyosho web site using online translator and you will see the 4 stroke engine kit for FW-05r and V-ONE-RRR. They also have a nice video( but you have to download at original site). you can see the V-ONE-RRR Running.
So, if geared right, 4-stroke will have much better acceleration?
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Old 08-03-2004, 09:02 PM   #12
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if geared right, a 4 stroke will unglue the tires!!
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Old 08-03-2004, 10:48 PM   #13
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Default 2stroke vs. 4stroke?? What????

First let me say your all on crack!!!

At this time there is NO 4stroke r/c engine that will out run a 2stroke. The technology of todays r/c 4stroke engines is way behind that of ALL r/c 2stroke engines. Even the cheap RTR engines are way ahead of todays r/c 4stroke engines.

If you were to compare a .12 sport engine (Fantom .12 for instance) to a .26 4stroke engine (OS Surpass .26 car engine), first you would get a max rpm difference of around 17,500 rpm. The .12 2stroke would have a max rpm of say 32,500 and the .26 4stroke would have a max rpm of 16,000. So gearing would definitly have a crucial role in comparing.

The 4stroke makes 1 power stroke per 2 rev. of the crank where the 2stroke makes 1 power stroke per rev of the crank.
4strokes make more torque on their power stroke due to the fact that the combustion pressure acts on the piston all the way down the power stroke. 2strokes on the other hand let the combustion pressure excape the cylinder around 2/3'ds the way down, and out the exhaust port. To make matters worse on the 2 stroke, the piston is fighting secondary(crankcase) compression at this time.
Your average 2stroke has a 85deg. power phase duration, where
your average 4stroke has a 155deg. power phase duration.
However the 2stroke gets to make a power stroke every rev. so that bumps the 2strokes power phase duration to 170deg., 10% more than the 4 stroke.

That said, you would need to double the displacement of your 4stroke to mathmaticaly equal the power of a 2 stroke.

Now to correct a few statements:
4 strokes run much hotter than 2 strokes. Always. (Remember the Kyosho Super 10 four, is required a fan driven off the crank to keep it cool).

There are no 4 strokes capable of 30,000 rpm. Valve float limits this physically.

A 2 stroke will wind out alot quicker due to the drastically reduced rotating mass compared to a 4 stroke.

The 4 stroke will NOT have twice the top end of a 2stroke, valve float prevents a 4 stroke from having rpm capabilities anywhere near a 2 stroke.

A modern r/c 2 stroke has the luxury of taking advantage of tuned pipes which makes them way more volumetrically efficient than a 4 stroke could ever hope to be.

Compare a 125cc 2 stroke mx bike with a 125cc 4stroke bike. 2stroke= 38hp, 4stroke =15hp.

Until very recently technology of 4 stroke singles has been in the stone ages. In the last 3 years 4 stroke single technology in the mx field has improved enough that 250cc 4strokes are now able to compete with 125cc 2 strokes. And that took F1 type technology to accomplish!

I challenge anyone to compare a .12 2 stroke to a .26 4 stroke on a dyno and show me how a .26 4 stroke could possibly make more power.

BK
Factory Honda mechanic for Mike LaRocco
Designer of the X-Dyno for Xtreme r/c magazine

http://www.nitrodynesystems.com
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Old 08-03-2004, 11:23 PM   #14
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Wow Thanks everyone for the information.
I am overwhelmed. Although I am still confused. ( due to my lack of basic knowledge of the engine)
THEN, back to my original question, why would kyosho make 4 stroke engine for their car? what advantage do they see by doing this?

Hey BK, You are the guy in X-RC CAR Mag right?
Are you having fun testing all the engine?
I was wondering what engines are gonna be on the next Issue?
Keep up the good work....
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Old 08-03-2004, 11:45 PM   #15
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Quote:
Originally posted by dragoneuh
back to my original question, why would kyosho make 4 stroke engine for their car? what advantage do they see by doing this?
i guess this is because the japanese like to try something different all the time. most of us would just want the fastest engine we can afford (can we handle the power ? we will worry about it later).

i think maybe with the right gearings, a 4 stroke car can do good on a small, technical track. that would be a competition of skills, not guts. but without actully drove one, it is hard to tell.

data
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