Proof of what we say, if all manufacturers made 2 strokes.

[rbigair40]

ther were a bunch of 2 strokes in the class but more 4 strokes i watched that class while i was there ,i think a third of them was 2stroke

[factoryX]

How am I wrong? Short rod = more rpms So when you throw a larger piston you will regain lost torque, which also allows you to run larger valves. This is their way of pulling more power out of the 4 stroke engine while making it lighter in the process. As for porting, the majority of 2 strokes already use case induction, and there are such things as bridges in the middle of ports to keep rings on . What I am talking is plausible, and this is the reason of success with the modern 4 strokes. These motors are not equal in anyway. In the last 20 years the 4 stroke motor has been transformed while two strokes remain similar to 70's/80's design.

[TMKIWI]

Short rod = more rpms. Yes i wasnt argueing that.
You said to replicate it in a 2 stroke. Best of luck.

As I said 2 completely different types of motors that achieve things a different way.
How is a 250 2 stroke going to get enough port area with a 55mm bore.?
Not sure what you mean by port bridges & case induction. You can only move the ports around a bore so much before you run into turbulence problems.

2 stroke MX engines do not need high rpm's.

4 stroke engines can NOT make good horsepower Without high rpm's. AND THAT IS THE PROBLEM WITH THEM.
Short rod = high rpms = $$$$$

[factoryX]

but wouldn't a larger piston on short stroke increase torque and top end on a two stroke? It may be not be logical, but neither are $20,000 4 stroke motors.

[TMKIWI]

Piston size dosn't really play a part in torque.
Normally the longer the stroke the higher the torque.
But for any given rpm the longer the stroke the higher the piston speed.
4 strokes by design need to run at very high rpm's to make power even close to a 2 stroke.
Look at Moto GP . The modern engines are doing 18,000rpm to make 240Hp out of a 1000cc engine.
Go back 10 years the 500's were putting out 210Hp at 13,000rpm.
The motors are 100% bigger turning 30% more making only 13% more Hp.

Half the problem with the 4 stroke is the piston skirt length or lack of.That thing wears so quick its stupid.
But to lengthen the skirt the piston would then be too heavy for the rpm,s they are doing. The designers have dug themselfs abit of a hole they can't get out of.
Ive said before they are a brilliant peice of race engineering for a factory race team but for the public 

[SachsGS]

Long stroke 2T motors are considered to have a traction advantage as well.This was more or less pioneered by Maico and eventually all 250 2Ts copied Maico's engine geometry (don't forget the YZ 68mm stroke long rod upgrade kits).

When you are comparing 2 cycle and 4 cycle engines don't forget as well that per unit time the 2T engine generates two power impulses to the 4T$ one impulse.Soiricho Honda's solution was to spin the 4T engine twice as fast to generate the same output.That is why we are where we are now.

[bearorso]

FactoryX,

How is designing an engine the way it has to be, to be competitive, CHEATING?

It's what you do as an engineer. A 4t has bugger all torque, when compared to a 2t with a comparable level of tune, so 4ts have always had to go the route of revs to get their HP. So be it. HP is a product of torque, multiplied by revs, then divided by a constant (5252).

TMKIWi has it right.

Now, tech like DFI may allow 2ts to get more  mixture into the combustion chamber with a short stroke format (by replacing air charge lost by shorter stroke / shorter duration transfers and inlets) - it depends on the tech used for the pressure/ volume of the stratified charge. That's where the arguments put up against DFI being heavy / complex can come in - to get very high pressures / volumes of the stratified charge, for short stroke 2ts, is going to require tech / parts that will be far to bulky for dirt bikes, at least for the foreseeable future. The DFI outboards seem to have gone to over square dimensions, and bigger capacity engines, ironically - part of the weight benefit of 2ts , you can use a bigger engine, when you are dealing with an Output oriented sport / market.

Let the 4ts rev their tits off - they just keep getting 'pipier and pipier' (11 / 12krpm 450s, hitting the rev limiter constantly - I never thought I'd witness that).

Mind you, Moto 3's regulations, limiting revs to 13,000 (lower than most std 250f MXers rev to) rpm will, keep things in hand - the customer spec Honda 250 is claimed to have 35.5 KW = 47.6 HP, that shows what is still to come with 4ts, without mind blowing revs. They are allowed to use 81mm pistons, yet Honda has gone only to 78, as with the rev limit set, they have seemed to believe that there's no need for the max. sized piston. And that HP level, Has to be produced at a noise level much lower than allowed at the GPs (115Db), for those bikes to be run at race tracks around the world. Check out the huge, under case uffler it has. The GP bikes, will probably have open , or near to it, pipes.

To make Moto 3 interesting, the homologated engines, are going to have to pump out 55 /65 HP, to get the speeds of the 125s. It will be interesting to see what is to come.

Though, it should have been a class that allowed 4ts And 2ts, with spec / cost controls - better still, it Should have been 125s, with spec / cost controls. That would have delivered low cost racing, much more effectively.

[factoryX]

What I pointed out is exactly why its considered cheating. A modern two stroke piston is 66mm-68mm, while a modern 250 4t piston is 78-80mm... A 78mm piston is about enough for a 370cc big bore kit for a 250 2t. That's why its cheating. And at this point I agree with TMWIKI and you as well.right hilarious.

[TMKIWI]

FactoryX,
 The DFI outboards seem to have gone to over square dimensions, and bigger capacity engines, ironically -

The outboards were actually oversquare to start with. It was needed to keep the V-Block engines compact.

FactoryX,
Mind you, Moto 3's regulations, limiting revs to 13,000 (lower than most std 250f MXers rev to) rpm

Easiest way to make 4 strokes more reliable.
RPM's & noise control. Drop both and you have a more reliable motor.
Less HP but I don't care.

[bearorso]

It's not considered cheating by anyone I've ever come across, until you.

Put it to the uninitiated - all they will care about is the capacity. When I point out to people that the 4ts, that commentators are usually raving  about,  are up to twice the capacity, by the rules, Every time, I get a comment along the lines that that is unfair / cheating. The general public, actually have a good grasp of what is fair, and what is not, when they are informed of the current, biased rules.

 Short Stroke - It is how most modern 4ts are made. So be it. I've no problem whatsoever with it, if engineers want to go that way in engine design. I've actually put forward in other sites, that I'd like to see a true 'open class', with 2ts and 4ts, with someone like Buell, Katech, perhaps making a modern, long stroke, big capacity, utterly minimalistic, push rod engine, for dirt use. Idiots could not get away from their '450 4ts are the greatest bikes ever made', mindset. It was quite hilarious. Usually, those same drongos loved their big old push rod engined muscle cars. And despised the modern car engines. Classic. I grew up with BSAs and CCMs in the family, and loved the 630cc CCM engine that was in one of the bikes. Whilst rabidly charging around on 125 2ts, and stirring up my Dad and Uncle about their old boomers, at the same time.

Let 4ts be screaming, peaky engines, it's not what I want from an engine. That's why I ride a 5500 / 6000 rpm, 500 2t.

As for the stroke on outboards, well, short stroke can force use of a wider V, as against the narrower V a longer stroke can allow.  Depends on what you regard as compact / want to compact. It's a case of either, either.  My 500, has an over square bore and stroke - indeed, many open class 2ts have been over-square, as many were developed from 250 modules. A matter of expediency, for many manufacturers, but also, it might have been exactly what they wanted from their engines. Oh, by the way, I've owned several Maicos, so don't bother with trying to inform me how 'magic' their engines were / are - I know a fair bit about them., and I am quite a devotee of the brand..

[factoryX]

I wasn't going to inform you about maico engines, as I know nothing of them.   The only reason this hasn't popped up before is that people have not noticed or did not realize that there was that much of a difference. You're right, TMKIWI is right, but then I have point as well. Either way 2 strokes have to change or face death, as people are to stupid to understand otherwise. There are still a handful of people who ride 2 strokes, but then again there are still a handful of people who ride 3 wheelers, fl250/350/400s, 2 stroke utility quads, etc..

[ACMX]

You blow me away when you say stuff like that. Seriously two strokes are becoming more popular where I'm at. When you say 'face their death' I say BS they are coming back.

[factoryX]

Not in America, its gone to point of being political.

[VintageBlueSmoke]

Simple fact is that regardless of what the manufactures make to sell, the RULES dictate what people will buy - even if they don't race.

Basically you have 3 types of consumers in the dirt bike market. Racers (MX'ers, desert, enduro, etc), and trail riders or newbs. The trail riders sit on the fence between off-roaders and newbs but that is not a derogatory statement.

Racers buy a bike as a TOOL. They want the best product for the job at hand. No one is going to buy a bike that is not going to be competitive in their chosen class. Fortunately for the 2T, the off-road rules are based on capacity rather than stroke and the 4$ are not given a handicap. This make the 2T often a better TOOL. For these people, the products from the manufacturers are valid. They create TOOLS based upon the RULES, (not the RULES based upon the TOOLS). Want proof of this? Do you see a 175 class? A 200 class? A 350 class? No, but the manufacturers build these bikes for two reasons; 1) because there are people who will buy them to use as a better TOOL for their job or 2) there is somewhere with flexible enough RULES to allow their use. In American Enduros/Hare Scrambles etc, it is 0-200cc. In Europe, E2 is 0-175cc. (MX2 is 125-150cc).

Serious Trail Riders buy TOOLS. That is why the XR and KDX still sell today and why KTM is the largest producer of off-road vehicles. For all these groups, those who buy TOOLS, the manufacturers are in constant competition to build a better tool.

For the casual buyer and the newb...they have to have what the PROS have. Why spend $7000 on a much more useful and reliable KDX or KLX when you can have a KX450F just like Villapoto! Then drop $100 on Monster/PC graphics and nifty matching riding gear! THESE ARE THE PEOPLE THE MANUFACTURERS ARE TARGETING. The racer will always buy the best TOOL. The newb kid that wants to look like Dungey or the newb big guy thinks a 250 is too small for is 200 lb butt. The Racer will drop $20k into suspension and motor mods; the newb will just let it hand grenade and buy a new one!

Now back to my first statement. The FIM and AMA have taken responsibility for the SPORT; like is their charter. They dictate the rules. If you want to race, you will use X range cc motorcycle. You as the consumer/competitor choose the best TOOL for the job based upon your ability with that tool, the RULES, and you budget.

@Factoryx - What you are saying is correct but...you can only go so far before other variables come into play. That is what TMKIWI et al are trying to say. No so much that you are wrong but that you have gone too far in your measurements for it to work as you intend.

[Chris2T]

that highly oversquare piston is what put 4 strokes back in motocross, as it allowed them to rev high to find their horsepower. Totally fair in my opinion - a 250cc engine is 250cc no matter how you slice it.

And THAT is the beauty of direct injection. Because now, 2 strokes can be oversquare!! They no longer need to depend on port timing like conventional 2 strokes. Check this out: one of the DI 2 stroke outboards (evinrude etec) is running 433cc cylinders at 91mm bore X 66mm stroke. Not as oversquare as the 450F's, but oversquare nonetheless. Can you imagine an open class 2 stroke that revs to the moon?!