4 stroke vs. 2 stroke

[cass38a]

If you have a look at the brochures where 2 and 4 stroke models are avail you will find there is stuff all difference in weight.

2 strokes are best for short infrequently used engines due to the high cost of fuel and short engine life.

4 Strokes last longer, cost less in fuel and have about 50 times less emmissions for similar horsepower. That is why cars and road bikes (i know that suziki made 2 stroke cars in the 70's and you can get some 2 bannger road bikes) use 4 strokes.

 

[numroe]

Such an old debate. BUT with a new twist in the facts.

So many web sites exist to explain the techno diffs of the engines. Note that modern directed injected 2-strokes are about to come out in KTM dirt bikes. These new generation 2-strokes are super fuel efficient and clean running.

4 strokes obviously rule in senior and pro MX and SX racing. No debate. Closed case. Unbeatable "flat" torque delivery over a wide RPM range. It will be interesting to see MX developments now that some countries are allowing equal engine capacity for 2 strokes compared with 4 strokes! ie. 250cc 2 strokes against the 250Fs.

2 strokes are making a large come back in pro enduro racing. This is for factory teams as well. For evidence, just watch the GNCC racing on Fuel-TV. So many more 2s on the start lines, particularly in the events with more tight, twisting single line trails. The 2 strokes being lighter on the scales, and also having less rotating mass so they "flick" from left to right much easier in tight and unpredictable turns.

Note that the future (KTM) direct injected 2 strokes will also have far less (near zero) problems with oil filling the exhaust packing material, so these future 2 strokes will I expect be pretty quiet when new and old.

A lot of people try to find one dirt bike that does everything. That's a mythical bike which does not exist. I believe every keen rider needs at least 3 bikes: A 250F or 450F for MX. A 200 to 300cc sized 2 stroke for the bush, and a good pit bike for mini tracks!

2 strokes are far from dead or dying ...

 

[orion125proseries06]

Honda have stopped making 2 strokes (doing the greenie thing) but a guy that worked at a yami shop told me that they might ban 2 banger racing (they probably wont) , but yami will keep making 2 strokes, just dummed down ones, but will come with a racing kit, to make it like a stock racer again.

ok this bit i dont remember so well, so if it is wrong, say it in the forum and i will edit it

I think he said that because there might be a law or something that they cant sell those bikes in racing from the shop, but they will come with a racing kit for it so it will b like the stock bikes they have now

 

[XCHSER]

Sorry mate your wrong about 4 stroke and two strokes. New high performance four strokes rev out just as high as a two stroke and thats why they need to have a top end rebuild after ever 40-60 hours of riding. Same as a two stroke. Ktm 4 strokes are known for having soft rings and have to be done every 40-50hrs of riding . Other brand four stroke can get 60-80 hours on the top end.

2-strokes are easy and cheap to maintain .

4-strokes are expensive to maintain . And when things go boom its Big $$$$$$$$$$.

 

[numroe]

Honda have stopped making 2 strokes (doing the greenie thing) but a guy that worked at a yami shop told me that they might ban 2 banger racing (they probably wont)

Regarding being "green": The new generation 2 strokes (direct injected) are nothing like today's 2 strokes! They have zero oil mixed in the fuel. They WILL be cleaner/greener than the current generation of *carburettor fed* 4 strokes (made by Honda or whoever). No government will ban 2 strokes specifically. They don't ban designs. Governments will make emission laws tougher. Which changes designs - mainly that of road registrable bikes.

In racing (on private closed fence properties) the racing authorities make the rules on bike designs. Once again, not the governments. As for bans on 2 stroke racing - It's just the opposite. They are being promoted for a come back because they are cheaper to run. The logic is pretty simple. Modern 4s have awesome bottom end torque plus rev so damn high that for example 250Fs blow away 125s on the track. As down side the 4s wear out pretty fast (although 450Fs are quite tough). So major MX authorities like FIM, AMA and MCA will (I believe) follow the lead set in NZ, and allow 250F to race against 250cc and so on. The larger capacity 2 strokes when tuned appropriately will be able to produce good smooth bottom end torque (where its at for MX and SX racing and also produce ample top end HP.

Honda will no doubt lobby all kinds of crap. The bottom line is IMHO "sucked in Honda!" and good stuff KTM and Yamaha.

 

[red_demon24]

hey guys i see theres a bit of good and bad about both but im tossing up wether to get a honda crf250x or a ktm 250 exc but i think i would prefer the 250exc as less money has to be spent on it if things go wrong and i like the power of a 2stroke but but the crf250x has court my eye.
i just dont wont to get one bike and wish i got the other.
so what do you think i should get?

 

[numroe]

My tip: Get neither. The 200exc has way more grunt than the crf250x, and weighs only 96kg compared with the 250x at 110kg or there abouts.

 

[red_demon24]

^^^^why get neither???

 

[cass38a]

Do you need to mix oil with the fuel for "direct injected" 2 strokes or do they work more like a Diesel 2 stroke (diesel 2 strokes are used in many heavy duty trucks and need a turbo to fill the combustion chamber). If you still need to mix fuel and Oil they will never be "green" compared to a 4 banger.

 

[cass38a]

It is a Myth that 2 stroke bikes are light.

YZ250 (2 stroke) = 96kg
YZ250F (4 stroke) = 92kg
YZ450F (4 stroke) = 99kg

KTM
250SX (2 stroke) = 95.4kg
250SXF (4 stroke) = 98kg
450SXF (4 stroke) = 104.6kg

Kawasaki
KX250 (2 stroke) = 97kg
KX250F (4 stroke) = 92.5kg
KX450F (4 stroke) = 99.8kg

There is stuff all in it, it may have been true 20 years ago but not now. Honda know that it is pointless developing 2 stroke engins due to emmissions which is why they dumped them early. Best to spend the R&D dollar on 4 strokes.

Yamaha Motor Australia
Kawasaki Motors Australia [Kawasaki.com.au] - The home quality Motorcycle, ATV, MULE utility vehicle and JET SKI® watercraft.
KTM Australia New - Home

 

[Cactus Jack]

Mate .... this is excellent reading !!!!!! Now that's what I like to see !!!!

An expansion chamber equipped two stroke 250 racing a 250 four stroke is as fair and "intelligent" as pitting one 250lb boxer who's allowed to use both hands and use a performance enhancing drug such as amphetamines or steroids ....... to fight another boxer of the exact same weight who has one arm tied behind his back and isn't allowed to use any secret performance enhancers ...... it borders on "Ridiculous" and "Cowardly" .......

 

[numroe]

Do you need to mix oil with the fuel for "direct injected" 2 strokes or do they work more like a Diesel 2 stroke (diesel 2 strokes are used in many heavy duty trucks and need a turbo to fill the combustion chamber). If you still need to mix fuel and Oil they will never be "green" compared to a 4 banger.

Zero oil in the fuel in direct injected 2 strokes.

In the outboard and snowmobile markets, these new 2 strokes are already cleaner/greener than the 4 strokes they compete against. That's even against fuel injected 4 strokes.

Search the web, there is heaps of info on these new engines. The crank case can still be used as the induction pump if desired (using sealed main bearings or special oil lube techniques). Or a supercharger can be used instead.

 

[numroe]

It is a Myth that 2 stroke bikes are light.

KTM
250SX (2 stroke) = 95.4kg
250SXF (4 stroke) = 98kg

There is stuff all in it, it may have been true 20 years ago but not now. Honda know that it is pointless developing 2 stroke engins due to emmissions which is why they dumped them early. Best to spend the R&D dollar on 4 strokes.

There are three flaws in your argument.
* Firstly your figures for the KTM 250s contradict yourself.
* Secondly you wrote "bikes" and not "engines". An equiv tech 2 stroke *engine* is always lighter. The 250F *bikes* are so light because the makers go to so much extremes to get weight out of other parts. eg. the Ti exhaust and Ti footpegs, and the high tensile *hollow* alum swing arm bolt on my KX450F. Also consider weights of rims and tyres and so on. Most 250 2s have "450F" spec rolling gear.
* Thirdly, only KTM quote real bike weights. eg. No 250F actually weighs anywhere near 92kg.

The new direct injected 2 strokes will be good. What is being talked about is just the beginning of the development. Very clean and economical. Lighter for the equivalent $ cost. And best of all much simpler and cheaper to maintain. That means cheaper for young people to get into MX and off road racing. Good things I say.

 

[numroe]

An expansion chamber equipped two stroke 250 racing a 250 four stroke is as fair and "intelligent" as .....

Cactus, you never actually stated your belief.

Talking about MX bikes in MX racing, any beliefs need to be backed up with lap times. It's all about lap times and power delivery over an RPM range. Peak HP is largely irrelevant.

I am not sure if you regularly have watched all AMA MX racing on TV or video for the past 5 years, but in that arena it became obvious that 4 strokes (with double the engine capacity) totally blew away the 2 strokes. More recently it is observed that the 250Fs with the best riders are lapping with times *typically* only 2 seconds slower than 450Fs. And remember that a 450F totally blows away a current generation 250 2 stroke. Sure there are many unknowns and implications. My message is: Things are not as obvious (in MX racing) as you might first guess.

It is time that the 2 stokes had some R&D invested. They (basically 90s tech engines) are surely lagging behind. That's where direct injection steps in.

 

[Cactus Jack]

Don't you worry , I've looked at it from all angles and watch the racing all the time .. I've participated in all types of racing too including MX ... I have always predicted that 4 strokes are better for MX when set up and tuned right to be competitive . So what's your philosophy on it all ..... give the 2 strokes a "pensioners" concession by handicapping the 4 strokes ???? ..... You can make 2 strokes more ridable with a much stronger bottom end pull !!!!!!! Simply lower the ports , change the shape of the expansion chamber ... and give up some of the top end . Or go under square on the bore x stroke ..... You can't have it so that one engine that's burning more dynamic capacity is allowed to race a much higher strung engine that's burning half the dynamic capacity ..... just because they pull the same lap times on a given track ..... IF they can both accelerate at the same rate in a straight line drag then that's it ..... bad luck to the bike that's slower on an MX track .....

 

[cass38a]

I didnt contradict myself. I included the KTM because if i didn't somebody would have come in and said I left them out to make the sats look good. A 250 2 stroke and a 450 4 stroke are a fair comparison and as I stated there is stuff all difference in the weight. I am well aware that the engins are lighter but you dont ride the engine you ride the bike. The 2 stroke needs 450 strength running gear as it has more grunt thab a 250 4 stroke.

It is possible that the reason that KTM 4 stroke bikes are heavy is because they lag behind the Japs in 4 stroke development. (normally when you hear people rave about KTM's they are referring to the 2 strokes).

 

[numroe]

Cactus, Okay if I read you right then your belief appears to be that the 2 strokes of the same CC have an unfair advantage of some kind. On the other hand you agree that the 4 strokes yield faster lap times. One could claim you've contradicted yourself.

What you wrote about making more bottom end in the 2 stroke, is exactly what I was one about in a previous posting in this thread. Agreed.

You can't have it so that one engine that's burning more dynamic capacity is allowed to race a much higher strung engine that's burning half the dynamic capacity

Hey, ask yourself "why not". Seriously. The overall objectives for the FIM and AMA etc, are basic things like: increased rider participation (of all ages and skills levels and budgets), increased spectator attendance, and so on. Those organisations have a tough job trying to keep everyone happy. I think in offroad enduros they are on the right track with many categories and overall winners often coming from different categories. In MX it is not so simple, due to the need to cater for juniors, and yet 250F vs 450F performance diffs now coming down to nil. The cost thing is a big issue. With your "you can't ..." claim, I think you are not thinking outside the square.

I am not claiming I have all the answers. Far from it. *If* I am making a statement of any kind, then it would only be that the industry (and nobodies like us) need to be open minded - and ignore marketing fluff from companies like Honda who have put themselves hard in one corner. It's sounds like you have a soft spot for the 2 stroke just like I do. I used to race them too, and drop in new pistons in 60 mins and check my squish bands and so on. I know you also love your 4 strokes. But in MX and SX, the 250F and even 450F maint schedules are a nightmare for the average amateur or parent. If my little man grows up and wants to race MX, then no way could I support him on one of today's 250Fs. Things have to change. in NZ they have, and good on them.

 

[cass38a]

Just add another one to keep it real

RM250 (2 stroke) = 96kg
RMZ250 (4 stroke) = 92kg
RMZ450 (4 stroke) = 101.5kg

 

[numroe]

I am well aware that the [2 stroke] engins are lighter.

Ok cool. So we agree with each other. No more debate. Talking about engines and not bikes. As per this thread subject. Glad you cleared this up. So obviously if the 2 stroke engines were wrapped in the equivalent cost+spec chassis, then the bike will weigh less.

normally when you hear people rave about KTM's they are referring to the 2 strokes

Agreed. I'd be one of those people too.

About bike weights: KTM are the most honest with their weights, plus they state weights without fuel but otherwise ready to ride. My KX450F-06 is the lightest year model KX450F made to date, and it literally weighs 103Kg, with no fuel but with suspension oil, with radiator coolant and with engine oil. The stated 99.8kg is meaningless. All the Jap makers do it like Kawi. I agree with you that 103Kg actual weight is amazing for a typical 450F, but that figure has a lot to do with the chassis.

 

[cass38a]

If you put them in the same chassis the 2 stroke would destroy the chassis and running gear and make the bike just as expensive to maintain as the 4 stroke.

Different strokes for different blokes.