2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Here is a lovely ~40 year old Cosworth powered example of an ( unsuccessful) attempt to beat 2Ts with F1 4T-tech..

http://www.bonhams.com/auctions/22125/lot/158/

A pretty machine, & how much would it have made - if it had been a success?

[flynfrog]

http://motocrossactionmag.com/news/moto ... 2001-cr500 ill just leave this here. I do love my 2ts but but a 4t is much easier to ride and faster around a track.

Thanks FF,

Easier = boring?

"Faster around a track" - that kinda depends on the track, & the rider, as the article reports..
& to be fair - the CR 500 was a very basic `80s-90s design that really hadn't seen much development in its final years,
- yet was/is still capable of providing a pretty good account of itself..

As noted a bit earlier ( recent posts - on the 'Engine Technology Free-for-all' thread)..
IMO, a modern-current 2T design of ~400cc that incorporated the various functional improvements
seen in smaller capacity classes - would have to do better than a big ol' CR/KX 500 blunderbus, fun as they are..

If you are bored on the MX track you are doing it wrong. I agree the 500 was a sledge hammer compared to the modern scalpel that is a modern 4T bike. I quit competitively racing right about the time of the 4 strokes becoming common. I raced Quads back then and my last engine made just shy of 70hp out of 350cc. I still dust it off now and then to scare myself.

[flynfrog]

have you guys seen this



new maco 700 for when your 500 wasn't hard enough to ride.

[Andres125sx]

A-125, you need to learn a few realities..

As for "high power" - the specific output of Moto GP 4T is less than what 2T roadbikes were making, decades ago..

The showroom production Aprilia RS 250 (Suzuki engine) was rated at ~70hp, or ~280hp/litre..
..more specific output than Moto GP..

Right, but I said high power, no high specific output

An RS 125 has a similar specific output, but I wouldn´t say it´s a high power bike

Maybe it´s the term high power what confuse you, I mean engines with lots of bhp, engines or vehicles with so much power they need a talented driver to control the power delivery, no matter what the specific output is.

For those vehicles, the increased traction 4t engines provide are a big advantage, wich means they´re faster and easier to drive/ride. And easier does not mean a top driver/rider will solve the problem, but any driver/rider, including a top one, will be faster.

[Andres125sx]

http://motocrossactionmag.com/news/moto ... 2001-cr500 ill just leave this here. I do love my 2ts but but a 4t is much easier to ride and faster around a track.

Thanks FF,

Easier = boring?

"Faster around a track" - that kinda depends on the track, & the rider, as the article reports..
& to be fair - the CR 500 was a very basic `80s-90s design that really hadn't seen much development in its final years,
- yet was/is still capable of providing a pretty good account of itself..

And is a different category to the 450... wich is the reason it´s not beaten easy

That comparison is like comparing a 250 4t 2014 with a 250 2t 2004, 2t will be faster hands down. The comparison is actually more unfair as the 2t is a bigger displacement engine.

I agree it will always depend on the rider and track, considering same driver it will still depend on the track, with a very slippery track 4t will win consistently, with wet (no mud) tracks 2t will be a tougher contender, but will never beat 4t´s as easy as they will do with 2t´s on slipery/hard tracks.


If the comparison is between smaller engines then 2t will be more competitive, but again, with poor traction 4t will be imposible contenders for 2t´s. I know what I´m talking about, this is me with my favourite bike from all the MX bike I´ve owned, KTM 125 sx 2003 wich is the reason for my nickname


It was the funniest bike I´ve ever had despite it´s nervous direction, but fun does not mean fast, for racing I´d have switched it with a 250 4t on 80% of the races I participated. Trying to keep up with a 250 4t going out of a flat corner was frustrating, as many other situations were traction matters. And I´m not a pro rider, but I knew my rivals, and they´re the same I beated on wet tracks, and was unable to chase on hard tracks. Traction change it all for 2t´s, on surfaces with good traction they´re competitive, but if there´s no traction they´re a PITA, and a powerful engine means you´ll miss traction on any surface

[J.A.W.]

Here are a couple of meaningfully dirty 2Ts as featured in MX Action..

& the MX Action "Wrecking Crew" - really know - what they are talking about..


"...the most desired off-road motorcycle..." ..KTM 300..

http://www.motocrossactionmag.com/bike- ... two-stroke

&, for those who find 450 4Ts boring.. & "...want the ultimate racing weapon.." ..KTM/KX 500..

http://www.motocrossactionmag.com/news/ ... oject-bike

[J.A.W.]

Handicapping/banning 2Ts in racing competition - to make lazy 4Ts look good - goes back decades..

Check out these wild 2T F750 powered dirt-bikes - from the `70s..

http://www.superbikeplanet.com/2013/Dec/131213verve.htm

Tyre tech back then was barely able to cope with 100+hp bikes on the road-race track,
( & prompted the introduction of fat sticky slicks for bikes) - let alone dirt track tyres..

Kenny Roberts pioneered the use of road-race 'wets' - as a means of getting traction on the dirt..

[riff_raff]

I used to do some desert riding, and while a 2T bike worked good for dirt track riding, you had to be careful riding a 2T bike at high speeds over long distances in the desert. Under these riding conditions the 2T engines would often seize-up.

[J.A.W.]

Any poorly prepared bike.. likely might..

So, r-r - I guess you missed that 150mph 50cc 2T land-speed record bike running WFO across the salt?
( its on the "...shameless enginephiles..." thread)

& this guy Danny Hamel.. won numerous desert races - inc' the Baja 1000.. ..on a 2T..

http://motorcyclemuseum.org/halloffame/ ... acerID=464



& this 2T MX bike seized due to.. riding across too much water.. https://www.youtube.com/watch?v=TYB7DYWI4G8

[J.A.W.]

A-125, a couple of quick comments on your ill-founded recent posts..
..such as.. you wrote..

"...it's like comparing a 250cc 4T... with a 250cc 2T...
...the comparison is actually more unfair as the 2T is a bigger displacement engine."

&,

"...what confuse you... "

Since, surely 250cc=250cc, no?

& as regards a 280hp/litre 125cc 2T.. ..you wrote..

"I wouldn't say its a high power bike"..

How would a just such a 2T 125cc MX bike go.. ..compared to an equal capacity (125cc ) 4T single?
The 4T would be downright gutless by "comparison" - wouldn't it?

Try & be serious, since you named yourself .....125, after all..

( & of course - Uniflow has already specifically noted this cc parity aspect - in his post at the top of page 26)..

[wuzak]

Since, surely 250cc=250cc, no?

No.

$ strokes only take intake once every two strokes. So while the swept capacity is nominally the same, a 2 stroke consumes approximately twice the amount of air. And, thus, twice the amount of fuel. For an the same swept capacity.

A2 s troke bult to the current F1 fuel flow rules will either have to be smaller than 1.6l or run at lower rpm. Since the 1.6l capacity is required that means fewer rpm.

[J.A.W.]

Since, surely 250cc=250cc, no?

No.

$ strokes only take intake once every two strokes. So while the swept capacity is nominally the same, a 2 stroke consumes approximately twice the amount of air. And, thus, twice the amount of fuel. For an the same swept capacity.

A2 s troke bult to the current F1 fuel flow rules will either have to be smaller than 1.6l or run at lower rpm. Since the 1.6l capacity is required that means fewer rpm.

Yes, actually W.. & 250cc=250cm3 too..

If you go back a couple of pages, you will find your previous ( & almost identical) post (wrongly) asserting this..
..has like-wise already received - an up to date answer..

As noted - all other things being equal - 4Ts cannot compete with 2Ts on a cc for cc basis,
& in power-to-weight ratio, for racing purposes..
..such as - for example Moto GP, or F1 - hence the handicap &/or outright bans..

Indeed, if you go back to page 5 of this thread..
& review the cited NASA/Garrett high-efficiency 2T turbo-compound proposal,
you will understand why the F1 ban on 2Ts , even on a fixed fuel burn scheme - has not been rescinded..

[gruntguru]

This thread has moved into the displacement equivalency realm. Let's throw in the Wankel which has a "true" displacement three times that stated by its makers. For example, the Mazda 12A nominally less than 1200cc. is actually almost a 3.5 litre four stroke. No wonder the things make so much power!

[hollus]

JAW, I think the conversation would benefit enormously from you being right less than 100% of the time, refuting the others less than 100% of the time and acknowledging that your opinion is not the only valid one 100% of the time. It is OK to disagree without shooting the other poster down. You are not the only one guilty of these sins, though, and what you write is often most interesting, it is just that the tone makes a level-headed conversation almost impossible.

Since this is now an equivalence discussion (and a great one), I'd like to add an outsider's perspective. Not knowing much about engines, I can easily ignore how many cycles involve combustion, swept volumes, etc. The way I see it, the only fair comparison would involve not the mechanism of the engine, but its function. This way one can compare 4Ts with 2Ts, Wankels, turbines and anything else. And you guys know so many examples that surely there is a set of engines that can help here.
The way I see it, the fair comparison to do would be comparing engines of different types that have similar:
a) total weight
b) total volume of the engine (turbos included here, obviously, as is possibly cooling if external, which also has weight)
c) fuel consumption
And then comparing power, response characteristics, etc. Alternatively, if two of the three and power are similar, the third element would decide the comparison.
Anyone dares to come with examples under these comparison rules?

[Andres125sx]

Here are a couple of meaningfully dirty 2Ts as featured in MX Action..

& the MX Action "Wrecking Crew" - really know - what they are talking about..

One important caveat in the dream-bike scenario is that the bike cannot have a 450cc four-stroke engine. Why would it? Four-strokes are readily available and thus not dreamy enough. That means the ultimate motocross bike would most likely be powered by a 500cc two-stroke engine.It is the rarest of engines

That´s a great argument, the ultimate bike must have the rarest of engines, perfomance doesn´t matter, it´s rareness what counts.... they sure know what they´re talking about...

Since, surely 250cc=250cc, no?

Yes, but one will produce around double power and will use more than double fuel, do you really think that´s the fair comparison?

How would a just such a 2T 125cc MX bike go.. ..compared to an equal capacity (125cc ) 4T single?
The 4T would be downright gutless by "comparison" - wouldn't it?

Try & be serious, since you named yourself .....125, after all..

You obviously missed the point.... That´s exactly what I was pointing out. That comment was about flyinfrog link of the cr 500 2t vs cr 450 4t comparison. I said on that comparison the 500 2t could keep up because they are different category bikes, and that´s like comparing a 250 4t with a 250 2t, obviously the 2t will win, because it´s not a fair comparison. And even so the 450 4t is not clearly beaten, despite being a lower category.

&, for those who find 450 4Ts boring.. & "...want the ultimate racing weapon.." ..KTM/KX 500..

Those who find a 450 4t boring have never ridden a 450 4t

They never said that, please do not invent absurd argumentation