2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Thanks, T-C..

Suzuki also sold ( mini) cars & 4WDs powered by 2-strokes..

http://www.japanesenostalgiccar.com/201 ... ki-fronte/

A keen Kiwi bloke stuck a Suzuki 100+ hp TR 750 2-stroke triple racing mill into a Fronte - for a bit of fun..
Turned out to be a wee bit of a handful.. ..something like this..

https://www.youtube.com/watch?v=uT4Jwu5mQTE

The tiny, seemingly toy like 4WD Jimny was also surprisingly capable off road too - due to being so light..

[J.A.W.]

The fundamental 2-stroke advantage - Tim Hickox lays it out..

http://www.pit-lane.biz/t5235-2-stroke- ... tim-hickox

[Tommy Cookers]

brilliant link !
though race performance from 300cc N/A cylinders is not their focus ?

ie whether or not a 300cc piston-ported 2 stroke N/A cylinder can have enough port area to beat the 300cc N/A F1 cylinder
the bhp/litre of the 300cc 2 stroke is anyway significantly less than that given by a 125cc 2 stroke cylinder

iirc in 2 stroke 500 GPs evaluation of reducing cylinder count to 2 the power was about 25% less than the 4 cyl power
imo calculation suggests rpm would be about 10-12% less but whole-engine port area is 21% less (for the twin compared with the 4)
ie the inherent reduction in port size relative to demand (with the enlargement of the cylinders) was the driver of power

btw
good wishes to the efforts of those who do stuff with eg 2 strokes ..... rather than just (as I do) talk about them

[Andres125sx]

The tiny, seemingly toy like 4WD Jimny was also surprisingly capable off road too - due to being so light..

Light, and short, and narrow. A true off-road car must be all this, today with trucks like Cayene, X5, ML, Tuareg, etc. people think big is good for off-road, but no, big is quite bad actually

Sorry I don´t know the term of these technical specs, but they have lower AOA (to start or finish a ramp and avoid bumpers hitting the ground), lower bumps capapabilities (to pass big bump without hitting the ground), to be able to pass through thick brushes...

And light to avoid getting stucked into the mud or sand, wich is the main problem for most extreme off-road situations.

Only problem for Jimmy is it misses differential lock, and that´s a big mistake for such a good off-road car. With it it would be unbeatable off-road wise....


PS: sorry for the OT

[uniflow]

brilliant link !
though race performance from 300cc N/A cylinders is not their focus ?

ie whether or not a 300cc piston-ported 2 stroke N/A cylinder can have enough port area to beat the 300cc N/A F1 cylinder
the bhp/litre of the 300cc 2 stroke is anyway significantly less than that given by a 125cc 2 stroke cylinder

iirc in 2 stroke 500 GPs evaluation of reducing cylinder count to 2 the power was about 25% less than the 4 cyl power
imo calculation suggests rpm would be about 10-12% less but whole-engine port area is 21% less (for the twin compared with the 4)
ie the inherent reduction in port size relative to demand (with the enlargement of the cylinders) was the driver of power

btw
good wishes to the efforts of those who do stuff with eg 2 strokes ..... rather than just (as I do) talk about them

You can clearly see then that the sleeve 2T has much more time / area, both exhaust and inlet and potentially adjustable on the fly too.

[J.A.W.]

T-C for all your fixation on cylinder dimensions.. ..how much did those super-high rpm N/A F1 mills cost?

Honda built an affordable production racer V-twin 500cc GP bike based on a tuned version of its MX 250 cylinder,
- it was good for a reliable/rideable ~300hp/litre in a 110kg bike..

That could be scaled up to a 900hp 3litre V12, ( & could be given a harder tune for more power, too),
& that would make an inexpensive - but exciting - alternative as an F1 mill, even today..

PC concerns could be addressed by utilizing DFI tech too..
..let alone providing a potential base for Uniflow-type sleeve valve & Manolis' opposed piston designs..

[wuzak]

If 2 strokes were to be allowed to run along side 4 strokes in a capacity restricted class (such as 3l or 2.4l F1) they would have a equivalency factor applied.

Theoretically the equivalency factor would be 2, as the 2 stroke has twice the power strokes per revolution. In practice having 4T twice the capacity gives them an enormous advantage. Even the recent 800cc Moto GP bikes would have the 2T bikes covered for power. This suggests an equivalence factor of around 1.6, maybe a little less. So a 2t F1 in the 3l formula would be ~1.875l.

That may give them equivalent power to the 4T, but what about the fuel efficiency?

DI 2T may have a leg up on port injected 4T, but what about DI 4Ts? Several manufacturers were playing with Sarich's Orbital 2 stroke, but lost interest as Di took over in regular production cars.

Under the current fuel flow formula the 2 stroke engines may be a little smaller and more compact, and woudl probably give around the same hp.

While the Crecy was an amazing device, I doubt that sleeve valve have much of a future in 2 strokes. It seems to be a case of, to quote Earnest Hives of Rolls-Royce: "Give it to us, we'll design teh simplicity out of it" (said referring to Whittle's jet).

[J.A.W.]

W, 4Ts wouldn't stand a chance - unless 2Ts were cruelled by a capacity handicap - as in bike racing..

Even though it could be reasonably argued that 2Ts ought to have their effective swept volume measured..
..from TDC to the exhaust port, & thus be due an actual capacity equivalency advantage over 4Ts..

Traditional 4T paths to power, via very high rpm or supercharging are comparatively very costly,
in complexity/cost/mass, & make a sleeve valve set-up look simple..

Not that a sleeve valve design would be any more likely to escape an F1 tech-ban than the BRV,
even if it was in a 4T mill..

[wuzak]

Even though it could be reasonably argued that 2Ts ought to have their effective swept volume measured..
..from TDC to the exhaust port, & thus be due an actual capacity equivalency advantage over 4Ts..

The fact of matter is that 4 strokes only have one intake event for every 2 revolutions. The effective capacity is half the nominal capacity (pumps half as much air as capacity implies). That's why the theoretical equivalence is 2.

The effective swept volume argument is why the real equivalence is something like 1.6.

If 2 strokes and 4 strokes competed with equal capacity basis then the 2 stroke will use a lot more fuel. So if fuel capacity is limited (to 100kg, say, like in F1) then they will not be able to run to their potential.

If airflow is limied (by a restrictor, as several racing classes do or have done) then the 4 stroke will be able to be bigger and/or rev harder.

If fuel flow is limited then the air required is set and the 4 stroke can be bigger in capacity and/or rev harder.

The fuel flow limit is, perhaps, the best rule under which the 2 stroke and 4 stroke could compete on equal terms.

[J.A.W.]

W, FYI - the Tim Hickox link - in the 2nd post from the top - of this page ..
.. refers to recent developments in 2T scavenge/BSFC which tend to contradict your efficiency view-point..

Also note the weight issue.. how much extra does the 4T mass/complexity cost?

[Andres125sx]

I know nothing about theory, but have some real experience with MX bikes. I´ve been riding a 250 2T for several years while all my friends switched to 450 4T

Power wise, 4t were a bit more powerfull, but difference was not huge

Fuel consumption was better for 4T and that´s providing a bit more power, so if the restriction is fuel flow, 4t will beat 2t hands down

Weight was better for 2t, not that much but I always wondered how much would weight a 2t with materials used on 4t as 2t were traditional material with no concerns about weight while 4t used modern materials like magnesium, aluminium more extensively, etc.

But you all are ignoring what IMHO is the most important factor, driveability or rideability. Here is were 4t makes a a world of difference, day and night. At this respect 2t simply can´t compete, they´re too sharp, too violent, too touchy.

This is nice for inventions like those videos JAW posted about the suzuki fronte, were the lack of power makes this problem irrelevant, but when you´re talking about powerful vehicles, driveability becomes as important as power, if not even more.

A 900hp 2t F1 would be simply undriveable, as simple as that. If some people complain about power delivery of turbo engines, that´s a smooth and progresive delivery compared to a 2t engine. No tires would handle that delivery.

And I love 2t engines, my KX 250 ´04 was awesome, I loved it, and with nice terrain (wet but with no mud) it could compete with 4t perfectly, but with slippery terrains (mud, hard and compact terrain) the difference was like if different categories. Actually even a 250 4t could beat a 250 2t with hard and compact terrain, traction and power delivery makes a world of difference, and IMHO that´s the reason 2t are something of the past, even when their power/litre is way better.

For invetions like Manolis flying machine 2t will be awesome, but for ground use with high power ratios, 4t are the way to go. You need to drive two competitive vehicles to realice how difficult to control 2t engines are.

[uniflow]

I know nothing about theory, but have some real experience with MX bikes. I´ve been riding a 250 2T for several years while all my friends switched to 450 4T

Power wise, 4t were a bit more powerfull, but difference was not huge

Fuel consumption was better for 4T and that´s providing a bit more power, so if the restriction is fuel flow, 4t will beat 2t hands down

Weight was better for 2t, not that much but I always wondered how much would weight a 2t with materials used on 4t as 2t were traditional material with no concerns about weight while 4t used modern materials like magnesium, aluminium more extensively, etc.

But you all are ignoring what IMHO is the most important factor, driveability or rideability. Here is were 4t makes a a world of difference, day and night. At this respect 2t simply can´t compete, they´re too sharp, too violent, too touchy.

This is nice for inventions like those videos JAW posted about the suzuki fronte, were the lack of power makes this problem irrelevant, but when you´re talking about powerful vehicles, driveability becomes as important as power, if not even more.

A 900hp 2t F1 would be simply undriveable, as simple as that. If some people complain about power delivery of turbo engines, that´s a smooth and progresive delivery compared to a 2t engine. No tires would handle that delivery.

And I love 2t engines, my KX 250 ´04 was awesome, I loved it, and with nice terrain (wet but with no mud) it could compete with 4t perfectly, but with slippery terrains (mud, hard and compact terrain) the difference was like if different categories. Actually even a 250 4t could beat a 250 2t with hard and compact terrain, traction and power delivery makes a world of difference, and IMHO that´s the reason 2t are something of the past, even when their power/litre is way better.

For invetions like Manolis flying machine 2t will be awesome, but for ground use with high power ratios, 4t are the way to go. You need to drive two competitive vehicles to realice how difficult to control 2t engines are.

But that is where development stopped for the 2T. With fuel injection I can show "real" control on the 2T. Missed injection cycles at lower rpm ( no fuel wasted ) can create 4T type traction, ECU controled throttle gets rid of the sharp power delivery. There is so much more to be had from the 2T, but no one is interested in development apart from the kart guys. I try on my limited budget but it's slow work. Results so far are encouraging ( YZ250 EFI , F9 Kawasaki ).

[J.A.W.]

A-125 is incorrect about 2T tractability, since GP bikes running at up to ~440hp/litre were clearly rideable.

The fact remains that the 250cc 4T Moto 3 replacement for 125cc 2T GP is still slower around the track..
(& ~7 seconds a lap slower than the 250cc 2T GP bikes..)

& it was the Aprilia Cube, a 1 litre 3cyl virtual slice off an F1 mill - that was expected to be the best power-to-weight
machine of the new Moto GP 4Ts - yet which turned out to be very difficult to ride, & failed to gain results..

That brutal power delivery was useable/normal in an F1 car, so the low inertia, low weight,quicker rpm response 2T,
would likely show its advantages in lap times like-wise in an F1 machine..

[riff_raff]

It is debatable whether the 2T 500cc GP bikes were truly "rideable". These bikes required expert throttle control to keep the engine within its power band.

However, I would love to see what an unlimited 2T F1 engine could do.

[J.A.W.]

Well r-r, certainly they took some riding talent.. ..but then bikes always require more than cars..

As for rideability.. check this out.. https://www.youtube.com/watch?v=28dbVSAu65g
If they were on porky, unforgiving 4T Moto 2s, some riders would likely have been killed..

Ask M.Doohan.. ..He won X 5 - 500cc World Championships..
..He was one of - very few - WSBK (4T Superbikes) race winners to go on to do well on 2Ts..

Or, as the likes of V.Rossi reckons.. that current Moto GP ( 'cept for Ducati..)is rather too easy..

& C.Stoner rates 4T Moto GP as "boring", even though he was - solely - able to put the difficult
to ride Ducati around the track - to consistent winning effect,
- but adds that he'd loved to have had the opportunity to race 2T 500s, & would return - if they did..

I do agree on your wish to see a full-house 2T F1 mill - in action - though..