2 stroke thread (with occasional F1 relevance!)

[Tommy Cookers]

Alcohol fuels run cool, as such usage of methanol as a race fuel allows 'classic' air-cooled bikes to
run sans the power-robbing heat-soak they suffered from by racing on petrol, back then.

there is no such thing as 'power-robbing heat soak'
engines work by in-cylinder conversion of heat into work

the amount of alcohol that can burn in-cylinder adds more heat in-cylinder than does the equivalent amount of petrol
roughly 5% more with ethanol and 10% more with methanol
it's simple chemistry

that's why 'they' use methanol
that's how methanol gives about 10% more power without any increase in the CR

people should get this into their heads
the methanol engine should have the same gas temperature pre-spark as should the petrol engine
cylinder cooling was generally reduced for methanol use eg the JAP speedway engine that won about 20000 races

yes even if cylinder cooling wasn't reduced power would still be better - hence the 'cool is good' myth
usually methanol is overfuelled because the jets had anyway to be huge ... and ....
methanol's much wider explosive range allowed/encouraged far more over-fuelling than would petrol

[johnny comelately]

Alcohol fuels run cool, as such usage of methanol as a race fuel allows 'classic' air-cooled bikes to
run sans the power-robbing heat-soak they suffered from by racing on petrol, back then.

there is no such thing as 'power-robbing heat soak'

the amount of alcohol that can burn in-cylinder adds more heat in-cylinder than does the equivalent amount of petrol
roughly 5% more with ethanol and 10% more with methanol
it's simple chemistry

that's why 'they' use methanol
that's how methanol gives about 10% more power without any increase in the CR

why can't people get this into their heads ?

The piston soaks it up by negative egress and changes phase thus robbing power (hybridised comment )

[J.A.W.]

Alcohol fuels run cool, as such usage of methanol as a race fuel allows 'classic' air-cooled bikes to
run sans the power-robbing heat-soak they suffered from by racing on petrol, back then.

there is no such thing as 'power-robbing heat soak'
engines work by in-cylinder conversion of heat into work

the amount of alcohol that can burn in-cylinder adds more heat in-cylinder than does the equivalent amount of petrol
roughly 5% more with ethanol and 10% more with methanol
it's simple chemistry

that's why 'they' use methanol
that's how methanol gives about 10% more power without any increase in the CR

people should get this into their heads
the methanol engine should have the same gas temperature pre-spark as should the petrol engine
cylinder cooling was generally reduced for methanol use eg the JAP speedway engine that won about 20000 races

yes even if cylinder cooling wasn't reduced power would still be better - hence the 'cool is good' myth
usually methanol is overfuelled because the jets had anyway to be huge ... and ....
methanol's much wider explosive range allowed/encouraged far more over-fuelling than would petrol

"Cool is good" is no "myth", high output crankcase induction 2Ts must run cool, for G.P. racing they
went to water-cooling; non-ferrous cylinder liners; pumped gear-set lubrication (to keep hot oil low),
auxiliary injector jets on closed throttle over-run, & other needful developments.

Heat soak/power fade is real, along with the razor-edge tune required to make best power yet not
run hotter as a result for hard-tuned air-cooled 2Ts.

Alcohol-based fuels not only offer a significantly better 'latent heat' cooling effect for crankcase
induction, it is markedly less sensitive to exactitude in jetting, being far more tolerant of rich
mixtures which aid top-end cooling.

Anyone with experiential/empirical - 'hands on' knowledge of these things knows it to be a fact...

[johnny comelately]

Some light hearted 2 stroke comparisons sort of entertainment

[johnny comelately]

500 Gas Gas (KTM) gas exchange (BRC Racing) using TPI which you can see

[J.A.W.]

500 Gas Gas (KTM) gas exchange (BRC Racing) using TPI which you can see
https://images-wixmp-ed30a86b8c4ca88777 ... tfZxZ6O8SY

Yeah, &...?

Well, anyhow Johnny, this mob reckon they can do a 600cc 2T roadbike:

https://brcracing.ca/brc-r600/

[J.A.W.]

2-stroke high-performance research-development continues, (even if excluded from Moto GP),
hit the link posted below to see how a commercially available kit enables a humble 2T Vespa
scooter to pump out 44hp!

https://scooterlab.uk/quattrini-adds-30 ... ts-tuning/

[J.A.W.]

By comparison, here's a recently designed 250cc twin (in road-tune) on the dyno: 76hp @ 11,800rpm.
(So, a fair bit more hp/litre than the current Moto GP bikes, & it also shames the tedious Moto 3 4T 250's)

[Tommy Cookers]

By comparison, here's a recently designed 250cc twin (in road-tune) on the dyno: 76hp @ 11,800rpm.

road-tune means a continuously progressive torque curve (not the now biker-normalised partly degressive one)

isn't it is now a certification requirement ? - (it should be)
continuously progressive and better than F1's 'monotonically rising'

because ....
a machine on freeway-type roads should never need downshifting
a machine there should be controllable eg at night for wind and slope and manoeuvre by twistgrip position only

middle-aged car drivers (in talk about EVs) now speak the hitherto-unspeakable ....
that their driving pre-EV has been dictated by the modern car's devalued torque curve
(though they don't mention their effect on the driver behind)

not so long ago even 2-stroke cars had 3 gears (not 6 or 7)

[J.A.W.]

By comparison, here's a recently designed 250cc twin (in road-tune) on the dyno: 76hp @ 11,800rpm.

road-tune means a continuously progressive torque curve (not the now biker-normalised partly degressive one)

isn't it is now a certification requirement ? - (it should be)
continuously progressive and better than F1's 'monotonically rising'

because ....
a machine on freeway-type roads should never need downshifting
a machine there should be controllable eg at night for wind and slope and manoeuvre by twistgrip position only

middle-aged car drivers (in talk about EVs) now speak the hitherto-unspeakable ....
that their driving pre-EV has been dictated by the modern car's devalued torque curve
(though they don't mention their effect on the driver behind)

not so long ago even 2-stroke cars had 3 gears (not 6 or 7)

The dyno power curves produced are charted & may be seen by viewing the video, but
IIRC, Suzuki 250cc 2T road bike twins featured 6-ratios in the gearbox from the mid 1960s,
(indeed one of the sales points of Royal Oilfield's 1960s 4T 250cc 'GT' was a 5-speed box).

The excitingly 'sporty' feel of a lightweight 2T 'roadster' is a desired quality for the well-heeled
buyers of this 'bespoke/exclusive' (expensive) machine, (& ironically, that 'sporty' 2T attribute was
regarded as 'a negative' by 'ordinary' drivers who used Orbital 2T powered small cars on long-term
regular road use evaluation ~1/4 century ago).

A 'road tune' in the current instance, involves various 'soft' outputs, from power curves to sound levels,
by comparison to 'track/race' tune.

[Big Tea]

By comparison, here's a recently designed 250cc twin (in road-tune) on the dyno: 76hp @ 11,800rpm.

road-tune means a continuously progressive torque curve (not the now biker-normalised partly degressive one)

isn't it is now a certification requirement ? - (it should be)
continuously progressive and better than F1's 'monotonically rising'

because ....
a machine on freeway-type roads should never need downshifting
a machine there should be controllable eg at night for wind and slope and manoeuvre by twistgrip position only

middle-aged car drivers (in talk about EVs) now speak the hitherto-unspeakable ....
that their driving pre-EV has been dictated by the modern car's devalued torque curve
(though they don't mention their effect on the driver behind)

not so long ago even 2-stroke cars had 3 gears (not 6 or 7)

The dyno power curves produced are charted & may be seen by viewing the video, but
IIRC, Suzuki 250cc 2T road bike twins featured 6-ratios in the gearbox from the mid 1960s,
(indeed one of the sales points of Royal Oilfield's 1960s 4T 250cc 'GT' was a 5-speed box).

The excitingly 'sporty' feel of a lightweight 2T 'roadster' is a desired quality for the well-heeled
buyers of this 'bespoke/exclusive' (expensive) machine, (& ironically, that 'sporty' 2T attribute was
regarded as 'a negative' by 'ordinary' drivers who used Orbital 2T powered small cars on long-term
regular road use evaluation ~1/4 century ago).

A 'road tune' in the current instance, involves various 'soft' outputs, from power curves to sound levels,
by comparison to 'track/race' tune.

The Suzuki 'super six' T20 and T200 'invader' came out in 1966 and at the time some 4 strokes still had 3 gears. I think it was 1969 when the small BSA got a 4 speed.

[Pinger]

It's quite surprising to note the spread between lowest ratio (1st) and top gear on any gearbox is really very slight - around three, Eg, an Aprilia RS 125 (Rotax 122) has circa 3:1 1st gear and around 1;1 sixth gear. The 4sp auto behind a 5.7l SBC V8 has 1st gear ratio of 2.48:1 and 4th at 0.75:1.Two very different engines with very similar spans across the range of ratios. A greater amount of ratios merely allows operation over an ever narrower rpm band where efficiency has been maximised.

A 2T doesn't have to have its torque biased toward the top of the rpm range. See outboards where low down torque to get them 'out of the water' is what matters.



More to the point though, rather than niche race engines what is needed are 2Ts capable of running on either bio or synthetic fuels, the former being less volatile than gasoline which when injected directly into the cylinder already has vaporisation difficulties.
When the realisation that electrification is not viable for all applications that were once IC dominated, and/or the supporting infrastructure is found wanting and tooling for 4Ts has been scrapped, there will IMO be a need for a simple cheap to build, easy to tool for short gestation period engine capable of running on whatever fuel is available. Step up 2T!

[J.A.W.]

It's quite surprising to note the spread between lowest ratio (1st) and top gear on any gearbox is really very slight - around three, Eg, an Aprilia RS 125 (Rotax 122) has circa 3:1 1st gear and around 1;1 sixth gear. The 4sp auto behind a 5.7l SBC V8 has 1st gear ratio of 2.48:1 and 4th at 0.75:1.Two very different engines with very similar spans across the range of ratios. A greater amount of ratios merely allows operation over an ever narrower rpm band where efficiency has been maximised.

A 2T doesn't have to have its torque biased toward the top of the rpm range. See outboards where low down torque to get them 'out of the water' is what matters.

https://1drv.ms/u/s!AiiEuyCZ7ElP2EUU_RlFJ3S6SkxX

More to the point though, rather than niche race engines what is needed are 2Ts capable of running on either bio or synthetic fuels, the former being less volatile than gasoline which when injected directly into the cylinder already has vaporisation difficulties.
When the realisation that electrification is not viable for all applications that were once IC dominated, and/or the supporting infrastructure is found wanting and tooling for 4Ts has been scrapped, there will IMO be a need for a simple cheap to build, easy to tool for short gestation period engine capable of running on whatever fuel is available. Step up 2T!

Evinrude (BRP) did offer those (long-wanted by the military) multi-fuel options with their E-TEC 2Ts,
but BRP canned Evinrude in the early days of the Covid 19 epidemic (likely a contra-deal 'business call'),
unfortunately...

There are many possibilities for clean-tech 2Ts, from small handy power units, up to large generation
units, based - as ever - on power-density/mass/packaging potential...

[Pinger]

Evinrude (BRP) did offer those (long-wanted by the military) multi-fuel options with their E-TEC 2Ts,
but BRP canned Evinrude in the early days of the Covid 19 epidemic (likely a contra-deal 'business call'),
unfortunately...

I recall seeing those at the time - but they seem to have disappeared from the internet. From what I recall, an adaptation of E-TEC (high pressure direct injection) engines.

There are many possibilities for clean-tech 2Ts, from small handy power units, up to large generation
units, based - as ever - on power-density/mass/packaging potential...

At very large scale diesel 2T is prevalent (but suffering (piston/ring scuffing IIRC) from the lower sulphur content fuel in marine application) and will likely endure for some considerable time.

E-TEC and Orbital based air assisted systems are effective to a point - but have had to be supplemented with injection into either the crankcase or transfer ports for higher rpm operation eg, sleds - lack of fuel volatility being crucial here.

But still nothing for smaller scale (handheld) beyond the limited HC emissions reduction from stratified charge has increased their chance of survival.

And, despite the (almost complete) reduction of HC emissions in 2T outboards with the E-TEC and Orbital based air assisted systems, those engines have all but disappeared from the market to be replaced by 4Ts - for no obvious reason. Is DI inherently flawed? Why reject it in favour of heavier, more complex, less power dense, higher NOx emitting, more expensive to build 4T?

Are there any other 2T technologies available that would make 2T the go-to engine when electrification is found wanting?

[J.A.W.]

The US/NATO military have put funds into Cummins development of 2T opposed-piston CI engines with multi-fuel
capability, & see below for a vid showing development progress on a backyard shed built O-P unit with crankcase
pumping intake controlled by a disc-valve featuring a sliding-shutter intake-tract (plus internal F.I.), as hand-made
by member here, 'Uniflow':