2 stroke thread (with occasional F1 relevance!)

[uniflow]

Lock them both ( 2t, 4t) at 500cc, allow DFI ( for both if you like ) and then lets see what happens?

[J.A.W.]

Lastly, why are engine types abbreviated to 2T & 4T instead of 2S & 4S?

Well, it's probably a German thing where T means Takt, which is the same as stroke.

Regarding the bsfc of the two and four stroke motorcycle engines, this document(page 16) from http://www.grandprixengines.co.uk states that in 2002, both 500cc 2S and 990cc 4S engines were allowed and that the 4S type was more efficient. The limits on fuel consumption(24l for 4S and 32l for 2S for the race) seem to confirm that.

And the 4 strokes had 40-50hp more, not even achieving (or trying to) the specific power of F1 engines at the time.

That academic style article fails to note that while 500cc GP bikes ceased development in 2002 & were subsequently
banned altogether, the 2T GP engine continued developmental power improvement with its 125cc based cylinder,
& gave quicker lap times - right up to the time where the 250cc twins, & then 125cc singles were also banned..

As W notes, attempts to directly utilize F1 engine tech for GP bikes - viz the 3cyl Aprilia Cube, failed..

Bike engines need to be more controllably progressive in their power characteristics, particularly on part
throttle, & ironically although significantly higher in specific output, 2T's with their low rotational inertia,
& lower mass, proved more amenable to skilled control.

4T's needed expensive 'fixes' from 'slipper' clutches ( to reduce fierce 'engine braking') & extensive electronics
suites to for fuel injection/torque limitation/traction control & etc..

As E. Bugatti said about the Bentley.. Moto GP became "The fastest trucks in the world"..

I note that the Moto 3 250cc 4Ts - which replaced the 125cc 2Ts - are yet to improve on 125 race speeds/lap times..

[Tommy Cookers]

if we scale down our N/A F1 engine from before the rpm limit days to 125 cc cylinders as J.A.Ws 2 stroke
the bore and stroke become 73.7% of their original value

we can run at 16.5% more rpm for the same piston acceleration as the original
or (conceptually) 35.6% more rpm for the same piston speed as the original

given that the piston weight will tend towards 40% of the original's piston weight
I guess that we can actually run 22% faster
and so get say 22% more bhp/litre than the original (eg consider that at this rpm piston speed will be less than originally)

so whether we look at the 2001 GPs vs 2001 F1 or 2013 2 strokes vs 2013 F1 (without the rpm and other freeze restrictions)
the F1 4 stroke has overcome the conventional 2 stroke's bhp/litre dominance of the 70s - 90s

to put it another way, consider scaling up the 125cc 2 stroke cylinder to the 300cc F1 cylinder size
the max rpm would fall imo by more than 22% (consider the piston weight tends towards 250% of the original's weight)
the port areas will be increased by only 84.1% so the power/litre will fall by more than 22%
(similarly the race 350 Yamahas always had less bhp/litre than their related 250s because the 350 port areas were relatively smaller)

and with 8 or 10 cylinder 2 stroke the bore spacing will be rather large (because the ports consume a lot of space)
so the engine won't be specially light or compact (the reason outboards kept deflector-piston porting not loop-scavenge)

[J.A.W.]

Very speculative there T-C, & in the absence of actually operational 2T F1 engines - as proof..
..sadly they were, & are.. very much on the BANNED list.. ..so we wont know for sure..

4Ts have to be built much more heavily to stand the very high rpm &/or boost levels required to overcome
their inherently lazy 1/2 speed BMEP production. OHC drives/poppet valves are also mass-bulky.. & expensive..

Those proven 55hp 125cc 2T cylinders could make a 1320hp N/A 3.0 litre H-24 engine, if rules allowed..
No N/A 4T F1 3.0 litre mill got anywhere near that output..

[uniflow]

If the engines are a V configuration then wide ports have no relevants.
Can a N/A 125 single 4T develop more than 55HP? Soon 125cc 2T will be around 60HP.
The exhausts would be more of a problem than the cylinder spacing.

[Tommy Cookers]

......Those proven 55hp 125cc 2T cylinders could make a 1320hp N/A 3.0 litre H-24 engine, if rules allowed..
No N/A 4T F1 3.0 litre mill got anywhere near that output..

Renault said that they had bench run at 23000 rpm (maybe their 111 deg engine ?)
Honda once said that they had a 1000 bhp in qualy trim capability back at the factory
a lot of power was recovered after the rpm cut to 18000, then 17000, and the injection and induction manifold cutbacks

so using all the goodies, maybe 1080 bhp could be found from the 3 litre 10 cyl or pro rata from the 2.4 litre 8 cyl
and (as I'm saying) the 24 cyl 3 litre 4 stroke should give 22% more specific power than those
there's the 1320 bhp (at 25000+ rpm)

[J.A.W.]

Yeah - Honda eh..

Honda tried real hard to compete with its super-high rpm 4Ts against the 2Ts..
.. in GP bike racing, both in smaller classes ( 5cyl 125cc) in the `60s..

& later with a 500cc oblong piston V4 ( defacto V8) spinning at 22,000+rpm ..
all the while spending like a drunken sailor on liberty, but still had to admit defeat, & go 2T to win..

This was unacceptable to the core Honda 4T ethos..

So a rules change to accommodate 4Ts was necessary, & then an actual explicit ban on 2Ts..

If you want a sardonic laugh, do check out the moronic/ludicrous engine history section at the Moto GP site..

[Pierce89]

Yeah - Honda eh..

Honda tried real hard to compete with its super-high rpm 4Ts against the 2Ts..
.. in GP bike racing, both in smaller classes ( 5cyl 125cc) in the `60s..

& later with a 500cc oblong piston V4 ( defacto V8) spinning at 22,000+rpm ..
all the while spending like a drunken sailor on liberty, but still had to admit defeat, & go 2T to win..

This was unacceptable to the core Honda 4T ethos..

So a rules change to accommodate 4Ts was necessary, & then an actual explicit ban on 2Ts..

If you want a sardonic laugh, do check out the moronic/ludicrous engine history section at the Moto GP site..

Well you've at least got to admit Honda's oval piston v4(8) made the most haunting sound ever heard from a motorcycle.

[J.A.W.]

No way..

My pick for most "haunting" racing motorcycle sound?

Try running the Daytona sequence from the movie classic - 'On Any Sunday'..
.. with the factory BSA/Triumph F 750 triples fanging around the banking..
.. & on a decent sound system at a good volume level..

Now - that's what I reckon to be.. "haunting"..

[flynfrog]

No way..

My pick for most "haunting" racing motorcycle sound?

Try running the Daytona sequence from the movie classic - 'On Any Sunday'..
.. with the factory BSA/Triumph F 750 triples fanging around the banking..
.. & on a decent sound system at a good volume level..

Now - that's what I reckon to be.. "haunting"..

I had to dig this out and watch it now.

[J.A.W.]

Yeah baby!
So did I, & did you dig that "eerie moaning howl" ?
Sounds almost 2-stroke like - in a way..

& there really is something attractively tonal - about regular firing multiples of 3..

[flynfrog]

Ive always been a tz sucker

[J.A.W.]

Firing 2 cylinders at once, the TZ inline 4 sounds much like the twin,
& for sure - they're not as tuneful/musical sounding as a 120`triple..

Def' not "haunting" either.. ..more of a brassy blowfly buzzing.. ..not that there's anything wrong with that..

[bdr529]

https://www.youtube.com/watch?v=VbH2vMoGvaw


Ive always been a tz sucker

I can't say any thing bad about the TZ, but I have to go with the 83 Honda NS 500 3 cyl. it's got that classic chainsaw sound

No way..
My pick for most "haunting" racing motorcycle sound?
Try running the Daytona sequence from the movie classic - 'On Any Sunday'..
.. with the factory BSA/Triumph F 750 triples fanging around the banking..
.. & on a decent sound system at a good volume level..
Now - that's what I reckon to be.. "haunting"..

My pic for "haunting" motorcycle sound
MV Agusta 500 3cyl.

[Tommy Cookers]

good post J.A.W ! (the 50cc Suzuki 3 cyl in the other thread)
reminds us that smaller cylinders give more favourable port sizes (in any type of engine, including the Sabre)
Kaaden advocated something similar to the Suzuki

the NR500 Honda was rumoured to have run without piston rings (not really needed at high rpm)
at Silverstone I saw it doing about 100 mph with the engine stopped and unstartable (a likely symptom of ringlessness)
both riders (Mick Grant and Barry Ditchburn) dwarfed the machine
unlike the MV Ags it was quiet (due to the noise limit from 1977 on)

the 2 stroke (DKW copy engine) Saab won the big rallys around 1960
and the Auto Union & DKW cars had credibility
the early Audi was really the castoff V6 DKW 2 stroke car with a high turbulence 4 stroke castoff Merc engine
Lorenzo Bandini driving the 3 cyl 2 stroke Berkeley (Brit sportscar) won in class at Monza, beating all the Fiats (1960?)
and those 350 Bridgestones and Kawasakis with their big shiny disc-valve layout had real credibilty, before ''superbikes' existed

iirc the Ford Ka was intended to have a supercharged 2 stroke (that's why the engine bay was so small only the pushrod 4 strokes fit)
low in NOx, so needing only an oxidation catalyst (and no closed loop sensor)
the leap in Europe straight to the 3 way catalyst (by tightening NOx limits) killed it