2 stroke thread (with occasional F1 relevance!)

[Tommy Cookers]

the post quoting R-2800 procedures shows turning starter-on ignition-off was used as a check on hydraulic lock (due to any pooling engine-off)
presumably oil scavenge layout was arranged out to prevent pooling in running

http://www.airliners.net/forum/viewtopic.php?t=761365
http://forum.keypublishing.com/showthre ... il-systems

this includes mention of kits for recirculating oil from low cylinders
http://www.pprune.org/archive/index.php/t-257627.html

btw some might learn from the incidental examples of 3000-4000 hr TBO (TBO the actual on-condition figure not the 'book' figure that now gets quoted)
an airforce (regulator-exempt of course) wanting to keep engines can do a lot, an airline that wants new engines or aircraft can do the opposite
and this (post by Walter Atkinson)http://www.pprune.org/archive/index.php/t-533489.html
elsewhere a poster says his employers ordered QECs (quick engine change ?) when plugs needed renewal on 28 cyl R 4360s

and some Centaurus photos
http://www.practicalmachinist.com/vb/an ... =centaurus

[Pinger]

Thanks TC - much appreciated.
Couldn't access the lubrication line pics linked in one of your linked pieces but guessing that while running there was some rudimentary scavenging (from the base of the lowest cylinder?) of oil back to the tank. Parked up - well the guys knew what to check for!

Currently reading the (very interesting) RR book on the Crecy - and it occurred to me that apart from Uniflow's sleeve valve motor, I'd never heard of a sleeve valve engine that didn't employ a forced lube system (ie not petroil). Is Uniflow's one the only one in existence? (The comments in the Crecy book re cold starting with the difficulty of overcoming the viscous friction on both sides of the sleeve was an eye-opener. Presumably straight grade oils at the time and a modern day multigrade would be more forgiving).

[Tim.Wright]

Obviously, given 2 engines with identical peak power but one with a flat torque curve and the other with a rising torque curve, you are going to accelerate much faster with the constant torque motor.

Not necessarily T.W., see the dyno charts linked below.. & compare the two Kawasaki machines..
http://www.kawtriple.com/mraxl/articles ... bikes2.htm

The 4T 900/4 develops nearly identical peak hp to the 2T 750/3, via flat torque, spinning @ higher rpm..

As for actual on road effects: https://www.youtube.com/watch?v=1N5rm0glYwY

Those plots prove exactly my point if you look at them properly. Taking into account the different rev limits the 903 is producing 63HP at 80% of its rev limit while the 750 is only making only 60HP. I.e. the 4T has got a wider power band because of the better torque it produces at lower engine regimes.

Same deal after the power peak where the 903 exhibits less power drop-off. In fact, the 903 plot has a mistake in it. If it really does make the torque curve shown then the power plot is wrong from 8000rpm onwards. It would actually make 68HP not 64HP peak precisely because it has a flatter torque curve with less drop off after it's peak.

Basically, those plots prove that you have more tractive power both above and below the peak power operating point if your torque curve is flatter. The exact opposite of what you are trying to prove - well done.

As for actual on road effects - your video is again a perfect example of why a rising torque is a disadvantage. It's a slug from stand still and has more power than it can put down at higher engine speeds. Driveability is reduced and you are slower through the rev range.

BTW: the 0.1s diff in the ET in favour of the 750 is due it being 33kg lighter - giving it 10% more acceleration capability than the 903 for the same power.

[J.A.W.]

Again T.W., not necessarily..

The video hardly shows a 2T "slug" - its running a simple throttle roll on.. & yet 'wheelies' effortlessly..
In the linked test - the description of a quick start is even more dramatic:

"It bolts out of the gate so hard that moving your feet up to the footpegs is a major effort."

A really proficient rider could clip another 1/2 second or so, off the time the magazine recorded..

Having the torque peak rising close to the hp peak rpm-wise also assists in pulling top-end speed more rapidly..
& as the text reports, the gearing ensures the 'punch' of its rising torque 'hit' is always available..

[Tim.Wright]

Again T.W., not necessarily..

Yea necessarily. That's the nice thing about physics - it's true even if you don't believe it...

If you think about it logically you'll understand why. Given two engines with same peak power, the one with the rising torque curve will, by definition, have less rear wheel torque than one with a flat torque delivery at every operating point apart from that of the peak power.

As shown by the dyno results you posted:

[J.A.W.]

Ah, T.W., good effort at providing a classic example of the old 'lies, damned lies, & statistics' saw..

In fact if you refer to the dyno charts, you will see that the 2T 750/3 makes significantly higher torque..
..than the 4T 900/4, all the way from around 3,000 rpm to well above its (soft tune) power peak at 7,000+ rpm..

[gruntguru]

Nice analysis Tim. I have often mused on the best way to compare motors with very different torque characteristics. The plot you posted gives a very useful representation although I think the use of "rpm limit" for re-scaling the speed axis will produce variable results.

"Peak power rpm" might be a better choice although it gives an undeserved advantage to an engine that has a rev limit very soon after the power peak.

Perhaps "Peak power minus 5%" would work?

The other thing people often misunderstand is "width of power band". You might hear "the power band spans 3,000 rpm - awesome!" The reality is 3,000 rpm is very narrow for a 20,000 rpm F1 engine whereas truck engine with a power band from 1,200 to 2,200 has a very "wide" power band.

So "width of power band" needs to be defined as a percentage of the total rev range (or better still - a percentage of the peak power rpm) so an engine that makes more than 80% of its peak power from 4,000 to 8,000 and peak power at 6,000 would have a "80% power band" of (8,000-4,000)/6,000 = 0.66 (66%) which would be a very wide power band indeed.

[gruntguru]

Ah, T.W., good effort at providing a classic example of the old 'lies, damned lies, & statistics' saw..

In fact if you refer to the dyno charts, you will see that the 2T 750/3 makes significantly higher torque..
..than the 4T 900/4, all the way from around 3,000 rpm to well above its (soft tune) power peak at 7,000+ rpm..

Although torque and power define each other in terms of rpm, it is only power that should be compared between engines - rpm becomes irrelevant - the engines should be compared using a dimensionless speed.

Which is why an analysis like Tim's is needed - to provide the real answer. Done properly, it becomes possible to compare completely different engines - a 20,000 rpm gas turbine with very little torque can be compared to a 1,000 rpm locomotive engine with similar power and their relative ability to haul a train can be assessed.

[J.A.W.]

Ah, T.W., good effort at providing a classic example of the old 'lies, damned lies, & statistics' saw..

In fact if you refer to the dyno charts, you will see that the 2T 750/3 makes significantly higher torque..
..than the 4T 900/4, all the way from around 3,000 rpm to well above its (soft tune) power peak at 7,000+ rpm..

Although torque and power define each other in terms of rpm, it is only power that should be compared between engines - rpm becomes irrelevant - the engines should be compared using a dimensionless speed.

Which is why an analysis like Tim's is needed - to provide the real answer. Done properly, it becomes possible to compare completely different engines - a 20,000 rpm gas turbine with very little torque can be compared to a 1,000 rpm locomotive engine with similar power and their relative ability to haul a train can be assessed.

& yet, gg, if you refer to the dyno charts, you will see that the 2T 750/3 makes significantly higher horsepower..
..than the 4T 900/4 all the way from around 3,000 rpm to well above its ( soft tune) power peak at 7,000+ rpm..

Ooh, that's spooky.. a bit of technical deja vu.. happening there.. & which provides "...the real answer."

That is, the rider of the 2T 750/3 is going to enjoy a more potent powerband than the 'flat torque' 4T 900/4 rider..
..since even if the apparent advantage of the higher 4T rpm range is used, a gearchange by the 2T will nullify it..

Again gg, this is the practical/experiential - "...real answer." - rather than T.W.'s esoteric mathematical exercise..

[gruntguru]

Ah, T.W., good effort at providing a classic example of the old 'lies, damned lies, & statistics' saw..

In fact if you refer to the dyno charts, you will see that the 2T 750/3 makes significantly higher torque..
..than the 4T 900/4, all the way from around 3,000 rpm to well above its (soft tune) power peak at 7,000+ rpm..

Although torque and power define each other in terms of rpm, it is only power that should be compared between engines - rpm becomes irrelevant - the engines should be compared using a dimensionless speed.

Which is why an analysis like Tim's is needed - to provide the real answer. Done properly, it becomes possible to compare completely different engines - a 20,000 rpm gas turbine with very little torque can be compared to a 1,000 rpm locomotive engine with similar power and their relative ability to haul a train can be assessed.

& yet, gg, if you refer to the dyno charts, you will see that the 2T 750/3 makes significantly higher horsepower..
..than the 4T 900/4 all the way from around 3,000 rpm to well above its ( soft tune) power peak at 7,000+ rpm..

Ooh, that's spooky.. a bit of technical deja vu.. happening there.. & which provides "...the real answer."

That is, the rider of the 2T 750/3 is going to enjoy a more potent powerband than the 'flat torque' 4T 900/4 rider..
..since even if the apparent advantage of the higher 4T rpm range is used, a gearchange by the 2T will nullify it..

Again gg, this is the practical/experiential - "...real answer." - rather than T.W.'s esoteric mathematical exercise..

Nothing esoteric about that. The problem here is you are comparing a lower-speed engine. If you put both bikes in a gear that gives the same road-speed at red-line, you find that the 4-stroke has more power at every road-speed.

It is like saying the diesel locomotive engine has more power at every speed from 100 - 1000 rpm than the gas turbine.

[J.A.W.]

No gg, actually - its quite the opposite..
..since in the real world, of everyday road use -very little time indeed is spent in the last 1,000 rpm up near 'redline'..
..& even in racing, that last 1,000 rpm will not compensate for the time/ground lost in the previous several thousand..

[Tim.Wright]

Gruntguru, I agree about normalising at peak power. An even better way to represent the problem would be to use the gear ratios and plot the tractive force in function of vehicle speed for each gear. This will effectively show the shift points as the moments when the tractive force from one gear crosses another gear.

As for j.a.w... You never have had the faintest idea about any of this kind of stuff have you. Engine torque means precisely squat in these comparisons. As shown by the practically identical ET's over the quarter mile.

[J.A.W.]

Gruntguru, I agree about normalising at peak power. An even better way to represent the problem would be to use the gear ratios and plot the tractive force in function of vehicle speed for each gear. This will effectively show the shift points as the moments when the tractive force from one gear crosses another gear.

As for j.a.w... You never have had the faintest idea about any of this kind of stuff have you. Engine torque means precisely squat in these comparisons. As shown by the practically identical ET's over the quarter mile.

& I'm guessing t.w., that you have "squat" time running the 1/4 mile - in the saddle of either of these machines..
.. certainly seems so - from not having the "faintest idea" about the actual variables - outside your pocket calculator..

Since, as I noted earlier, the livelier 2T machine requires more riding skill to get the very best from it..
.. but - as the test shows.. it still does enough, even with a circumspect rider - to shut down the bigger machine..

(FYI, a quick way to do an 'on paper exercise' testing your query..
..would be to imput the specific data sets into the 'analyzer' link posted in the previous page, 2nd last post).

[J.A.W.]

An even better way to represent the problem would be to use the gear ratios and plot the tractive force in function of vehicle speed for each gear. This will effectively show the shift points as the moments when the tractive force from one gear crosses another gear.

Curiously, a decades old mech-tech text book uses the 2T 750/3 under current discussion - via its 'running performance curves'...
..based on the period Kawasaki factory data..

& duly notes:
"The 1st-gear curve shows a driving force of 550 pounds at a speed of about 40 mph. With a lightweight rider, bike & rider could weigh less than 550 pounds.If there were traction, (s)he could ride this superbike straight up at 40 mph!"

A little excitable perhaps, but it both confirms what the video shows, & what Manolis intends to demonstrate - in one..

( Edit: comment about dubious downvotes received above in this page deleted,.. issue duly referred by report per policy) ..

[J.A.W.]

@ T-C, I thought this might be of interest, a home-build 2T (development of KX 250) claiming 72.9 hp from a 211cc cylinder..
https://www.youtube.com/watch?v=bEKxrJZGeTQ

& for Manolis..

Here below - is a 4T rotary sleeve valve design which was made commercially, but failed..
..due to, as the makers note - problems with heat flows, even on the small scale..

http://www.rcvengines.com/technology_ro ... valve.html