2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello J.A.W>

You write:
"I'll add this actual test result, obtained by a skilled rider, who got into the mid 12 sec range on 1/4 mile acceleration,
& tucked in well for the top-end run.. (albeit it is an earlier, lesser-powered, if evidently well-tuned 1983 RZ 350)."


In the graphs generated by the RoadLoad program for the Yamaha RD350LC the total load (i.e. the weight of the "rider, passenger and luggage") has been taken as 170Kp (375lb).

With only a rider weighing 80Kp (175lb), the time for the 400m (~ 1/4 of a mile) drops at 12.36sec (speed at the end of the 400m distance: 164Km/h).

With only a rider weighing 50Kp (110lb), the time for the 400m (~ 1/4 of a mile) drops to 11,9sec with the exiting speed at 168Km/h.

Thanks
Manolis Pattakos

[J.A.W.]

Thanks Manolis..

The skill variables of actual riding performance do of course show in 'real-world' results..
..for example in the 2T 750/3 VS 4T 900/4 test under recent discussion..

For the 1/4 mile acceleration tests, the 2T was geared down by use of an optional lower final drive ratio..
..as might be done in a sports competition event by enthusiast/expert riders..
..but in the actual test event, this evidently caused difficulties for the magazine staff test-riders..
..by making the launch/start more problematic, given the violent clutch/tyre-traction/wheel-stand trade-off..

Further, the gearing down measure meant that the 2T had 'topped out' max power rpm-wise before the end of the 1/4 mile, thus effectively losing speed/time at both ends of the 1/4 mile test strip.. meanwhile the easy launching,
more docile, higher revving 4T was still gaining speed - to cross the line at a (fractionally) higher top speed..

As I noted previously, the sporting 'competition record' for the stock production 2T 750/3 Kawasaki was in the high 11 sec range, a better figure obtained due to riding skill.. ( 'Factory' claim was 12.0 sec).

[manolis]

Hello Tim.Wright

You write:
"Nice program. Obviously this is the best way to compare powertrains if you have the complete gearing information. How do you deal with the initial launch phase where you are grip and/or wheelie limited?"


In the "Soft use of clutch" mode, at the beginning of the acceleration the rider keeps the engine at the revs wherein the torque curve starts.

In the case of the RD350LC of the example , this is the point at 3,500rpm / 4Kp*m (40mN).

This way, the rider has, until the clutch to engage completely (no slip) 4Kp*m (~ 40mN) of torque from the engine.

This is shown in the plot under the title: "Soft Use of Clutch": from 0Km/h to 25Km/h the accelerating force from the engine equals to the force available at 25Km/h (3,500rpm for the engine).
The slight drop of torque of the RD350LC after the 3,500rpm means that after the full engagement of the clutch at 3,500rpm,the accelerating force from the engine drops a little (util the speed to get at 31km/h) and then it increases again.

Worth to mention: from 49 to 53Km/h the accelerating force drops (because of the "hole" at 7,500rpm of the torque of the RD350LC) and then it increases again until the 56Km/h (8,000rpm) wherein the torque curve has a "local peak".



In the "Hard use of clutch" mode, during the initial acceleration the rider keeps the engine at the maximum torque revs (7,000rpm) and the clutch slips as required (100% slippage at 0Km/h, 50% slippage at 24.5Km/h, 0% slippage at 49Km/h wherein the clutch is completely engaged).

From 50Km/h to 56Km/h the clutch has to slip again (but slightly this time) in order to avoid the torque hole at 7,500rpm.

From 66Km/h to 69Km/h (gear change from 1st to second) the clutch needs to slip slightly, again, in order to maximize the available force on the rear wheel.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis..
..it is interesting to read the 'model' analysis of a 'hard launch', albeit obviously of a 'generic' type..

I still own a number of RD/RZ Yamahas, & I've found a quick start technique that works well..
The Yamaha clutch is usefully forgiving & easily modulated which assists considerably..

I select 1st gear, & feed the clutch out fairly smoothly/promptly while holding about 6,000 rpm,
this will launch the bike quickly - with the front wheel hovering about 20cm above the road through 1st..
..once the clutch is fully engaged the lever is not moved again, each up-shift is done using only
the gear lever coordinated with a very brief throttle back movement to unload the gear dogs..

The low rotating inertia of the 2T, does, as noted by gg.. make this approach a bit less brutal - than it reads..

[gruntguru]

No gg, the "main takeaway" is that the 2T 750/3 bested the 4T 900/4 in the actual comparison.. inc' on the dyno..

Well I can't comment on that as I haven't seen the dyno charts - unless they are the same ones Tim used to produce his chart - in which case the 4T bested the 2T on the dyno.

[Tim.Wright]

unless they are the same ones Tim used to produce his chart - in which case the 4T bested the 2T on the dyno.

Yea it's the same ones.

[manolis]

Hello J.A.W.

You write:
"I select 1st gear, & feed the clutch out fairly smoothly/promptly while holding about 6,000 rpm"


According the torque curve of the Yamaha RD350LC (page 137, top),
if you do the same holding the engine at 6,500rpm (where the engine makes 49mN, i.e. some 10% more than at 6,000rpm),
you will burn a little more friction material in the clutch,
you will heat the clutch a little more,
however until 45Km/h (fully engaged clutch in both cases) you have some 10% higher acceleration, which means that you gain some 0.1 seconds of time and some 1.2m of distance.

Differently: in 2 seconds the one method achieves some 4.5Km/h higher exit speed than the other (say, 45Km/h vs 50Km/h).


When you try it, please let me know whether the theory predicted the practice.


PS.

By holding the engine at 7,500rpm you gain nothing as compared to holding the engine at 6,000tpm.
By holding the engine at 9,200tpm (wherein the torque is substantially lower) everything happens slower at the initial acceleration.

The general rule is that for achieving the best possible acceleration (until the complete engagement of the clutch) you need to hold the engine where it makes its maximum torque.

Thanks
Manolis Pattakos

[J.A.W.]

No gg, the "main takeaway" is that the 2T 750/3 bested the 4T 900/4 in the actual comparison.. inc' on the dyno..

Well I can't comment on that as I haven't seen the dyno charts - unless they are the same ones Tim used to produce his chart - in which case the 4T bested the 2T on the dyno.

Well gg, if you haven't even bothered to read the ( linked numerous times) real bike test..
..then 'spose you will have to go by the 'fudge factor' test.. as your sole data set.. flawed or not..

Kinda puts a 'credulity factor' on your recent posts here on this topic, though..

[J.A.W.]

Hello J.A.W.

You write:
"I select 1st gear, & feed the clutch out fairly smoothly/promptly while holding about 6,000 rpm"


According the torque curve of the Yamaha RD350LC (page 137, top),
if you do the same holding the engine at 6,500rpm (where the engine makes 49mN, i.e. some 10% more than at 6,000rpm),
you will burn a little more friction material in the clutch,
you will heat the clutch a little more,
however until 45Km/h (fully engaged clutch in both cases) you have some 10% higher acceleration, which means that you gain some 0.1 seconds of time and some 1.2m of distance.

Differently: in 2 seconds the one method achieves some 4.5Km/h higher exit speed than the other (say, 45Km/h vs 50Km/h).


When you try it, please let me know whether the theory predicted the practice.


PS.

By holding the engine at 7,500rpm you gain nothing as compared to holding the engine at 6,000tpm.
By holding the engine at 9,200tpm (wherein the torque is substantially lower) everything happens slower at the initial acceleration.

The general rule is that for achieving the best possible acceleration (until the complete engagement of the clutch) you need to hold the engine where it makes its maximum torque.

Thanks
Manolis Pattakos

Hi Manolis, & thanks for your interest..

A couple of things.. your model program does not factor in the conduct of the 'YPVS' variable exhaust..
..you have to 'trick' the valve into not 'fluttering', - this what causes the 'hole' you see on the dyno chart..

Experience shows that deft throttle control can minimise that artefact, & give a more rapid result..

& a modicum of wheel-spin ( accounting for ambient surface friction ) allows for less clutch slip/abuse,
while still preventing the lofted front wheel from rotating fully, & flipping over..

[J.A.W.]

unless they are the same ones Tim used to produce his chart - in which case the 4T bested the 2T on the dyno.

Yea it's the same ones.

Yea verily.. lo & behold.. esp' for those who came into the discussion late:

http://www.kawtriple.com/mraxl/articles ... bikes2.htm

& as even 'Blind Freddy' can patently see..
..it was the 4T (indeed all of them) which was - in fact - beasted.. ah yeah, I mean.. bested..

[Tim.Wright]

As always I agree J.A.W. The facts from this "real world" test are:

The 2T with tricked gear ratios for the 1/4 mile and a massive weight advantage set effectively the same ET as a stock 4T. I've shown conclusively why - it's takes a little grey matter to understand though so I completely understand why it's gone over your head.

Moreover there are the driveability problems of the 2T which are detailed in the linked page as well as this little gem:

When the dyno testing had been completed, only one motorcycle-—the 903—left us puzzled. Both it and the Mach IV had produced nearly identical quarter-mile figures –low twelves at 110 mph—and both had produced 64 horsepower on the dynamometer. But the 903 didn’t have the Mach IV’s gearing advantage, and it had to deal with a weight penalty of 73 pounds.

All in all it's 100% coherent with the objective data I've shown on the previous page (obviously excluding your questionable correction based on driver skill which could equally be applied to the 903).

[henry]

CVTs are compromised. The simple self regulating (belt) type by the contrary sensitivities required to upshift and backshift, the more complex car type (steel 'belt') by the parasitic losses incurred through hydraulic control.
In the former case I believe more could be done, in the latter, probably not. Suspect DCTs are on their way out, so back to stick shifting manuals (the H gate is an anachronism I'd be happy to never again encounter) or TC autos. Pity the OEMs devoted so much energy to DCTs when a bit of time spent on a sequential manual (ie, robotised conventional manual box) would by now have delivered the lightest, simplest, most efficient transmission of them all. As usual, they chased the showroom glitz to maximise the sticker price.

Does Manolis' CVT answer the "contrary sensitivities" issue of simple belt driven types?

I'm familiar with DCT, I drive a VW with DSG. So I'd be interested in why you think they are on the way out? VW continue to extend the range of models on which it is offered. Down to the Polo now.

What is a "TC Auto" ?

[Tommy Cookers]

TC = torque converter
though strictly speaking the car TC should be classified as a converter coupling not a torque converter
because it (can and frequently does) have moving input and output and simultaneously multiplies torque
a (fluid) coupling has moving input and output but cannot multiply torque
(strictly) a torque converter is a device having moving input but a notionally non-moving (torque) output

my peeves
(1) all TC automatics now lock the converter in cruise but this important factor is concealed and made undetectable in use
ok now the TCA has greater ratio range (emulating the CVT) and more gears and some 'hard-wired' TC lock or TC 'bypass' ?
(2) many 'non-TCAs' have (friction) clutches, to emulate TC creep they wear - non-creep (centrifugal) clutches are better
(3) automatics having to be an exact substitute foe a manual impairs auto design, especially CVTs
(4) commercial politics affects the uptake of auto types (car maker X won't buy anything from conglomerate Y co-owned by X's rival)
(5) cultural expectations - including 'design by salesmen'

we may be persuaded that the control intelligence etc of modern Autos has eliminated the traditional need for automatic-specific engine variants
would it do enough for our cars to have 350 Yamaha type engines ?

[Pinger]

Does Manolis' CVT answer the "contrary sensitivities" issue of simple belt driven types?

Superficially at first glance yes. But that version is countering the back shift resistance by further forcing load onto the front driven pulley. The compression forces within the belt as it passes over that pulley will be increased - possibly to its detriment.
Instead, as increased torque sensitivity is required for back shifting (without compromising max acceleration shift out ) I'd work on the secondary clutch.

That type (rubber belted) of CVT is only of use on light vehicles so doubtful if there's any appetite to improve it as by now its known foibles are accepted by those who appreciate its other benefits.
Whether some of its mechanisms could usefully be applied to heavier duty (steel belt) types to reduce or eliminate the hydraulic control parasitic losses is open to question. But with the current crop of engineers going straight to the electronic solution without giving mechanical methods much of a shot - I doubt that that will ever happen.

I'm familiar with DCT, I drive a VW with DSG. So I'd be interested in why you think they are on the way out? VW continue to extend the range of models on which it is offered. Down to the Polo now.

Something I read recently - though can't remember where - suggested (or stated ) that most OEM were resorting to TC autos rather than DCTs. Cannot comment on the veracity of the claim but given the lubrication difficulties experienced and the plethora of sensors required over other transmissions, it sounds plausible to me. Time will tell I guess.

What is a "TC Auto" ?

As per TC's reply!

[Pinger]

my peeves
(1) all TC automatics now lock the converter in cruise but this important factor is concealed and made undetectable in use...

What peeves you about lock-up convertors? Admittedly they introduce an element that can (and sometimes do) fail, but given the efficiency gain...

we may be persuaded that the control intelligence etc of modern Autos has eliminated the traditional need for automatic-specific engine variants
would it do enough for our cars to have 350 Yamaha type engines ?

Never.
Even if a transmission were flexible enough to keep the rpm where it needed to be, the (piston) rings would never have the required longevity.
If 2T is ever to feature as a viable engine for cars it will be in 8bar BMEP guise - where the rpm is moderate and the exhaust tuning delivers a broad and flat torque curve. (Incidentally, although such an engine may not have the absolute flatness of torque curve as a similarly powerful 4T - its torque output will be higher. Typically torque in lbs.ft numbers are usefully higher than their hp numbers.(Witness, eg, Saab 850 with Tmax of 59lbs.ft and Pmax of 38-42hp)
This is seldom true for the 4T.)