Lugging at low rpm vs BSFC

[alvaro84]

Originally Posted by sendler

I read a lot of superstition too. Some old school bikers will argue to the end about how they think you are totally out of control of the bike and are about to crash if you ever coast with the clutch in. Silly! They insist that you MUST engine brake down through every gear every time you come up to a stop light. Rrr, Rrr, Rrr, Rrrrrr! Look at me! I'm so cool!

I use a narrow rpm range, which makes this process especially uncomfortable and disturbing for me. I was so happy to learn that coasting is a good thing back then...

Your BMW may be so torquey that the term lugging may not even apply. You could probably just dump the clutch when you take off without even stalling.

No, she's not. At idle she's weaker than our 250, instead. If I try to just let her roll at idle rpms, she quickly stalls. Even in 1st. I can only do it when she's cold (I mean after a cold start, at winter) therefore the idle speed is temporarily elevated to (or close to) 2000. All that 'flat' torque curve seems to start very sharp somewhere down there.

My CBR250R bucks violently if I try to give it any throttle below 2,500 and high revving bikes like the Ninja250 have no power whatsoever below 4,000. My Ninja doesn't buck as much being a twin but I know that it is in a poor efficiency range when trying to accelerate for a pulse at that rpm. This lack of productivity is also what I call lugging.

But what you say here gives some food for my thoughts. I shoud try P&G'ing in 4th, at the speeds I usually P&G in 5th and see what happens. When weather stabilizes a bit I'll probably try it. That wouldn't hurt as much as cruising at higher revs.

[user removed]

My CBR will maintain a constant speed down to 3k. If you try to accelerate slightly you need to be at 3.5k and higher rates of acceleration need to begin no lower than 4k RPM.

Lugging is a combination of two things, but with fuel injection it is primarily due to RPM being so low that you can feel each power pulse and the oscillations in pressure that occurred when the harmonics of air flow are insufficient to keep a fairly consistent pressure into the cylinder.

In the old days lugging was aggravated by the issue of the volume of fuel that was added to the normal flow by the accelerator pump. When you pushed the gas pedal at to low a speed the fuel delivery was far too much for proper atomization and combustion. The inconsistent mixture was a recipe for pre ignition with high percentages of the fuel delivered not being atomized and burned properly.

Most of the bikes I have been on in recent years will basically "tell" you when they are happy with the RPM and load conditions they are experiencing. The Vulcan really starts to smooth out at 50 MPH in 6th gear. I think the CBR is close to that same RPM when it really starts to produce a smooth flow of power. My guess would be in the CBR your best P&G range would be from 4-6k RPM with manifold vacuum at 80% of atmospheric or higher if it does not have full load enrichment.

regards
Mech

[alvaro84]

I tried to P&G in my usual range in 4th instead of 5th yesterday, on the way home.
It was strange first, then I adapted - Teresa was still more headstrong at those revs (man, sometimes I went up to 5000! Scary! - redline is at 7-7.5k), but I found that if I take a longer glide down to 60km/h (~38mph?), I can rev match at 3000rmp almost as easily as before, yet did not use the sub-3k range. Still, she feels "too strong" here to use normally (though I'm sure that many wouldn't agree with me)

Now I'll rest this experiment though, and play nice, because the drive belt shows clear signs of wear. It was not exactly new, and I planned to replace it at the "100k" maintenance (by odometer which was rewound once, by the seller...), but now it looks much more urgent, has a couple of loose teeth. So it must be a 90k. An early 90k, perhaps.

I order the new belt as soon as I can overcome my inner resistance against any kind of bureucracy and repair my paypal account somehow... I've already exchanged a couple of emails with their support but it haven't solved my problem. I'll bite the bullet and create a new account, probably...

[alvaro84]

I've got numbers for the tank containing that high rpm experiment, and I unfortunately couldn't get any info out of the huge noise: the tank is over 400km long and the experiment was a mere 23km, after all. And the weather was changeable all the time, temps ranging from 0 to 22C (32-72F), wind from any possible direction sometimes with gusts over 50km/h ~ 30mph, and damp roads after rain one day. I also did a quite fast run on a (not) twisty (enough) road last weekend, with lots of pulses above my usual speed (which does not necessarily hurt, my best tanks were done on the superslab with numerous pulses up to 120-130km/h ~ 75-80mph and large delta).

All in all, I'm getting a very normal spring FE increase, this tank became 2.95l/100km ~ 79.8 mpgUS. Should it cover anything.

edit. on the belt: I feel lucky because I could arrange a slightly used one (good condition, lacking the cracks on mine) with an f650.hu member, I'll probably get it next Monday. It can be replaced during an advance "90k" maintenance and Teresa will be ready for Austria and Romania in May.

[sendler]

Looking at the torque curve you posted, I would think you would do well to stay below 4,000 rpm. It is very flat.

[renault_megane_dci]

Alvaro :
My 250 rolls easily on idle because she is very light but more importantly, the 1K rpm speed in 1st is very probably pretty low compared to your bigger engined bike.
So that is not really relevant.

My conception of lugging is really focused on my bike : if I ride it slower than 50 kms/hour in 5th (yes, those small engines are geared very low), she doesnt like it at all but to be honest, i'd rather stay at 50 km/h in 5th rather than drop down a gear to have her happier (and closer to the torque peak).

It is all very confusing for me because when the throttle is lightly opened, the pumping losses are very high (yes losses, that doesnt sound efficient at all) and yet we want to be in the higher gears (=> with small openings) as much as possible.

[sendler]

Originally Posted by renault_megane_dci

It is all very confusing for me because when the throttle is lightly opened, the pumping losses are very high (yes losses, that doesnt sound efficient at all) and yet we want to be in the higher gears (=> with small openings) as much as possible.

This is why you get the best economy by using pulse and glide. Big throttle openings at the most efficient rpm to accelerate and then glide at idle with the clutch in until you need to accelerate again.

[serialk11r]

Originally Posted by renault_megane_dci

It is all very confusing for me because when the throttle is lightly opened, the pumping losses are very high (yes losses, that doesnt sound efficient at all) and yet we want to be in the higher gears (=> with small openings) as much as possible.

When the engine speed is lower, the throttle position needed to maintain the same manifold pressure is lower, so without an electronic throttle, a lower throttle position could be giving you less vacuum and less pumping losses (and usually will)

[alvaro84]

Originally Posted by serialk11r

When the engine speed is lower, the throttle position needed to maintain the same manifold pressure is lower, so without an electronic throttle, a lower throttle position could be giving you less vacuum and less pumping losses (and usually will)

Interesting. I'll try to observe this phenomenon. I hope my spirit is not covered with snows of cynicism and the ice of pessimism enough to limit my improvements at FE

[Miller88]

I know nothing about motorcycles, but on cars ... I was always under the impression that "lugging" was when you have it in too high of a gear and try to accelerate too hard causing the rod bearings to lose their oil jacket. Hence the "tractor" noise it makes.