Power Flat Spots

[Ryland3210]

In looking at a "standard" fuel delivery chart, it appears that mixture is leaned out at 4,000 RPM, then richens again at higher RPMs.

 

There have been reports of a flat spot in that range. Ratchethack feels the difference is not enough to account for the flat spot, and that there are other factors. motoguzznix also made comments to that effect.

 

Let's see if the collective wisdom of our members can enlighten us all, and give us a method of eliminating it.

 

Perhaps dlaing can insert the standard fuel delivery map here.

Skeeve said:

All of which begs the question: is the 4k rpm flat spot caused by too much or too little fuel? If it's a lean stumble, then wouldn't it be interesting if the easiest fix is just to substitute the H-D tps in for the stock unit, rather than spending all the time & expense on a PCIII & mapping on an otherwise stock motor?

 

Ryland's response:

 

It's simpler than that. Look at the fuel delivery chart at 4000 RPM, large throttle openings. It leans out compared to delivery at the higher and lower adjacent RPMs

 

There are places in the charts like this, where fuel and timing entries make no logical sense to me. For example, at 4,000 RPM, if I had a Tune Boy, the first thing I would do is set the fuel delivery at the midpoint between the adjacent columns. My predictions is that your flat spot goes away.

 

Here's another: between 5.18 and 21.46, at 3200 RPM on the ignition chart, timing is retarded compared to higher and lower RPM's. Why? If there isn't any preignition at the lower RPM, why retard the advance at 3200?

 

Motoguzznix commented:

 

The 4k flat spot is not influenced by the richness/weakness of the mixture.

I rectified the mixture and got better torque everywhere but the flat spot basically remained.

Remapping or a PC is the only way to adress mixture changes. The TPS is a measuring device, not for mixture tuning. Changing the calibration of the TPS changes the adresses in the map over a large area. This can cause a lot of unwanted side effects.

 

Ryland's response:

 

 

Please be specific about your first statement. Obviously mixture does affect power output, and the relatively lean mixture at 4000 RPM with standard tuning can explain a reduction in power output. knownothing.gif

 

What do you mean by "rectified the mixture"?

 

Ratchethack weighed in with:

 

Not very much, John -- and only within a relatively tiny range, assuming A/F is off to start with at a given RPM. If it were possible to "map out" every flat spot or dip on torque and power curves, this would certainly be convenient, but this is nowhere near the case. Many many other factors contribute to the shape of torque and power curves that are not related to A/F in the slightest. As Ernst has mentioned, the infamous 4K RPM "flat spot" is NOT a function of A/F.

 

As an example of this, (proven in the case of my own bike) replacement of the stock crossover with a Stucchi crossover nicely "fills in" the all-stock "dip" on the torque and power curves with NO change in A/F wotsoever. wink.gif

 

Check Doug Lofgren's charts and comments here:

 

NOTE: This isn't the series of charts I was looking for (Doug's stuff is suddenly not that easy to find) but they illustrate the principles involved.

 

http://www.visi.com/~moperfserv/mgv11ex.htm

 

To which Ryland responded with:

 

Without quantifying things, it's all subjective, and we could carry on that kind of discussion all day without advancing the cause of objective reasoning. "very much", "relatively tiny range", "rectified", "basically", and similar subjective terms are not enlightening. I look forward to motoguzznix answer.

 

F/A mixture affects output. That's clear. Obviously other factors do too. No one denies that. It's obvious. I want to know what motoguzznix experience is, and which other factor(s) he believes caused the flat spot. Furthermore, his message is not clear on how he "rectified" the mixture and to what extent. We may learn something from that.

 

In any event, I think this discussion should move to another thread on the subject of flat spots. anigrin.gif

 

And so here we are!

[emry]

Engines are dynamic devices. They operate over a broad range of rpm's, temp's and pressures. Not to mention fuel quality etc. Unfortunatley while the engine is a dynamic device the components it is made up of are mostly static devices. Exceptions being igntion timing and fueling. It is well documented about the tuned length of the intake, exhaust, flow and velocity of the intake and exhaust, port size, cam timing and valve lift, bore, stroke blah blah blah. At times (rpm) these static systems work well, at others they work poorly. When all of the static systems are working well together you get really good power, when only a few are working well your output is ok, and when they all are out of wack, power stinks. Finding the right combination is a very tricky matter and many people claim to have the proper solution which may produce good results, even though it can vary from another method that produces as good as results.

 

Car makers (and some mc makers) have been adding dynamic systems to the engines, multi-length intakes, variable valve timing and lift, exhaust backpressure valves, etc. Even experiments with variable compression have been done. Most of these systems are better able to perform over a broader rpm range thus minimizing the "out of wack" flat spots.

 

Engines are very simple devices that mainly are design to ingest a quantity of air, heat it up really fast, and use the expanding gas (nitrogen) to do something, move a piston, turn a rotor, spin a turbine, etc. The more air in, the hotter you get it, the more power you get out the the fuel.

 

Most likely the imfamous "flat spot" and resulting lean running is not just a fueling / timing issue. Otherwise a simple reprogram would solve the problem quickly. Many have reported sucess by changing the crossover and reprograming, I am sure there is dyno chart around here somewhere. Could a cylinder head re-design (proper porting) and correct cam also solve the problem. Maybe.

[BrianG]

I can attest to the assertion that this 4000rpm flat spot is not simply a A/F issue. I ran a baseline dyno run with OEM parts, and noted the flat spot. Then I ran with Mistral cans and a drilled air-box lid, which demonstrated a small increase in Hp above the flat spot, but this made the flat spot more noticable to the seat-of-the-pants, negatively affecting "drivability". Then I ran with a PCIII on the dynotech computer coupled dyno. This flattened the flat spot somewhat and added another couple of Hp, but from down around 2000 rpm all the way to over 5000rpm, which was very noticable to the seat-of-the-pants, very positively affecting "drivability".

 

My take is that there is some room for improvement of the "V-11 flat-spot" through mixture tuning, but the issue is larger than just that.

[Ryland3210]

What if the intake and exhaust passages are intentionally sized to resonate above 5000 RPM to maximize peak HP, at the expense of diminishing mid range output? Not an uncommon practice, and for those fortunate enough to ride on the Autobahn that like to take advantage of the freedom to fly low, top end power is important.

[Baldini]

I don't know much myself but - LM11, T3, V11 - all the Guzzis I've had have a flat spot around 4k rpm. I've improved it with breathing & fuel changes on all of them but it's always there to some degree. I've been told many times it's an issue related to head design on this motor.

 

KB

[dlaing]

Without quantifying things, it's all subjective, and we could carry on that kind of discussion all day without advancing the cause of objective reasoning. "very much", "relatively tiny range", "rectified", "basically", and similar subjective terms are not enlightening. I look forward to motoguzznix answer.

 

F/A mixture affects output. That's clear. Obviously other factors do too. No one denies that. It's obvious. I want to know what motoguzznix experience is, and which other factor(s) he believes caused the flat spot. Furthermore, his message is not clear on how he "rectified" the mixture and to what extent. We may learn something from that.

 

In any event, I think this discussion should move to another thread on the subject of flat spots.

Oh Fun!

Another thread on relativism!!!!

Flat spots can be caused by many things.

Postings of dyno tuner's experiences on this forum have shown that changing fueling across both cylinders does little to reduce the flat spot.

Postings here have also indicated that starting in 2003 Guzzi fixed the flat spot with a balance pipe and other alleged changes..

And of course aftermarket crossovers and the Quat D have been shown to virtually eliminate it, sometimes at the expense of top end.

I kind of like the exhilaration of leaving the flat spot!!!

It may be possible to fix the flat spot with ignition advance and individual cylinder fuel tuning????

EDIT after examining the ignition advance curve, the hump is right about where the hole is.(get your mind out of gutter) Did Guzzi try to fix hole with advance or was the hole aggravated by too much advance? Or maybe it needs MORE advance????

Sorry image too large...and linearity of curve is a little warped do to my inability to use NeoOffice, based on Open Office.

[motoguzznix]

Here is an excerpt of my power- and A/F measurements and how they influence each other:

 

I will start with the WOT A/F measurement of my stock 2000 V11

 

http://www.v11lemans.com/forums/index.php?...ost&id=3746

 

at 3000 the mixture is extremely lean, this is where the engine tended to ping.

at 4000 A/F is at 13:1 what is near the optimum.

 

Here is what the remapping can do for power:

 

http://www.v11lemans.com/forums/index.php?...ost&id=6112

The bike was equipped with Stucchi X-over and my modified stock mufflers on all 3 runs.

 

green is with the stock mapping in the Weber Marelli computer

red is with first modifications doing Lambda-measurements on the road and modifying the fuel map accordingly - a little scary driving approx.180 km/h in 4th gear at max rpm on public roads

blue is the result of further measurements and modifications on the dyno

 

further gains were made by reducing the spark advance for 3° (off the figures dlaing posted above):

http://www.v11lemans.com/forums/index.php?...ost&id=6113

 

And here is how the remapping changed the A/F ratio:

 

 

orange is the stock measurement like above left cyl.

green is the left cyl.

magenta ist the right cyl

after the remapping that corresponds to the last power graph

 

Although there was a lot of power found in midrange to top, the torque flatspot is still present. The A/F figures need to be refined on both cylinders and the spark advance may be reduced to a further extent which may will lead to further gains, but I am sure the flat spot will still be there.

 

That leads me to the conclusion that the flat spot is not caused by the mixture. But by what else?

Ram effects could be the answer. Different exhaust systems can influence the flat spot as David states above.

Maybe the valves and ports are too big and not efficient enough. The cam may has too much overlap and opening time. This is backed up by the fact the power curve does not drop significantly after peak power. An undervalved engine looses power very rapidly after the max power is reached.

 

A lot of work undone on these engines.

 

Ryland

The remapping was done by the use of the Ultimap software that allows changes on the fuel and spark maps. At 2700 p.ex. the change in fuel was +50% to get rid of the lean condition at 3000 rpm. You have to consider the lean condition gets worse when an open exhaust is added to the stock mapped bike! Can get dangerous for th engine.

[Ryland3210]

Think of what you've written here. In the map you can only see the amount of injected fuel, or, even more correct, the basis for the pulsewidth calculation at this map point.

 

You cannot see any sign of how much air is delivered to the engine at this point (depending on balancing, exhaust, airbox size/shape and many more). Even a wideband O2 sensor can't give a 100% correct answer to the question of how much fuel gets correctly burned and how much of it gets lost.

 

And before we forget mentioning it: of course the PF3 and the PF4 are different sensors. They may be cheap (in production), but such a difference is never caused just by tolerances.

 

Hubert

 

There IS clearly A sign of how much air is delivered: That is the Thottle position. Of course we know it is not the only factor.

 

In another message, I mentioned resonance as a possible cause. It is possible for the relatively lower fuel delivery to explain the flat spot. However, as I have said before, without quantifying the various factors, we cannot draw conclusions. For all I know at this point (which is very limited), resonance results in an optimum power output at 4000 RPM with the fuel delivery shown in the chart.

 

What is your basis for "such" a difference. A 10% tolerance in potentiometers is not uncommon in my experience. They can be purchased with tighter specifications at higher price, of course, even to 1% or better. But as I have said before, unless we see the specifications for the two sensors and know the accuracy of the angle and voltage measurements taken in comparing them, we cannot be sure our conclusions are valid. I am not saying the data does not exist, I just haven't seen it.

[Ryland3210]

This is the WOT A/F measurement of my 2000 V11

 

http://www.v11lemans.com/forums/index.php?...ost&id=3746

 

at 3000 the mixture is extremely lean, this is where the engine tends to ping.

at 4000 A/F is at 13:1 what is near the optimum.

 

The following is the power graph that corresponds to the A/F line above (red line):

 

http://www.v11lemans.com/forums/index.php?...ost&id=6102

 

Very interesting. Thanks for the data. It's not easy to read the text. Is the tuning standard? If so, that is convincing evidence that the relatively lower fuel delivery at 4,000 is not the dominant factor in the flat spot! Even more surprising is the high output at 3,000 in spite of the overlean condition. I suppose if it were richened at that point, say at least to 14.7, the flat spot at 4,000 would be even more noticeable.

 

In my case, I would rather have the extra power at 3000 and reduce the pinging and accept the deeper valley at 4000. I have noticed the pinging also, which requires me to use the highest octane fuel.

 

In the case of my Yamaha Venture, the manual recommends regular octane fuel, and it works fine with never any pinging on any brand of gasoline. It produces about 96 HP from 1300 cc's and gets 48.5 MPG at the same cruise conditions as the Guzzi, which is at 41 MPG just now. That is less specific HP/cc than the Guzzi's 1100, at lower RPM. I'm not complaining about my Guzzi's performance. It's terrific, but it would be nice not to have to worry about pinging, even though one can never spend much time at WOT and 3000 RPM!

[dlaing]

 

green is the left cyl.

magenta ist the right cyl

 

At 4000RPM, one of the few points where I expected to see left right not balanced, is exactly where it balances.

I guess the fact that it switches over there and at 5200RPM may indicate that something is happening with the exhaust waves, but interestingly at 5200 it just about makes maximum torque while at 4000 performance is lame.

Probably would not hurt to run it a little leaner at 4000, just to keep it cleaner, afterall, whatever you do there does not effect power.

[luhbo]

...

What is your basis for "such" a difference. ...

 

TPS are an important product line of the company I'm working for.

 

All the other information you want to see is available here on this forum, just do a search, or make the whole long way through the ECU thread.

 

You might find usefull also this link, the same as previously posted not only once:

 

CTS Corporation

 

Hubert

[Ryland3210]

TPS are an important product line of the company I'm working for.

 

All the other information you want to see is available here on this forum, just do a search, or make the whole long way through the ECU thread.

 

You might find usefull also this link, the same as previously posted not only once:

 

CTS Corporation

 

Hubert

 

Thanks, Hubert.

 

I haven't been around this forum long enough to know which topics have already been handled thoroughly.

 

The link is interesting, but a search of PF3 and PF4 gives no information. I'll take your word for it on the difference. Is there another part number I can use to look up the specs on the Harley and MG versions?

 

John

[emry]

There IS clearly A sign of how much air is delivered: That is the Thottle position.

 

Unfortunatly not true. TP values just report how far the throttle is open. This valve corrolates to a predicted airflow. Which may or may not be right.

[BRENTTODD]

I plan to add crossover and be remaped over the winter. I already have mistral cans and power comander. Ill post how i make out

[dlaing]

The 4k flat spot is not influenced by the richness/weakness of the mixture.

I rectified the mixture and got better torque everywhere but the flat spot basically remained.

Remapping or a PC is the only way to adress mixture changes. The TPS is a measuring device, not for mixture tuning. Changing the calibration of the TPS changes the adresses in the map over a large area. This can cause a lot of unwanted side effects.

Please be specific about your first statement. Obviously mixture does affect power output, and the relatively lean mixture at 4000 RPM with standard tuning can explain a reduction in power output.

 

What do you mean by "rectified the mixture"?

Think of what you've written here. In the map you can only see the amount of injected fuel, or, even more correct, the basis for the pulsewidth calculation at this map point.

 

You cannot see any sign of how much air is delivered to the engine at this point (depending on balancing, exhaust, airbox size/shape and many more). Even a wideband O2 sensor can't give a 100% correct answer to the question of how much fuel gets correctly burned and how much of it gets lost.

 

 

There IS clearly A sign of how much air is delivered: That is the Thottle position. Of course we know it is not the only factor.

Throttle position is clearly the most important indicator that the ECU on our bikes uses to guess how much air will actually be delivered.

Of course, throttle position does not accurately measure how much air is actually delivered. But combined with other information from other sensors, it can estimate well enough for the bike to miraculously run!

Of course everyone else is essentially correct too. So what are we arguing about? probably semantics, again...