Power Flat Spots

[dlaing]

David

 

I would be careful with these predictions.You might be far from the truth and on the Dyno there might be a lot to learn in that area.

For any 4stroke engine, backpressure is bad for power. Of big influence is the tuning length of the exhaust pipe. This has to be taken into account for comparisons.

The fuel can be mapped independently for each cylinder, the ignition timing not. For the fuel, there is a base map for both cylinders and an offset map for the right one.

 

I doubt it, but hey, you never know.

I sure was surprised to learn from your posts that the mixture was perfectly balanced at 4000RPM.

Effects of back pressure are fairly easy to predict.

Effects of tuning length are more difficult to predict.

With the crossover all evidence is that the stock muffler does not lose low end and may in fact gain it over what is typically used, free-er flowing shorter tuning length muffers that give the bike more high RPM power.

Predicting that the same will happen without a crossover, where we are potentially getting more back pressure, does not seem to be making a risky prediction.

I suppose the back pressure with stock muffler and no crossover might produce so much back pressure that the power is robbed below 4500RPM but I doubt it, and I am positive it won't gain more power above 6500RPM and will likely lose a lot.

Going to the free flowing mufflers, back pressure is pointing us at less bottom end and more top end. I don't think that is a bold prediction.

If I said that no crossover and free flowing muffers would make more power in the low end, mid range or the high end than a typical stucchi/mistral combo, that would be a bold prediction.

I think such an arrangement will make less overall power but I have no idea where it might do better or worse.

Yah, I know, another bold prediction.

I hope Ryland proves it wrong

[GuzziMoto]

I say give it a go. My guess is more top end and less mid-range, but until you try we won't really know.

[Ryland3210]

With a crossover, the length of pipe from engine to the crossover form one natural frequency to influence engine output. In the stock mufflers, another one is created by the length of the pipe from the crossover to where that pipe terminates in the rear end of the muffler. There are also other complex relationships between volumes and natural frequencies of various elements, including the crossover itself.

 

In contrast, independent straight pipes are easier to tune to a given range of RPM. Whether it increases power at top end or middle primarily depends on the length, it seems to me.

 

Here's a crude approximation and food for thought:

At 4000 RPM, each cylinder generates exhaust pulses at the rate of 33-1/3 per second.

For a speed of sound of 1100 feet per second, one wavelength is 33 feet, and a quarter wavelength is 8.25 feet.

At 8000 RPM, the quarter wavelength is 4.125 feet, not far from the length of the OE exhaust pipes.

[dlaing]

Here's a crude approximation and food for thought:

At 4000 RPM, each cylinder generates exhaust pulses at the rate of 33-1/3 per second.

For a speed of sound of 1100 feet per second, one wavelength is 33 feet, and a quarter wavelength is 8.25 feet.

At 8000 RPM, the quarter wavelength is 4.125 feet, not far from the length of the OE exhaust pipes.

I have trouble understanding tuning length theory. Trial and error probably works better.

My rough measurement is that it is about seven feet (between a quarter and a fifth of a wave length at 4000RPM)from exhaust valve to the outlet of my Mistral muffler.

The stock muffler is has nearly three times the tuning length of the Mistral' muffler section, so add on about maybe five more feet giving a length of about 12 feet, or maybe a third of the wave length. at 4000RPM.

Maybe if the exhaust was just over 8 feet for a quarter wave, the hole at 4000RPM would magically go away, but I doubt it

At maximum Torque, 5250RPM, the seven foot would be about a quarter wave length and at 12 feet would be about 2/5 wave length(surprised that works well)

At 8000RPM seven feet would be about 7/16 of a wave length and 12 feet is about 3/4 wave length, both pretty good for making peak HP, perhaps an 8.25 foot exhaust would make ideal power at 8000RPM, But I'll be 12.3 foot is fine too, and the loss of power is from the restrictiveness of the stock muffler, not the tuning length.

Aside from the hole in the torque curve at 4000 RPM, it is a fine curve. Way to go Luigi!

According to Motoguzznix's Dyno work, there is an appearance that the left cylinder pulls harder till 4000RPM where both cylinders pull equally but power is disappointing and then the right cylinder pulls harder until they balance again at maximum torque point of 5250RPM, and then it switches back to the left cylinder pulling harder.

Presumably the wave of boost is working best 5250RPM and worst at 4000RPM, a difference of 1250 RPM.

You will find this same effect with either the OEM or typical aftermarket slip-ons, both of very different tuning length.

[docc]

I'm a little vague on how one cylinder can be measured agianst the other.

 

Riding yesterday I pondered the antithesis of the flat spot: the sweet spot. You know, right there about 5,000 rpm where the world begins to spin on greased grooves.

[BrianG]

...................................

I sure was surprised to learn from your posts that the mixture was perfectly balanced at 4000RPM.

.....................................

 

Of interest to me was the fact that the dyno did not always show best-power being made a 12.4:1 A/F as demonstrated on the WB 02 sensor (which is the theoretical best power mixture). I used to operate on the premise that target A/F ratio, as read by the Innovate Motorsport WB O2 system, was a very efficient method of maximizing performance. The dyno shows otherwise.

 

It seems that 02-sensors are falling from favor with high-end tuners. They are now turning to CO reading as a more accurate determinant of combustion efficiency. Unfortunately, that technology is still very expensive......

[Guest ratchethack]

I have trouble understanding tuning length theory. Trial and error probably works better.

Dave, FYI -- it dawned on me recently that your penchant for wild speculation seems to've been turned up a few notches on the familiar dlaing speculation-o-meter.

 

After thinking about it, I realized that I'm in the subconscious habit of scanning your posts for raw speculation and mentally ignoring it whenever possible -- unless of course, it's particularly flamboyant, and/or preposterously egregious, and then of course I'm compelled to call you on it. And this just gets tiresome, so I've backed way off lately, just out o' sheer boredom.

 

You see, (and I'm about as certain as I can be that I'm not alone in this) I've found that wild speculation on the ol' Tech Forum has about as much value as tits on a boar hog -- or more pointedly, as much value as the aforementioned proverbial loose fire hose shooting off in all directions while the wildfire consumes everything in its path. . . It'd be one thing if we had Forum topics like "How many angels can dance on the head of a pin?", but this here is a Technical Forum . By my estimation today, after thinking about it, I figure somewhere north of 95% of the raw, baseless speculation on this Forum comes from your posts.

 

Then I thought, now let's not be too critical, Ratch. . . You know you've been awfully hard on the boy. Could it be that I've just imagined this? Wot if it's ME who's guilty of raw speculation?! Well, it'd be easy enough to do a little check, so why not?

 

So here's wot I found in this thread:

 

14 dlaing posts. This is a list of the kinds of lead-in words from those posts that I've come to recognize as announcements of raw speculation. They've become my cue to skip wotever it is that follows. The list was de-duped. Some entries on the list have up to 3-4 recurrences in this thread, and many recur even within the same post. By far and away, "I suppose" and "I suspect" were the most frequent fliers.

 

It may be possible

I guess

Probably would not hurt

appears to be

They could have

I suppose

Perhaps

I suspect

I think

I am almost certain

It appears as if

Not sure about

I doubt it will

I doubt it, but hey, you never know

I have no idea

probably works better

Presumably

Maybe if

there is an appearance that

 

Now I'm not saying that ALL your posts aren't of value, Dave. Some of wot you come up with is actually helpful and has high value, though separating reality from fantasy becomes quite a task for the reader when you evidently haven't passed your thoughts through any kind of a reality filter before posting, difficult as this kind of unfamiliar discipline may be. . . .

 

Now I know that wildly imaginative speculation is simply your nature, Dave, and I hope this isn't quite like asking a fish not to swim. But d'you suppose you could just notch it back down a few clicks? It'd be much easier to follow the topics without having to empty all the useless dreck that gets caught in the speculation trap every couple minutes.

 

TIA

[dlaing]

Dave, FYI -- it dawned on me recently that your penchant for wild speculation seems to've been turned up a few notches on the familiar dlaing speculation-o-meter.

 

After thinking about it, I realized that I'm in the subconscious habit of scanning your posts for raw speculation and mentally ignoring it whenever possible -- unless of course, it's particularly flamboyant, and preposterously egregious, and then of course I'm compelled to call you on it. And this just gets tiresome, so I've backed way off, just out o' boredom.

 

You see, (and I seriously doubt I'm alone in this) I've found that wild speculation on the ol' Tech Forum has about as much value as tits on a boar hog -- or more pointedly, as the aforementioned loose fire hose shooting off in all directions as the wildfire consumes everything in its path. . . By my estimation today, after thinking about it, I figure somewhere over 95% of the raw, baseless speculation on this Forum comes from your posts.

 

Then I thought, now let's not be too critical, Ratch. . . You know you've been awfully hard on the boy. Could it be that I've just imagined this? Wot if it's ME who's guilty of raw speculation?! Well, it'd be easy to do a little check, so why not?

 

So here's wot I found in this thread:

 

14 dlaing posts. This is a list of the kinds of lead-in words from those posts that I've come to recognize as announcements of raw speculation to follow. They've become my cue to ignore wot follows. The list was de-duped. Some entries on the list have up to 3-4 recurrences in this thread, and some even in the same post. By far and away, "I suppose" and "I suspect" were the most frequent fliers.

 

It may be possible

I guess

Probably would not hurt

appears to be

They could have

I suppose

Perhaps

I suspect

I think

I am almost certain

It appears as if

Not sure about

I doubt it will

I doubt it, but hey, you never know

I have no idea

probably works better

Maybe if

there is an appearance that

 

Now I'm not saying that ALL your posts aren't of value, Dave. Some of wot you come up with is actually helpful and has value, though separating reality from fantasy becomes quite a task for the reader when you evidently haven't passed your thoughts through any kind of a reality filter before posting, difficult as this kind of unfamiliar discipline may be for you. . . .

 

Now I know that wild speculation is simply your nature, Dave, and I hope this isn't quite like asking a fish not to swim. But d'you suppose you could just notch it down a few clicks? It'd be much easier to follow the topics without having to empty all the useless dreck that gets caught in the speculation trap every couple minutes.

 

TIA

No, you ingrate, my speculative nature has been of great value to this forum.

Not all enjoy speculative banter. They prefer to sit back in their high chairs and swallow spoon fed crap. Not my cup of tea

I suppose I should thank you for training me to use many of those listed words, as they are a defense mechanism against your attacks. A pity you are so bored that you took time to look every word that frustrated you in your endeavor to corner me when I make an error. But I am sure your adoring fans will be grateful for your diligent work and will give you an attaboy for pegging me so precisely.

 

(Hey look, I only speculated once )

 

I'm a little vague on how one cylinder can be measured agianst the other.

 

Riding yesterday I pondered the antithesis of the flat spot: the sweet spot. You know, right there about 5,000 rpm where the world begins to spin on greased grooves.

You can hook up a WBO2 to each exhaust pipe, before the X-over.

The leanness tends to indicate that that cylinder is working harder at that RPM.

(I have to use the speculative term 'tends' because there exceptions to the theory)

 

 

Of interest to me was the fact that the dyno did not always show best-power being made a 12.4:1 A/F as demonstrated on the WB 02 sensor (which is the theoretical best power mixture). I used to operate on the premise that target A/F ratio, as read by the Innovate Motorsport WB O2 system, was a very efficient method of maximizing performance. The dyno shows otherwise.

 

It seems that 02-sensors are falling from favor with high-end tuners. They are now turning to CO reading as a more accurate determinant of combustion efficiency. Unfortunately, that technology is still very expensive......

Read the infamous ECU thread!

Derrick Capito (spelling???) presents a compelling argument

http://www.v11lemans.com/forums/index.php?...c=4152&st=0

Who do you suppose started that thread...

[Guest ratchethack]

I suppose I should thank you for training me to use many of those listed words, as they are a defense mechanism against your attacks.

Hmmmm. Yet another "frequent flier" recurrence of "I suppose" on this thread's speculation list.

 

Now lemme see if I've got this straight. . .

 

I've trained you to use words such as:

 

It may be possible

I guess

Probably would not hurt

appears to be

They could have

I suppose

Perhaps

I suspect

I think

I am almost certain

It appears as if

Not sure about

I doubt it will

I doubt it, but hey, you never know

I have no idea

probably works better

Presumably

Maybe if

there is an appearance that

 

. . .as a "defense mechanism" against my attacks?? Hmmmmmmmm.

 

Does this mean that without my training , you'd simply be stating all your wild, groundless speculations shooting off in all directions as if they were hard facts , without the qualifying prefaces above??

 

. . . So you're saying that I've trained you to be honest about the true nature of your most prolifically speculative posts??

 

Well, I reckon all the training hasn't been for naught then. A measure of honesty's at least a start. . .

 

Now then. Once again -- How about just a few more degrees of separation between reality and fantasy on the ol' dlaing Speculation-o-meter, por favor??

[emry]

I really hate to get drawn into this but, Ratch you are off base here. This is a Technical forum, but many do not have the technical background so they speculate. I see no folly in someone wanting to learn or improve something.

 

But picking apart someones posts. I found no techincal insight in your responses to dlaing. If you have something to offer towards the posts intent, then please add it. If you just want to vent on someone who has an idea please send them a personal email and lets try to keep our posts on track.

 

 

As for desinging an exhaust system there are numerous formulas that are used for designing an exhaust. Im sure a little google action would turn them up. Normally exhaust tuning is used to take advantage of a negative pressure wave during valve overlap so that the fresh incoming intake charge does not go straight out the open exhaust valve.

[Guest ratchethack]

I found no techincal insight in your responses to dlaing. If you have something to offer towards the posts intent, then please add it.

Hm. Sorry to disagree, Emry, but I reckon you didn't find my previous post then (see below).

 

To put it in context:

The stock crossover appears to be the cause of the flatspot.

I wouldn't agree with this, no. Not at all. The flat spot exists whether the stock crossover is installed, an aftermarket crossover is installed, or there's no crossover at all, and depends on a complex combination of many factors, most of them centered around head flow and the engine's characteristic intake and power pulse wave dynamics, which can be greatly affected by many aspects of head, valve, cam, and piston crown configuration and design. External to the heads, overall characteristics of intake and exhaust breathing contribute heavily to the shape of the curves on a dyno. Changing the crossover can improve the exhaust wave pulse harmonics on a V11 to a limited degree. But best case, taken by itself, this can only "fill in the dip" on the torque and power charts slightly at 4K - 4.5K RPM. The flat spot is still there. Many engines of all configurations have a flat spot or multiple flat spots in the torque and/or power curves, regardless of any crossover.

To which came the following response and my reply:

. . . the waves that engine generates are not caused by the exhaust but their reverberations and how they move are greatly effected by the exhaust.

[. . . sigh . . .]

I've found that an abundance of raw, groundless speculation leads immediately into unqualified statements (such as the above) that're obviously confused at best, and haven't the faintest semblance of reality -- or value to anyone.

I see no folly in someone wanting to learn or improve something.

Nor do I. Asking straightforward questions in an honest manner is one thing, and of course is always welcome here. However, the practice of making stuff up out of thin air and putting it out on the Web in the form of statements of sheer speculation, apparently just to see whether anyone shoots it down or leaves it alone is another thing. Here's where I find the folly. As a continuing habit, I find this to be disingenuous, at least potentially damaging, and that it erodes the credibility and value of any public Forum. Sadly, there are some who don't seem to have much of any built-in monitoring capability for recognition of when they're in over their heads, or for separating reality from fantasy. Somebody's gotta make the appropriate challenges, Emry. I reckon making and defending challenges are a primary benefit of Web discussion, or very quickly there's no value left in the Forum.

 

But hey -- that's just me.

[emry]

Touche, Ratch. As usual you do a very good job of backing up your statements.

 

Evidenced by many of your previous posts you have both knowledge and experience, a key requirement in many technical fields. So how about this, instead of pointing out in detail the flawed logic (or fantasy) of others, take the opportunity to educate them. Find a link or two related to the subject and expand on them. You have stated in the past that you spend a great deal of time in front of a computer, and we both know the wealth of knowledge that is available online if you know were or how to look.

 

As for your responses, I was only refering the ones on page 4. Sorry for any confusion.

 

Don't forget flight was fantasy as was many other things that are taken for granted. Let us steer thoose to the resources that will allow subjects like this to move forward instead of trying to silence them.

 

Here dlaing, exhaust theory. Just one I picked from google.

 

 

quote]As a continuing habit, I find this to be disingenuous, potentially damaging, and that it erodes the credibility and value of any public Forum. Sadly, there are some who don't seem to have much of any built-in monitoring capability for recognition of when they're in over their heads, or for separating fact from fantasy. Somebody's gotta make the appropriate challenges, Emry. I reckon making and defending challenges are a primary benefit of Web discussion, or very quickly there's no value left in the Forum.

 

I really do appricate your challanges, normally they are insightful, but lately they do seem more like an a attack (towards some). As a previous educator I was rather put off. Curiosity = Diveristy. It is Ok to let someone know that their ideas are not realistic, but lets spend the time to educate them as to why, and if you want to add credibilty to the forum bring in outside supporting info.

 

That way we all benefit.

[Ryland3210]

Touche, Ratch. As usual you do a very good job of backing up your statements.

 

Evidenced by many of your previous posts you have both knowledge and experience, a key requirement in many technical fields. So how about this, instead of pointing out in detail the flawed logic (or fantasy) of others, take the opportunity to educate them. Find a link or two related to the subject and expand on them. You have stated in the past that you spend a great deal of time in front of a computer, and we both know the wealth of knowledge that is available online if you know were or how to look.

 

As for your responses, I was only refering the ones on page 4. Sorry for any confusion.

 

Don't forget flight was fantasy as was many other things that are taken for granted. Let us steer thoose to the resources that will allow subjects like this to move forward instead of trying to silence them.

 

Here dlaing, exhaust theory. Just one I picked from google.

quote]As a continuing habit, I find this to be disingenuous, potentially damaging, and that it erodes the credibility and value of any public Forum. Sadly, there are some who don't seem to have much of any built-in monitoring capability for recognition of when they're in over their heads, or for separating fact from fantasy. Somebody's gotta make the appropriate challenges, Emry. I reckon making and defending challenges are a primary benefit of Web discussion, or very quickly there's no value left in the Forum.

 

I really do appricate your challanges, normally they are insightful, but lately they do seem more like an a attack (towards some). As a previous educator I was rather put off. Curiosity = Diveristy. It is Ok to let someone know that their ideas are not realistic, but lets spend the time to educate them as to why, and if you want to add credibilty to the forum bring in outside supporting info.

 

That way we all benefit.

 

Yes, please. Let's have mercy on those that come after us searching for solid technical answers, and not have them sifting through pages of side issue verbosity to find them. Let's be mindful and compassionate in criticism when a correction is appropriate and defend challenges with objective facts and enlighten in the process.

[docc]

Voices of reason rise above the din . . . ah, the 'sweet spot' . . .I could ride on forever . . .

[dlaing]

Here dlaing, exhaust theory. Just one I picked from google.

Thanks Emry!

Any ideas how Ryland might calculate this independent header design?

I tried some thumper sites looking for ideas, speculating that they might know how to design an exhaust without crossovers and two into ones.

But I found nothing but aftermarket slip-on options, with SuperTrapp being an apparent frequent favorite.

Thumper makers and most motorcycle makers seem to make the length of the exhaust fit the bike.

125cc-650cc, all about the same length, but diameter changes a bit.

The Buell Blast might be an exception amongst singles, although the innards of the exhaust could go back and forth a couple of times increasing the tuning length.

I wonder if the engineers even bother with tuning length?

Enzo's Cobra was allegedly great for power, but it was loud and must have been a pain during oil changes.

SORRY