[Kitt]

Originally Posted by taxonomy

Basically, air is elastic

haha, damn... my engineering degree didn't do shit for me, all this time I thought air was treated as a theoretical fluid....

sounds to me bro, like you're the time that wears cool denim jeans with the air (ergo elastic) waist... Has wayyyy too much time on their hands, and isn't quite convinced of your intellect... so what you do is, you sit inside all day using your philosophical logic to try to make heads or tails from real physics... I read most of the babble you've tainted our wonderful NESR site with, and it seems to me like your damn clueless... Which is why most of your buddies answers sounded like they supported your ideas, because your questions, as well as the answers you "thought" you heard, were biased from the start in hopes that convincing us you're two digit IQ actually surpasses that 140 you dream of having.

I wont get into the power gains, the immense advantage to weight loss on any performance vehicle, because Mr. tax, I know that you could single-handedly bring this thread to 10 pages or more, so I will end rant (which started merely because of the 5 minutes of my life I carelessly wasted reading your muck)...

g'day sir.

[taxonomy]

Originally Posted by Kitt

haha, damn... my engineering degree didn't do shit for me, all this time I thought air was treated as a theoretical fluid....

Pneumatic valves?

What about under some conditions it has elastic properties?

I need to go find a belt now.

[taxonomy]

For those interested they may want to look at this. Intake and Exhaust system tuning

Most of the time I have spent thinking about this is on my commute back and forth to work. This guy goes into more detail than I am can but it's similar conclusions. It's not back pressure, it's pulse timing. Thanks to those that have responded.

Also, just for laughs. Exhaust Length,exhaust pipe,induction

My regards to all. Good luck to the racers.

[ZX-12R]

Originally Posted by taxonomy

If you are not using the full amount of torque (riding at WOT) adding more does not do any good.

That is incorrect. If the exhaust system changed in a way that allowed for an increase in torque without an increase in fuel being burned then the efficiency and power of the engine has increased resulting in better milage and increased performance.

Originally Posted by taxonomy

...and I don't think they are demanding the maximum rate of change in RPM (throttle response)

Originally Posted by taxonomy

Throttle response may be increased or decreased depending on your throttle position, and RPM and how the pipe interacts just there.

If there was, theoretically, an increase in throttle response we would have to demand it to make use of it.

In a situation where we roll on the throttle I doubt that anyone here is doing it quickly enough so that we are going to ask for more response than the stock bike is capable of delivering when the bike is leaned over exiting a corner considering the type of hardware that people are using on this list.

A "rate of change" is an acceleration and that is not what throttle response is. The characteristic you are describing is more an acceleration profile which is a function of a lot of variables outside of the engine. Throttle response is how quickly an engine increases its power output in response to an increase in throttle input. Ideally you want the delay to be as small as possible (better response) so the engine closely matches what your hand is instructing it to do.

[taxonomy]

Originally Posted by ZX-12R

That is incorrect. If the exhaust system changed in a way that allowed for an increase in torque without an increase in fuel being burned then the efficiency of the engine has increased resulting in better milage.

OK, fair enough. Not really a sport riding issue, but point taken.

Originally Posted by ZX-12R

A "rate of change" is an acceleration and that is not what throttle response is. The characteristic you are describing is more an acceleration profile which is a function of a lot of variables outside of the engine. Throttle response is how quickly an engine increases its power output in response to an increase in throttle input. Ideally you want the delay to be as small as possible (better response) so the engine closely matches what your hand is instructing it to do.

True, I had confused these issues/terms. They are closely related. I guess if your hand is only asking for small increases it should be pretty easy for the engine to follow it the throttle input.

Thanks for taking the time to actually read this an make salient points. My thinking on this is enriched.

The Airhead article above is interesting reading.

Adam

[ZX-12R]

Originally Posted by taxonomy

OK, fair enough. Not really a sport riding issue, but point taken.

I'm curious why this wouldn't be a sport riding issue. In the example, the amount of fuel required to get a certain torque output was reduced but the engine is still capable of buring that larger amount of fuel. This is where you get into jetting and fuel remapping to take advantage of the efficiency gains of the new exhaust system. By increasing the amount of fuel at that given throttle input you can increase the power of the engine over stock (a sportrider's or HP nut's goal). This also means you can have power gains all throughout the RPM and throttle range as opposed to WOT only.

[Jayspeed]

To simply describe throttle response is like you just tightened some slack in your throttle cable.

[taxonomy]

Originally Posted by ZX-12R

I'm curious why this wouldn't be a sport riding issue. In the example, the amount of fuel required to get a certain torque output was reduced but the engine is still capable of buring that larger amount of fuel. This is where you get into jetting and fuel remapping to take advantage of the efficiency gains of the new exhaust system. By increasing the amount of fuel at that given throttle input you can increase the power of the engine over stock (a sportrider's or HP nut's goal). This also means you can have power gains all throughout the RPM and throttle range as opposed to WOT only.

There's a couple of things going on here. I am trying to consider the pipe alone only. I know it's multi factorial but for the purposes of this discussion assume that the hypothetical bike in question is properly fuel mapped with and without a pipe. If we start adding other things we might as well add cams and raise compression too.

It's true, at say 25% throttle rotation you can have a gain, but how could that matter if you could have that same gain at 27% throttle rotation without the pipe?

If you accept that it's pulse timing (do you?) that makes power in an after market exhaust and not a reduction in back pressure then you have to ask if logically part throttle will effect pulse timing.

If it does effect pulse timing, and I don't see how it couldn't if air intake is radically changed because the butterfly is closed, pressure in the cylinder is reduced etc.

I totally agree that after market exhausts can increase performance under some conditions, those conditions are the ones the exhaust was designed to exploit, namely high gas escape velocity from the cylinder e.g. WOT.

I just think that by definition people don't ride at WOT if they are rolling on the throttle. Where is it being rolled on from? Part throttle.

[Jayspeed]

Originally Posted by taxonomy

It's true, at say 25% throttle rotation you can have a gain, but how could that matter if you could have that same gain at 27% throttle rotation without the pipe?

Because 27% will have a gain too. The gain from exhaust is minimal on a stock motor. It could span the whole rpm range. In some cases, it may arch upward more in some areas than others. Seeing how your practical, don't buy one. If I were you though, I'd get one just to see for yourself so you could end your eternal research.

[taxonomy]

Originally Posted by Jayspeed

Because 27% will have a gain too. The gain from exhaust is minimal on a stock motor. It could span the whole rpm range. In some cases, it may arch upward more in some areas than others. Seeing how your practical, don't buy one. If I were you though, I'd get one just to see for yourself so you could end your eternal research.

If you never use more than 80% of throttle position you could just dial in a couple more degrees. Do people ride fast bikes with the throttle all the way open? On the street?

I actually bought a used bike with a Two Brothers can on it. I purchased a stock system to replace it with. All of this arose basically because I was riding back and forth to work and wondering what the change would be. The I started asking myself how this stuff actually works. I can't imagine it'll matter to me to go back to stock, but we'll see.

I had a CB1 with and without an exhaust. That was interesting. That bike got ridden wide open a lot.

Just from a theory point of view I'd think a really good fuel mapping system, like a Power Commander III would offer the best real world gains for most people at more throttle positions and RPMs. I think rejetting could offer real world gains too.

I can build the Puch Maxi Moped to it's limits for a lot less than $1000. Raise compression, displacement, pipe , carb, intake, reed valves. So, it'll be interesting to experiment with. For that much money I can build wheels with Aluminum rims too. It'll be interesting to do some tuning again.

[g®eg]

I got a new pipe for the XR-L

huge improvement

[Kurlon]

If your theory was the only method of explaining how an exhaust works, throttle position wouldn't matter. Partial throttle, WOT, based on the amount of impact you're saying pipe harmonics have you'd never see anything other than sawtooth power curves zigzagging up and down.

That theory is only one way of looking at a pipe's operation. It doesn't fully describe the system though.

[taxonomy]

Originally Posted by Kurlon

If your theory was the only method of explaining how an exhaust works, throttle position wouldn't matter. Partial throttle, WOT, based on the amount of impact you're saying pipe harmonics have you'd never see anything other than sawtooth power curves zigzagging up and down.

That theory is only one way of looking at a pipe's operation. It doesn't fully describe the system though.

I'm not sure you don't see sawtooth curves for the +/- 10% torque being added (or taken away?). I don't know. I can't really say how long the length of that sawtooth wave is. Maybe it's not jagged, maybe it's long. Maybe it's long enough that it covers most of the area under graph while it's "up". I hadn't thought of that before.

Maybe there's something I am missing, there surely is. I will admit I really can't describe something that complicated.

From the "serious" stuff I have seen on intake and exhaust tuning, diameter and length, that's what it is. It's Heimholtz. It's resonance. It's actually tuning. That's why I always thought the Yamaha tuning fork logo was cool, even though it's not what it means. Motors really do hum at some level.

Are you racing the CRF? I'd like to find something really little worth tuning. Somthing cheap enough to fool around with, something with gears that will support a 180 pound adult. I rode and very much liked some little two stroke things in Europe way back, Zundapps? The Puch fell in my lap and there's a lot of cheap performance kits for them, oddly enough. I'd be very happy tuning that if it only had gears.

[BCT748]

Originally Posted by taxonomy

I can't really say how long the length
maybe it's long. Maybe it's long enough
while it's "up".

Maybe there's something I am missing, there surely is. I will admit I really can't describe something that complicated.

diameter and length, that's what it is.
I hum at some level.

[Jayspeed]

Originally Posted by taxonomy

If you never use more than 80% of throttle position you could just dial in a couple more degrees. Do people ride fast bikes with the throttle all the way open? On the street?

Yes. And some of them do it at more extremes at the track too.

[ZX-12R]

Originally Posted by taxonomy

If you accept that it's pulse timing (do you?) that makes power in an after market exhaust and not a reduction in back pressure then you have to ask if logically part throttle will effect pulse timing.

I think the majority of power gains in a full system aftermarket exhaust is due to the reduced back pressure. The tuning of the pipe is the little something extra that makes the better manufactures consistantly show higher gains with their systems over lesser known or cheaper brands.

A slip-on is mostly for sound and looks as you don't often see more than 5HP gains with them.

[taxonomy]

Originally Posted by ZX-12R

I think the majority of power gains in a full system aftermarket exhaust is due to the reduced back pressure. The tuning of the pipe is the little something extra that makes the better manufactures consistantly show higher gains with their systems over lesser known or cheaper brands.

A slip-on is mostly for sound and looks as you don't often see more than 5HP gains with them.

This is where we part company. If you are interested take a look at the link I posted above or at SSearchVT's post earlier in this thread.

Most of the efficiency gains are pulse timing and scavenging from what I have read. Lyle Cummings is another pretty good technical writer about this stuff. Heir to the Cummings engine fortune.

Anyhow, if you look around and dig into the SAE kind of stuff I think you'll see it's pulse timing. This is my understanding of it anyhow.

[SSearchVT]

Originally Posted by taxonomy

This is where we part company. If you are interested take a look at the link I posted above or at SSearchVT's post earlier in this thread.

Most of the efficiency gains are pulse timing and scavenging from what I have read. Lyle Cummings is another pretty good technical writer about this stuff. Heir to the Cummings engine fortune.

Anyhow, if you look around and dig into the SAE kind of stuff I think you'll see it's pulse timing. This is my understanding of it anyhow.

Pulse timing and scavenging are only two of many variables that affect the efficiency or performance (they're not necessarily related) of engines.

Pulse timing is a result of gas flow and engine harmonics (combustion occuring at a certain rate, and being pushed through a pipe). But the geometry, material, surface condition, and temperature of the pipe all play a role.

All of the variables need to be considered - starting from the air before it passes through the filter, and the fuel in the tank - and ending with the exhaust gases as they exit the tailpipe - for a true statement to be made about performance or efficiency. You will also get different results if the engine is on a dyno or in an actual vehicle (ram air affect, and the pressure area around the tailpipe).

[taxonomy]

Originally Posted by SSearchVT

Pulse timing and scavenging are only two of many variables that affect the efficiency or performance (they're not necessarily related) of engines.

All said above by SsearchVT is probably the most accurate of statements made during this whole discourse. From what I know reduced back pressure is a player, but a lesser one and one of many.

I think if you put a 1 HP shop vac in blower mode to the intake and of an exhaust it would blow through pretty easily, even a "tight" stock exhaust. It's not like you're using up gobs of HP forcing air through teh DOT pipe that you suddely win back when you take a sawsall to the muffler.

It's all very much like mods were people drill their stock airbox or install individual filters. Sure, the restriction goes down but the other effects are destroyed and the dyno chart suffers.

[Kurlon]

Originally Posted by taxonomy

I think if you put a 1 HP shop vac in blower mode to the intake and of an exhaust it would blow through pretty easily, even a "tight" stock exhaust. It's not like you're using up gobs of HP forcing air through teh DOT pipe that you suddely win back when you take a sawsall to the muffler.

While the resistance to low flow may not change much, removing a baffle can and does affect the percieved backpressure the engine observes by removing a reflecting wave.

This is why there is a trend for larger and larger diameter OEM canisters now, more flow/hp while retaining sound deadening ability.

And there are bikes that respond greatly to airbox modifications without 'destroying' their midrange or dyno curves. Again, my ST3 is a great example, three holes in the airbox lid, positive gain across the board. I could have gone with a kit 'lid' that basically eliminates the top and just provides enough of a ring to retain the air filter for larger gains, but I ride in the wet quite a bit, so I reduce liquid water intrusion significantly by retaining the front of the lid.

I have seen midrange suffer on a bike where the airbox was removed to make room for pod filters, but the gain on top provided what that rider wanted so who am I to say he's doing it wrong?

[taxonomy]

Originally Posted by Kurlon

While the resistance to low flow may not change much, removing a baffle can and does affect the percieved backpressure the engine observes by removing a reflecting wave.

This is why there is a trend for larger and larger diameter OEM canisters now, more flow/hp while retaining sound deadening ability.

This is a useful observation. Thanks for that,

I think if you reposition the wave enough, at some throttle openings and some RPM you can actually reposition the wave so it's a vacuum when the valve opens. That's when exhausts become "magic" free HP.

Crossover pipes and EXUP values can maximize the conditions that this occurs under.

[ZX-12R]

Originally Posted by taxonomy

I think if you put a 1 HP shop vac in blower mode to the intake and of an exhaust it would blow through pretty easily, even a "tight" stock exhaust. It's not like you're using up gobs of HP forcing air through teh DOT pipe that you suddely win back when you take a sawsall to the muffler.

You can't visualize the system like that for a few reasons. First, a shop vac provides a steady state flow as opposed to pulses. Second, the shop vac doesn't flow enough air to mimic an engine (especially larger ones). Third, a shop vac doesn't produce enough pressure to mimic an engine.

The muffler isn't the only portion of the exhaust that restricts flow. Messy welds, improper bends, catalytic converters, etc., are all part of the equation. You also use more HP than you realize forcing exhaust out of the engine. Modern 600's are lucky to make 50lbs-ft of torque which is substantially less than what an average person can muster with a wrench. Even though their torque is low, they make large HP numbers because they rev extremely high. At high RPMs, a small change in torque can translate into a significant change in HP. If a 600 is producing 45lbs-ft at 13K it is making about 111HP. A small increase in torque to 47lbs-ft at 13K translates to 116HP which is a rather significant gain.

[SSearchVT]

Tax - you're trying to force the results to fit your conclusion by focusing on certain variables and ignoring others.

Modifying the power delivery from an internal combustion engine needs to be approached systemically starting with the proposed use (race bike, tow vehicle, top fuel drag car...). Proper design examines the current system and finds the limiting factor - be it the air filter, intake throats, head flow, valve shrouding, etc - in the desired operating scenario.

[ChR1s]

[taxonomy]

Awesome. My old VFR, with Supertrapp! Used bikes almost always come with pipes, unfortunately. I also hated that Chase Harper tank bag.

I think this has devolved into pure semantics.

My only point at the start of this whole thing was that throttle position plays a role in this. That's it. It plays a role because it's a tuned system and throttle position is a huge variable.

It's not a simple matter of reducing back pressure. Whoa, what too complicated for a forum discussion, and I only sort of know what I am talking about and I am addressing like three or four issues at once, and all sorts of other arguments are being dragged into the conversation. Too confusing!

That's it. Throttle position plays a big role in the performance of an exhaust and it's ability to enhance performance. The only other thing is that the most prominent data set we have, dyno charts are all data sets from WOT. So, I don't think they're great tools for assessing part throttle effects from pipes.