Well, for your very technical question I can only offer you a non-technical answer. Based on all I have read and the knowledge I have obtained, Triumph has the Exup valve in place for the sole reason of passing exhaust restrictions in place. It is my belief there is no actual advantage to the device, nor any gains to be noted due to its presence.

Most people remove it because it is prone to freezing and is a constant problem for owners. It is merely a matter of time. Triumph will fix the valve under warranty. They spend a lot of time doing so and no doubt lose money doing it. It is a known design flaw so you would think the brilliant minds at Triumph would work it out of the design since it is so prone to failure and, consequently, costing them money. There is one reason it is still there...because it has to be so they can continue to sell bikes.

After removing mine and tuning for it, I assure you I experienced no performance difference one way or another. Take all of this with a grain of salt; I'm merely a firefighter/paramedic.

Sent from my HTC One

 

Damn double posts.

 

Blast from the past:

http://www.triumph675.net/forum/showthread.php?t=31029

 

Thanks for posting that up hordboy. If nothing else than for a humorous read!

 

Right, as long as you tune for it, it won't hurt performance at all. But if all you do is remove it, then you might feel a difference. I felt a minor dip in power in the 4-5k range when I did this (again, without changing the tune).

Basically listen to whatever Hordboy says. He knows what he's doing.

 

Thanks everyone. Is the biggest issue a lean condition that is created when the valve is removed? Seems like a good tuner like Bazzaz or PCV would remedy that situation quickly.

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Hordboy, thanks a bunch. Just what I was looking for.

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Yes, with EXUP removal the fueling goes quite lean. I haven't messed with Bazzaz or PC's much on 675's so I don't know if you could tune it correctly with those or not. With Tuneboy/TuneECU, it takes substantial changes to the F & L tables to make the fueling correct.

The way I see it, the main reason for EXUP and intake flapper gizmos on modern bikes is so they can be tuned to meet noise requirements in many different markets (via software) with one set of hardware. YMMV.

 

When you say "Exup Removal", do you mean welding in a straight pipe and removing it completely? Or do you mean just turning it off in TuneECU, removing the motor and letting the return spring hold the valve open all the time?

I just did the latter of the two until I can find a decent local welder to modify my stock header with a straight pipe in place of the Cat and Exup.... Or get an aftermarket header if I win the lottery...

Runs fine with the EXUP motor and cables removed entirely. The spring holds open the valve by default, as long as it's not stuck in place after removing the motor and cables.. (thanks for those of you who answered my question about this a few weeks ago when I was reinstalling my motor). Just make sure to turn off the EXUP in TuneECU.

I dont have any data to back this up, but I didn't notice any difference whatsoever with the exup functioning as it did from the factory vs. having the valve 100% open all the time. Honestly, I didn't even notice any difference in the way the bike sounds..

But I was playing with the valve when I first started the bike to see what it sounded like at idle and revving it to 2-3K when it was open all the way vs. when I manually closed it all or part of the way. With a side by side comparison, I did notice it was quieter, but ONLY when it was closed as far as I could twist it by hand... and ONLY at idle.

I hope that answers some of your questions.

Some people would argue... "If the EXUP valve was so beneficial, why don't aftermarket headers have them?". The main reason is that the aftermarket headers are intended for more specific riding conditions than the stock header. Aftermarket headers are designed to add power, mostly in the upper RPM range when it's needed for racers. Whereas the stock header needs to be designed to meet a ton of standards all across the world, and appeal to a very broad market. Maybe helps improve driveability for a variety of different conditions the bike "could" be in. Aftermarket headers are designed for a specific set of conditions. And the EXUP valve doesn't help one bit for those specific conditions the aftermarket headers were designed for.

I'd like to see different types of crossover pipes, and different length tubes experimented with in aftermarket header designs... That's where the power can be extracted. The factory headers have straight tube crossover pipes.. What about X-shaped crossover pipes placed at specific points (closer or further away from the header flange to coincide with the exhaust timing between the 3 cylinders to improve scavenging, or simply changing the length for certain cylinders to get the same type of result. You see it in V8 car header designs and midpipe designs all the time..

Homer

 

Hordboy, I spent an hr reading through the post. Good work.

I'm an engine calibrator for a large automaker in the US. I focus specifically in drivability tuning of small turbocharged gas engines.

I believe the valve exists on this engine for noise control. Period.

If triumph could make the same curves with some enrichment and no valve they would in a heartbeat. That's more profit in their pockets and less Tgw (things gone wrong) to worry about. Based on the track record of this valve I'm sure they would do anything to get rid of it entirely.

Truth is they can't do so because govt regs simply don't allow it. And if they don't pass cert, they don't sell bikes. Nuff said.

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A/F

Yes, quite funny indeed.

I noticed that some of the curves have an A/F of approx 13-13.2 during open loop WOT. This came to me as a surprise, as in my industry, car engines are tuned during mapping to a bit richer for peak torque (LBT).

Is the general consensus that LBT for this engine is approx 13? If so, does this include the low end torque lean condition from removing the EXUP? In other words, does that region benefit from further enrichment beyond 13 or so to achieve a smooth torque curve? If so, I'd appreciate some insight (backed with data, if possible).

Also, I have to agree with others who posted that people with excellent backgrounds in engine theory and development often times get deterred from going to forums because of what they read. There tends to be more misinformation on these sites than helpful info for those who are willing to listen and learn.

For example, the concept that running slightly rich will burn up your cats is absurd. cats like rich conditions where there is less oxygen when it comes to CO emissions. We typically run engines at stoic not because we want to, but because, for example the 3-way catalyst is most efficient at reducing nitrogen compounds to N2 and O2 at this ratio. If you look at any trace of NOx generation, you will find that on a car without a cat running rich, the amount of NOx produced is actually reduced substantially on the rich side of 14.7A/F. But its not what the engine produces, its what the catalyst WANTS at its input in order to be most efficient. This is what most don't understand. A catalyst WANTS a 14.7A/F in order to convert the NOx most efficiently. So for an engine tuned for a cat, the NOx at the input to the cat is higher than if we were to tune for low NOx without a cat, but the net result out the tailpipe is an overall reduction of NOx.

The issue with running slightly rich is simple...Most vehicles disable injectors on coast downs to save on fuel and get better MPG. If the catalyst contains a fair amount of unburnt fuel and is then exposed to a high level of oxygen (from injector shutdown) then the fuel will tend to burn and get the catalyst VERY hot, potentially damaging it. It also runs less efficient after injector shutdown because it needs to rejuvenate itself with fuel compounds through enrichment to be again, most efficient. After cutout, we tend to add a small amount of enrichment for a brief period to counteract the lean condition on throttle tip out.
Why you see o2 sensors toggling is not because the o2 sensor is dumb. We do this with wideband sensors as well. We purposely do this to ensure the catalyst metals have the correct amount of compounds to be, again, most efficient at reducing pollutants.

So in the end, my 25 year emissions development engineer friend and coworker knows what he is talking about. I listen to him. And as far as running slightly rich goes... OEM manufacturers do it all the time to protect the catalyst from overheating and failing. If you tow, you are likely enriched heavily, and potentially for very long periods if you are climbing grades. The EPA would prefer short time higher pollutants in order to protect the cat vs a lifetime of a failed catalyst polluting daily. The cat won't be damaged with minor enrichment. If it worries you, run the stock map from time to time to rejuvenate the cat. Its that simple. I don't expect the 675 engine disables injectors on tip outs. The engine does not have enough inertia and could easily stall if the RPM were not high enough. Shutoff also introduces a NVH (noise vibration harshness) condition upon reenable. Likely just not worth it nor worth the risk to Triumph for the fuel economy gains on this type of bike that is not intended for Fuel Economy leadership.

If anyone feels the need to argue, its not warranted. Facts are facts.

Oh and for people to assume stoichiometry of gasoline changes as a function of different variables, that is a myth. stoic is a chemical ratio that has nothing to do with ambient conditions, unless one suggests the chemical composition of gasoline in my tank changes as I vary my altitude:rofl2:

 

Yes, quite funny indeed.

I noticed that some of the curves have an A/F of approx 13-13.2 during open loop WOT. This came to me as a surprise, as in my industry, car engines are tuned during mapping to a bit richer for peak torque (LBT).

Is the general consensus that LBT for this engine is approx 13? If so, does this include the low end torque lean condition from removing the EXUP? In other words, does that region benefit from further enrichment beyond 13 or so to achieve a smooth torque curve? If so, I'd appreciate some insight (backed with data, if possible).

Also, I have to agree with others who posted that people with excellent backgrounds in engine theory and development often times get deterred from going to forums because of what they read. There tends to be more misinformation on these sites than helpful info for those who are willing to listen and learn.

For example, the concept that running slightly rich will burn up your cats is absurd. cats like rich conditions where there is less oxygen when it comes to CO emissions. We typically run engines at stoic not because we want to, but because, for example the 3-way catalyst is most efficient at reducing nitrogen compounds to N2 and O2 at this ratio. If you look at any trace of NOx generation, you will find that on a car without a cat running rich, the amount of NOx produced is actually reduced substantially on the rich side of 14.7A/F. But its not what the engine produces, its what the catalyst WANTS at its input in order to be most efficient. This is what most don't understand. A catalyst WANTS a 14.7A/F in order to convert the NOx most efficiently. So for an engine tuned for a cat, the NOx at the input to the cat is higher than if we were to tune for low NOx without a cat, but the net result out the tailpipe is an overall reduction of NOx.

The issue with running slightly rich is simple...Most vehicles disable injectors on coast downs to save on fuel and get better MPG. If the catalyst contains a fair amount of unburnt fuel and is then exposed to a high level of oxygen (from injector shutdown) then the fuel will tend to burn and get the catalyst VERY hot, potentially damaging it. It also runs less efficient after injector shutdown because it needs to rejuvenate itself with fuel compounds through enrichment to be again, most efficient. After cutout, we tend to add a small amount of enrichment for a brief period to counteract the lean condition on throttle tip out.
Why you see o2 sensors toggling is not because the o2 sensor is dumb. We do this with wideband sensors as well. We purposely do this to ensure the catalyst metals have the correct amount of compounds to be, again, most efficient at reducing pollutants.

So in the end, my 25 year emissions development engineer friend and coworker knows what he is talking about. I listen to him. And as far as running slightly rich goes... OEM manufacturers do it all the time to protect the catalyst from overheating and failing. If you tow, you are likely enriched heavily, and potentially for very long periods if you are climbing grades. The EPA would prefer short time higher pollutants in order to protect the cat vs a lifetime of a failed catalyst polluting daily. The cat won't be damaged with minor enrichment. If it worries you, run the stock map from time to time to rejuvenate the cat. Its that simple. I don't expect the 675 engine disables injectors on tip outs. The engine does not have enough inertia and could easily stall if the RPM were not high enough. Shutoff also introduces a NVH (noise vibration harshness) condition upon reenable. Likely just not worth it nor worth the risk to Triumph for the fuel economy gains on this type of bike that is not intended for Fuel Economy leadership.

If anyone feels the need to argue, its not warranted. Facts are facts.

Oh and for people to assume stoichiometry of gasoline changes as a function of different variables, that is a myth. stoic is a chemical ratio that has nothing to do with ambient conditions, unless one suggests the chemical composition of gasoline in my tank changes as I vary my altitude:rofl2:

I have a lot less experience than you in this particular field, but I know how rich is too rich for catalytic converters.... I can't tell you the exact air fuel ratio, but you'll know it right off the bat if it happens... your cat(s) will smell like rotten eggs. It happened to me when I brought my 83 T-Top Mustang GT with me when I moved to a county in Pennsylvania that just happened to require an additional "emissions sticker" next to the inspection sticker on the windshield. My 83 Mustang has a 302 with an Edelbrock 600CFM carburetor that always runs rich no matter what I do. Anyway, in order to register my car in this county with the extra emissions requirements, I had to install 2 new cats on it. And from then on until I gutted those damn things a few months later, it always smelled like rotten eggs, especially cruising around town. I could lean out the idle mixture but I needed jets to change the mid and high speed mix (the primary and secondaries as they are called).

I'm willing to bet that thing cruised in the 12.0 to 12.5 AFR, and the more you put your foot in it the richer it got.

Our bikes are fuel injected technological marvels with sophisticated and precise fuel delivery. Leaps and bounds ahead of the stone age carburetor tech in my 83 Mustang (I love that car, bless it's heart).

You made some great points about why it's not a bad thing to add slightly more fuel. Very interesting and valuable info that will be very helpful for me as I hone my TuneECU skills. With gasoline tunes, I've always gone slightly leaner for the cruising RPM, especially between 5000 and 6500 RPM where I'm usually not accelerating or decelerating....With the goal of improving highway fuel mileage on long trips when the engine is in its sweet spot. I've also kept it lean during throttle positions under 30% where I'm accelerating lightly and don't need a ton of extra power. Again, this is to help improve fuel economy.

But on the other hand, as I have learned while tuning my 99 Mustang Cobra running a Procharger and 12 lbs of boost with 10.5:1 compression: adding fuel is a good safeguard. From what I learned tuning that monstrosity, it's always been a habit to go a half point richer than the rich suggestions people make when nearing redline RPM with 90-100% TPS. Dumping fuel right at the last hurrah is one extra little safeguard against a catastrophic failure right when the engine is at peak load, stress, rpm, etc..

Adding fuel cools things down too.. Although I have never had an overheating problem, I would richen the mixture at idle, right at the same time where there's no air flowing across the radiator and the temp starts to climb. That helps a little...

Like I said before, I've always been one to err on the lean side to try and make power while still keeping enough margin of error to avoid detonation.. I typically don't push it to the limit but I push it to the end of my comfort level.

But keep in mind I haven't done any mods to my bike that really require extra fuel... (exactly the opposite if my boosted mustang), so I've always been working to optimize the stock style map...

I'll need to buy an expensive bolt on in order to have the need for more fuel (gasoline anyway). But I don't see that happening anytime soon unless someone with a header and/or a slip on is interested in trading for some extra parts I have, like a set of 2 woodcraft stator and timing chain covers, some bodywork, engine assemblies, and what have you.

But going back to the topic at hand....

I doubt you're gonna over fuel the cat unless you accidentally install a map designed for a power adder like a turbo... or you take my E-85 only map and fill it with gasoline instead (that has an air fuel ratio of around 9.7:1 instead if 14.7:1. I'll say anything richer than....maybe 11:1 at low RPM and TPS, you'll get a whiff if rotten eggs.

Anyone agree or disagree?

 

If the exup truly did improve low end tq, I certainly don't see it. My bike with the exup is worthless for acceleration below 7k so even if removal did hurt behavior with a bone stock tune, I wouldn't care. Even when cruising I am likely at 7k or higher.

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There is a huge misconception about "rotten egg" smells among consumers.
Here are the facts:

1. Rotten egg smell is caused by sulfur in the FUEL...not the catalyst materials.
2. Years ago, North American fuels used to contain 500ppm of Sulfur. Nowadays, the count is less than 20 ppm.
3. The rotten egg smell triggers in catalysts comprised of platinum, but with a substandard amount of nickel. Nickel is cheap. European cats were more susceptible to inadequate nickel content because the regulators there used to believe that compounds of nickel were poisonous, however, in the US, they did not. Non-US cars were more susceptible to the smell because of this.
4. Rotten egg smell is Hydrogen Sulfide, or H2S. It is created when
a. The catalyst is running below a nominal operating temperature (typical nominal temps are above 800F)
b. The engine is running lean (this stores SO2 in the catalyst, which then gets converted to SO3, and then a more complex sulfur compound which, in the presense of a rich condition, gets released from the catalyst as H2S.

So you cant get the rotten egg smell unless the engine previously ran lean and stored the compounds which eventually led to the rotten egg smell.

A catalyst that is always seeing a rich mixture should never get the smell.

Likewise, a good designed catalyst in the presence of modern fuels should never smell like rotten eggs because of at least one of the following:
1. It is not platinum based
2. It is platinum based but contains adequate amounts of nickel
3. Most importantly, the quantity of sulfur in modern gasoline is simply too small.

This information was taken from an archived calibration guide we used to counteract the smell that resulted from high sulfur content fuels. It is accurate and correct.

Anecdotal evidence is not evidence to an engineer.

Lastly, I always get a kick out of the aftermarket talking about A/F. In the industry, we only refer to it is Equivalence ratio, or lambda. This is the ratio of actual A/F over stoichiometric A/F. We use it for two reasons:

1. All O2 (UEGO, HEGO, etc) sensors deliver an equivalence ratio that is normalized to whatever fuel is being used. It simply measures relative oxygen content, so the type of fuel is washed out of the equation. Additionally, when we write the ECM software, equivalence ratio is used because it prevents us from ever needing to have unique calibrations based on fuel type. Lambda is lambda. The work to determine stoichiometry is up front. I never understood why aftermarket tuners keep using A/F. It is poor usage because the A/F of a fuel with 10% ethanol is not the same as a fuel with no ethanol.

I would love to see a tuner use lambda instead of A/F. A/F can be misleading otherwise. If OEMs use it, I can guarantee it is the most accurate form of measurement.

 

Lastly, I always get a kick out of the aftermarket talking about A/F. In the industry, we only refer to it is Equivalence ratio, or lambda. This is the ratio of actual A/F over stoichiometric A/F. We use it for two reasons:

1. All O2 (UEGO, HEGO, etc) sensors deliver an equivalence ratio that is normalized to whatever fuel is being used. It simply measures relative oxygen content, so the type of fuel is washed out of the equation. Additionally, when we write the ECM software, equivalence ratio is used because it prevents us from ever needing to have unique calibrations based on fuel type. Lambda is lambda. The work to determine stoichiometry is up front. I never understood why aftermarket tuners keep using A/F. It is poor usage because the A/F of a fuel with 10% ethanol is not the same as a fuel with no ethanol.

I would love to see a tuner use lambda instead of A/F. A/F can be misleading otherwise. If OEMs use it, I can guarantee it is the most accurate form of measurement.

Some do refer to lambda. Most refer to A/F because they are tuning a bike for maximum output using a specific fuel. If this fuel is 10% ethanol so be it. 'aftermarket tuners' as you call them do not have the restrictions that manufacturers do. They can tune a bike for one fuel and improve output when compared a tune that has to work with different types of fuel in a variety of environments.

Comparing what a manufacturer does is similar to comparing what a racer does.

Manufacturers have limitations, regulations, and per unit budgets that individuals don't. Their equipment has to work for everyone in every situation (more or less). Individuals can modify this mass produced piece of equipment to work better FOR THEM and the way THEY USE the equipment.

Racers are on the other extreme. By racer I am referring to big money racing such as Moto GP, and other professional series...Many people compare what a racer does or how a race bike is set up to how a daily driver, budget minded track day rider, or club racer does. Professional racers have the financial backing that individuals don't, they can tear apart their engine and suspension after a day's use, we cant. Not to say their equpment does not have to last, but they have the means to make it a bit more disposable than most of us.

In the end both of these comparisons are fallible, but for different reasons.

 

There is a huge misconception about "rotten egg" smells among consumers.
Here are the facts:

1. Rotten egg smell is caused by sulfur in the FUEL...not the catalyst materials.
2. Years ago, North American fuels used to contain 500ppm of Sulfur. Nowadays, the count is less than 20 ppm.
3. The rotten egg smell triggers in catalysts comprised of platinum, but with a substandard amount of nickel. Nickel is cheap. European cats were more susceptible to inadequate nickel content because the regulators there used to believe that compounds of nickel were poisonous, however, in the US, they did not. Non-US cars were more susceptible to the smell because of this.
4. Rotten egg smell is Hydrogen Sulfide, or H2S. It is created when
a. The catalyst is running below a nominal operating temperature (typical nominal temps are above 800F)
b. The engine is running lean (this stores SO2 in the catalyst, which then gets converted to SO3, and then a more complex sulfur compound which, in the presense of a rich condition, gets released from the catalyst as H2S.

So you cant get the rotten egg smell unless the engine previously ran lean and stored the compounds which eventually led to the rotten egg smell.

A catalyst that is always seeing a rich mixture should never get the smell.

Likewise, a good designed catalyst in the presence of modern fuels should never smell like rotten eggs because of at least one of the following:
1. It is not platinum based
2. It is platinum based but contains adequate amounts of nickel
3. Most importantly, the quantity of sulfur in modern gasoline is simply too small.

This information was taken from an archived calibration guide we used to counteract the smell that resulted from high sulfur content fuels. It is accurate and correct.

Anecdotal evidence is not evidence to an engineer.

Lastly, I always get a kick out of the aftermarket talking about A/F. In the industry, we only refer to it is Equivalence ratio, or lambda. This is the ratio of actual A/F over stoichiometric A/F. We use it for two reasons:

1. All O2 (UEGO, HEGO, etc) sensors deliver an equivalence ratio that is normalized to whatever fuel is being used. It simply measures relative oxygen content, so the type of fuel is washed out of the equation. Additionally, when we write the ECM software, equivalence ratio is used because it prevents us from ever needing to have unique calibrations based on fuel type. Lambda is lambda. The work to determine stoichiometry is up front. I never understood why aftermarket tuners keep using A/F. It is poor usage because the A/F of a fuel with 10% ethanol is not the same as a fuel with no ethanol.

I would love to see a tuner use lambda instead of A/F. A/F can be misleading otherwise. If OEMs use it, I can guarantee it is the most accurate form of measurement.

That's really awesome information. You have far more knowledge than I do about these things. \

All I know is that my carbureted 83 T-Top mustang GT smelled like rotten eggs after the local mom & pop exhaust shop / "emissions inspection shop" installed a set of off the shelf, no-name cats on my existing exhaust system where there were none before. The car ran rich under most conditions, but hardly ran lean. (maybe the it had a lean idle at some point or another because that's the only mixture you can adjust without changing jets)

This was about 15 years ago, and they were far from high quality cats.

You mentioned that the rotten egg smell is sometimes caused by an insufficient operating temperature... I.E. Something's causing them to not run as hot as they should. A rich air/fuel ratio can cause this.. But I think it was compounded by the fact that the cats installed on my mustang were a little further downstream than they should have been. On OEM midpipes (and aftermarket midpipes with high flow cats), the cats are usually mounted as close to the connection to the exhaust manifolds as possible, usually 6 inches to 12 inches, but hardly more. The cats in my 83 were mounted about 2 feet from the midpipe's connection to the exhaust manifolds. They were square underneath the car next to the middle of the transmission. Being that far away from the exhaust manifold can also cause insufficient heating.

Nevertheless, that's a completely different topic. The point I was trying to make was that EFI tuning is so much more precise and efficient than my old carbureted mustang and it's unlikely you'll have problems with your cat caused by too rich of an air fuel ratio.

I'm glad you mentioned lambda because I recently wrote an E-85 tune for my bike and finally got the balls to load it on the computer and pour a tank full of the stuff. Sure as shit, it started right up. The mid range power increase was "stunning" to say the least. I have an AEM Wideband Failsafe gauge in my 99 supercharged mustang, but I have it set up with a quick disconnector on the main 16 pin wiring harness (for 12V, TPS, RPM inputs, but mostly a wide variety of datalogging outputs) so I can leave the wiring permanently installed in the car and then plug in to the same connector I installed on my bike after running the wiring. I still have to remove the UEGO sensor from my car and put it on the bike, but that's a separate harness altogether, so no big deal.

Anyway, I usually view the actual Air/Fuel ratio when it's in my car because I'm most familiar with what the values should be in a boosted application running on gasoline.

To avoid confusing myself when fine-tuning my E-85 base map (which has worked out better than I could have imagined so far), I plan on reconfiguring the gauge (via USB cable and included software) so the primary OLED screen will display the Lambda value in this case. But for reference, I'll use the outside LED ring and corresponding faceplate to show the actual AFR values as well.
(It also has a customizable 3 color LED ring around the outside that can be It has a number of different faceplates that either show AFR values, lambda values, or vacuum numbers (in/hg) or boost & vac numbers (PSI & in/hg).

I'll be hooking that up this weekend. I can't wait. It won't be permanently installed on the bike, but used for a week or so until I can get enough different datalogs under various riding conditions from the on board datalogger on the AEM Wideband Failsafe Gauge itslef (Reads AFR/Lambda, RPM, and MAP, in addition to the OBDII datalogs im collecting from ELM327 wifi data adapter, iPhone and DashCommand app (or any other more meaningful apps I can find)

The whole reason why I mentioned E-85 in an otherwise unrelated thread is because you have to burn about 30% more of it. The stoich air fuel ratio is somewhere around 9.7:1, but 8:1 is a good ratio at WOT. That's RICH.

I'm not sure if an air fuel ratio that rich will have the same affect on my cat the OP was asking about. Also it burns a lot cooler than gasoline, so the 02 sensor won't heat up as much. (Average engine temp on gas is 195 deg F, on E-85 is 165 degrees.) If I do have problems with it, I'll just cut it out, but I'm curious nonetheless.

Just curious

 

I looked into the cam timing and duration on the D675's.

Another piece of info to clarify to folks considering removing their Exup.

Question: Why does the engine run lean in the low RPM band when EXUP removed and stock tune used?

A possible answer (Dyno testing would be the proof)

Has to do with air charge scavenging. On an engine with moderate to high overlap and low RPM, there is a phenomenon called "blow through". This is where the exhaust pressure is somewhat low. In fact, it is typically lower than the intake pressure coming into the cylinder. When this happens, the cylinder achieves high VolEff (maximum air charge) because gas flow continuity actually causes intake air to be pushed out of the exhaust valve when both are open at the same time. This can sometimes be tough to model s it can only be done with open loop control. The added unburned oxygen can affect closed loop A/F control. Manufacturers incorporating variable valve timing actually adjust the exhuast valve timing to allow for late exhaust valve closing in order to take advantage of this "supercharging" effect and achieve the highest possible level of brake torque whe the customer requests max performance.

As the engine speed increases and exhaust pressure builds (IE from turbo wastegate or restrictive catalyst/exhaust) then the "blow through" phenomenon gets reversed (higher exhaust pressure vs intake pressure) and now the problem becomes an issue with burned gas residuals not being scavenged properly out the valve. This causes reduced VolEff and less power. This is why the exhaust valve closing is made earlier at high RPM, as it prevents reduced VolEff.

My theory is that the exup increases exhaust pressure and thus prevents the blow-through from occurring. As a result, the open loop tuning requires less fueling since VolEff is reduced (Basically there is less air to burn). So when you remove the exup, the open loop control doesn't know this, and thus is sending less fuel to the injectors than the air requires. If these bikes used mass airflow sensors, this would be less of an issue. But since they are "speed density" (Based on MAP, throttle plate angle and air temp), the ECM simply doesn't know how to compensate. As a result, you get a lean condition. This will not happen during closed loop control, contrary to opinion. The fueling will compensate and should only happen during open loop operation (Typically above a certain throttle opening when max torque is desired by the customer)

Exhaust wave theory could play a role as well, but as I said before, I don't believe the EXUP is being used to promote exhaust scavenging. I believe it is an easy way to tune the bike for different markets with different drive by noise laws, yet not have to deal with a restrictive exhaust at high RPM. I guarantee the exup cal for EU bikes differs from the cal for US bikes.

Anyway...Just a thought.

 

I was just talking with my fellow "engine buddy" at work the other day about the overlap on these bikes... According to MacBandit, the D675 has 50.75 degrees of overlap and the Street Triple has 25.35 degrees of overlap.

It would make sense to use a variable restriction in the exhaust to reduce "blow through".

Then again, on a race motor, the only time it becomes a concern is during the specific RPM range that the engine is operating at on the track. They could care less about "Blow through" at idle and lower RPM's.

On a race motor (on the street), perhaps it can be tuned to reduce any negative effects of blow through.

But keep in mind that there's only one EXUP valve.. for all 3 cylinders, all at different points in the combustion cycle. If one were to use a valve to control blow through, it makes more sense (in my twisted head anyway) to have one for each individual cylinder. I know, I know, that adds a ton of complexity and potential for malfunction (especially if they build them like the standard EXUP valves).

I could see if the timing of the 3 cylinders was "juuust right" where a single EXUP valve could be of great help to avoid overlap.

Now that I'm really starting to think about it, Do you ever see a valve in the exhaust of any other engine (factory produced, race derived, street legal) besides those in motorcycles? Do you ever see it emblemized on any type of performance vehicle the same way it's shown off on the graphics of some motorcycles *cough"* honda&yamaha *cough* No. You see "EXUP" graphics all over a Honda CBR the same way you see "VTEC" graphics all over Honda's cars. But you don't see exup systems in cars, trucks, ATV's or anything else (If anyone can find other examples, please point them out because I could be wrong, I'm making an assumption based on my memory of vehicles I can recall at this instant.)

We see an Exup valve in all sorts of motorcycle engine configurations such as I-4's (Even the R1's flat plane crank motor), I-3's, I-2's, V-2's, and so on. These motors all have a wide variety of firing orders, overlaps, and other variables. Regardless of the engine configuration, there's probably at least 1 common effect of a single exhaust valve downstream of the collector, such as noise reduction and any "general" benefits of backpressure that aren't related to firing order/timing.

But, given the wide variety of engine configurations, firing orders, cam, overlap & timing specs, and other cylinder/timing specific information of all these different types of engines, I'm not sure how much an effect the EXUP valve will have on "Blow through" due to cam overlap, or any other scavenging type effect... IF it is highly dependent on firing order or any of the criteria I mentioned at the beginning of this paragraph. Rather, I think it could be of great benefit if it is designed specifically with the engine configuration, firing order, and timing of all the relevant events that take place in the combustion cycle.

Furthermore, you also don't see EXUP valves in aftermarket headers. Maybe they choose to not include them to reduce costs, or because they feel the amount of R&D they'd have to put into it would be cost prohibitive, or whatever. Or maybe you don't see EXUP valves in aftermarket exhausts because the guys who designed them (the real experts on exhaust design) don't see any sort of performance benefit to using them, as opposed to more basic things in exhaust design such as length, pipe size, type & location of the colletor(s), etc.

I would really like to see aftermarket header manufacturers take the things you mentioned into account, such as blow through, scavenging, etc. etc. I'd like to see a 3 cylinder header that's designed specifically for our engine that uses design characteristics such as unequal length pipes, crossover pipes of certain sizes at certain locations, X shaped crossover pipes instead of H shaped crossover pipes. and other things that are beyond my knowledge as an enthusiast that I would expect an exhaust engineer to know about.

Blow through is a big deal, and it's something I've been thinking about a lot when I just tuned by bike to run on E-85. Without getting into it in great deal, the engine runs great on E-85. Just so you all know, the stock fuel system is capable of providing enough extra fuel for a stock motor. But it got me thinking about whether or not there's a relationship between blow through and the "injector pulse width".

Using only TuneECU to convert the bike to run on E85 without any actual physical modifications, the software simply increased the injector pulse width, or the amount of time the injectors stay open. By lengthening the time fuel is sprayed through the injectors, fuel is now flowing during a time in the cycle before top dead center when it didn't flow before. Because I've now increased the duration of the fuel spray cycle, I'm not sure specifically what effect that has on blow through and combustion as a whole. (I can say that it cools the intake valve, and the net result is positive in this case, but it may be allowing more unburned fuel to flow out the exhaust valve if the injector is now firing during the overlap cycle). Gasoline might not have been as forgiving.. Not sure.

I did this E85 conversion on my stock motor as one of many tests for my other motor that's being built specifically to take advantage of E-85 with the highest possible compression I can get, specifically with a shaved head, thinner head gasket, and perhaps different pistons if I can find them. But I also plan on doing some more complex things with regard to the dynamic compression that require a lot of testing and research beforehand with regard to the the cam selection, duration, overlap, and cam timing. Without going on too much (more) of a tangent, I'm deciding on whether or not it would be worth it to run a different exhaust cam with less duration to increase dynamic compression and reduce blow through.

But also, trying to figure out when overlap takes place compared to the injector timing to understand if blow through has an effect on the air fuel ratio (or wasted fuel) if the pulse width is increased by a significant amount.

Of course, there are ways around this. Rather than increasing the pulse width, I could increase the fuel pressure, and/or the injector size. Both of which would allow me to shorten the pulse width or "injector timing" so "Blow through" doesn't waste fuel or adversely affect the air fuel ratio.

Coming back to the exhaust valve, I'm going to do some tests this afternoon to see whether or not it can help me improve the idle quality and this awkward spot right after idle when running E85. Doubtful. But worth a short amount of time.

Does anyone know of a header for our bikes that's a lot different than most designs? One that actually uses the bike's firing order, engine configuration, and other things to its own advantage, rather than just a fancy piece with bigger pipes?

Sorry for the long post. I think out loud. I hate reading long posts as much as you all probably do.

Homer

 

One last comment about Secondary air injection (SAI).

Yet ANOTHER area of misinformation.

1. This gadget only works when the bike is in open loop fueling mode. Otherwise it would completely skew lambda readings downstream
2. It will not affect open loop performance because it has no effect on the combustion process in the cylinder. Nor will it affect closed loop performance s it is disabled in that condition.
3. It is a clever way to reduce HC emissions when the catalyst is likely not hot enough (AKA not efficient) to burn the pollutants on its own.
4. It simply uses a reed valve to suck air from the airbox into the exhaust port when a pressure drop is seen at the valve. The oxygen heats up the exhaust, burns previously unburned fuel and likely lights off the cat quicker.
5. the solenoid controlling it uses a 20 ohm coil. I assume the ECM uses a 5V reference circuit to control it. Perhaps 12V but less probable. You dont need to fuss with tuneboy or the dealer if you don't want the CEL. Just go to Radio shack, but a resistor and trick the ecm with a 20 ohm load. By the way...V = IR. 5v/20 ohm = 0.25A...P = IV....0.25*5 = 1.25W @ 5V. The key is to get the load such that the pull-up resistor detecting a circuit fault does not see either reference voltage or a ground. Its nothing more than a simple voltage divider circuit in the ECM. Standard practice. This task can be done with an easily available 10 ohm or 47 ohm resistor at Radio shack...But buy a 10w resistor to reduce heat and future failure as it will be adequate for either 12V or 5V circuits. Same goes for the carbon canister purge valve solenoid. Same 20 ohm load.
6. I suspect it is only used when the bike is in open loop mode at startup as the EPA tests emissions pretty heavily soon after a cold start. It may even help the catalyst warm up quicker as it pumps oxygen into the exhaust. after a cold start, the o2 sensor is not being used anyway. Its not accurate enough until it also heats up (hence why they all have little resistors in them to heat up the element). It is tiypical for OEMs to add "reserve" during cold starts. This is simply another way to say that the spark is being significantly retarded and the throttle is opened further to compensate for the CA50 (50% burn crank angle change). This must be done to achieve the same target engine speed. Late CA50 means more energy in the exhaust and not in the combustion chamber producing work. Faster cat lightoff. Too late of a spark timing means poor combustion and even worse emissions. So a delicate balance. Cold start tuning is an art. Very difficult.

I can't see any other use for it unless certain markets test a bike at higher load and in open loop mode. But I guarantee it is not used in closed loop mode.

Removing it will not screw up the ECM tune. It will just cause more pollutants, likely when the bike is cold.