not to thread jack but the question of why a bike or car would "Afterfire as ty called it" when letting off the throttle has caused some intereting theories to come up. I am a jet engine engineer, Granted i am not a combustion speacilist, but i have access to them and they arn't positive either why it would take place.

Two things come up everyone says it is because it has extra unburnt fuel and it is burning off. But if this was the case adding unburnt fuel means a rich mixture, which means less air ornormal quantityair mixed with increase fuel quantities,this wont cause an "explosion". For the fuel source to "explode" it would have to be introduced to aquantity of air greater than the quantity of fuel. Which wont be the case if it was a rich environment. i agree a bike will go momentarily rich when you let off a throttle introducing a larger quantity of unburnt fuel. BUT where is the large quantity of air coming from to mix with this fuel. It can't be when theexhaustfuel mixturereaches the end of the exhaust pipe because it would have cooled too much it ignite itself.So the air fuel mixture that would cause an explosion has to take place in the exhaut system much closer to the exhaust manifold where it is hot enough to ignite itself. MY FINAL THEORY when you let off the throttle the ECU cuts injectors off butonly the last ones make it intime not to spray fuel to to timing, the first couple still spray because it has alreadly sent the signal. RESULTS IN 2 cylinders going rich and to cylinders going lean. GIVING YOU A FINAL... LARGE AIR TO LARGE FUEL... MIXTURE MIXTING AT THE VERY BEGGINGING OF THE EXHAUST PORT...you could test this on a dyno and what to see cylinder temps on a live time. and see exactly what happens to each cylinder as you let off the throttle.

 

Sweetdeal, I already said that most afterfire occurs just outside of the block, deep in the exhaust. It takes a lot of extra fuel to make it all the way out the pipe, especially in a car. And yes, a cat slows the exhaust down and acts as a muffler, so although it has no direct impact on the combustion, it will reduce the effects.

SD - Where did that come from? That's a lot of hate there buddy. Is that really necessary? Have I made something up? So if I have an intake flapper and I know that it is always going to be open above 5500 RPM, and that it closes with vacuum pressure, and that the open position feeds air 25-50 degrees cooler, why could I not decelerate to 4k and start the run with a track full of warmer air, then disable the flapper and do the same run with cooler air?

The point is that most flapper mod dyno charts show gains all the way to redline. While we know that the system is in exactly the same configuration before and after the mod from 5500-redline. The gains associated with the flapper mod past 5500 are residual and depend on several variables such as the RPM that the run starts from, whether it is a crack start or a roll, and the ambient temperature INSIDE of the fairings, among others. With simple knowledge of the system, it is very easy to show gains while in fact the gains were nil. The "rigged run" is just the term I was using to describe the runs in which the variables are in favorable conditions. I had no better term to describe a legit run that had been, purposefully or not, skewed by the actions of the staff. It is very common to start a dyno run at 4k-5k RPM. That just happens to be perfect timing to exploit the weak area of the flapper's function. By starting the run from a steady 6k, there would be absolutely no difference because they are the same at that point.

SD - I encourage you to know the function of the parts prior to talking a bunch of smack about someone. See, you may not know this, but Honda makes other vehicles than bikes. The flapper mod is actually much more commonin the VTEC Preludes. They really serve much more purpose in a car, as they switch between two sets of intake runners, whereas they don't really serve any performance purpose in a bike to the best that I can tell. Those in the Honda performance world familiar with Prelude engines will recognize the flapper valve as the same as the valve that comes in some of their cars, specifically the5thgenerationPrelude motor.

The valve has a slight variable function to it so as not to create an extreme vacuum in the runners while switching intake runner sets. It moves with a resistance to it, so to speak. It is incapable of slamming open or closed. The flap can be manipulated to stay halfway open by using a vacuum regulator and adjusting it until the desired position is reached. This was cheap but widely replaced with removing the flapper system altogether in order to open both runners. Note that in the car, there were serious low end power losses, but the high end gains were equivalent to swapping the intake manifold for a freer flowing unit. Most autocrossers perform this mod in the street class, as they are not allowed to swap the manifold.

I would appreciate some sort of apology for your tirade there, and an edit of that post as it seems to be quite uncalled for. I assume that you have some sort of problem with me, which I would be glad to work out with you without publicly trying to humiliate each other. I'm not making this stuff up, just trying to share with others that may not know. Google the words "Prelude flapper mod" and see for yourself. Yes, it is the exact same part. Honda likes doing that with leftover stuff.

 

Missed your post while I was typing there sweetdeal. You are correct in assuming that the combination of cylinders creates the necessary fuel/air mixture in the exhaust track. Some cylinders will run rich, then some will run lean on decel, with the combination meeting in the exhaust manifold somewhere. It all deends on the speed of the fuel computer processor as to just how many cylinders will fire rich. In the event that the mixture is rich enough to make it all the way out, it will ignite slightly before the end of the exhaust, as fuel past it's flashpoint is actively seeking molecules to burn with and pulls ambient air into the exhaust pipe and begins to burn. It doesn't change the whole flow, but acts as a backdraft kind of. For the flames to make it out, they usually have to be burning the whole way, which is easier than it sounds. The fuel will cool on it's way out if there is not combustion occuring or a superheated exhaust, which leads the the "rich" smell without the flames and popping.

If you know the processor speed of the computer in your vehicle or bike, you can determine how many cylinders will recieve fuel that shouldn't. I do not have that information here.

 

Ty,

I admit I should have been more civil in my post here, but Frankly I’m really fed up with you. Time after time you’ve lectured people about making stuff up, not learning how things work, bla bla bla, and yet you continually commit these same offenses yourself.

Contrary to what you said, the CBR1000RR does not have this variable position flapper function. Simply admit you made this up or name your source of information. Hint: If your "source" includes references to other vehicles, then we already know where it came from- your imagination.

How were you able to determine that the open position of the inlet flapperfeeds the engine25 to 50 degrees cooler air? Did you take measurements? 50 degrees is a lot.

2.5 milliseconds is an eternity in the microprocessor world and there’s no reason to think the CBR’s ECU would be unable to react in that length of time unless you’ve run controlled tests. The feeble PIC18F processors (running at 8 Mhz) that I use regularly can execute 5000 instructions in 2.5 ms. What kind of work have you done with embedded controllers? Do you really know what you're talking about or are you just winging it here with all these figures?

 

god bless you...lol

And i did find a source at work today that states how a momentarily lean p;oint will put way to much air in teh engine causeing a misfire, which then opens teh exhaust valve releasing a large air, and unburnt fuel into the exhaust port, the next revolution when then fire appropriatly realeasing Hot exhaust and a little unburnt fuel (under regular conditions) when then ignites the lean mixture causeing an "explosion" or after fire, which would result in flames shooting...this topic bores me now.

 

maube you can get some feedback on www.1000rr.net trying to sell them this

 

SD - I thought this was common knowledge. Flappers have been in use since the early 90's on VTEC engines. Open it up. Why don't you tell us why it has both a vacuum line and an electrical connection? Obviously, when exposed to atmospheric pressure, the electrical portion is overridden and the flap is open, thus the disconnection of the vacuum line keeps the flap open and that's how we all do the mod. That means that WOT produces an open flap even at low RPM. The cars, however, benefit from the flapper being stuck in the middle, allowing both sets of intake runners to be utilized. I don't know what is so hard to understand about the ease of manipulating a run when you can understand also....

The outer flapper holes lead to the inside of the fairings; thecenter one leads to ambient air. How much difference in air temperature do you think there is between the inside and outside of the fairings? I was under the impression that the inside of the fairings was quite a bit warmer, especially if it's cool outside.

And your right, processors run much faster than the engine would theoretically require. The problem lies not in the speed of the processor, although a rough estimate of reaction time can be determined if the processor speed is known. Typical OBD2 emissions regulation fuel controllers had around 100 millisecond reaction times. Bikes have less info that needs to be processed and thus have recently been advertised as having 10 millisecond or less reaction time. Remember, there are a lot of things that need to happen outside of the computer. How long do you feel it takes the injectors to stop from the time the throttle is released? I was under the impression that there is a very small delay, about 10 milliseconds or more, causing the deceleration popping we are all so familiar with. It's the entire reason behind the PAIR system. Do you think they would have put that there if they didn't need to?

SD - I don't recall ever having a problem with you before, and post infrequently at best. I'm having a hard time understanding why you are so upset. I don't think that I know you off the forum in any way, so don't think that the attack is really necessary. Instead of simply telling me that I'm wrong about all these things, maybe you could tell us what you believe to be accurate information. Do you have any estimates of fuel delivery system reaction time, or do you simply not like mine? Do you have any real measurements of the air temperature difference inside and outside the fairings, or do you just not like my 25-50 estimate? Would you care to explain how you think the vacuum portion of the flapper works, or are you just not happy with the way I explained it?

We all know how these things work, and yes, my estimate of 25-50 degrees was an estimate, so if you have information that you would like to share about how the temperature is not 25 degrees higher inside of the fairings, then I would like to hear it. I am talking about dyno mounted bikes here, not bikes rolling out at 100 MPH. Fuel controller reaction times are readily available andusuallydetermine the price of an ECU. Haltech computers are expensive, but can translate inputs and create the necessary outputs faster than just about anything else. They replace the ECU, shortening the overall reaction time. A piggyback controller, such as a Dynojet PC3, can correct the fuel delivery but slows the actual function of the injectors even more as the signal still travels everywhere that it used to, plus it has to be run through the PC. I would be interested to hear how long you believe that time to be.

You seem to work with electronics and know how long the distance between components is, and how they are all connected, and wh

 

Wow Ty, that wasa lot of words. Yet againyou offered no evidence orinformation sources to back the same bogus theory you've reiterated a million times. That fact that cars(of a different design) may have modulating intake flaps, is completely irrelevant.

Do you know what a check valve is? It's a valve that allows flow in only one direction. The flapper'svacuum reservoir has a check valve at the port that runs to the engine. That means once a vacuum is established in the reservoir, the flapper will never open unless the solenoid is de-energized. WOT at any RPM below 5500 means a fully closed flapper.IfWOTopened the flap, then the system would be self-defeating.Duh.

Want proof? Take a look atthis picture. If you know as much as you claim to, you should be able to understand the significance of what is shown. You see,I actually test things.

So we won't be hearing any more BS statements from you like, "Obviously, when exposed to atmospheric pressure, the electrical portion is overridden and the flap is open."Or "That means that WOT produces an open flap even at low RPM"

[IMG]local://upfiles/15079/1C31FD3652F64C2A8152AC1D09B36405.jpg[/IMG]

 

You are exactly right with the picture, but the solenoid does not remain energized based on RPM alone. It will only electrically close with the bike in gear, clutch engaged, load on the motor, and not WOT. The voltage comes from the ECU. The system is made to be self defeating, as it is simply a means to meet sound emissions requirements. Were the solenoid energized on RPM alone, then the flap would be closed while idling in neutral, which it is not.

 

This is ludicrous. Earlier you said the flap opens at low RPM because WOT causes a drop in vacuum that overrides the "electrical portion". Now that I've made you aware of the check valve that prevents this, you're changing your story to say the ECU is shutting off the solenoid at low RPM when the throttle is wide open?You've personally tested this? Of course you haven't.

If the ECU allows the flap to open at WOT, then why does disabling the flapper cause such a huge increasein induction noise at lower RPM? Don't try to say the flap is slow to open.

I'm not sure if you know this, but nobody rides around or does dyno runs with thetransmission in neutral. So you can give that a rest too.