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Air filter opinions pleeze!


sandman

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It's a controlled burn, not an explosion. -Yeah yeah...very technical of you.

Plus the fuel is not mixed in the air box whose prime purpose is to provide a still air enviornment for the intake bell mouths to work in. Turbulance in the combustion chamber - good, turbulance in the air box=bad.

Technology 101. Correct me if I'm wrong, but if the air in the air filter box is turbulent, is it not going to be turbulent in the combustion chamber?

Plus, the distance between the air box and the chamber is quite short on a bike, isn't it?

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Consider yourself corrected. In point of fact, turbulance, as in random disturbed motion, is not all that desireable in a combustion chamber. Swirl, on the other hand, which might be considered a directed form of turbulance is desireable as it can aid removal of spent gases and allow leaner mixtures to start burning via insuring a more homogeneuos mixture in the combustion chamber.

Starting at the bellmouths of the induction system, any turbulant air will disturb the delicate flow relationship and actually reduce flow. The goal is smooth flow from the bellmouth, down through the port and to the valve. There, the shape of the roof of the port and the back of the valve and the valve seats as well as the walls/floor and later, the piston top,, will determine the amount and direction of swirl therein.

As to the very technical comment, it is very technical. What happens in the combustion chamber IS a controlled burn. If it were an explosion, as you so wrongly state, the temperatures would skyrocket as would the pressure and would damage parts and produce much less power. Detonation, when it occurs, resembles an explosion but is actually just a bit less severe. The shock waves created in the chamber do interesting things like knocking the center electrode right off spark plugs and collapsing piston tops. The extra hot gases melt the ground electrodes off, burn holes in the valves and piston tops as well.

Technology 201

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I think now we can discuss laminar flow, eddy vortices and then finish with flame front and flame propagation. :shock:

By the way an experience I had with my car on a dyno.

First run with the mods I had done to my car (different air intake to the airbox, higher rate injectors, K&N filter in stock air box, std ECU programm)

and I get 122.5 hp.

Next the so called 'tuner' guy, chips my ECU wjth a 'programm from Italy' and on the next run there is 2 hp less not to mention the cliff-like diagramm after P-max.

They claim that this is because of the injectors- rich mixture (yeah they sniffed it) . So i remove the air filter and the airbox cover, only to lose another 1 hp.

Slightly off-topic (regarding the car) but turbulent flow is a no-no. Also we should not forget that the airbox acts as the air reservoir for the engine. 'nough

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Consider yourself corrected. In point of fact, turbulance, as in random disturbed motion, is not all that desireable in a combustion chamber. Swirl, on the other hand, which might be considered a directed form of turbulance is desireable as it can aid removal of spent gases and allow leaner mixtures to start burning via insuring a more homogeneuos mixture in the combustion chamber.

Starting at the bellmouths of the induction system, any turbulant air will disturb the delicate flow relationship and actually reduce flow. The goal is smooth flow from the bellmouth, down through the port and to the valve. There, the shape of the roof of the port and the back of the valve and the valve seats as well as the walls/floor and later, the piston top,, will determine the amount and direction of swirl therein.

As to the very technical comment, it is very technical. What happens in the combustion chamber IS a controlled burn. If it were an explosion, as you so wrongly state, the temperatures would skyrocket as would the pressure and would damage parts and produce much less power. Detonation, when it occurs, resembles an explosion but is actually just a bit less severe. The shock waves created in the chamber do interesting things like knocking the center electrode right off spark plugs and collapsing piston tops. The extra hot gases melt the ground electrodes off, burn holes in the valves and piston tops as well.

Technology 201

U say controled burn, I say explosion!!! :D

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:lol:

Yep...

I thought about chimming in on this one as well, but...

Ed's all over it so...

Have fun...

PS. Flame travel in a combustion chamber is somewhere inbetween 3-10 meters per second, with it largerly being depended on CR and turbulance, I beleive.

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great read all yall,,,just now getting time to catch up,,,,just have one thing to add on the idle mixture screw thingy,,,,,don't matter what it is if you just turn them all the same way 1/4 turn at a time the same way of course and if it speeds up it is better,,,,,if it slows down,,(idle wise) wrong,,,,always adjust the idle to the correct speed after,,,,,,be sure to wait for the change in speed of idle,,,,sometimes takes a few min.

I thought that it was on most carbs an air screw and if you screwed it out more than 1 turn you needed a smaller idle jet, and richer if in more than one.

(edit,,most are 1 1/2 turns out from closed)

now don't beat be up for my typing in the dark and no caps and posting in dead post and not saying anything about kn air filters

(but the only way to know if they are better is to measure the air box vacuum with both)

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I thought that it was on most carbs an air screw

Before the bowl air. after the bowl fuel.

what kind of carbs are after,,,???

Who me? No carbs anymore, FI Bird. :lol:

Generally:

2-strokes - its an airscrew

4-strokes - its a fuel screw

At least this is what I have found in Mikunis, Keihins and Dellortos.

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  • 3 weeks later...

Interesting study of several aftermarket filters (including K&N and Uni) on a GM Duramax Diesel. Filter efficiency, air flow resistance, dirt passed through, etc. all addressed.

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

I respect everyone else's opinions, but after reading more than one air filter threads, and this article, mine is as follows:

While I've had K&Ns in the past on other vehicles, and the idea of reuseability is attractive, I think I'll be sticking with the OEM stuff I have in my car and bikes until an aftermarket manufacturer demonstrates a superior product. There's a guy on the FJR site that is an engineer with GM -- I think about 30 years -- and I recall reading his take on oil and air filters, which was pretty persuasive. Essentially, he suggested that the OEM stuff is subjected to the most rigorous testing if for no other reason than that the vehicle manufacturer has the $$ to do it in spec'ing the parts for manufacture, and is the one with the most to lose if there are failures. By contrast, he noted that there are no testing standards for aftermarket filter manufacturers, no real liability, little money put into testing and a huge profit incentive. He suggested that a lot of consumers want to increase performance and will buy into marketing that promises greater power and/or cleaner oil and air. According to him, neither is likely to happen, and if it does, it's going to be negligible.

None of that is to say that there aren't other good reasons to have a reusable filter. Just thought I'd add the study to a never ending, regularly flogged topic of discussion I doubt we'll all agree upon while we're all still young enough to ride and wrench. (Stole it from such a discussion on another site, BTW.)

:D:lol::D

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God I hate to post in this debacle but............

Yes it flows more air (which isn't necessarily a good thing) but you left out the fact that the tests show the K&N let more dirt pass and clogged sooner than the stock filter. Now that requires engineering.............

image010.jpg

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Just like cars I think the limiting factor on our XX's are the 2 small openings to the airbox. After that it's the carb/TB throat size.

To prove this take your airbox lid off and leave the filter in. The bike will run awful needing rejeted/maped due to the increase of air going in.

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I don't understand that one. Have you actually done this? I think your theory is flawed.

Keep in mind that the engine is an air pump. It should run fine up to the point that you meet/exceed the system's original flow requirements. You will, of course, lose the ram air effect for which the system is mapped/jetted but that will cause the engine to run richer not leaner.

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