Help me understand what they do....

l0g1c wrote:

Not to muddy the waters, but I'm seeing some things contrary to what I believe.

I don't think pods will give you better gas mileage. More air, more fuel, more power, sure. It defies logic that you could get better fuel economy as well, unless something was off-kilter to begin with....

The idea behind better fuel economy, and also the reasoning that K&N and other aftermarket intake companies use to justify better fuel economy is this:

Yes, more air, more fuel, more power HOWEVER, you are increasing horsepower and therefore get better fuel economy because under normal driving conditions and at cruising speeds (not trying to beat the guy with the Harley style of driving driving), you use less fuel because you are getting more power, you must throttle back from where you would have prior to pods to sustain your speed.

clutch wrote: "The idea behind better fuel economy, and also the reasoning that K&N and other aftermarket intake companies use to justify better fuel economy is this:
Yes, more air, more fuel, more power HOWEVER, you are increasing horsepower and therefore get better fuel economy because under normal driving conditions and at cruising speeds (not trying to beat the guy with the Harley style of driving driving), you use less fuel because you are getting more power, you must throttle back from where you would have prior to pods to sustain your speed."

I respectfully disagree. Following that logic, a blown and injected 426 Hemi would get extraordinary fuel economy compared to a Ford Focus if they were both driving along at 55 MPH in top gear. Ed

N0NB wrote:

In the January 1983 issue of Cycle World Technical Editor Steve Anderson takes on the topic of intake and exhaust modifcations in the article "In Search of the Free Lunch". It runs six full pages and a column on the seventh. If anyone is interested I'd be happy to scan it and pass it along.

I'd very much like to read this, if it's not too much trouble. :woohoo:

650ed wrote:

clutch wrote: "The idea behind better fuel economy, and also the reasoning that K&N and other aftermarket intake companies use to justify better fuel economy is this:
Yes, more air, more fuel, more power HOWEVER, you are increasing horsepower and therefore get better fuel economy because under normal driving conditions and at cruising speeds (not trying to beat the guy with the Harley style of driving driving), you use less fuel because you are getting more power, you must throttle back from where you would have prior to pods to sustain your speed."

I respectfully disagree. Following that logic, a blown and injected 426 Hemi would get extraordinary fuel economy compared to a Ford Focus if they were both driving along at 55 MPH in top gear. Ed

Comparing two completely different vehicles in your example doesn't really make any sense in making your case. I understand your thoughts behind it, but fail to see how two cars of different weight, aerodynamics, gear ratios, etc can be compared to say that I am wrong. I am talking about using a different type of air filter on the same vehicle, not two different ones. I can't scientifically prove to you on an online forum that I am right or wrong, all I can say is try it. Though, to produce ideal test conditions would be nearly impossible as you would have to drive exactly the same way, hit the same number of stop lights, signs, etc, have the exact same atmospheric conditions, drive the exact same trips, etc, etc, etc to achieve results that could not be disputed.

We could go on and on all day about whether or not aftermarket intakes would produce better fuel economy, and I think we would both be right. Under certain driving conditions it may increase or decrease, but the difference is rather small and negligible and when weighing ups and downs to decide whether to use them or not and should probably not be a factor in your decision...

clutch wrote:
Under certain driving conditions it may increase or decrease, but the difference is rather small and negligible and when weighing ups and downs to decide whether to use them or not and should probably not be a factor in your decision...

This I certainly agree with. Ed

650ed wrote:

clutch wrote:
Under certain driving conditions it may increase or decrease, but the difference is rather small and negligible and when weighing ups and downs to decide whether to use them or not and should probably not be a factor in your decision...

This I certainly agree with. Ed

Awesome! Mutual ground! Hi five!

As a side note I was hunting for articles online proving my point...most pretty much said just that

As far as on the bike, I hadn't even thought about them getting wet. I use aftermarket exhausts on my cars/trucks and most of the time don't even think about that because they sit so high. I did come across an article or two saying that the oils used in some of the pod filters could possibly damage sensors as well (though I think that might not be an issue on a vintage bike).

My kz250 had a pod filter on it from a previous owner and I never gave much thought about it one way or the other because on the small framed bike, it was underneath the seat between the side covers so I didn't see it unless I was doing carb work or removed the seat for some reason or other. Had I had the choice of replacing it with the stock air box I would have just because of some slight idle issues due to running a little lean. My 750 has the stock air box, so I can't really say much about them on a bigger bike, though the points made above about them not getting dirty at the same rate make sense.

All in all, I bet you would find the group here would probably be fairly well split about whether or not they would/do use pods...seems like it's just a matter of preference more than anything

~Clutch

Wow, so much to respond to after a fri night of drinkin'.:blink: OK-

Pods- The advantages (radically simplified) are as follows: ease of access to the carbs by nixing the airbox, improved airflow creating improved performance (under semi-ideal conditions), overall bitching look.
I have new boots on my carbs, so the first isn't that big of an issue. The third is important (in a way) but not enough to jeopardize the second. So why not make some kind of plexi side covers to block wind and rain? This would effectively make the space behind the carbs and in front of the side covers/stock airbox one larger airbox (albeit a bit more drafty). Certainly I'm not the first person to think of such a setup (I'm not that clever/handy/experienced with manufacturing/photogenic/etc).

Pipes- I will definitely have to read through www.popularhotrodding.com/enginemasters/...505em_exh/index.html and

If anyone is interested I'd be happy to scan it and pass it along.

when I'm a bit more "ahem" inclined (yeah sure, that's the word) and less, uh, spinny (see opening sentence)? But the basics are this:
Properly tuned exhaust uses the pressure created from the recently fired valves to draw fuel into the valves preparing to fire. Add mathematics (ad-nauseum), bike performs more effectively.

What other concerns (beside je-jetting/jet tuning) should I consider when changing filters and exhausts?

650ed wrote:

Don't forget the disadvantages offered by pods. Aside from the obvious difficulty/expense in tuning carbs to compensate for airflow changes - problems with cross-winds and rain, additional stress on carb holders (more likely to create premature vacuum leaks) because rear of carbs are unsupported, side covers more likely to blow off at speed, more pain in the butt than single filter to clean (if K&N) and (if not K&N) more expensive to replace when dirty, less even airflow as they don't necessarily all get dirty at the same rate. Having said all that, some folks still love them - just like sissy bars. Ed

Why would anybody go to a sissy bar anyway?

clutch wrote:

...The 4 in to 1 exhaust baffles me a bit. The way you get more power out of an engine is to increase both inflow and outflow. How a 4 in to 1 would create better flow than a 4 in to 2 or straight headers ...

I'll go out on a limb & say it's simple math relating to area & volume.
One 2" circle has a greater surface area than two 1" circles, and of course it follows that a 2" cylinder has a greater volume than two 1" cylinders.

As an example, one 2" x 12" pipe has a volume of ~ 38 cubic inches, and two 1" X 12" pipes have a volume of 19 cubic inches... So a 2" pipe has double the volume of two 1" pipes.

The ID of the stock pipes on my bike is 1".
A Kerker system at BikeBandit has a 2" collector pipe (I'm assuming that's the ID).

As far as increasing fuel economy goes, it is most definitely possible to see an increase in fuel economy by improving the exhaust and intake sides. If you make the engine have to do less work to pump air, then you increase the overall efficiency of the system.

This is where the power increase comes from as well. All you have to do is look at modern machines to see this to the extreme. Even before fuel injection, they were getting way more power out of similar displacement engines and returning the same or better fuel economy.

The gains of course are all based on how bad the original parts where, of course. Some of the modern stuff is really hard to improve on in stock form.

Changing the size of the engine/changing cam timing, or things along those lines are a whole different ballgame. A big cam make an engine more efficient at higher RPM's, assuming the rest of the system(heads/carbs/exhaust) can keep up with the new airflow requirements.

However the engines become terribly inefficient at lower rpm ranges that they normally operate at when you aren't balls to the wall, so that kills the fuel economy.

This is why everyone says it is important to put together a performance build as a package. The advice from those who have been working and trying new things with these engines for years is invaluable. It's a good thing most of them post on this forum!

l0g1c wrote:

N0NB wrote:

In the January 1983 issue of Cycle World Technical Editor Steve Anderson takes on the topic of intake and exhaust modifcations in the article "In Search of the Free Lunch". It runs six full pages and a column on the seventh. If anyone is interested I'd be happy to scan it and pass it along.

I'd very much like to read this, if it's not too much trouble. :woohoo:

It is scanned and posted on my web host . It's about 3 Megabytes and 7 pages as a PDF.