Help me understand what they do....

Specifically pod filters (as opposed to stock airbox), and 4 into 1 exhaust (as opposed to individual, 4-2, etc).
Perhaps I don't understand the function of such mods other than the obvious, they look cooler!
No really, if it's power, torque, gas mileage, whatever, give me a quick (and relatively jargon free) synopsis. I'm still pretty green to this whole, motor-bicycle thing....

I can give you an idea about the pod filters. They give you less restricted air flow allowing more air (and in turn more fuel) into the engine for a better burn. They can increase both power and gas mileage. Using pod filters may require the need to "re-jet" your carbs (use bigger jets to allow more fuel flow) because they will most likely cause a lean mixture if you don't rejet.

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 is beyond me, unless it creates ideal back-pressure (like a flowmaster exhaust would do for your car or truck).

Anyway, that's what I know about it, and unless anyone has better info than me, I think it is fairly accurate (but would like to learn more as well)

~Clutch

Thanks for the pod info, I'd love to get a clear understanding of the exhaust just as you do.

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

clutch wrote:

I can give you an idea about the pod filters. They give you less restricted air flow allowing more air (and in turn more fuel) into the engine for a better burn. They can increase both power and gas mileage. Using pod filters may require the need to "re-jet" your carbs (use bigger jets to allow more fuel flow) because they will most likely cause a lean mixture if you don't rejet.

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 is beyond me, unless it creates ideal back-pressure (like a flowmaster exhaust would do for your car or truck).

Anyway, that's what I know about it, and unless anyone has better info than me, I think it is fairly accurate (but would like to learn more as well)

~Clutch

You don't want back pressure, you want scavenging and velocity.

Back pressure just lower the overall efficiency.

A 4 into 1 will scavenge better the 4 open pipes or a 2 into 1 because the previous exhaust pulse will help pull out the next one.
A well designed and sized exhaust can actually put a vacuum on the exhaust valve.

The size and length of the header pipes and collector vs. the size and power of the engine will dictate which RPM you get the optimum scavenging at.

Here is a good article about exhaust system design. It says it's for cars, but the same principles apply.

Popular Hotrodding-Exhaust Science Explained

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.

650ed got the disadvantages spot on. An advantage that I haven't seen posted is that it makes pulling carbs easier, but I'll let you weigh that against the disadvantages.

As far as the exhaust goes, running an unrestricted exhaust will get you some horsepower in the higher RPM's, but it robs the lower RPM's of it.

A 4-1 pipe will run hotter and will benefit from the flow of the other cylinders. I usually hear "scavenge" in terms of a 2-stroker, but I suppose it makes sense in this context as well.

I'm as fallible as the next guy though, so it won't hurt my feelings if someone corrects me. :laugh:

Just a couple of tweeks. Pods will also make getting the rack of carbs in and out of the bike easier. BUT if you have the airbox and new soft boots (connector hoses)this point is moot. IMO they also create a few headaches such as crosswinds leaning out the carbs and riding in the rain.

Unrestricted exhaust poses another problem. It attracts flashing lights. There are towns around here where they are enforcing a noise control legislation. Only stock mufflers are permitted and you will be ticketed. Plus if it is registered and inspected in this state you will have to get it to an official state inspection station who will only OK it if it has original exhaust. BUT, they do not seem to be fully enforcing it. The seem to only be harassing the obnoxiously loud exhausts.

basically pods are less restrictive allowing a greater amount of air in and 4 into 1 exhaust are the most efficient way of getting air out....in the internal combustion engine , getting air in and out as quickly and efficiently as possible is the name of the game ... there are a lot of sidebars and variables, but this is the big picture....just my .02.....keith

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.

Quick add, 4-1 exhausts are generally lighter than stock exhausts, cost less, and sometimes allow better cornering clearances. G

Hi SouPortugues,

Most folks who opt for pods do so because after struggling to get their carbs out past old stiff boots decide that it just plain easier to dump the airbox and go for pods for the reinstall. My bet is that a great new business would be one that could claim that "We make any new supple intake boots to fit your 30 year old bike."

On the exhaust side:

After market four into one and four into two systems are lighter than stock systems. While they can provide power benefits, most folks install them because stock systems are not available after the stock system either rusts out or gets damaged in a crash.

KZCSI

the 4-1 pipe if designed properly allows for better exhaust scavanging, in short the flow from one exhaust will actually help pull the exhaust from the other pipes.