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Discussion Starter #1
Reading through a few tech threads on getting pods for you bike, I thought I start a new thread about Stock air box vs Pods. I have K&N Pods on my CB750 with a Kerker exhaust. My carbs are jetted and it runs fine. The one thing I noticed is while running down the road I can detect a slight performance change when I move my legs around the bike. This lead me to think about airflow around the bike and how my legs were either blocking or helping the airflow to the carbs.

Thinking about this more - I'm seriously considering some sort of airflow director (AKA P51 scoop or 2-3" air pipe) to direct more even airflow to the carbs where my leg position on the bike will not have such an effect with performance. The stock airbox doesn't seem to be influenced by leg position while running at highway + speeds.

Has anyone else experienced this while using pods???

Bob
2 - 69 cb750's
1 - 71 cb750
 

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this is a common problem with pods and taller riders. Legs blocking airflow are nothing new. One solution is to make a rain shield (so called because they protect rain from entering in through the top and sides of the pods. They restrict airflow a little but it isn't as bad as having your leg pressed up against the filter blocking it totally (which has happend to me - don't know about you).

The stock airbox doesn't have this problem because the stock airbox draws air from the bottom of the box itself and the airbox chamber is specifically designed to hold enough air to prevent a restriction in flow. Plus it is less turbulent air so you get a smoother run through the rev range. A lot of people think airboxes are like the old chrome aircleaners on carbed cars but the reality is there is a lot of science that goes into their design since most bikes were sold (in the US) as high performance machines and the factories are seeking to maximize the efficency of a small engine sensitive to minute changes.

If you look at modern bikes they have "ram air" setups that pull air from the front into the airbox. Most of these use fake tank covers to direct air but I imagine with some careful routing you could probably fab up your own ram air setup with a piece of drier vent hose and some careful routing (maybe a rain shield).
 

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Also, I forgot to mention, since you have a 1969 cb750 you could get a reproduction stock airbox, install a K&N filter in it, and drill the top of the box (I would not destroy an original k0 airbox). It is a old drag racer's trick to get more air into the stocker and still have a semi-stock look.
 

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Discussion Starter #4
Thanks for the input...
One of the 69 is setup as a cafe, the other is now undergoing a classic overhaul. Since I don't have the original airbox, I will be picking up a reproduction air box for the classic. The cafe MC, I intend to keep the K&N's on it and fab some sort of air director to the filters to get rid of the leg problem.

Everything you wrote about is what I currently understand to be true - thanks for the note. I think other folks that are considering pods should see what other folks have experienced using them.

Bob
 

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The deal with any airbox is that it provides a still supply of air so that the same amount always enters the carbs regardless of the turbulence around the intake. Back in the day, as soon as you started making lots more HP the airbox would be too small and be restrictive. If you drilled the lid of the airbox you could increase flow, but you also increased turbulence and velocity which could lead to uneven amounts of air going to the various carbs. Ideally, you would want to have a huge airbox with a baffled intake that would flow more air in than the engine can pull out. That is why current sport bikes have giant airboxes under the tank with downdraft FI and all kinds sensors and intake devices. So if you are running pods you have an unlimited airbox size, but it can't deliver consistent undisturbed air.

Ken
 

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With the 1969 airboxes they are close enough to the frame that you are still pulling fairly still air in, provided you only drilled the top.


The more I think about it the more I like the idea of two prostock car style scoops coming out the sides of your bike for your legs to rest on (basically building a giant airbox out of the sides of the frame where the carbs are.
 

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sounds v-max-ish. cept max scoops were the horns. can't believe no one minded that fact (or didn't know). also can't believe with the success of mr. max that the other companies didn't rip off the scoop look. i think scopps would look kinda lame on a 69 cb though. c-max?
-parks
 

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quote:Originally posted by parks61

sounds v-max-ish. cept max scoops were the horns. can't believe no one minded that fact (or didn't know). also can't believe with the success of mr. max that the other companies didn't rip off the scoop look. i think scopps would look kinda lame on a 69 cb though. c-max?
-parks
That used to piss me off about the v-max until an engineer explained to my ignorant teenage ass (at the time) that the faux tank makes a better airbox and that the fuel was under the seat and makes a better center of gravity.
 
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