Topic: Opinions on Pods vs Air box, Stock vs. aftermarket?

[roach374]

I've been reading various opinions online about this, and having trouble sorting facts from opinions. I basically have two questions:

1) People seem to think that pod filters are not as good as an airbox w/ filter in general. Can anyone help me understand why that might be?
2) People also seem to think that the old CB bikes just won't run properly on anything but the stock airbox (which is getting harder and harder to find as an OEM part).

To be clear, I'm not considering swapping / modding any of these, but I do want to understand more about how my engine works, and how to keep it happy!

[Deltarider]

Do a search and you'll have enough material for the next weekend.

[seanbarney41]

Carbs as small and precise as ours need still air from which to draw laminar(basically means flow without turbulence)flow from.  This is what the Airbox and included velocity stacks provide.  Anything else is just requiring band aids to restore the performance loss.

Go ahead and try some different intakes after you have learned how to make your bike run on the stock box.  You will find that it takes hours of tuning and the results will be a poor facsimile of the part throttle response engineered into the stock system.

[PeWe]

Stock engine?
Modified engine with big bore, ported head, cam and 4-1 need better flow, Pods.

I never tested stock airbox with better flowing KN filter with 836 and more. The box itself restrict air.
It had pods that worked fine.

A stock bike look good with airbox that silent the inlet sound when twisting.

Im sure you can find jetting examples. Important fact is exhaust. Better flowing or more restrictive.

My K2 has no numbers 4-4 HM300 type with stock airbox.
Needles 1 step richer from middle, main 115.
Same carbs ran with more restrictive  HM341
Needles middle, 105 mains on my K6 when new.

Pods upon that more fuel.

[Tracksnblades1]

Do a search and you'll have enough material for the next weekend.

+1 👍

Don't forget to properly treat all that dirt too....😂

https://nicoclub.com/archives/kn-vs-oem-filter.html

[ekpent]

Your year and model/size of bike would be helpful for people to tell their experiences specifically with what you have.

[MauiK3]

Just a small point
It is my understanding that the stock air box on an early CB750 flows much more air than the engine can pull in, hence, no need to drill holes, etc.
Stock repop boxes are available through Yamiya (and other sources) as well as the all important velocity stacks.
Unless it’s just a visual thing, I am skeptical that an after market set of intake devices is engineered better than the stock box.
Just my $.02

[seanbarney41]

That is exactly right Maui...there is a restriction, but it is not the airbox, or the carbs.  It is the stock intake ports and valves.  So, even if you do get your bike to perform ok with the pods, you will make no more horsepower than stock.  (and to be honest, probably less, especially down low in the rpm range where these old hondas already kinda suck)

I would be curious to know how many cfm more flow does it take over stock before the stock airbox DOES become a retriction.

[seanbarney41]

Another point to consider...is the very finite amount of tuneability available with the stock keihin carbs.  Just go take a look at the Jetsrus website and note what is available for cb750 roundtops.  500/550 carbs? even less!  Now go look at what is available for Mikuni VM series carbs...another big reason why your buddy with the Kawasaki can't understand why you have not got rid of that clunky old airbox.

[roach374]

Your year and model/size of bike would be helpful for people to tell their experiences specifically with what you have.

YES! Sorry! My bike is a 1972 CB500K1.

[web]

I have a similar choice to make. I like the visual simplicity and sound of pod filters. Also the visual and mechanical access to the engine that opens up. Let's face it, elaborate stock airboxes are usually not pretty. And this is usually the main reason they get changed out on bikes, not power or filtration performance. The latter matters less if you only put a few Sunday miles on it anyway.

About restriction, I wouldn't take hearsay for that but tap into a vacuum line and measure. Every type of airbox is different and they weren't just designed with your preferred power curve in mind. They are also silencers, and designed within packaging constraints. So while most flow just fine, the occasional dog leaves the factory where maximum power wasn't too high on the priority list. Sometimes even intentionally, if the car or bike would otherwise compete too much with the more expensive model they prefer to sell.

But do your mods wrong and it's easy to sacrifice a lot of midrange for very little extra up top. If that's what your want though, by all means go for it.

The finicky carbs are a big issue though. Even the bigger Keihins on my twin really didn't like temporary removal of the stock airbox. Not just suboptimal running but even completely bogging down above 6k. No avoiding a serious re-jetting at least, if I should want to make that permanent.

[calj737]

Pods provide easier access.
Pods can "look" better on customized bikes.
Pods are an issue if you ride in the rain (water infiltrates the air/fuel mixture and bike dies, runs like crap, or you'll wish it did)
Pods can not control the amount of air equally to all 4 carbs uniformly.
Cheap pods are an even worse offender of these factors above.

Stock airbox has a single air inlet on top to control how much air enters the chamber.
Stock airbox is sealed against weather, turbulence of external air, and debris.
Stock airbox on small SOHCs can be a MF'er to install/remove and does cause cursing while trying to service certain aspects of your motor.
Stock airbox provides the best overall performance for a factory motor, even with some modifications. As stated earlier, the intake ports on the cylinder head are the restriction to performance, not the airbox.

If you want a technical understanding of the function of intake air control, do a bit of reading on "laminar flow" to see what the aribox provides versus "pods".

[evinrude7]

not to hijack here but can anyone shed light on k&n filter vs stock filter within the stock airbox?  i have the k&n because that's what i could find.  now i see the stock filter is available. 

[1976cb750f836]

I like pods, they can be a bear to tune though. I've never had a stock box. When I bought my bike, it was 3 different body colors, pods, rusty header.  But 600$ and I rode it home.
Pods make engine work , carb work, easier. I like the look. All of my customers but 1, wanted them for the look. Once dialed in, you can leave them alone. But, my first set, I removed at least 20 times to get the tune to suit me. I learned from that. Now I can usually get it in 5.
Unless it's a 100 point show bike, do what You like, and not others!

[maxheadflow]

not to hijack here but can anyone shed light on k&n filter vs stock filter within the stock airbox?  i have the k&n because that's what i could find.  now i see the stock filter is available.

I've measured flow through a cb750 airbox and there really isn't much difference between a used stock air filter and KnN if you are flowing through stock carb.  There is a slight difference measuring right at the stack but it's not big and the flow is way higher than what the carb can handle. 

[maxheadflow]

By running pods you are essentially removing about 2 inches of intake tract length.  Assuming overall flow is unaffected (pod does not restrict flow), the motor will likely loose low to mid range but pick up some HP up top.

Here is a CB750K modeled with intake tract differences.  (736cc, 10 to cr, web341).

[web]

Thinking about this I'm tentatively considering trumpets with pods. To add a few inches for midrange torque and laminar flow. Wondering if that too would be such a bear to jet.

[maxheadflow]

Thinking about this I'm tentatively considering trumpets with pods. To add a few inches for midrange torque and laminar flow. Wondering if that too would be such a bear to jet.

My bet is that it would be easier to jet than the shorter intake.  With a 35 to 40 degree intake close there will be low speed intake reversion.  Longer stack will help keep the fuel in the intake tract.

[1976cb750f836]

Learning which part of the carb to change by seat of pants test drive is over half the battle. Once you figure out, which change effects which part of acceleration, changing the part is easy (Except for needle settings on round top carbs, lol).  That's why your first set takes longer, the learning curve. And I didn't have the help of this forum, I had trial and error. If you post all your mods, and engine specs, we can get you close the first time!

[Don R]

 Most folks don't want to do the work involved in getting the cabs tuned properly. Even then, they might not run as good as the original tune up.
 I'm a glutton for punishment, I'm going with a pair of weber carbs. lol.

[roach374]

If you post all your mods, and engine specs, we can get you close the first time!

Unfortunately, it's an eBay bike. I know it's got pods (don't know which brand or model), but beyond that no info (no idea if it's been re-jetted or what). The bike is still in transit, but once it gets here, and inspected, I'll know more. Thanks for your help!

[PeWe]

Important to get the carbs tuned in right. Its really annoying if not perfect from idle and the few mm throttle lift after which make bike not comfortable in the city. That is more important than the easy to tune top by main jets.

My CB750 K2's air screws are noticed at 100kmh on 5:th gear when wrong. Easy to think they affect idle and decelerations only. I found out when bike behaved as fuel starvation time for reserve when 1/2 turn out too much.

The small pods my K6 had on its stock carbs in the 80's did not show any problems when riding in very heavy rain on Autobahn in high speed. Maybe my legs helped to cover.

Same bike today is more modified and use wider carbs with its pods more outwards.
When washing bike on sidestand carbs must be covered, especially 4th. It has got water inside twice. Pita to get out. Starter spray and a 50km ride will not get it out. Work OK as long as not twisting throttle a lot after 100kmh.

I removed drain plug, main jet, fuel screw,  sprayed carb cleaner and compressed air to get it right.
I have a long project to tune them perfectly.

[evinrude7]

not to hijack here but can anyone shed light on k&n filter vs stock filter within the stock airbox?  i have the k&n because that's what i could find.  now i see the stock filter is available.

I've measured flow through a cb750 airbox and there really isn't much difference between a used stock air filter and KnN if you are flowing through stock carb.  There is a slight difference measuring right at the stack but it's not big and the flow is way higher than what the carb can handle.

so you are saying that stock filter or k&n filter in the stock airbox creates flow at the stack way higher than the carbs can handle?  enough air so to speak. 

[maxheadflow]

not to hijack here but can anyone shed light on k&n filter vs stock filter within the stock airbox?  i have the k&n because that's what i could find.  now i see the stock filter is available.

I've measured flow through a cb750 airbox and there really isn't much difference between a used stock air filter and KnN if you are flowing through stock carb.  There is a slight difference measuring right at the stack but it's not big and the flow is way higher than what the carb can handle.

so you are saying that stock filter or k&n filter in the stock airbox creates flow at the stack way higher than the carbs can handle?  enough air so to speak.

No.. I'm simply stating that the stack and stock air cleaner (or KnN for that matter)  flows way more air than the carb does so it has very little effect on flow.

Carb is the limiting factor not the air cleaner.

[Tracksnblades1]

not to hijack here but can anyone shed light on k&n filter vs stock filter within the stock airbox?  i have the k&n because that's what i could find.  now i see the stock filter is available.

I've measured flow through a cb750 airbox and there really isn't much difference between a used stock air filter and KnN if you are flowing through stock carb.  There is a slight difference measuring right at the stack but it's not big and the flow is way higher than what the carb can handle.

so you are saying that stock filter or k&n filter in the stock airbox creates flow at the stack way higher than the carbs can handle?  enough air so to speak.

No.. I'm simply stating that the stack and stock air cleaner (or KnN for that matter)  flows way more air than the carb does so it has very little effect on flow.

Carb is the limiting factor not the air cleaner.

Can you share those numbers and how you derived them?