intake modifications

[vanzen]

Quite frankly, the stock intake system is designed quite well
to maximize torque delivery throughout a wide range of RPMs.

Scrapping the air-filter, air-box, and intake ductwork ...
replacing that system with "pods" –
Only serves to compromise real world road tractability at engine speeds below @ 4,000 RPM –
Intake velocity will suffer at these low to mid RPMs and one must then compensate with jetting -
i.e. larger idle jets and retuning transition in order to run correctly,
and still, less torque ...
It will be my experience that many of the popular after-market "pods"
will starve a built engine of air at top end –
Those little "pods" simply do not have enough surface area to provide adequate flow.

Gentlemen, pods may be a modification that looks cool,
but it will be one that might only function well in a track scenario,
a scenario that willingly sacrifices idle and low-end tractability for a bit of top-end HP.
Even in that event, stacks would be the better option.

[twist]

I really appreciate the great responses. Like I said, I've no interest in using the pod filters but I did wonder what advantage/disadvantage they offered. I like the way they look, on other bikes. I really like the stock system and the way it looks, on my bike. Just curious.

[mattcfish]

I've read that pods work better with Dellortos and not as well with CV type carbs like Bings. That said I ran pods on my stock Bings for 18 years without any noticeable damage to the top end.
On my new configuration I got the longest velocity stacks that Dellorto makes And mounted really big K&N Pods over them. I now actually have more filter area than the stock filter. I don't currently have a picture of this , but I'll get one.
I've made a lot of other mods to the engine, but the trumpets and pods did seem to improve response and add to high rpm power.

[Unclviny]

On the Norton that I am building I am running stacks with lengthened intakes (increasing intake length makes Norton's "perk up" in my experience) and using Shure SM-58 microphone windscreens as "filters" (they fit very well).

Vince

[vanzen]

On the Norton that I am building I am running stacks with lengthened intakes (increasing intake length makes Norton's "perk up" in my experience) and using Shure SM-58 microphone windscreens as "filters".

A similar strategy was used on racing airheads and popular back in the day , too.
Intake stubs were lengthened, then angled outward to "straighten" the intake path, and welded to the head.

[Unclviny]

The stacks that I am using are screened but I worry that all the screens will do is keep out Children and small Dogs, hence the "filters".

Vince

[the quinner]

-The "round" airbox works well for Duane's defined style of riding and his expectations.
-The drilled (R90S, and 1977 S/RS) round airbox works a little "better."
-The "square" (1981+) airbox flows a lot more air than either round airbox.
-The square airbox was very well designed...the round style was not.
-The square airbox is essentially two long velocity stacks (good for torque) breathing through a filter.
-It does not take very many engine modifications before any of the stock airboxes become the "limiting factor" (like Vanzen preaches...one must define performance before one can provide a solution. E.g., the quest for ultimate power is usually at the expense of low-end rideability).
-"Pod" filters alone do not organize the incoming air very well.
-"Proper" velocity stacks alone DO organize the incoming air very well...the design of the VS will dictate how it contributes to the characteristics of the engine as a whole.
-The "snap-on (lower case) screens" sold by Dell'orto keep large insects and birds (and gloves) out of the intake, but they also disrupt flow a little bit.
-Messing with any part of the system is messing with the whole system.

I've done/messed with all of the above...a lot. I DO have a bike with open velocity stacks that I run on the street and have done so for...uhh...about 9 or 10 years. Is it my daily driver? No...my DD has a stock, square airbox with a paper filter. The only modification is that the top of the airbox is from a 1980...the very short lived cast metal version. The reason for that is it eliminates a few "features" that might (or might not ) affect air flow.

[Major Softie]

Stacks give MUCH more intake roar. Pods don't decrease that too much. Everyone knows that an engine that sounds faster feels faster. This is where the real line lies between a cafe bike and a track bike.

ALL that matters on a track bike is winning - lower times per lap. Anything given up to achieve that goal is not a compromise, it is simply giving up something that does not help achieve the goal. Every modification is measured by that yardstick.

On a cafe bike, it is being built to satisfy the senses of the owner: visual, aural, and tactile. In that circumstance, the only measure of whether something is "a good idea," is whether or not it satisfies the owner . . . for any reason.

[Duane Ausherman]

I have to agree with remarks by quinner and the major. For most riders of a BMW, the stock configuration is quite good. I can be an interesting hobby to mess around with things and that is just fine. But don't make claims that can't be proven, as is so common. The real claim should be, "It makes me happy." and that is enough.

My shop road raced a bike for two years and it was successful, but far from stock. We competed in both prodution and GP, so on the GP side we were down on power quite a bit, but they had fun.

[twist]

"The square airbox was very well designed...the round style was not.
-The square airbox is essentially two long velocity stacks (good for torque) breathing through a filter"

I've been thinking of going to the square intake. I'm not keen on giving up my mid range power. Since a lot of my riding is on mountain roads and twisty roads I don't spend a lot of time in the high speeds but I do keep my rpm's high. I run mikuni tm 38 flat slides with a K&M filter,(I noticed a difference when I installed the filter and drilled air box). If there is more I can do without giving up mid range power I would like to study it. So far the only thing that hasn't been done the motor is to install a sport cam.