SOHC.co.uk Forums > CB350/400

Pod filters on a Cb400 f

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Mikep328:
Since the intake noise is louder with pod filters, removing the airbox/installing pod filters is frequently thought of as a performance improvement.  But this is due to the "Louder is Faster" phenomenon.  Objective dyno tests (NOT those shown in ads by the folks selling the "upgrade") do not support this.

Same is true with exhausts.  I have been involved in dyno tests where a factory muffler was removed and a "straight-through" muffler was installed.  It was a LOT louder... and produced less power!  ;)

K2-K6:
There's always been a long trailing myth about airbox removal I feel, for so many application.

There's significant benefit in having a still air plenum (that's what an airbox provides) that's difficult to match over extended rpm range, all while providing good idle characteristics and going on up to max output.

As Bryan notes, if there's very specific tuning and evaluation, that may be appropriate to target very narrow range in power output. That would likely encompass changes to piston, ports, compression ratio, cam timing etc in that focus. 

The biggest part of myth though, is that simply more flow (debatable anyway) will need bigger jets and give more power, just from that.

In reality, it changes the "vacuum" characteristics carefully built in by manufacturer to generate false calibration of existing jetting. Lifting jet size is usually needed in bringing some sort of response parity back to the setup., not producing more power.

If you wanted to try them, then minimum shift would be to go up in idle jet size by two steps, then trim off throttle idle mixture to compensate at lowest rpm. Further evaluation could then take place with the higher end jetting level.
A dyno plus A/F ratio detection under load would be the accurate way to confirm transient and absolute throttle load conditions in safely combusting the mixture, without blowing the guts out of it.

McCabe-Thiele (Ted):
As a teenager I liked the look of a big bore silencer, a bell mouth carb intake, the sound of air being sucked in, the noise of a loud exhaust at high revs. Improved performance was just in my mind.

Then along came my first Honda that was quiet, reliable, oil tight, economical.

florence:
When I built my bike back in 1995, the air box was missing, still is.  Just for practicality, I put on SM individual air filters as I had not been able to find an original air box. The jet size in the carbs was already up one or two values and I find it runs fine.  There is a weird flat spot at 2500 RPM but I am used to it and doesn't cause me any problems.  Starting and tick-over are spot on and performance throughout the rest of the rev range is fine.  Spark plug colour is correct.

It isn't something I would do by choice but as I was pushed in that direction by circumstance, I am perfectly happy with the way it is and have more important things to do than mess about trying to get it back to standard.  Also, I have had to take the carbs off more times than I care to think about, a horrible job but at least made easier with the SM filters.

Bryanj:
Its chasing the different flat spots and bogging that makes alteration a pain, if you can live with it its good, if you want the original smoothness it aint

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