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YOUR OPINION on air filters

  • Thread starter Thread starter NelanCustoms
  • Start date Start date
hampshirehog said:
I've pondered this for years and still can't make up my mind - and I've gone the pods / airbox / bellmouth / start again routes more times than I care to remember. From my own experience I've found VMs a doddle to tune in when changing the air intake whilst I don't think I've ever got CVs to work entirely satisfactorily.

From a performance point of view I'm more inclined to think I imagined any gains by dropping the box but I may be wrong.

In this month's CB mag there's an interesting observation about bellmouths: when the inlet valve closes the vapour that was heading towards the combustion chamber, through the carb, 'bounces' backwards. (You can see this big time on a tuned 2-stroke when the ports / reeds / discs close -literally spitting fuel out of the carb at low revs - different situation I know but the same sort of thing). When the 'sucking' starts again on the next cycle, this vapour is drawn back in, though some of it will have been lost to the atmosphere. The theory is that a bellmouth acts as a 'holding area' for some of this lost fuel mix but that the ultimate solution is a large capacity airbox.

I'm inclined to go along with this on the evidence that I have run bikes reasonably well with the airbox attached but no filter inside, whereas if I took the box off the thing would hardly run at all.

Having concluded, I think, that I'd rather stick with the airbox I do have to say that those filters on Renobruce's gleaming motor do look rather nice.

Wally
Click to expand...

I agree with your take on the bellmouth/velocity stacks. I have experimented quite extensively with 2 stroke expansion chambers on motorcycles and go carts. There is strong evidence that sound waves are beneficial to performance and that differing lengths,dimensions and shapes can drastically change an engines torque curve and duration.
I believe that the combination of the bellmouths and the airbox do enhance the range of performance on our stock engines and that volume and resonance have major influences on there output.

The other way to control the amount of back flow through the carb and bellmouth is to extend the inlet tract length. The drawback to this solution is that the tuned length changes and lowers the maximium HP output to a lower rpm. The upside however is an increase in torque at lower rpms.
I personally wouldn't bother with pods unless I was building an engine for all out racing. The fact that they are more difficult to tune isn't an issue for me!
IMO, a strong/ broad torque range is more important for road use than maximum HP.
 
tuned intake length on these bikes are 13inches for 10,000rpm up to 20 inches for 6000rpm Diameter of carb depends on the engine displacement... blah blah blah..

the air box keeps the bikes' carburation reliable and predictable at different altitudes and different temperatures,barometer too. it also gives the general tuned length and volume for smooth engine performance which equates to smooth riding.

Yanking the air box opens a can of worms that requires a master tuner to tame.
After the initial tuning every time the temperature and barometer changes the bike needs to be retuned or it will stumble -cough-studder- somewhere in the rev range. it all becomes a combination of compromises.

it is true you can get 6 or 8 more horses on a specific day after peak tuning by losing the box

BUT you will have a sewing machine smooth running machine everyday by keeping it on
 
Replace your stock filter with a UNI filter, you will get better air flow than with the stock, no rejetting, no noise increase, modest change in the feeling of accelleration.
 
airboxes

airboxes

have a gsx11et i fitted later model katana airbox as they have a rubber velocity stack fitted to help airflow,also fitted kn standard filter replacement element,you might be able to find the rubber vel.stack at a wreckers and mod your airbox to suit,after all the japs spend lots of money developing and refining their bikes,regards
 
I like the idea of keeping the stock airbox and replacing the filter with a newer/better one. I went with K&N's stock replacement. I don't get dirt inside the airbox, so that's not an issue, and it flows much better than the foam type.
 
Not to steal a thred but it sounds like the guy got his answer so I was wondering if they are a good idea on a 550?
 
nisom512 said:
...so I was wondering if they are a good idea on a 550?
Click to expand...
Let's see if I can give you a hint here.

Go back, re-read this entire thread, one post at a time. Anywhere you see an engine size mentioned, replace it with "550".

It all depends on what you call "a good idea".
Looks...go for it.
Sound...if you have a header, you might not hear the intake.
Power...can you notice a 2hp difference? No guarantee you'll get that much, even.
Weight savings...maybe a couple of pounds.
Ease of removing carbs...yeah, but how often do you really need to do that?
Ease of maintenance...now you have four filters to clean and oil properly.


.
 
nisom512 said:
Not to steal a thred but it sounds like the guy got his answer so I was wondering if they are a good idea on a 550?
Click to expand...

I've heard of people having more trouble getting the jetting right on the 550s compared to the others.
 
cool thank you. yeah I think I am gunna go stock just to make it easy and cheap
 
trippivot said:
It is true you can get 6 or 8 more horses on a specific day after peak tuning by losing the box

BUT you will have a sewing machine smooth running machine everyday by keeping it on
Click to expand...


I agree with Trippivot! I switched to K&M pods quite some time back on my 83 GS110esd to get better access to the battery. I used them for several years but noticed that it never really idle right even after re-jetting. After I installed the stock air box back on, my bike purred like a kitten.

Note: Go with GEL filled sealed batteries. You will never have to fill them up with water ever again and will also minimize removal of the air box. Sweet! \\:D/
 
Just wanted to chime in on this. You do make more horsepower with pods but its all up top. All the dynoruns we've made with stage 3 & 4 jet kits with pods have yielded higher horsepower but with the scarifice of torque. I dont know about everyone else but I use the midrange torque more than I do WOT riding around town. And if you have to pull your carbs that many times then you need to seal your tank or have your carbs done buy a professional.
 
jetting

jetting

gday mate,you reckon it never really idled right, but did you try changing the air jet, which is on the side of the carby,air box side as this controls air mixture at minimum slide lift, as when its idling, another thing to remember with cvs every jet runs thru the mainjet, thats why theres a rubber bung blocking the pilot, from the float bowl, have a look at a factory manual fuel flow diagram, regards
 
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