Hey,

I recently discovered that my street NSR has been running with no airfilter, and I'm wondering what the optimum airbox/filter setup is for street use. I have done a search but not found any conclusive (this is better than that) info.

As I see it the filter options are: (From past threads)

1. Stock
2. Daytona Turbo Filter
3. Uni Filter
4. Ramax Filter (Pod)
5. K&N Filter (Pod)

And for the airbox:

1. No airbox (Pods only)
2. No Lid
3. Holes in Lid
4. HRC box ('simular' to no lid)


What I want to know is which setup (with a filter of some sort) will give you the best performance. I have heard things like the number (area) of holes is important, suggesting no lid is not the best. And that Pod filters reduce the midrange. I have had a mechanical engineer tell me that you need the airbox as it is designed to resonate and effectively rams more air in, suggesting that it does more than maintain 'still air' as mentioned before. Tygas airbox lid keeps most of the lid intact and seems to be a standard lid with enlarged intake holes, which I have also heard people do.

With out too much flaming, it would be great if people could come forth with all their knowledge on the subject in the attempt to compile a conclusive thread that everyone can benefit from.

Well I run a stock airbox,filter and stock pipes on both my 18's but the lid has 4 25mm holes drilled in it,I didn't need to rejett because with the increase of air that is now going in the airbox and moving through the carbs will draw more fuel off the main jett's, you can use smaller main's but how much smaller I dont know and if I get it wrong then it will go pop so i'm happy with it as it is

I sawed the back end of the airbox off, and without filter was making 65hp.

I've never had it jetted right and on a dyno since I replaced the filter, but it sounds good! I'd expect a good 60 with the thing setup propery.

Cue the flaming!
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nsr.wayne I understand your theory that more airflow would draw more fuel off the jets but is that sufficient? From what I've heard deristricting the airbox requires rejetting or it will run too lean. My airbox was running no filter but I wasn't going to open it up or drill holes until I had a jet kit (although I'm not sure how useful the jet sizes etc will be).

Dave Ett, did you cut just the back off the lid (like the tyga lid) or the back off the whole box? That would be an intersting job trying to mount a filter like that.


I was all geared up for the flaming and hoping to pool some information for people to refer to but not much response. Cheers for the responses so far. I assume everyone else runs a stock box and filter right? Or just can't be bothered!

I run pods on mine. The older RS 250's and 125's I've seen do not run any type of air box so I'm not to sure of their importance unless you have the cool guy ram air. I also cut the top off my airbox before I got my RS carbs and pod filters.
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1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
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Im running stock box and filters, I'm waiting to hear what any Con's are about modifying the airbox lid.

For your info kowntafit I think after an airbox mod, pipes and wire splice people rejet to approximately 140 mains and 40 slow jets (or is this wrong guys??)

I too am keen on this thread, I know the pro's are more airflow=power but what are the cons (if any) ie poor starting/idle issues? Reliability.....?
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........."I love the smell of 2-stoke in the morning.......Smells like victory"............

MC21 Pentax SP...... TYGA'D

On one I run open carbs on the other a 20cm piece of rubber pipe.

they were like that when I bought them and I can't say much about the effect, except it sent us home from a trackday because of the wonderfull sound.

Cretins!
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

The 2 we have, one has all stock set-up & the other has Tyga (cut-off back) lid and Daytona filter. 2nd is much noiser (sounds cool) and a just little flat at very bottom, mid & peak power is great. The 1st is very streetable & smooth everywere. I had heard on a thread that K&N pods were not a good option, something about rough air flow. I had a set but never ran them. I had no filter with stock box when I first got my bike, maybe good for track, but roads are to dirty to no run anything.
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Standard airbox as Honda intended gives a solid 40~45hp as Honda and the Japanese government intended.

Modifying the standard airbox gives some more hp and adds some more induction noise. There really isn't anything lost by doing this, but you will need to re-jet for the increased airflow at the top. We went from stock #128 mains (MC21) up to #142's. This is a good modification and is pretty much free apart from the cost of the jets.

Taking off the airbox adds loads of noise, but not a huge power increase. It would seem that the major change here is doing away with the rubber 'velocity stacks' that connect the airbox to the carbs. These would help the bottom end power by keeping intake velocity high at low rpm, but aren't particularly good for absolute top end power. Had good results with keeping the airbox, but cutting down the stacks level with the airbox and smoothing them off a tad. Midrange is good, with extra top end mojo.

Guys i am comfused with all different opinions! i want to junk the airbox its too heavy seriously now is it bad if i use 2 good KN airfilters with good jetting? i dont care about low rpms!lets say we have a stock nsr.will it have better peak power with modified airbox or with aftermarket filters?

I've had best results with a couple of holes in the lid, no lid sounds cool though.
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Last edited by fontyyy on Sun Jul 09, 2006 12:51 pm; edited 1 time in total

I'm with you NSR-LOVER, I wanted to run K&N Pods too, one because apparently they sound cool, and secondly because it makes the carbs tidier and easier to work on, and it's just so cool. The downside is that they are expensive and I'm not sure how well they go with water and cleaning the bike.

Matts suggestion is probably the best for practicality and certainly far cheaper. My brother has a 4-stroke with straight through pipe and it sounds mad so I am really trying to keep up in the sound department

Does the induction noise with pods sound good or just annoying? I took the silencers off just to try in the garage, damn that sounds bad!!! (Runs like sh*t I know, I was just curious about the sound)

Fontyyy makes an interesting point though that I have heard before, a few holes is better than lots (or no lid) suggesting that maximum air (open carbs) or even pods are not the optimum solution, but someone mentioned that racers run open carbs. Can someone please clear this up?

Some racers may well run open carbs, just cause you race doesn't make you right, nor does it make your bike fast.
HRC run some form of airbox on just about all their bikes, the NSR's and RS's included, that really is all you need to know.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

StephenRC45's MC21 picked up just over 1hp removing the pod filters...



My MC21SE has the strongest mid-range of any NSR250 tested on GT's dyno so far...



That graph was with Ramax foam pod filters, HRC jet kit, Ethos race pipes, wire-splice and standard porting - and it's LOUD!
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Andy, your bike seems to run really nice with the ramax pods. StephenRC45's seems to dig in on the mids abit though, is his graph with or without the pods?

Have you got any pics of your pod setup so we can get an idea for size? Also are you running any box at all? I have heard some people run pods with part of the airbox base or a HRC box to reduce turbulent air around the pods.

Are ramax pods simmular to k&n? I think most high flow filters run dry don't they, k&n are oiled, is that a good idea?

Sorry for all the questions