Resonator spacer

[C George]

Has anybody ever run one of these ?

I've made so many changes that it's really going to be hard to say if it does much.

I made it a couple years ago and decided what ta heck , I'll use it on this build.

[C George]

Sorry to answer my own question but this was explained very well a couple years ago.
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rock@BDK » 06:20 am Sep 26 2013

Hello there,

In answer to the question - yes a spacer plate on the KIPS expansion bottle should make a performance improvement to the water cooled as well as the air-cooled models.

Essentially the resonator bottle or expansion bottle is lengthening the exhaust pipe when open, so that you now have two different length pipes depending on revs.

Exhaust pipes are designed to only one rev range (for example 7000rpm) where they will perform best and everywhere else is a compromise. The longer the pipe the lower in the rev range it is tuned to. Typically road pipes are tuned to perform best well below the red line where the manufacturer deems most riders will be cruising (and to discourage you from holding it next to the redline where longevity is compromised). Performance pipes are typically shorter and work best closer to the redline (more rpm, more bhp).

Having an expansion bottle allows you to have two rpm's where the pipe is close to ideal, giving you a boost in mid-range performance.

In fact for whatever reason on a few models (the KDX and KMX notably) the bottle was not quite big enough to produce best spread of power and this becomes more pronounced with a shorter performance pipe. Quite why they did this is anyone's guess, but reducing the visual 'barnacle' effect may have had an influence.

The above is not a thorough technical rendition, there is a lot going on there but it gives those that don't know a good grip on the situation. As mentioned by someone else before on a previous thread; once the KIPS resonator is closed you are back to normal so there is no compromise of top end power for this low to mid 'boost'.

In bhp terms the improvement will not be astounding (at low revs the engine isn't making much power anyway), but in terms of percentage it is significant for the cost and ease of fit and makes the bike more forgiving and flexible.

If it is of interest to any of you we produce a CNC machined spacer plate for these now with machined faces for good seal (gasket goo is fine), as the result of demand. If you don't have the facilities or motivation to make one up yourself then give us a call - if someone in Norfolk or thereabouts wants to bring their bike down to us we will arrange to have a before and after dyno comparison done.

All the very best,

Brock
01508 481713
Brock@BDK
Supporting Member

[C George]

http://bdkraceeng.co.uk/tc/products.php?226

[Tioli]

No I haven't tried one but its on my list. What he says about the KIPS not being quite big enough makes sense as the cover is for a 125 so a little extra size may well be needed.
I already have the material to make one 6,7&10mm. I believe there is 6mm.

[C George]

I don't think it has to be too exact as this was just a scrap piece of aluminum that
I whittled it out of. I think it's 3/16" ,

The one thats available from the UK is 10 mm.

Some get these chambers confused with boost bottles on the intake which
are totally different .

What years was this engine a 125 ? Assuming a KX ?

[Tioli]

It's a H 200, inside the KIPS cover is written KX125D. What year D is I don't know but we all have one so a spacer to make it 200 ish may be the go.

I have not yet taken the time to see in my head exactly how it works You say it's not a boost bottle so are you saying at no point does it take a pulse and send it back at a more convent time? Like a boost bottle does by absorbing the bounce back from closed reeds and incoming momentum then emptying in the next cycle.

[ohgood]

put a flat cover plate on it and compare that to the bottle. i'm interested in the results.

if it's a big positive, i'll whittle a 5/8" for my bike.

i
love
low end

[C George]

It's a H 200, inside the KIPS cover is written KX125D. What year D is I don't know but we all have one so a spacer to make it 200 ish may be the go.

I have not yet taken the time to see in my head exactly how it works You say it's not a boost bottle so are you saying at no point does it take a pulse and send it back at a more convent time? Like a boost bottle does by absorbing the bounce back from closed reeds and incoming momentum then emptying in the next cycle.

Not like an INTAKE boost bottle : )

[Jaguar]

I highly doubt the size of that space will have any noticable effect.
for one, it isn't the main exhaust path, maybe 20% of the exhaust passes that route.
second, it won't effectively "lengthen the pipe". any sound wave that enters there will immediately return, mostly to the cylinder, not as an addition to the pipe.
and the problem with people doing their own seat of the pants tests is that their own thoughts and expectations alters the way they perceive things, such as engine power. Knowing human nature, unless something makes a big difference then the results can only be reliably tested using a dyno.

[C George]

Are you trying to tell me that some mods have a placebo effect ????

Ha Ha Ha , too funny , I did learn something in physcology class.

[Jaguar]

hey, I've caught myself deceiving myself with my preconceived ideas.
it's bad when you know the psychological traps and yet due to our habits we just fall right into them.
engine modding provides psychologists the most rapid demonstration of the placebo effect, even more than taking "sugar pill" medicine.

[Jaguar]

Do this test:
have someone install/remove the spacer, not let you see which he did, then let you ride it. then have him do the opposite and go riding again. see if you thought there was a difference between the two. then repeat the sequence, not knowing if he actually made a change the third time.
If you gt two consistent reports of power change then that would be a fairly reliable indication of its success or failure.

[C George]

I'll tell a quick story . My son's bike had black front and rear fenders when we first built it.

When ever he or I rode it, we came with the same conclusion that the bike felt smaller and
handled different than my all green 220.

So the first year of college I took and swapped plastic and his bike was now all green.

When he came home I said , Take MY bike for a ride " his bike " and he came back and immediately
commented that ,,, Man , I wish my bike rode like this !

When I told him it WAS his bike , he couldn't believe it , no way.

He laughs still today and both bikes are all green.

[Tioli]

I agree that's why I like to go slowly and one change at a time. I'm also taking my time with this because for me to do it right I will need a 6 mm and 10 mm spacer to test back to back and both togeather. If I can't tell any difference by the seat of my pants then I can't.

I see mention whittle away, I'm not looking forward to having to file two up for possibly no reason so of course it's going to work

[CBaugh]

would there be any other tuning needed other than just installing the spacer? id like to give it a try

[Jaguar]

When I was testing the effect of different pipe back pressures (55cc motorized bicycle, one gear) I used a long steep ramp of a street that led up to a crossover across a highway. I approached its base each time at the same speed and recorded the speed I had at the top of the ramp. That test proved that the engine liked no back pressure. I was thinking the opposite but the speedometer don't lie.

[C George]

When I was testing the effect of different pipe back pressures (55cc motorized bicycle, one gear) I used a long steep ramp of a street that led up to a crossover across a highway. I approached its base each time at the same speed and recorded the speed I had at the top of the ramp. That test proved that the engine liked no back pressure. I was thinking the opposite but the speedometer don't lie.

The additional back pressure to the stock exhaust did nothing ,,,, what if you made it even freer flowing ?

[Julien D]

Even just a few millimeters of difference in length of a headpipe makes a noticeable and recordable difference for a 2 stroke engine. Even a small dent in the first few inches of a headpipe makes a recordable difference, as has been evidenced many times by dyno. Same principle here. More or less CC in that chamber will undoubtedly result in a measurable difference in power curves. Whether that change is beneficial or detrimental to the rider is completely dependent upon the rider.

[Tioli]

To answer your question CBaugh all you need is a spacer and a few gaskets. Two for a test and one to put back to standard is it does not work for you.

While talking about exhaust sensitivity. The intake is just as sensitive. Basically anything more than nothing is a restriction and they draw from the sides and they blow back every cycle. I don't know if you have ever stuck your nose in the air box of a two stroke GP bike but they are empty and big.

[Jaguar]

Julien: 1 inch of increased header length lowers the powerband only 100 RPM. 1 inch = 25.4mm

Like I said, the resonator space is only connected to the left side KIPS valve which is flowing maybe 20% of the total flow. Only a resonator connected to the main exhaust port would have any noticable effect.