The Aprilia RS123 as it has a powervalve is able to be tuned to a higher level over a shorter range than if the PV wasnt installed.
In general a steep angle rear cone creates a high peak power number in a narrow band with severe roll off of the power after peak.
Something I cant explain is that quite often in a sim having a small steeper section of cone down at the stinger will create more power - like was
used by Aprilia in the RSA / RSW.
But in many dyno tests of this, in reality, it doesnt work any better than a single angle - the same result for a shallow section up at the mid followed by a steeper section.
Both scenarios can be equalled or bettered on the dyno with the correct single cone.
For practical purposes 28* included is about the limit for a single cone,but there are special cases like the RS123 where having a powervalve, and a rev limiter
you get tuners ( like Arrow ) that want a big number to advertise and sell pipes, so they use a REALLY steep angle as it doesnt matter that there is no overev power.
You may get an improvement in power, over a narrow band with a very steep rear cone, but its a special case where running a very low port timing with a severe rear cone
and is not something I seriously want to even think about.
Here is the Arrow design, really dumb with incorrect header length etc, but it gives the result they intended.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Here's my attempt to do something useful in a similar vein TZ
The inner ring is the stub now welded onto the pipe. The oval is 26 by 35 so about 75% of area of the new port welded onto barrel with a triple port. This leaves quite a 6mm step top and bottom I have blended his to about 4mm since pics. Will trial like this, then take the step out to look more like your insert. If it was better with step I can push an insert back in.
it looks a bit prettier once I matched it up when welded on the barrel.
Don't you look at my accountant.
He's the only one I've got.
How the hell did you get a tripple port into a TZ ( old model based on RD cases I mean )
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Had the RS125 on the roller at the house of savoured youth tonight. See post here below (click the little blue and white arrow icon next to my user name 'chrisc')
The Aprilia RS123 as it has a powervalve is able to be tuned to a higher level over a shorter range than if the PV wasnt installed.
In general a steep angle rear cone creates a high peak power number in a narrow band with severe roll off of the power after peak.
Something I cant explain is that quite often in a sim having a small steeper section of cone down at the stinger will create more power - like was
used by Aprilia in the RSA / RSW.
But in many dyno tests of this, in reality, it doesnt work any better than a single angle - the same result for a shallow section up at the mid followed by a steeper section.
Both scenarios can be equalled or bettered on the dyno with the correct single cone.
For practical purposes 28* included is about the limit for a single cone,but there are special cases like the RS123 where having a powervalve, and a rev limiter
you get tuners ( like Arrow ) that want a big number to advertise and sell pipes, so they use a REALLY steep angle as it doesnt matter that there is no overev power.
You may get an improvement in power, over a narrow band with a very steep rear cone, but its a special case where running a very low port timing with a severe rear cone
and is not something I seriously want to even think about.
Here is the Arrow design, really dumb with incorrect header length etc, but it gives the result they intended.
Many Thanks Wob.
I am thinking about build a replica of Honda A-Kit pipe to test on my engine, I did this a couple of years ago, but the pipe is in 1mm mild steel, a litlle longer tuned lenght, shitty welds etc, so I think in build another in 0,8 with all the tools and pactrice I have now.
Looking for the drawing It can be seen a parallel 120 belly, other drawings have a slight increase diameter in the mid section about 1º or so, is this a good thing most of the time? What is the effect on the pressure bench?
The Honda A Kit is VERY old tech, it was basically the design Harold used on the lovely KTM GP efforts and was one ( main ) reason they were never really fast enough.
If you must copy something go with Aprilia Tubo 100+ layout, less the multi angle rear cone.
But using a 800mm tuned length with a very low exhaust port duration is off on a very weird tangent and who knows what result this will give you.
The A kits had 200* duration with that short pipe and needed every ignition trick and electronic powerjets to make that work correctly.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
The Honda A Kit is VERY old tech, it was basically the design Harold used on the lovely KTM GP efforts and was one ( main ) reason they were never really fast enough.
If you must copy something go with Aprilia Tubo 100+ layout, less the multi angle rear cone.
But using a 800mm tuned length with a very low exhaust port duration is off on a very weird tangent and who knows what result this will give you.
The A kits had 200* duration with that short pipe and needed every ignition trick and electronic powerjets to make that work correctly.
What you think of this pipe in the pic? I did it thinking about front side power, rather then overrev, but still overrev is good, I guess due to the ignitech curve falling fast after peak rpm.
I wanted a pipe to go on drag and use the A-kit pipe I did for overrev and top speed, but the bike is very similiar with both pipes
Hi Wob can you post the dimensions and walk us through the pipes features? Ta .....
Pipe design elements relating to variable with pipes
Originally Posted by wobbly
If I were to explain pipe design I would need to write a book,but in general things are pretty straight forward in relation to the % values.
End of header is always 31 to 33% and end of diffuser is always 62 to 68%.
To see the effect of a silly long header, you can watch the pressure ratio at the Ex port, and thus the effect this has on the depression in the cylinder.
We are looking for the lowest and widest negative ratio we can get around bdc when the transfers are fully open.
A long header delays the beginning of the depression too late in the cycle, when in the power band.
In a race 2T we are always fighting power range Vs peak power.
Shorter diffusers create steeper angles,thus greater wave amplitude, but this narrows the effective band width.
So - in general the best compromise is around 66%.
Originally Posted by wobbly
The % I quoted for header means that portion of the length from piston to rear cone end.
Its from the piston to the beginning of the diffuser, what happens in between isnt relevant.
Unless of course you use a small Ex duct and a bigger header, that makes more power.
And of course same for the diffuser end, that is simply 66% of the length from the piston to the end of the rear cone.
Frits Overmars
A powervalve does not really give you real resonance power; it just prevents the pipe pulses from completely messing up the power curve at low revs. I expect a sliding pipe will make more low-down power.
Imagine the valve passes 60 cc of fuel per minute, but the engine only needs 30 cc. How would you go about that? You could open the valve for 30 seconds and then shut it, but by that time the engine may have drowned.
Open it for one second, close it during one second, open it for one second, sounds more sensible, doesn't it? That is why I quoted the valve's frequency: 13 Hz.
That means it can open and close up to 13 times per second. This again means it could open for 1/13 of a second and close the rest of the second, or open for 12/13 of a second and close during 1/13 s, or everything in between. And of course it can stay completely open or closed; enough possibilities to govern the mixture.
The ignition timing does not have to be changed when you use an electronic power jet. But both the ignition timing and the powerjet timing are means of influencing the exhaust gas temperature. A late ignition and/or a lean mixture both cause a higher EGT, so you can match the exhaust resonance frequency to a rising engine rpm.
And if you have that power jet available, the ignition does not have to do it all by itself anymore, so you can search for a timing that gives a better overall result.
Originally Posted by Frits Overmars
You have to stay within certain length percentage limits for all elements of the exhaust system; you cannot make one part a lot longer or shorter in relation to the others without losing power somewhere.
It is best to concentrate on getting all dimensions correct for maximum power. In the high gears you don't ride low revs and in the low gears you'll have enough low-down power left to pull a wheelie or spin out the rear wheel (I'm not talking about buckets though, so you might want to reconsider your case).
If you have a decent setup for angle*areas, pipe, carburation and ignition, the necessary overrev potential will come naturally; no need to sacrifice maximum power in order to make it rev a little higher.
Originally Posted by wobbly
That old Honda pipe mod drawing is completely useless, it was never used by the factory in any form.The rear cone is insanely steep.
And the so called A Kit pipes were designed to work with high Ex ports - where the customer engines all had 83*ATDC to let them rev without an electric powerjet.
I have much better designs with a ton of dyno time on them, but of course they are all specific to 50Hp 125 cylinders, not 30Hp 100cc designs.
Here is one that has won dozens of 125 kart titles, but again it should just point you in the right direction for the 100.
Originally Posted by wobbly
Here is the A Kit spec RS125 pipe drawing.
Originally Posted by Frits Overmars
Ceramic coating shouldn't cost power; on the contrary. You'd just have to adjust the lengths, like you have to with stainless steel and titanium.
This graph shows the results of three pipes with identical dimensions but different materials on the same engine. Attachment 293077
Then try this, Romeu. That should keep you out of the boozer for a couple of evenings . Attachment 293078
The pipe design you have asked for is in the Frits files
Originally Posted by Frits Overmars
Here.
Let's hear it for Mental Trousers: he created a way for me to upload BIG files.
I will be offline for a couple of days, but this might keep you busy:
So there you have it - the A Kit pipe is shit in comparison to that layout.
You have a 2 stage header with the optimum angles of 3.5 and 5.5 * ( even better than Aprilias Tubo designs that to my knowledge never had a 2 stage )
with a 3 stage diffuser,the steepest in the middle with approx equal angled 1st and 3rd stages - all good.
The tapered belly section can be tapered either way, depending upon the engines response to the diffuser action and how much overev it is capable of ( or needed ) via a steep rear cone.
The only element that I have found to work better is the relationships in the header.
In your design the end of the first header is at around 75% = 200/268,but as in the empirical design guides for the whole pipe of 33% header 66% diffuser, the same applies to the header lengths.
End the first 3.5* cone at around 66%, so you would then have two equal headers of 91.5mm ie 60+25+91.5 = 176.5/268 = 66%, thus the second header at 5.5* is 91.5/268 = 34%.
Varying the length of the 1st diffuser changes the shape of the depression curve at and around BDC, thus tailoring to front side or overev power.
I have no idea what the superposition characteristics are of 190* with 800mm TL would be, as such a weird combination has never occurred to me - but as I well know anything I believe
should or should not work at all in a 2T, is very often complete rubbish when you get to analyse it properly in EngMod.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
So there you have it - the A Kit pipe is shit in comparison to that layout.
You have a 2 stage header with the optimum angles of 3.5 and 5.5 * ( even better than Aprilias Tubo designs that to my knowledge never had a 2 stage )
with a 3 stage diffuser,the steepest in the middle with approx equal angled 1st and 3rd stages - all good.
The tapered belly section can be tapered either way, depending upon the engines response to the diffuser action and how much overev it is capable of ( or needed ) via a steep rear cone.
The only element that I have found to work better is the relationships in the header.
In your design the end of the first header is at around 75% = 200/268,but as in the empirical design guides for the whole pipe of 33% header 66% diffuser, the same applies to the header lengths.
End the first 3.5* cone at around 66%, so you would then have two equal headers of 91.5mm ie 60+25+91.5 = 176.5/268 = 66%, thus the second header at 5.5* is 91.5/268 = 34%.
Varying the length of the 1st diffuser changes the shape of the depression curve at and around BDC, thus tailoring to front side or overev power.
I have no idea what the superposition characteristics are of 190* with 800mm TL would be, as such a weird combination has never occurred to me - but as I well know anything I believe
should or should not work at all in a 2T, is very often complete rubbish when you get to analyse it properly in EngMod.
I am talking about my NSR, that has ~198º exhaust, 190º was a scooter I needed to make a pipe.
From my side, and the tools I have with me I feel a lot uncapable to continue improvment. I have used the 2 stage header and 3 stage diffuser design mostly, sometimes does not seem to be the best, but in average seems to work fine.
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Originally Posted by TZ350
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