ESE's works engine tuner

[SwePatrick]

Gedday. It's been a while.
This discussion on exhaust shape and length is very timely, particularly to myself. For some time (and with many distractions) I have been trying to get the DCI system to show a hint of life. A previous version, which went into the A ports showed it operating, but this was masked by the fact that, around TDC, the port communicated with the crankcase because of the transfer cutout in the piston.

This time it is into the B port, with no such communication.

So, with a normal old style kart exhaust, it does not respond in terms of even a small speed change, irrespective of the nominal rpm set point, ranging from 8 to 14k rpm. I will admit to a totally out of control testing regime in terms of temps and mixture etc.

So, the question is would I be better off with a different exhaust, one that provides a stronger depression around TPO?

I’m convinced it’s gotta work.

Attachment 354125Attachment 354124

Without that little tiny push from crankhouse i doubt you will find any gains.
It might work yes, but no gains.
There is no free lunch

[crbbt]

No stress Wob,

Let me know if you have any luck.

I would imagine the pipes would have a pretty serious ignition map, porting and combustion chamber requirements

[aljaxon]

while we are at it has anyone got a pipe design for an rd350A with mild porting?**

i could exchange a load of designs for mobylette 50v's that DONT work

here's something that has just dawned on me. whenever the waves encounter a convergence in the pipe they send back a stuffing pulse.
so at the very end of the diffuser where the belly starts this will happen no? and at the wrong time? and the more abrupt the change the more energy is wasted?
so, can i "round off" or blend in the diffuser/belly joint to lessen the wasted energy? and again the belly to rear cone seems to me to be returning pulses for the over rev which in my front side cruising pipe is not wanted. if what i suspect is true i can see the advantages of hydroformed/flowing pipes. a short 10mm section either side of the belly could reduce the angles although also increasing the angled cones main angle ever so slightly.


**i made some pipes 10 years ago using blairs percentages slightly tweaked and they have nice power everywhere but no show stopping massive wheelie inducing hit. they go the bike up to 120mph actual. 100 sat bolt upright, which i was pleased with. now geared down to 110 cos im getting old.

glad to see im not the only one asking pipe questions. i previously felt like the pupil in the class always with his hand up - please sir!! please sir!

[JanBros]

waves are created when the diameter changes. at the end of the diffuser the diameter stays the same throughout the belly so no waves are created until the diameter changes again with the beginning of the baffle.

[wobbly]

Where there is no change in CSA there is no wave formation , the belly does nothing.
Except I sometimes use a slightly tapered mid to create an effect needed ( steeper or shallower ) before or after the mid ( up to 3* included )
Yes I have tried a two piece belly like a sharp hump back - no power/no loss.
But the shallow first cone in a 3 cone rear setup does conserve some of the finite wave energy to be made available later down the TL.

Hydro forming causes huge controversy in the pipe community in that some will swear by it , but I spent months at JL learning how to do it " properly ".
The vital part was using steel platens in a press to prevent the larger diameters from blowing out first , and finally I could make real nice looking pieces.
But no matter what , they always lost around 2 Hp to my hand welded cone pipes , on the dyno mule Rotax 125 used to test for the 256 used in Superkarts.
I made a split clamp thing to hold the belly section straight and round and got back 1/2 a Hp.
The smooth transitions between sections always lost 1 1/2 Hp and we ended up having CNC press tools made for just the labor intensive curved header section of the front pipe.
And I noted years later that's how the nice pipes were made on the KTM250GP.
Note the sharp end of the pressed header.

I got to talk to a Honda engineer at Silverstone where we were testing the new ZIpKart one weekend and asked about the split formed pipes they always made.
He said it was done using split female formed tools in an " explosive " process to ensure sharp angles were created.
Lost in translation somewhat , but Boom was the operative word.

[diesel pig]

Hydro forming causes huge controversy in the pipe community in that some will swear by it , but I spent months at JL learning how to do it " properly ".
The vital part was using steel platens in a press to prevent the larger diameters from blowing out first , and finally I could make real nice looking pieces.
But no matter what , they always lost around 2 Hp to my hand welded cone pipes ,

The irony of this is as long as the home hobbyist pays attention to the details when making there pipe, it will be as good as a factory pipe.

[aljaxon]

waves are created when the diameter changes. at the end of the diffuser the diameter stays the same throughout the belly so no waves are created until the diameter changes again with the beginning of the baffle.

its at the point where the diffuser meets the belly and where the belly meets the rear cone. those are the only two angles where any waves created are not wanted. in fact for the first third of the rear cones length im guessing those waves created are wasted on what i want for this front side cruising pipe.

wobblys boom moment noted - re sharp angle changes.

where you want them.

i was told any change in angle would trigger a returning wave. for that reason i was talked out of a twisty curly snail like pipe i'd made. whose many angles would rob energy. you do get told a lot of conflicting info on the net though.

i was told the waves are molecules handing over their energy to adjacent molecules and so on.
to my thinking the molecules on the outside of the diffuser when reaching the belly joint are suddenly forced right left or up down ie off trajectory and are behaving as if the diameter has changed. if not then they are in touch with their cousins 100mm away etc on the other side of the diffuser and have permission to carry on regardless. which seems a bit far fetched. but then again the whole process what happens inside the pipe is almost unbelievable and like magic.

im making one pipe with 10mm blending in sections either side of the belly and one without. plus 3 baffle/end cone combinations for each pipe.

hopefully mr dyno will be happy.

[wobbly]

A change in section area is not the same as a change in directional vector due to a pie cut , as in the second example there is no change in area.
Of course there are limits , and from experience I can say that a pie cut closer than 50mm from the port will affect power.
From observing the wash pattern in the duct it seems that any angle not on the vertical plane creates an asymmetric plugging action on the A/F stored in the duct.
And where a pipe is bent in one plane , like a KZ rear facing one , having the cone seam joints on the outside , looses nearly a Hp to a pipe with all the joins on the inner radius.
I didnt believe it , but was told to do it to the laser pattern .dxf by TM , and yes they were correct - humble pie.
As a general rule having pie cuts greater then 7* ie a 14* bend with 180* rotation will create turbulent eddies and power reduces.
The idea of having a " blending " section in front of the mid belly joint , will simply replicate the construction of a hydraulically formed pipe.
In a race only engine this lost power - but maybe having a slightly longer diffuser is what was needed anyway in a road bike application , and it may in fact be an advantage.

[Vannik]

Strictly speaking, the friction between the gas and the pipe wall also sends a very small positive wave back. This is one of the reasons a very long pipe on a low revving engine never seems as efficient as a short pipe on a high revving engine. A curve in a pipe increases this friction losses and does have an effect although small.

Comparing a blown pipe with an armadillo pipe the armadillo pipe always seem to win by a small amount. My thinking, although unproven, is that the sharp transitions scrub off the developing boundary layer and makes the wave see the full cross sectional diameter and / or minimizes the losses from the friction. How to prove and measure this without a full blown laboratory I do not know.

[philou]

Hello,

how to make search engine work of forum ? google no longer works on the site
I want to display posts as results. there are no results or displays the list of entry topics

[katinas]

Another KTM example of sharp transition between pipe fat sections after pressed or exploded process. Semi mass production pipe from KTM 125 for Red Bull Cup.

[JanBros]

its at the point where the diffuser meets the belly and where the belly meets the rear cone. those are the only two angles where any waves created are not wanted. in fact for the first third of the rear cones length im guessing those waves created are wasted on what i want for this front side cruising pipe.

you keep on reading your own thoughts in other peoples words.
a change in diameter (or better, cross section as Wobbly says, because you could also make a square exhaust) is not the same as a change in angle.

[koenich]

Another KTM example of sharp transition between pipe fat sections after pressed or exploded process. Semi mass production pipe from KTM 125 for Red Bull Cup.

there is also the "real" process of hydroforming, where you have a fullform negative die and a tube is pressed against the walls of the die oooor the parts could be simply deep drawn. both processes (if done properly) have the limitations of bending radius = ~1 x material thickness, so a transistion with t = 0,8 mm sheet metal can be made quite sharp.

[Wos]

there is also the "real" process of hydroforming, where you have a fullform negative die and a tube is pressed against the walls of the die oooor the parts could be simply deep drawn. both processes (if done properly) have the limitations of bending radius = ~1 x material thickness, so a transistion with t = 0,8 mm sheet metal can be made quite sharp.

Somebody talked about forming with explosives Daniel its possible to replikate surface of for example a money coin or even a oak leave absolutely sharp

In german its called " sprengformen or sprengplattieren"

https://de.m.wikipedia.org/wiki/Sprengplattieren

Let us try with your pipe first Daniel? insert a handgrenade... duck and cover


Grüße Wolfgang

[koenich]

Somebody talked about forming with explosives Daniel its possible to replikate surface of for example a money coin or even a oak leave absolutely sharp

i know, i know but doesn't make much sense if standard methods can be applied (or sth was lost in translation). nor does boomforming remove material limits (e.g. minimal bending radius).