ESE's works engine tuner

[JdG]

I know there has been a lot of talk about hydro formed exhaust, especially about the cons.

But I think this video is worth to watch.

https://youtu.be/nRP-MMZlzJQ?si=MG6j_xDxIMwnnb-k


Verzonden vanaf mijn iPhone met Tapatalk

[husaberg]

[Peljhan]

I know there has been a lot of talk about hydro formed exhaust, especially about the cons.

But I think this video is worth to watch.

Very good fabricating skills.
I made about 50 different hydroformed exhaust for mopeds, but my procedure was a bit different.
I cut the shape, weld the edge with TIG without rolling the edge, pump the exhaust with strong pressure washer and if the seam poped, weld it back together. Than I welded all the seams around with TIG again so it was smooth. Pressurized the exhaust with air and heated wrinkles with acetilene-oxy torch and a bit of hammering. Than cut and rotate where needed.
My way avoids so much hammering he demonstrated.

I think the 5-7% reduction adjustment in diameter he makes on template is same as welding the seam directly without rolling as welding "eats" a bit of metal. I also figured out how much tighter the radius gets after forming and I think the coefficient was around 0,81. If you want 100° bend, you shoud make it 81° on template.

I started building exhaust from cones later as I made them for racing mostly. Hydroformed were quite ok for stock mopeds. I never did comparison hydroformed and coned on dyno, but that would be my wish someday to compare the performance.

[ApolloMotoMoto]

Not at all what I had in mind.

Well then, what DID you have in mind?

[wobbly]

After winning the Superkart World Title with Hines at Zipkart I went and started work at JL Exhausts.
There I spent months learning how to do hydroformed pipes for the Rotax 256, as the front one was effectively a 180* bend straight off the manifold.
The biggest advancement was pumping up the pattern between two steel platens in a big press, that were slowly adjusted apart
This stopped the mid section from fully blowing up first, with the header forming last.

But even using a split clamp on the mid section, it was impossible to stop the diffuser end, and the rear cone start, from forming a smooth gradually changing angle.
Nothing like the correct design angles of cones.
This meant that no matter what techniques and no matter how nice the pipes looked, it was impossible to get within 2 Hp ( in just over 40 Hp ) of a fully welded section pipe on the dyno.
Eventually we gave up, and had a CNC machined press tool made for the header and initial diffuser U bend, just using cones for the rest of the pipe.
This was way less work and made identical Hp.
Interesting that KTM used exactly this setup on their 250GP parallel twin.
And Honda used split dies for years until Titanium became popular to reduce weight.

[Flettner]

Well then, what DID you have in mind?

I want a sliding pipe but do not have the room to fit one (or two as the case may be) ,
Ideally I'd like to shorten up the pipes, and it might be nice to sharpen up the reverse cone angle at the same time.

[Flettner]

After winning the Superkart World Title with Hines at Zipkart I went and started work at JL Exhausts.
There I spent months learning how to do hydroformed pipes for the Rotax 256, as the front one was effectively a 180* bend straight off the manifold.
The biggest advancement was pumping up the pattern between two steel platens in a big press, that were slowly adjusted apart
This stopped the mid section from fully blowing up first, with the header forming last.

But even using a split clamp on the mid section, it was impossible to stop the diffuser end, and the rear cone start, from forming a smooth gradually changing angle.
Nothing like the correct design angles of cones.
This meant that no matter what techniques and no matter how nice the pipes looked, it was impossible to get within 2 Hp ( in just over 40 Hp ) of a fully welded section pipe on the dyno.
Eventually we gave up, and had a CNC machined press tool made for the header and initial diffuser U bend, just using cones for the rest of the pipe.
This was way less work and made identical Hp.
Interesting that KTM used exactly this setup on their 250GP parallel twin.
And Honda used split dies for years until Titanium became popular to reduce weight.

I use press dies to get my pipes as identical as possible, being two pipes into one cylinder. Makes life much easier.

[husaberg]

I want a sliding pipe but do not have the room to fit one (or two as the case may be) ,
Ideally I'd like to shorten up the pipes, and it might be nice to sharpen up the reverse cone angle at the same time.

It didnt work on a road race bike ie Doohans NSR500 but water injection or actually cooling the header with a sleeve might work in an enduro situation.
This is how I believe the NSR actually worked.



The other option is the Atac valve, which in a rooundabout way also make the pipe longer.

[Flettner]

It didnt work on a road race bike ie Doohans NSR500 but water injection or actually cooling the header with a sleeve might work in an enduro situation.

Just because Honda couldn't do it, doesn't mean it can't be done.
Their requirements are different to mine.

[husaberg]

Just because Honda couldn't do it, doesn't mean it can't be done.
Their requirements are different to mine.
After all, I was told twin pipes wouldn't work together, they do, but a powervalve and water cooling is nessasary it seems.

I am still trying to add photos . But on second thoughts, atac is simipler and KISS.

I think it's not the case of honda not being able to do it, more a case of Doohan not needing it or wanting it.
One of Frits first posts was a hydraulic or maybe phnematic adjustable header.
okay its cable but KISS

[Flettner]

I am still trying to add photos . But on second thoughts, atac is simipler and KISS.

I think it's not the case of honda not being able to do it, more a case of Doohan not needing it or wanting it.
One of Frits first posts was a hydraulic or maybe phnematic adjustable header.
okay its cable but KISS

It's not like I've got room on an off road bike to move the pipe.

I'll report back when I have a working (tested) example.

[Flettner]

I am still trying to add photos . But on second thoughts, atac is simipler and KISS.

I think it's not the case of honda not being able to do it, more a case of Doohan not needing it or wanting it.
One of Frits first posts was a hydraulic or maybe phnematic adjustable header.
okay its cable but KISS

It's not like I've got room on an off road bike to move the pipe.

I'll report back when I have a working (tested) example. You don't know how simple my system is, yet.

I see the pictures, hardly off road friendly ��

[Frits Overmars]

I want a sliding pipe but do not have the room to fit one (or two as the case may be) ,
Ideally I'd like to shorten up the pipes, and it might be nice to sharpen up the reverse cone angle at the same time.

It didnt work on a road race bike ie Doohans NSR500 but water injection or actually cooling the header with a sleeve might work in an enduro situation....The other option is the Atac valve, which in a roundabout way also make the pipe longer.

To the best of my knowledge Honda never used sliding pipes. Accommodating those to their 500-4 would have been a nightmare anyway.
They did use ATAC (to avoid Yamaha's power valve patent) but ATAC was not so much a detour as an additional volume to lower the Helmholtz frequency of the exhaust system.
It disappeared when Honda introduced their sliding power valve that apparently was sufficiently different from Yamaha's rotating drum valve patent.

I think it's not the case of honda not being able to do it, more a case of Doohan not needing it or wanting it.

Water injection did work, both on Doohans Honda 500-4 and, years earlier, on the Aprilia RSW250 where it added 10 hp at 10.000 rpm.
But the rider (Reggiani) managed to keep the revs always above 11.000 rpm, so the water system was abandoned in the interest of KISS and weight.
It also appeared that the water effect took some time to wear off. After the injection stopped, the pipe was too slow in getting up to the higher temperature needed for the higher revs. That did not help rider confidence and lap times.
But if you can accommodate a sliding pipe, it will outperform any power valve, power jet etc. by far.
Here is a story about it that I wrote some time ago.
---------------------------------------------------------------------------
There are several options in lengthening an exhaust pipe. You can move the end cone, or you can lengthen the header, like a trombone.
The gas pressure generates a force that is proportional to the cross section area of the moving part and proportional to the pressure difference at either side of that area. For a moving end cone this force can be up to 6 times larger than for a sliding header. That is one reason to go for the trombone system rather than the moving cone system.

The second reason: sealing. The circumferential gap that has to be sealed, is three times shorter for the trombone system. That means three times less leakage and three times less friction.

The third reason: say you wish to lengthen the total length of the pipe by 10 %. If you do it by moving the end cone, you will also enlarge the pipe volume by a little over 10 %.
But in a good pipe configuration the header length is about 1/3 of total pipe length, so in the trombone system, lengthening the pipe by 10 % will be done by lengthening the header by about 30 %. That gives a far greater variation in the pipe's Helmholtz frequency than a 10 % volume change.

It is true that the length percentages of all pipe components should be in a rather fixed relation to each other. Varying the lengths of all components by the same percentage would be the theoretical optimum, but that is not feasible.
Lengthening the belly will disturb the optimum relations, as will lengthening the header. So the pipe in its lengthened version will not be the optimum for the low resonance rpm dictated by the length. But it will be a hell of a lot better than using an exhaust power valve that spoils the 180° effective exhaust timing, necessary for true resonance.
And a pipe shortened beyond its optimum may not show the optimum length relations between its components either, but it will be a lot more effective in overrev than artificially raising the exhaust gas temperature by retarding the ignition, or by weakening the mixture strength through closing a power jet, which has the disadvantage that not all inhaled air is used for combustion.

Video courtesy of Rimar Motors:
http://www.youtube.com/watch?v=0odVz...ature=youtu.be