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


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[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.