Hello, 
I am looking for information and pictures of improvement of the exhaust for Bultaco

Check out WES exhausts.

1 hour ago, b40rt said:

Check out WES exhausts.

I prefer to modify the original silencer

have a look at Vazquez and puma bikes, they have clubfoot with a smallerr back box and straight through pipe.

If the bultaco is old the best improvement you can do is repack the middle box.

The rear exhaust is based partly to the Helmholtz priniples with it's inner tubes and chambers these work great but are limiting the flow, they put an air cushion to the rear, thus btw. the lack of the typical two stoce sound.

To replace the old dampning wool is a good idea, a much bigger effect is provided by cleaning the holetube inside or replace it by a more modern style that is to cone shaped which will help to dampen different noise levels but can too help the engine to perform better.

There is not only a holetupe in the midle section but too in the rear section at the flat beginning up to the point where the rear silencer gets bulky, then you can too "play" with the length of the exhaust maifold wich changes behavior too very much, but you have to know what you do and the secrets are inside and hided, thus my tip is to do the math and calculations upon your needs, and too you have to try out, why I took apart the mid section from the manifold. The exhaust of my Sherpa is modified so I could keep the stamps and markings for our TÜV.

The transformed rear section:

The transformed midsection:

The transformed rear secton mounted, the mid section here original

 

 

 

 

Edited October 3, 20214 yr by pschrauber

It s good ? 

That new holetube is providing less area for the exhaust fumes to get out of the muffler then before and the hole tube isn't a real one either, thus I have some personal concerns.

This modification idée not good ? 

I don't know what you want to archive.

At least the diameter of the tube should not get decrease instead increase then the holetube at the beginning is not cleaned up, the self made hole tube has too little holes and will due to the curves even more limiting the fumes to get out out. 

At the rear exhaust you want to get rid of thefumes as quickas possible but too get rid of the noise, you can use a hile tube and insulation as an absorber to let thefumes out while absorbing the noise here it will not happen so well because the flow for the fumes is not provided.

Le 03/10/2021 à 19h55, pschrauber a déclaré :

Je ne sais pas ce que vous voulez archiver.

Au moins le diamètre du tube ne devrait pas diminuer, mais augmenter, puis le tube troué au début n'est pas nettoyé, le tube de trou auto-fait trop peu de trous et limitera encore plus les fumées à sortir en raison des courbes.

À l'échappement arrière, vous voulez vous débarrasser des fumées le plus rapidement possible, mais aussi vous débarrasser du bruit, vous pouvez utiliser un tube de hile et une isolation comme absorbeur pour laisser les fumées sortir tout en absorbant le bruit ici, cela ne se produira pas si bien parce que le débit des fumées n'est pas fourni.

It s good ?

A bit more Volume, think about the area / Volume the both original tubes of the Bultaco have and do you now have more or less? 

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