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I've just received a Mistral muffler for my Saturno. I thought it would slip straight on to the standard header pipe, but the pipe needs to be shortened for the muffler to fit. Is there a correct amount to shorten the pipe for the Mistral muffler? I'm a bit concerned about losing mid-range power - will that be an issue?

And any thoughts on carburetor tuning? A previous owner ditched the airbox, so I'm running a long Unifilter pod. Seems likely the combination of Unifilter, shorter pipe and Mistral muffler will need non-standard jetting.

http://gileraclub.de/viewtopic.php?p=3 ... mer#p31371

unfortunatelly the mentioned link isn't valid anymore
Maybe Felix still has the graph

Cuting the pipe you will loose some midrange power and will earn some power at high revs.
On the other hand... if you have no original damper and have to mount the Mistral part you will loose all the power becaus it wont fit

ciao Joachim

here it is
blue is original
red is short

Hast du zufaellig auch die Zeichnung mit den Angaben wie viel abgesaegt worden ist?
Irgendwo hatte ich die mal.....

ciao Joachim

(Google Translate ...)

Vielen Dank an Sie beide.

Hans-Peter Krause schickte mir eine Werkskizze, aus der hervorgeht, dass 10 cm abgeschnitten werden sollen.
Klingt das richtig? Ich muss nur etwas mehr als 7 cm entfernen, damit der Schalldämpfer passt.

sorry for switching the langauge.
Next time i will try to think first, and then write

Thats the little scetch i was talking about
I would give the 7cm a try first.

BTW thanks for your question. I also was thinking about that buying such a damper.
Keep us informed how it works

ciao Joachim

I decided to go with the gilera tuning notes and took 10cm off the pipe. With the Mistral muffler the cross sectional area at the pipe end will be not as large as with the Lafranconi muffler and the distance short before the cross section narrows at the entrance to the baffle. There will be a small volume, but effects of resonance in there will probably not be significant. I am hoping this will split the difference on the dyno graphs that FelixMotalia supplied.
Waiting on getting the front sprocket EDM drilled so I can safety wire it, and on carburetor jets. And then we shall see.

Notes from fitting the muffler:

• The standard exhaust clamp is wider than the one supplied with the muffler, so the slits at the front end had to be lengthened before I could get a tight fit on the pipe.

• The mounting tab is thinner than the original - I used a washer to pack it out for a firm fit with the mounting rubbers.

• You really do need to use the db killer for road use - it sounds wonderful without it, but it is very loud.

• For jetting I went with the 155 main and second notch on the needle as recommended by Ju. (I'm running long Unifilter pod and header pipe shortened by 10 cm)

Up to 4500 rpm power feels quite similar to before, the step up at 5000 is still there but feels a bit smoothed out, then a more progressive build to the next step up around 6500. I haven't had a chance yet to properly test full throttle - I'll book a dyno session some time soon to refine the jetting and find out how much the db killer is costing me.

155 main jet was too big with the db killer in, so I've changed to 150. Dyno run is booked for June 12.

Got the dyno run done today, jetting has ended up 142 main with needle lowered one notch from middle - on New Zealand 91 octane, with long Unifilter (no airbox), header pipe shortened by 10 cm, Mistral muffler. 150/70 rear tyre (there was a better selection at the time ...).

Power/Torque: Power/ air fuel ratio: I'm intrigued by the air:fuel graph you can see when the throttle gets wound open at 4000 the accelerator pump doesn't fully compensate - ratio leans out to 15.5:1 briefly.

Dyno runs on the charts were done with the Db killer removed. When it was refitted it made no difference to the power (very surprised) so we left the jetting as it stood. What did make a difference was fuel. For the final run the tank was topped up with 95 octane and there was an instant extra 1 and a bit horsepower. So I'll stop being cheap and go back to 95