View Full Version : How to remove the restrictors from a stock exhaust

11-01-2007, 02:19 PM
This has been done before but I'll spell it out again.

The stock exhaust uses about 32mm tubing with maybe 2mm walls (?). The flanges for both headers have been very well welded. A bit too well actually ...

Assuming 2mm wall thickness the internal diameter is 28mm, radius is 14 mm. So the area of the exhaust is Pi x Radius squared = 3.142 x 14 x 14 = 615 sq. mm

In my road bike exhaust the welds protuded internally by at least 2mm all round.

Therefore the exhaust diameter there is 3.142 x 12 x 12 = 452 sq. mm

The weld area is 452/615 x 100 = 73%, so there is effectively a 27% restrictor in the exhaust.

Filing off these welds removes the 27% restrictors! Whoever welds the stock exhausts has welded all the way through so filing off the inside of the welds still leaves strong joints.


king karl
11-01-2007, 02:43 PM
fanks for that :WTF:

11-01-2007, 02:46 PM
fanks for that :WTF:

i still have your world famous exhaust in unrestricted form,fook its loud

01-13-2009, 04:52 AM
See this link (http://www.apriliaforum.com/forums/showthread.php?t=169532) which has some pictures.