BlasterBoy

Member
Aug 5, 2000
7
0
What's the deal with the pipes on most modern trials bikes? They don't appear to be expansion chamber, actually they look more like fourstroke headpipes. Is this because a large expansion chamber could get hung up on obstacles?
 

Doc

Two-Stroke Nut
LIFETIME SPONSOR
May 9, 2000
78
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Beta and Montesa use pipes with expanding sections in front of the center box. GasGas, Sherco, and Scorpa use a constant diameter pipe. The expanding head pipe would give better negative waves for scavenging, but it does not make a big difference. All are designed to give a positive wave back from the expansion box (center box). The Beta TR 32 and TR 33 had expansion chambers and they were a little pipey. In European and Eastern US trials conditions, it is important to have very linear power because if you get a little unexpected power when accelerating at the traction limit you will dab at best, not get the traction you need to make an obstacle (5), or crash into the obstacle :scream:.

Doc
 

David Trustrum

~SPONSOR~
Jan 25, 2001
1,396
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Also bear in mind most trials bikes put out about 10 hp. Not very good for bragging at the pub but I am constantly amazed at the ability of these seemingly puny engines. In the bad old days 2 strokes relied on the crankcase as a pump & the exhaust was merely to bleed the gasses out & if you were lucky quieten things a bit. Seems this primitive idea produced smooth power if you use ports that prevent gas short-circuiting too easily.

Indeed my TR3# has a chamber of sorts but my GasGas does not though interestingly the primary muffler was changed between the 2000 & 2001 models supposedly for an improvement in torque.
 
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