'79 T140E with TT Pipes - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 5 (permalink) Old 11-05-2012, 02:53 PM Thread Starter
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Minitwins
Main Motorcycle: 1979 Bonneville T140E
 
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Location: Kansas City, MO, USA
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'79 T140E with TT Pipes

When I got the bike this summer, the TT pipes had short mufflers welded on the ends. They were rattling so I cut them off and added 8 1/2" baffle inserts into the pipes to be a good neighbor. But I noticed afterward that I had lost power in the upper rpm range. I could hardly keep the bike at 75 mph on an uphill grade.

I removed the baffles this weekend and OH, BABY! When the motor hits about 5000 rpm, it takes off! It's not that much louder either. The low end power doesn't seem to be that much less. The bike is stock otherwise with standard jets in the carburetor.

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post #2 of 5 (permalink) Old 11-05-2012, 07:15 PM
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I found the same with T140s - they do like free-flowing 'zorsts. As you say, 5000 is the powerband - certainly was on my old T140s. My current TR7 has a powerband at just over 4000, on almost straight-through TR6C type pipes and E3134 profile exhaust cam.

It may be wise to check the plugs - my T140s needed main jets increased from 190 to 230, then to 240 & finally 260 with the final stage (32mm carbs, no air filters, straight through pipes, 9:1 pistons).
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post #3 of 5 (permalink) Old 11-06-2012, 07:28 PM Thread Starter
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Minitwins
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Thanks for the ideas. I'm haven't decided what I want to do with the exhaust long term. I never liked the stock cross-over pipe. But, I want at least stock performance. The 1-3/4" pipe diameter seems to do that for me. Maybe 1-3/4" pipes with reverse cone megaphones?
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post #4 of 5 (permalink) Old 11-06-2012, 08:05 PM
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Maybe 1-1/2" OD pipes would be too big,unless you mostly ride at more than 6000 rpm.Bigger is not better,it just kills exhaust velocity and you lose torque.

If you never exceed 8000 rpm,1-1/2" is OK.

Long mega/mufflers should work OK.If the baffles bolt in at the rear,you have the opportunity for experiment and improvement.Short mufflers are either very loud or very restrictive.
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post #5 of 5 (permalink) Old 11-07-2012, 09:18 PM Thread Starter
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Minitwins
Main Motorcycle: 1979 Bonneville T140E
 
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Thanks much. I'll probably do a little study this winter on exhaust design.
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