my 996S had low speed popping etc with standard cans but only after my 1st year 4000 mile service. Don't know what they did (shims I think) but it was 10 times worse after that. 50mm open race carbon termis and Ultimap UM239 chip and was a new bike. Could actually ride bike as low as 3000rpm
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So does the 54mm system make any disernable extra horsepower? I never felt any extra HP after fitting open 50mm race termis.