Hi,
Does anyone know the difference between the traditional 28mm u-bend and the new ish step diameter one from TM with 26/28mm. 26mm on the for half?
Different diameter u-bend, inserts, exhaust flange thickness, reed stiffeners are the easy bits you can use to manipulate the engine output to favor low-end torque vs high end revving.
A smaller diameter creates a higher venturi effect, which in theory should increase efficiency at low rpms so it should work well for racetracks that are short/twisty or with slow corners. When you are using it in combination with other things, you may see a little bit of gain at low rpms.
Anectodally, I can tell you there are tuners who believe in this 100%, others that play with stiffeners only, others that use exhaust flange only, others that use different pipes through selection, some do all of the above together…since they are trading places every weekend, I don’t think this is the secret sauce that will drastically change the engine output so don’t expect a huge difference. Test it, see if you notice any difference and move from there! Driving style makes a ton of difference too, so even if the gain is there, you may not notice it or even like it