I have had numerous discussions with Ducati sellers and Ducati buyers alike over the years on this particular topic and have also read a great deal of comments on many blogs/forums as regards what is the correct number of reference. There appears to be a great deal of confusion as to which part of the exhaust tube should be measured, as well as how that measurement can in fact properly be taken, when it comes to Termignoni exhausts. When referring to exhaust measurements (in all material respects, be it in terms of performance or of a representation made for the purposes of a sale description/purchase): (a) is the exhaust measured from the outer or the inner side of the exhaust tube? and, (b) is the exhaust tip/trim to be taken into account at all? To answer the conundrum as far as Termignoni exhausts go, it is the outer diameter of the exhaust tube that is taken into account. Where that outer diameter measurements are consistent to all parts making up the exhaust system from bore-to-silencer, then we are taking about a full system of that mm designation (whereas when the mm measurements vary at bore as we go up towards the silencers, we may be talking about what is know as a half system). When measuring the outer diameter of the exhaust tube however, caution must be had that we are not measuring over a connecting part of the exhaust tube that is intended to fit/slip over another (since that welded enlarged part is expected to yield a larger outer measurement). The inner diameter of the exhaust tube (same measuring at least 2mm less than the outer diameter due to the 1mm thickness of the construction material used either side of the tube), as well as the lip/trim of the exhaust, are not to be taken into account (at least in defining the mm designation of the exhaust system).
My experience tells me that when exhausts are marketed as 45, 50, 54mm or whatever, it is the OD of the pipe that is the reference. e.g. my 916 has 50mm Termis and they measure 50mm OD, my M900 has 45mm Termis and they measure 45mm OD, My Guzzi has 40mm Lafranconis and they measure 40mm OD etc.
I agree with the above. My 916 SP3 has its original 45/50 set-up and it’s all OD measured along the tubes.
Slightly O/T but the 40mm downpipes on my Guzzi have 2mm walls whereas the original 38mm are only 1mm wall meaning that the +2mm 'performance' exhaust is only actually +1mm whilst weighing around twice as much. So I'm not convinced how much of an 'upgrade' it really is?
My 916 is 50mm all the way OD. I wonder where i sourced my 50mm manifold end pipes from though as theres no inner knee heat shield fixing, but thats never bothered me. Unlike my 70mm 1198 which cooked my right calf. I still have my orig 45mm bottom bits.
There is zero difference between them. A 40mm tube with a 2mm wall has a 36mm ID. A 38mm tube with a 1mm wall also has a 36mm ID. The wall thickness is seen twice when comparing OD to ID. In other news... as a rule tubing is sized by it's OD and pipe is sized by it's ID so yes, the tubing used to make an exhaust pipe would be measured on it's OD.
You are, of course correct and I stand corrected. In which case they are even less of an upgrade. Actually I've removed them anyway as the flange broke off (again) on the LH pipe. They are awaiting repair in the project 'pile' but at the bottom of the list of priorities - so it's running with the 44 year old originals.
