Morning.
Trumpet length is never the same for different engines but in general the consensus is Long for low speed and short for high speed running,
Just watch a variable trumpet system on a formula 1 race car and you will see them doing exactly that!
However you must realize that it's the gas velocity that matters, (cubic ft./min through a given orifice) therefore you will get very different results from the same trumpet from one engine to another depending bore / stroke ratio, cam choice, and especially engine displacement!
Saying that, The single most important area on any trumpet is the shape of the actual trumpet itself. We have found massive gains in flow by just re-shaping the bell. Not only that but the pulse wave effect in the inlet really has only a very small effect on the engines most of us are playing with and is not really worth worrying too much about below 7000 rpm! You would be much better advised to think about the ram effect of the incoming air, this has a very large effect on engines with fairly heavy cams and can significantly increase power by ramming the mixture in even when your piston is quite high up on it's compression stroke! Remembering that the dynamic pressure is proportional to the square of the inlet air speed, so by making the passage narrower or longer the dynamic pressure is increased. That's why we don't just go for massive inlet ports and the biggest valves possible!
Julian