My old yamaha service data from back in the day says DT2 trail 37mm to top of exhaust port & DT2MX 34mm. So 36mm doesn't sound too wild [me thinks guessing] Not piston port i know but!!. I 'do' have a DT1MX cylinder on one of my relics [not gyt kit chrome but cast original off the first mx in probably 1970 after the gyt kit--give me that chrome bore anyday lol. Don't have my cylinder off to measure. Anyway i've got a 360 crank in mine 70x70. I bought [a life time ago] an IT400 motor & fitted it into a mono DT250 frame. Someone had ported it & got carried away i think & with the pipe i used which was adapted from a 465 or something--big enough & long enough for the job. but the thing had a terrible roadracing type power & came on so strong & so high up it wasn't going to last long, was a pain. So added 100mm [4 inches] to the header pipe & fixed it 100%. Only guessed 4 inches as it was 'so far' off the scale i thought it's need plenty more length to get what wanted.
Meant to say--it had 192 degrees duration on the exhaust [talking the IT400 still] Not sure what they're suppose to have but was guessing it's way too much, hence the header extension because that was easiest for me--& my rough methods.
