Hi Chris: Not sure of the venturi throat diameter but it is stock LA40S size. That is a Bruline slip-on filter, coarse mesh, that effectively chokes the venturi a bit. It runs about the same without it but it keeps crud out in grass landings with no landing gear. The motor has plastic back plate and stock remote OS NVA. The muffler is a Randy Smith tube muffler, about half the weight as stock muffler and very little restriction while cutting the noise a lot. Also it just looks cool. My other LA 40S (in Smoothie) has metal backplate and Randy Smith (similar to Super Tiger) venturi-mounted NVA, also a good stunt motor with 11-4 prop. I would stick with a modern smooth-running engine like the LA over old-tech engines, unless you like them for nostalgia's sake. Which is totally fine. I tend to agree the LA46 would be a lot of motor for your Streak but, it weighs a bit less than the LA40 and runs even better. Wants a larger prop like 11.5 x 4. All these LA engines want to run in solid 2-stroke, see suggestions from Brett Buck and Randy Smith for running them. Attached is better picture of the Half Fast setup (I know, landing gear on a combat model is weird but I fly off pavement).