as another option if you want turbo sound to match a 737 at takeoff you could do what i did and swap in a holset HE221W with 14" of 4" exhaust dumping straight down and out (it doesn't bother me and i had a full exhaust system on it for a while and lost a good deal of power so i just ended up running the down pipe only. plus the 617 sounds quite good over 5000 rpm.)

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P