under square bore stroke doesn't limit rpm/performance like you would think. the BMW S54 in the E46 M3 is an under square in-line 6 (86mm bore 89.6mm stroke) that revs to 8000 rpm. the real limiter is the structural limits of the rods and ring flutter. the 617 can handle up to 6000 rpm on stock parts. the longer stroke can help breathing in some cases. the S54 uses a larger rod stroke ratio to play with dwell at BDC and TDC to improve the VE (for certain rpm bands it is over 100%) in conjunction with a tuned length intake tract. something else to think about is the effect bigger elements have on diesels notable the shorter injection pulse width, higher peak pressures, and finer atomization. my fuel economy went up slightly at steady state cruise after i installed the 8mm M pump on my car. with that the new turbo and exhaust i have been clocking around 33-35MPG @70 on the highway averaged out over the past 7 tanks. before i swapped everything i got 28-31. also you don't always have to add more air or fuel to get more power dieselmeken has shown on the dyno that a N/A 617 can produce over 100HP with mild port work and larger fuel elements set to the stock fueling. and all this is not even getting into the effects cam timing and injection timing can have on your power. these engines were designed with emissions and smoothness of operation in mind not performance.

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