View Single Post
      09-26-2013, 09:03 AM   #30

Drives: No BMW for now
Join Date: Jun 2006
Location: Canton, MI

iTrader: (1)

Originally Posted by NISFAN View Post
True, the fact that the old stroke size is the new bore size adds some weight to that assumption
We are thinking alike here...

BTW, the torque output from changing bore/stroke combo's can be simulated. There are specialist engine simulation software available, which computes loads/vibrations/torque, etc. But rule of thumb is a longer stroke always gives more torque than same displacement short stroke engine.
I've seen the claim many times but never the proof. One thing I have done is looked for evidence among production engines and there is no consistency. Now granted, I have never examined the entire torque curves.

The elephant in the room here is that we are suggesting that BMW chose a very long 90mm stroke design for the S54 - far from optimal for a high revving design - all in the name of engine torque which we all know can be adjusted at the wheels with gearing. I call shenanigans. The long stroke is there only to get to 3.2L with a 91mm bore center, I say, which they needed to hit power goals. If they had been given a starting platform with a 98mn bore center (for example), then I would bet my life we'd have seen a short stroke engine more like an S65. And furthermore, I doubt peak torque would be appreciably less for such an engine.