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