By increasing the bore from 92mm (stock) to 95mm (MM), displacement increases from 3430cc (stock) to 3657cc (MM). It offers a nice increase in torque when combined with a 10.5:1 compression increase.
Displacement increases twice as fast by boring compared to firing. Displacement, through boring, is increased without the expense of a firing crankshaft or the penalty of adding piston speed (shorter engine life).
A MM 3700 rally engine has an improved rod ratio of 1.66 (143mm rod/86mm stroke = 1.66 RR) vs 1.57 RR for an M30/B34 cylinder head with a shorter 135mm rod.
The piston and rod assembly in a MM 3700 rally uae email list engine is only 950 g versus 1435 grams for a stock BMW M30 engine. For a total weight reduction of over 6.5# (2910g).
This huge reduction in reciprocating mass helps the engine spool up (accelerate) faster, makes the engine smoother, and greatly increases engine life.
Under equal driving conditions, even though a MM 3700 rally engine generates 30% more horsepower over the best BMW M30 engine, it will live approximately 2.5 times longer.Tolerances
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The longevity of a high performance engine is dictated by proven, high quality parts, maintaining tight tolerances without producing a failure. This takes many years of experience to develop.