Ken,
determination of counterweight and overall crankshaft mass is a matter of many aspects most important ones concerned with loads imposed on the assembly by the alternating masses.
Apart from other considerations such as idle stability, softer and more regular engine behaviour (which might not be of interest), depending on layout of engine (IL4, IL5, V6, V8 or whatever) quantity of needed masses (counterweights and flywheel) vary quite significantly. So it is not true the least the better, also taking in mind any balancing on each throw not taken care directly by the corrispnding counterweight will be transferred to the main journals, those being much more stressed together with main bearings. Lightening must be done with the right knowhow.
One of the worst layouts as mass needs is the IL4 180° throws. One tuner I know, some years ago tuned a IL4 engine for a local racing championship. After all the blueprinting he lightened all the cranckshaft and flywheel masses as much as he could. The result was on the main track's straight the car was 20 Km/h slower than with the stock crank and flywheel assembly (only balanced). Then someone (
) suggested he had gone too far with the lightening and after having done the job correctly not only the missing 20 Km/h came back, but he gained another approx 10Km/h top speed in the same place.
The IL5 with 72° throws is much better than the IL4 180°, but still not good enaugh not needing flywheel masses at all.
The Ø20mm OEM pin should be good enaugh for most of the application, while if going much over the 700 Nm and 600 Hp a Ø22-24mm pin might be safer.
Of course the bigger pin will increase overall alternating mass therefore its dimensions must be chosen accordingly with the real load they will be asked to withstand.
Marco
determination of counterweight and overall crankshaft mass is a matter of many aspects most important ones concerned with loads imposed on the assembly by the alternating masses.
Apart from other considerations such as idle stability, softer and more regular engine behaviour (which might not be of interest), depending on layout of engine (IL4, IL5, V6, V8 or whatever) quantity of needed masses (counterweights and flywheel) vary quite significantly. So it is not true the least the better, also taking in mind any balancing on each throw not taken care directly by the corrispnding counterweight will be transferred to the main journals, those being much more stressed together with main bearings. Lightening must be done with the right knowhow.
One of the worst layouts as mass needs is the IL4 180° throws. One tuner I know, some years ago tuned a IL4 engine for a local racing championship. After all the blueprinting he lightened all the cranckshaft and flywheel masses as much as he could. The result was on the main track's straight the car was 20 Km/h slower than with the stock crank and flywheel assembly (only balanced). Then someone (
) suggested he had gone too far with the lightening and after having done the job correctly not only the missing 20 Km/h came back, but he gained another approx 10Km/h top speed in the same place.The IL5 with 72° throws is much better than the IL4 180°, but still not good enaugh not needing flywheel masses at all.
The Ø20mm OEM pin should be good enaugh for most of the application, while if going much over the 700 Nm and 600 Hp a Ø22-24mm pin might be safer.
Of course the bigger pin will increase overall alternating mass therefore its dimensions must be chosen accordingly with the real load they will be asked to withstand.
Marco
Originally posted by auditude
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