The SP 661 LF is the clearest published illustration in this guide of a principle that costs buyers real money: optimum and maximum are different numbers. The head cuts to 700 mm as standard and up to roughly 810 mm with the optional cutting system, but its highest-productivity range is published as approximately 160-510 mm diameter at breast height.
That gap is the whole buying lesson. A contractor whose stand sits in the 160-510 mm band is buying a head working at its designed best. A contractor who selects it because the maximum figure covers occasional large stems is paying for capacity used rarely while working outside the range the head is optimised for on most of the stems that fill the day.
Indicative published manufacturer and distributor information. Confirm every figure, lift chart and hydraulic requirement with the manufacturer or authorised dealer before purchase.
A specification table tells you what the machine is. This is what each of those numbers means for the work you would put it to.
Each of these can fail independently, and passing one says nothing about the others. Weight class alone is the weakest of the four and the one most often relied on.
Beyond the standard buying criteria for the class, these are the questions this machine in particular raises.
Working inside the optimum band is itself an economic decision. A head processing predominantly within its designed range consumes less, cycles faster and holds more reliably than one routinely worked at its limits, and the difference compounds across a season.
Consumables — chains, bars, delimbing knives, feed rollers — are consumed per cubic metre, not per hour. Tracking consumable cost per cubic metre makes both a technique problem and a species mismatch visible early.
Where the mill pays on measured volume, calibration is a revenue control. Confirm the calibration regime and how drift is detected before purchase.
Not the largest stems, the distribution. If most of the volume falls inside roughly 160-510 mm this head is well matched; if a substantial share sits above it, a heavier head is the honest answer.
A carrier that just meets 200 L/min will run the head, not run it well. Headroom above the minimum is what delivers the published feed speed in field conditions rather than in a demonstration.
Roller and knife configuration should follow your species and, where applicable, the mill's debarking specification. A configuration suited to softwood will underperform in eucalyptus regardless of the head's capacity.
Other harvester heads covered in this guide.
Heavy processor head for demanding hardwood and softwood, 815 mm butt-saw capacity on a 27 t+ carrier.
Heavier SP head for heavy softwood, crooked hardwood and demanding processing — 800 mm capacity, 250-500 mm optimum.
Excavator-class harvesting head for ~21-25 t carriers, with eucalyptus roller configurations available.
The heavier Log Max head for ~25-30 t carriers — more capacity and feed force, at 555 kg more mass.
The highest-volume softwood configuration, and the one with the greatest exposure to bottleneck mismatch. Either a full-tree chain or a cut-to-length pair, depending on terrain, mill requirements and contamination tolerance.
Thinning rewards manoeuvrability and restraint. The corridors are narrow, the residual crop has real future value, and the largest machine on the market is usually the wrong answer.
Australian hardwood plantation work places very different demands on a head from radiata pine. Feed force, debarking and durability dominate the specification.