31 May 1996

Extra power just

when its needed

Squeezing a quart out of a pint pot is how Sisu might describe the novel concept of its latest Valmet tractor which delivers 160hp or 190hp, depending on how it is being used. Peter Hill reports on an exclusive First Drive of the new machine

OUTWARDLY, there is nothing to give the game away, other than the fact that the Valmet Mega 8750 is a decidedly compact tractor for a 190hp machine.

But then that power resource is meant for operating pto-driven machinery rather than heavy draft equipment, so outright size and weight is not a priority.

Instead, this Valmet (Machinery, May 3) is built light and fitted with an engine that develops 160hp – unless sensors on the crank and power take-off shafts indicate that sufficient power is being consumed by the pto for the six-cylinder turbo engine to start pumping out 190hp.

It is an intriguing concept, probably born out of Sisus wish to get into the top horsepower class, despite having no suitable transmission to do so, but resulting in a machine with a number of positive attributes – principally modest size and weight for high pto power potential.

Tractors capable of converting high power outputs into high tractive effort tend to need bulky transmissions, in order to handle the torque loads involved, and sufficient weight to gain grip on firm, greasy stubble and loose broken land alike.

Wasteful weight

But weight is a wasteful consumer of power and a cause of compaction when it is not needed. And it is not needed for non-tractive pto-powered operations, such as forage harvesting or operating a big round baler, and when it is only there to counter the weight of mounted pto-driven implements such as power harrows and rotary tillers. The Valmet is well-placed in the latter respect because the position of the engine over the front axle provides a greater counter-balancing effect than normal.

But comparison with other 190hp tractors in minimum weight trim shows that the 8750 is indeed a slim Jim.

It weighs just over 2t less than a Case Magnum, 2.25 to 2.5t less than a Massey Ferguson MF8150 and Fendt 818, and more than 3t less than the John Deere 8100 and New Holland Series 70/G-series.

The 190hp trio from the Same stable comes closest to the low weight-high power concept with tractors only a little more than half a tonne heavier than the Valmet.

Valmet maker Sisu suggests that for every 3t of additional weight there is a corresponding 0.5t increase in rolling resistance; it puts the cost of that, in terms of the power absorbed to overcome the extra rolling resistance, at up to 12hp at 4.5mph and 17hp at 10.5mph. Sisu also makes the point that lower weight equals less soil compaction and it is illuminating to see from the Michelin tyre manual that, assuming the tractors have to carry only their own weight, a 650/65 x 38 tyre on the back of the Valmet could be run at two-thirds of the inflation pressure of the same tyre on the heaviest alternative tractor.

All of which, says Sisu, makes the Valmet Mega 8750 an efficient, manoeuvrable, soil compaction-conscious power source for horsepower-hungry pto-driven implements, as well as a competent 160hp tractive machine.

From the inside, just as from the outside, there are few clues to the 8750s split power personality. There is certainly no shove in the back, plume of smoke or change in engine note to signify a change in power output. Just an illuminated "ETB" on the instrument panel that suggests "extra turbo boost" but which signifies that the tractors engine management system has turned up the fuel pump to extract an extra 30hp.

The real evidence is the way the 8750 powers into a grass swath without hiccuping and commands progress through lumps in the swath.

Contractor David Adamson, who provided Kemper reverse drive and Mengele trailed forage harvesters, normally hires-in a 190hp tractor for the Mengele and was worried that the Sigma Power system would not cut in soon enough to maintain progress on entering the swath. His doubts were soon dispelled.

Standard fare

Dash display and under-bonnet electronics apart, the 8750 is standard Valmet fare, albeit with a beefed up transmission to handle the extra power of the new 160hp and 160hp/190hp models and some improvements elsewhere.

An implement cushioning system has been added to the hydraulic lift, for example, while a single rocker switch replaces the separate up/down buttons, and there is a larger, more comfortable seat.

The Delta powershift transmission has 36 ratios in forward and reverse, selected using a combination of four-speed synchro gearbox, three push-button powershift speeds, and a three-plus-creep range gearbox. Forward-reverse is engaged manually using a gearstick alongside the main gear levers.

In TwinTrac reverse drive mode, the Valmet makes a convincing alternative to a small self-propelled forage harvester, particularly for maize when the configuration avoids customer angst by opening up crops cleanly.

The tractors duplicate pedals and small offset steering wheel – which leaves a largely uncluttered "forward" view for the driver – are easily mastered, but the gear levers and powershift buttons are awkward to get at with the seat facing the rear of the machine and the lack of duplicate engine and transmission warning lights is a surprise.

Nonetheless, with a claimed 176hp at the pto, on which basis the 8750 outranks all but the Same Titan 190, which runs 1000rpm nearer the engines peak power output, the Valmet clearly has the resources to effectively operate big powered implements while offering the economy and running costs of a 160hp machine for draft operations. &#42


Tractor comparison

CaseFendtDeereMFNH FordSameValmet

7220818810081508770**Titan 190***8750

Magnum

EngineCase Fam IIMANDeereValmet NHSame WTIRValmet

62ODS634DS

Power at

rated speed (hp)190190185180190189160

Max power (hp)200190200180196189190

Pto power (hp)167160160160169181172

Wheelbase (mm)3,0002,8402,9502,9303,005*2,8502,748

Min weight (kg)7,3007,6808,2857,4358,5175,8005,170

List price (£)61,30577,65071,67266,00068,38363,50061,400

* 3115mm and 8744kg with Super Steer front axle; ** also NH Fiatagri G190; *** also Lamborghini 190 Racing – £64,750 and Hurlimann H6190 – £64,800.

Inside the cab its standard Valmet fare. Clustered to the drivers right are Delta powershift levers, hydraulic controls and information console.

Above: A tractor that punches above its weight. The Valmet 8750 may be rated at 160hp but it is capable of packing 172hp at the pto. It scales a modest 5.2t. Right: Power-sapping pto work, such as foraging, is where the Mega 8750 really comes into its own.