High horse power four cylinders can’t sustainably do the same job as a larger six pot of similar HP. Tell me I’m wrong

dave mountain said:

Whether that 10% would prove correct in real world use I'm not sure, although I do doubt it. If so I would say that particular comparison would be the exception rather than the rule, having compared t6.175, t6.180, t7.170 n154 and t154. the difference in fuel consumption will vary between 4 and 6 pot being more economical depending on the exact tractors you are comparing, the difference in internal losses between a 4 and 6 is negligible, the only time a 6 might use more is at idle, and that is due to the displacement not the number of cylinders. With modern 4 pots getting bigger displacements this difference disappears anyway. All this aside, a 4 will never be as smooth as a 6 due to fires per revolution.

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Have a read yourself. Fuel consumption difference of 3 - 7% like for like.

Wellytrack said:

https://pruefberichte.dlg.org/filestorage/0315_NewHolland_T6.pdf

https://pruefberichte.dlg.org/filestorage/pbdocs/traktoren/NH_T6-175_SPS_en.pdf

Have a read yourself. Fuel consumption difference of 3 - 7% like for like.

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Im sure there is that difference measured in a lab, doesnt seem to carry over into real world use though, which i think is because you dont usually need to drive a 6cyl quite as hard even if it is the same power on paper. Also you are trying to compare CVT to powershift there. They are also different tractors to what i measured, which were T6.175 4cyl electrocommand, T6.180 6cyl electrocommand, and an older T7.170 6cyl rangecommand. Wasnt much between the 2 newer tractors, 4cyl slightly heavier on diesel but not much. T7 was similar/slightly better on fuel on heavy work but worse on light work, mainly due to weight i suspect.

Wellytrack said:

https://pruefberichte.dlg.org/filestorage/0315_NewHolland_T6.pdf

https://pruefberichte.dlg.org/filestorage/pbdocs/traktoren/NH_T6-175_SPS_en.pdf

Have a read yourself. Fuel consumption difference of 3 - 7% like for like.

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Would be better if they were both profi tests and in english and both same age of tractor

daveydiesel1 said:

Would be better if they were both profi tests and in english and both same age of tractor

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Profi use DLG Data.

mf7480 said:

But wouldn’t it be fair to say the majority of 4 cylinders literally do sound like a bag of rocks in a washing machine

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No it wouldn't. All engines from the same family sound similar except that a four cylinder engine fires every 180 degrees of crank rotation and the three cylinder every 240 degrees. Thats 720 divided by three. Deduct 180 from 240 and you find that the three cylinder engine is only without a power stroke for 60 degrees out of a revolution. Problem is that secondary forces make a three rock backwards and forwards, not side to side.

Far a four 720/4=180. So it fires at every 180 degrees of crank rotation. Deduct 180 [a piston's travel from top to bottom] from 180 = 0 This means that an in line four is always on a power stroke. Therefore it is better than a three cylinder and will not rock backward and forwards as a result of always being on a power stroke. Also it has a perfect primary balance because two pistons going up are always balanced by two going down. The secondary balance is poor though because all four pistons actually stop at the same time. The two outer cylinders will be at the top at the same time as the two inner ones are at the bottom with all four transitioning to the reverse direction at the same time. This means that the four needs two balancing shafts, counter-rotating, at twice the crank speed, because the pistons stop twice in every 360 degrees [one revolution].

A six cylinder engine 720/6=120. So a firing stroke happens every 120 degrees. Deduct 180 from 120 and you a 60 degree overlap of firing strokes. There is always a piston on the power stroke and for part of every power stroke there are two. This means that both primary and secondary forces are eliminated. No tendency to rock either side to side or back to front. Due to pistons travelling further and faster at the top of the stroke compared to the bottom, sometimes compounded by offset gudgeon pins to minimise side thrust [piston slap] on the power stroke, there may be torsional vibrations which try to speed and slow the crank, or twist it if you like, hence the almost universal fitment of torsional vibration dampers at one or other end of the crankshaft.

dave mountain said:

Im sure there is that difference measured in a lab, doesnt seem to carry over into real world use though, which i think is because you dont usually need to drive a 6cyl quite as hard even if it is the same power on paper. Also you are trying to compare CVT to powershift there. They are also different tractors to what i measured, which were T6.175 4cyl electrocommand, T6.180 6cyl electrocommand, and an older T7.170 6cyl rangecommand. Wasnt much between the 2 newer tractors, 4cyl slightly heavier on diesel but not much. T7 was similar/slightly better on fuel on heavy work but worse on light work, mainly due to weight i suspect.

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Those are PTO results, not drawbar tests. A drawbar test may give a different set of data points as weight/traction.

Point is modern Agri engines are capable of about 170nm of torque per litre, the curves are electronically governed to give constant power anything from 1000 rpm through to 1600.

Wellytrack said:

Those are PTO results, not drawbar tests. A drawbar test may give a different set of data points as weight/traction.

Point is modern Agri engines are capable of about 170nm of torque per litre, the curves are electronically governed to give constant power anything from 1000 rpm through to 1600.

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Car engines are even more impressive at up to 250Nm per litre at about the same revs as a tractor. That's the peak torque occurring at around 1600 to 1900 rpm. Absolutely amazing engineering and performance as far as I'm concerned.

Cowabunga said:

The idea that four cylinder engines are not as smooth as six is a load of twaddle. There are out of balance forces in both. Both use different kinds of balancers to ensure smoothness as all revs and loads. Four cylinder engines are commonly fitted with two balancer shaft running at twice engine revs to counteract the secondary forces that occur at every 180 degrees of crank throw.
Six cylinder engines almost universally need dynamic balancers on the nose of the crank to counteract destructive torsional vibration of the crankshaft even though both primary and secondary forces should be balanced.
If either type of engine was not balanced they would not last long and would sound like a bag of rocks inside a washing machine.

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Clearly they are both balanced, but it's still a fair comment that 6 cyl engines are smoother than 4, in exactly the same way that an E type V12 engine is smoother than a ford 7000. Neither is out of balance but I know which is smoother.

dave mountain said:

Clearly they are both balanced, but it's still a fair comment that 6 cyl engines are smoother than 4, in exactly the same way that an E type V12 engine is smoother than a ford 7000. Neither is out of balance but I know which is smoother.

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You confuse the frequency of the noise with smoothness. A fair comparison is to use the same engine family. The Ford 7610 and Ford 7810 for instance. Both engine sound like a bag of nails and both made the windows of my house vibrate because that is just how they are. Both like a big can half full of nails amplified by 1000 times. The only difference being that for every 1000 revs per minute the four cylinder had 1000 power strokes while the six cylinder has 1500. In each case every single piston has 500 power strokes or 8.3 per second. It sounds like the six cylinder is running half as fast again as the four and as I explained in the previous post, while there is no gap in the power strokes like a three cylinder in the four, the six cylinder has an overlap between power strokes which evens out the noise. That is what evens out the noise. It's because the six constantly has a cylinder nearer the ignition point in the power stroke.

It does not mean that the engines have anything but a different noise. A different tone and amplitude not that one is actually noisier than the other. One has a four cylinder sound and the other has a six cylinder sound. My only preference is that both should be much much quieter all round and comply with current and future on-road drive-by noise regulations. They've managed to quieten truck engines down amazingly over the last two decades, so why not tractors?

I get a milk lorry collecting here between 4 and 6am every morning and the current Scania's are whisper quiet. Up until about 15 years ago the lorries were tractor-loud and made my windows rattle like the old Ford 7810 did. I'm not saying that modern tractors are anywhere near that bad these days, but neither are they as quiet as the Scania or my diesel car engines either.

traineefarmer said:

Turbo engines will have a flatter torque curve and achieve maximum torque at lower rpms.

As for displacement vs. forced induction, fag packet maths will tell you that 1bar of boost will effectively "double" the displacement of an engine as you are doubling the the mass of air and fuel capable of being burnt on each cycle. This is rarely practically achievable due poor breathing, mechanical inefficiency and thermodynamics, especially in tractors, but there are plenty of 2.0 petrol turbo car engines producing 250+bhp reliably when a NA 4.0 V8 is barely managing 50bhp more.

The internal components on a turbo engine are obviously under more strain, but these days the engineering is well understood and widespread so there should be little difference on longevity.

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remember though, that both the 4 and 6 cylinder are probably turboed, so the turbo v NA argment is not applicable.
I agree. the statement about discplacement is pointless, as with a turbo, its all about the mass of air in the cylinder at the time the fuel is inected.
a 4cylinder will have less parasitic losses than a 6. Only 4 pistons rubbing up and down the liner, only 4 big ends etc etc

Hazza6930 said:

We have a 6715s and a 7615 , the 67 was lagging behind the 7615 on the muck spreaders

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Do you know what power each tractor is actually producing though. The 7615 could be running at more than the 150 its meant to be at. I'm sure not every tractor comes out the factory at "brochure" power.

Hazza6930 said:

We have had both on the dyno , the 7618 topped at 160 and the 6715s topped at 170 but that’s on boost. We have steep hills and when put side to side and pointed up hill the larger six could run rings round the four cylinder. You can drag those six cylinders right down but not nearly as much reserve on the four.

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The 6 pot sisu is a great luggin engine

Having used both the N174 and T174 valtras I think I can comment. The smaller 4 cylinder actually boosts higher than the 6 and yet ploughing it was rubbish on steep ground, had to change down and rev the engine which caused wheel slip whereas the 6 could just keep ticking along below 1400rpm.
Pto work they are similar but towing loads on hills the 4 though lighter just died away.
Only a place for a 4 cylinder on our farm is in the yard.

Cowabunga said:

You are wrong. The four will be more efficient, will have sharper response and recovery, will be just as reliable while being cheaper to run, maintain and repair. Engines tend to last longer than ever before, no matter how many cylinders. Some are not, but their six cylinders are equally as unreliable as their four cylinder engines. But at least the four only has four of every main moving part.
The torque and torque rise, and even the start-off torque of most four cylinder engines today at least equal that of the six cylinder version of the same horsepower from the same engine family.
Just look at how far car Diesel engine have advanced in recent years. The same goes for tractors. My 2.0 Volvo four cylinder engine was 20% more powerful and 30% more torque at similar low revs to my 4.2 litre turbo-intercooler Land Cruiser engine and uses literally half the fuel to go way faster with less noise as a bonus.

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Just the sound that lets them down!!! A friend has a new 4 pot Valtra, loves it but said it sounds like a bag of spanners and I had to agree with him

Hazza6930 said:

We have had both on the dyno , the 7618 topped at 160 and the 6715s topped at 170 but that’s on boost. We have steep hills and when put side to side and pointed up hill the larger six could run rings round the four cylinder. You can drag those six cylinders right down but not nearly as much reserve on the four.

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Spear said:

Having used both the N174 and T174 valtras I think I can comment. The smaller 4 cylinder actually boosts higher than the 6 and yet ploughing it was rubbish on steep ground, had to change down and rev the engine which caused wheel slip whereas the 6 could just keep ticking along below 1400rpm.
Pto work they are similar but towing loads on hills the 4 though lighter just died away.
Only a place for a 4 cylinder on our farm is in the yard.

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Surely this answers the original post case closed

There was a whole topic comparing a fendt 516 and a jd 6150r , the four pot pulled better and saved on fuel and time ,same kit ,same fields , same operator

yorkie said:

There was a whole topic comparing a fendt 516 and a jd 6150r , the four pot pulled better and saved on fuel and time ,same kit ,same fields , same operator

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But the jd engine is known to be a bit thirsty and the deutz engine is frugal

Why aren't manufacturers trying to push 4 cylinders across all models besides perceptions?

Unusual thread. Would be far more incendiary if it was 'what engine in a pickup' thread.

Conclusion then is that you can't go wrong with a 4 or a 6 cylinder, so long as it's a Valtra.