Of course it all depends what you call better. Since I use the coupe about 40.000 km per year, my interest would be long life.
The example I like to use is that of the Roman emperors. They were all total lunatics, absolute nutcases. It took almost 2000 years to find the cause.
Scientists of the old Rome had found that lining the amphora with lead made them hold the wine better. They did not realize that the lead dissolves quite easily in the sligthly acid wine.
In AD 68 women got equal rights and were also allowed to drink wine. As a consequence a phoetus was already poisoned by lead from day 1, Since more wine was drunk in higher circles, the emperors suffered most from the lead poisoning.
I am not arguing that scientists are always wrong. The point I like to make is that there is always something we don't know.
If the matter would be investigated by someone from another solar system he might conclude that:
1. giving women equal rights is not a good thing
2. it is better to be a slave than an emperor because slaves don't drink wine
rocker wear
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Thomas
Re: rocker wear
Contrary to the recommendation from wiser men, I did actually loose some sleep last night over your question.
1) consider two extremes:
the rocker shoe is an edge, or this shoe is a flat surface. Either geometry will have no incidence on the movement when the lobe of the cam is at its apex (relative to the rocker) or at its lowest position (where the cam follows a purely cylindrical pattern).
Therefore, the shoe's geometry will only affect the transition movement between open and closed, i.e. the characteristics of the "attack" and "repose" movements where the contact between rocker and cam moves along the cam's shoulder.
It is during those periods that the curvature of the rocker shoe may be relevant. You question is then essentially to know whether a variation in radius of the shoe will affect performance.
I lack the knowledge of the thermodynamics of the internal combustion engine to assess this. But I suggest to look at the same question from a different angle.
2) We assume the attack and repose movements to be symmetrical.
This is however only true if the shoe/cam contact makes a straight movement (i.e. a translation); but this is only a reasonable assumption if the distance between the rocker pivot and the shoe/cam contact is very long as compared to the amplitude of the contact surface's movement; in effect, and as we are here considering theoretical detail, we must recognise that the rocker/cam contact actually rotates (probably more a very small complex zigzagging movement, but nevertheless one with a rotation component).
So if we were to design the ultimate engine, and again assuming that the attack and repose movements should be symmetrical, it follows from the above that the rocker shoe should be assymmetrical in order to compensate for the rotation component of the rocker. In other words, the left and right lobes of the rocker shoe should not be the same with small differences in convexity.
Therefore, if checking the rocker shoe reveals a difference between its two lobes (accountable for else than wear), you may reasonably assume that the radius of the rocker shoe is (very) relevant. Otherwise, probably not.
1) consider two extremes:
the rocker shoe is an edge, or this shoe is a flat surface. Either geometry will have no incidence on the movement when the lobe of the cam is at its apex (relative to the rocker) or at its lowest position (where the cam follows a purely cylindrical pattern).
Therefore, the shoe's geometry will only affect the transition movement between open and closed, i.e. the characteristics of the "attack" and "repose" movements where the contact between rocker and cam moves along the cam's shoulder.
It is during those periods that the curvature of the rocker shoe may be relevant. You question is then essentially to know whether a variation in radius of the shoe will affect performance.
I lack the knowledge of the thermodynamics of the internal combustion engine to assess this. But I suggest to look at the same question from a different angle.
2) We assume the attack and repose movements to be symmetrical.
This is however only true if the shoe/cam contact makes a straight movement (i.e. a translation); but this is only a reasonable assumption if the distance between the rocker pivot and the shoe/cam contact is very long as compared to the amplitude of the contact surface's movement; in effect, and as we are here considering theoretical detail, we must recognise that the rocker/cam contact actually rotates (probably more a very small complex zigzagging movement, but nevertheless one with a rotation component).
So if we were to design the ultimate engine, and again assuming that the attack and repose movements should be symmetrical, it follows from the above that the rocker shoe should be assymmetrical in order to compensate for the rotation component of the rocker. In other words, the left and right lobes of the rocker shoe should not be the same with small differences in convexity.
Therefore, if checking the rocker shoe reveals a difference between its two lobes (accountable for else than wear), you may reasonably assume that the radius of the rocker shoe is (very) relevant. Otherwise, probably not.
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Peter de Wit
Re: rocker wear
William, Maarten has done the grinding on mine! It is a good practice to do that when you fit new high spec cams. You would not want to eat them up.
If you ruin them, I have a spare set of hf rockers. Polished indeed.
If you ruin them, I have a spare set of hf rockers. Polished indeed.
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william
Re: rocker wear
This is a very theoretic and thought over reply. You are presumably right. It means that everything is in a balance which cannot be easilly changed for the better.
Many people running engines with modified camshafts have done so by regrinding an original shaft. This is done by reducing the camlobe base circle to get more lift and or duration. In most cases the rocker shoe remains unaltered which gives in effect a bigger shoe radius in relation to the cam. I have one reground cam and have compaired the duration with an original. Camlobe basecircle went from 23.5mm to 22mm on the reground cam. Theoretical duration was the same. With my dial indicator on the tappetscrew the diference was about 9 crankshaft degrees in favour of the reground cam!
Just with a smaller base circle and nothing else. You win some you loose some...
Lancia designers were no emperical technicians. They really thought things through!
Many people running engines with modified camshafts have done so by regrinding an original shaft. This is done by reducing the camlobe base circle to get more lift and or duration. In most cases the rocker shoe remains unaltered which gives in effect a bigger shoe radius in relation to the cam. I have one reground cam and have compaired the duration with an original. Camlobe basecircle went from 23.5mm to 22mm on the reground cam. Theoretical duration was the same. With my dial indicator on the tappetscrew the diference was about 9 crankshaft degrees in favour of the reground cam!
Just with a smaller base circle and nothing else. You win some you loose some...
Lancia designers were no emperical technicians. They really thought things through!
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Huib
Re: rocker wear
I don't think Lancia engineers really thought all things through. There are enough design errors on the Fulvia. And there are always things you don't know as in the example of the roman emperors.
I have been a design engineer myself for many years and know how it works. If one would have to really calculate everything then even designing a car like a Fulvia would require an organisation like NASA. There is always a balance between experience, calculation, just doing it without thinking, intuition, trying and plain stupidity. All of course within the limits of the manufacturing people and equipment and of course cost.
I have been a design engineer myself for many years and know how it works. If one would have to really calculate everything then even designing a car like a Fulvia would require an organisation like NASA. There is always a balance between experience, calculation, just doing it without thinking, intuition, trying and plain stupidity. All of course within the limits of the manufacturing people and equipment and of course cost.
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P. de R. Leclercq
Re: rocker wear
Quite so, Huib - and it was said that Lancia lost money on every Fulvia made.
And this when a 1300 coupé rubber mats and all, in 1967 cost about the same as a 3.4 litre Jaguar.
You do NOT have to ask which I would choose!
Paul
And this when a 1300 coupé rubber mats and all, in 1967 cost about the same as a 3.4 litre Jaguar.
You do NOT have to ask which I would choose!
Paul