Mr Whippy
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| posted on 8/6/23 at 11:57 AM |
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Alloy vs Iron head
Watching vid on youtube, one thing that was mentioned was that changing an engine from an iron head to aluminum one would reduce performance down
about 10% due as the poster said, the aluminum taking away the heat from combustion so much faster that less was available to convert to power to the
wheels. He was a old race car driver so seemed to know what he was taking about but still...
hmm 
In my head that explanation would mean that you'd then expect quite a significant increase in water temperature as the lost energy would have to
be going somewhere i.e. into the water and the engine now overheats. Generally I thought the use of alloy heads reduced the risk of overheating.
Conversely if the poster is right and you replaced the head with something very poor at transmitting heat, like wood! (ignoring that it catches fire)
would you expect the engine to suddenly produce more power, before it melted...
Doesn't seem to add up.
Any views??
[Edited on 1 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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nick205
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| posted on 8/6/23 at 12:18 PM |
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Tin tops have iron and more recently alloy engine casings.
If the theory holds true then the design engineers will have designed them (and the cooling systems) appropriately to deal with thermal issues. I do
know that alloy engine blocks have iron cylinder liners fitted (dry or wet).
I suspect it's a subject that would take more study and mathematics/physics to really understand.
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Mr Whippy
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| posted on 8/6/23 at 12:29 PM |
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quote:
Originally posted by nick205
Tin tops have iron and more recently alloy engine casings.
If the theory holds true then the design engineers will have designed them (and the cooling systems) appropriately to deal with thermal issues. I do
know that alloy engine blocks have iron cylinder liners fitted (dry or wet).
I suspect it's a subject that would take more study and mathematics/physics to really understand.
with the blocks they have iron liners more for a durable wear surface more than anything else but the same argument exists, would an alloy engine
actually loose power over an iron one just because it transmits heat to the coolant more effectively? Is there really enough time between each power
stroke lasting a small faction of a second for the heat from combustion to leak away to the water to be lost? seems unlikely.
Fame is when your old car is plastered all over the internet
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nick205
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| posted on 8/6/23 at 02:27 PM |
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Agreed, it doesseem unlikely, but I'm by no means a thermondynamicist.
Alloy engines (block & head) are generally lighter than cast iron ones. So I gues there could be a counter argument that reducing vehicle mass
means less power is needed.
Does casting alloy free up the designer to achieve better engine characteristics (ports etc)?
Overall, probably an interesting subject to know more about, but as above, I suspect you'd need to have quite a grasp on the maths and physics
side of things.
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adithorp
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| posted on 8/6/23 at 06:05 PM |
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Complete codswallop!
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gremlin1234
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| posted on 8/6/23 at 08:37 PM |
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some modern engines with iron blocks and ali heads have two thermostats. **
one for head, one for block,
but really these are only important during the initial warm up phase.
** for example... ford ecoboost 1L 3 cylinder turbo
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Mr Whippy
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| posted on 8/6/23 at 10:58 PM |
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I really don't know the answer as I'm not an engineer However I think alloy heads do reduce the chances of overheating, plus anyone
who's had a pinto head off will be well aware just how heavy an iron head is!
On my old car, everything seems to weigh at least 3 times what you'd expect! I see an ad for an alloy upgraded head... I'm very tempted
Fame is when your old car is plastered all over the internet
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chillis
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| posted on 9/6/23 at 12:12 PM |
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Youtube, that bastien of irrefutable truth - oh no wait.....
Never under estimate the ingenuity of an idiot!
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mcerd1
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| posted on 9/6/23 at 01:12 PM |
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there is always a danger that someone take the results from a single test/experience or some massively outdated study and starts preaching the results
as gospel (assuming they didn't just misunderstand the results in the first place)
as everyone has already said - if alloy heads were really that bad, no cars would have them - but in reality almost all do
there may well have been a some specific engines were the alloy head was worse but there are too many variable to make broad statements like
'alloy is worse'
but did they really understand why it was worse ?
in the past there was a lot of 'educated' guess work as they didn't have the tools to actually measure it
was it even a fair comparison ?
a bad alloy head is always going to be worse than a good iron one / if you set everything up for the iron head and don't do anything to take
advantage of the benefits of the alloy head etc....
if knock if limiting the old engines CR, then maybe an alloy head would let you run more compression....
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gremlin1234
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| posted on 9/6/23 at 02:54 PM |
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one other advantage of alloy heads is that you know they have hardened valve seats/inserts. (was important when unleaded fuel was introduced)
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coyoteboy
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| posted on 9/6/23 at 06:49 PM |
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So.... looking at it from an engineering perspective - yes the combustion chamber walls *do* have an effect on cooling the charge and the peak cyl
pressures available (hence torque) but this can be engineered. I don't have to well connect the chamber wall to the water jacket, or the rest of
the block, but that obviously has strength/stiffness effects. Similarly, if you do thermally connect the chamber to the rest of the head well, it
doesn't mean it overheats more, it means you have more scope to suck that heat out with coolant and oil and get shut of it, making it LESS likely
to overheat. These are literally the every day complexities that engineers deal with.
Check out the ceramic combustion chamber coatings used in F1 to minimise heat transfer to the walls/pistons, the more heat you keep in the charge, the
more power you get.
Of course how many engines do you know where you can direct swap an iron for an alu with no other changes, none, so very hard to verify on a real
engine and it's all back to theory.
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