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]

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.

quote:

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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.

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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.

Complete codswallop!

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

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

Youtube, that bastien of irrefutable truth - oh no wait.....

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....

one other advantage of alloy heads is that you know they have hardened valve seats/inserts. (was important when unleaded fuel was introduced)

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.