Ally versus cast iron

If you made two engines identical - apart from one having ally block and head while the other cast iron - which would warm up fastest after a cold start?

Reply to
Dave Plowman (News)
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Air or water coooled? Aluminium is a better conductor of heat, so presumably the coolant used for the ally block would would warm up quicker. But if they were air-cooled engines, heat would be lost quicker to the air from the ally block.

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Reply to
Willy Eckerslyke

Water cooled. My experience of ally engines says they are slower to warm up. Of course newer ones will have a much lower water content than older designs and many newer designs use some if not all ally. Hence the theoretical question.

Reply to
Dave Plowman (News)

I suppose there could still be a large degree of air cooling going on, even with a water cooled engine. So even if heat is conducted quicker into the coolant, this is balanced by more heat being lost to the air. Or something...

Reply to
Willy Eckerslyke

Thermall Capacity of iron's .46 KJ/kg, thermal capacity of aluminium is .91, but engine blocks tend to be similar volumes rather than weights and allys a1/3 of the density. But given ally's 3 times as conductive I suspect the whole engine warms up evenly, in a cast iron engine the coolants heated in the head faster than the block warms up.

Reply to
Duncan Wood

The RV8 in the _back_ of my camper (not much air cooling there) is very slow to warm up; that's an ally engine.

Reply to
asahartz

Yes they are. But of course it's an old design with large water capacity.

Reply to
Dave Plowman (News)

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Duncan Wood" saying something like:

Which is right, ime. Ally heads and blocks distribute heat better and alleviate hot spots. As which actually warms up quicker overall, I've known both of equivalent sizes to warm up at pretty much the same rate, but it's all down to age of the design and the cleverness involved. For decades now, thin-wall CI blocks have been taken for granted and they tend to warm up a bit quicker than traditionally thick castings. Overall though, I'd say ally warms up quicker overall (ie, the heater works more quickly), but CI warms up the combustion chamber quicker - and that's just down to the conduction factor.

Reply to
Grimly Curmudgeon

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