Best Material For Cylinder Head?

[Galviniser]

Hey,

Just doing materials at college and one of the questions is what would be the best material to use as a cylinder head, now i know most engines now are an aluminium alloy, surely this would be to reduce the most weight at the cheapest price, but cost out of the equation what would be the best material? I was thinking the least weight and surely the most thermal conductive material to warm up fast but also regulate the temperature

Chris

[jambo]

I suppose that depends on your definition of "best".

Aluminium is pretty light, not terribly expensive and available in a range of grades depending on strength and cost concerns. The pressures in a cylinder head for a road engine aren't too extravagant.

I suppose you could use Titanium, it melts about 1,600 C rather than Aluminium's 660C, but as you generally use a coolant that becomes steam a few hundred degrees lower than that it's not generally a problem. Exhaust valves have a much harder time getting shot of the heat so are sometimes made of Titanium due to hight melting point and low weight.

I suppose you could use a ceramic in the hope that it wouldn't absorb the heat from the combustion chamber in the first place, but then it wouldn't take heat away from the valves as they closed on the seats either, so that would probably end with burnt valves and a lovely cool head.

Jambo

Thinking about it I think I'm going to go with a Titanium head with a ceramic coating on the exhaust ports after the valve seats. Let me know when you've knocked one up :)

[wideguy]

For a variety of reasons, mostly good heat transfer and ease of casting and machining, aluminum works great.
Titanium would suck. It doesn't transfer heat and it's difficult to work with.

[Eulaca]

In the case of an engine, the cost of manufacture would probably play a big role in the material used. The majority of cylinder heads are cast then finished so that would make something like titanium pretty expensive to use.

[wideguy]

Cast iron is a good candidate too, but not for motorcycles that are trying to be as light as possible, or at the least, reasonably light. It's cheaper than aluminum and casts and machines very well. I guess it's back to , what do you mean by 'best'?
There are usually good reasons why what's being used is being used.

[embee]

Cylinder head castings are very often in LM25 (http://www.alumascprecision.co.uk/AlloyLM25.php) (in old designation) or a very similar alloy. This is suited to fine detail casting processes (water jackets) without porosity, heat treats well and ease of machining. The resultant item will have good hot fatigue strength and heat conductivity appropriate for a cylinder head.

The industry is continuously working on materials and processes to improve properties allowing reduced weight and lower cost, and making more complex components possible (e.g. integrating several components into one, like integral exhaust manifolds on cylinder heads). Manufacturers don't choose any old material.