What do aluminum heads add overall?
 

Forgive the ignorance but why would I want aluminum heads. What does it add and how? Other than HP is there any other pro's (or con's). Is reliability a factor. What are the different options, considerations, roller rockers etc.. I know thats a lot of information, but if there's any sites out there that discuss the comparisons I'd appreciate it
Thanks
Trueoo7

I think you will find them to be more tolerant of compression on pump gas so you won't get as much pinging. Plus the lighter weight and usually better flow.

Yup, what he said. 3 main benefits- 1. you can run .5 to 1 point higher compression ratio than you can with cast iron, 2. new aluminum heads means new design, better technology and better flow and 3. aluminum is significantly lighter.

The way it was explained to me (and it makes sense using a model of a combustion engine and some heat transfer), based on a hp standpoint, cast iron heads make more horsepower....in a combustion engine, you want a really cold intake charge and a hot combustion.....the bigger differential between these two, the more hp you make. Aluminum dissipates heat better, so the combustion is not that hot. I'd say the difference is hp is made up by the difference in weight however.

But like the other guys said, with aluminum heads you can run a little bit more compression. Probably for the same reason as above. It dissipates heat, so it keeps the mixture from pre-igniting.

The truth of the matter is this - it is FAR easier to cast aluminium than iron. And there are FAR more foundries working in ally than iron.

Therefore, any aftermarket supplier is automatically going to offer ally heads, and in whatever way, will try to market them as somehow "better" than iron. They usually are better than the OE iron heads, but only because of modifications to valve sizes and combustion chamber and port profiles leading to better breathing.

The truth is that if you could get these new designs in iron, they would be better, from a thermodynamic perspective, than when in ally. I am discounting the weight advantage of ally here.

WIlife-
Aren't you also discounting the benefit of the increased compression ratio that you can run with AL?

I think aluminum looks Impressive! I will be running Aluminum heads because that is what the engine I'm buying comes with but other than that I'd be completely happy with Cast Iron.

To expand on what blykins said, the ability to run up to a full point higher compression is offset by the heads pulling the heat out of the combustion chamber. They are much easier to fix if you grind through while porting or if you crack them. On Hughes web site they have dyno sheets from diferent heads and intakes. They made the most power with iron heads in this case. But that doesn't mean AL wouldn't in other cases as the iron heads had a lot of work done to them.

To quote thier web here:

Aluminum heads dissipate (get rid of) heat much faster than iron heads. The rapid heat loss from the combustion chamber results in reduced combustion chamber pressures (heat equals pressure); similar to the effect that lowering the compression ratio lowers cylinder pressure. When switching to aluminum heads you MUST raise the compression ratio to prevent a power loss. This is a good opportunity for our customers to take advantage of our computer calculated compression ratio service. This software assures them of getting the maximum power out of their purchase; it's a no-charge service for our customers.

Aluminum heads will not automatically create more power than iron heads unless they flow more air and are installed on a higher compression ratio engine. In cases where you have a decent port job on a set of iron heads it is possible to bolt on a set of out-of-the box aluminum heads and lose power. Aluminum is automatically lighter but not faster. Yeah, yeah I've read all of those magazine articles that told you how they installed brand X widget and picked up 500 HP and 4 seconds in the 1/4 mile (we have even been the victim of these articles). What you must keep in mind is that those magazines and the writers (???) are paid by the advertisers, not by that $19.99 you send in once a year. So you can expect that advertised products always look good even when they screw the test up and the "results" are not what they should be, (been there done that!). They are under a deadline and the rent has to be paid so the facts sometimes take a back seat. In some cases the engine would have produced more power with a set of well ported, iron heads, and at a lower price.


Quick Facts: Aluminum vs Iron


Weight: Aluminum heads weigh about 45 to 50 lbs., a pair, less than iron heads
Durability: "Ported iron heads can crack if the engine is badly over-heated". Yes this is true, but if the engine got that hot the aluminum head would have melted or been badly warped. The seat rings would have also fallen out, but the head might not crack. Anyone who lets his engine get that hot deserves to buy new heads or have an expensive repair bill
Reparability: This is a trick question. Yes, aluminum heads are easier to repair if the damage is very bad and that is a good thing because they are much more fragile and more prone to damage than a hard, iron head
Cost: Aluminum heads cost more, and then there may be the hidden cost of raising the compression ratio
Airflow: You get very similar airflow results from ported, stock heads and "stock replacement" type heads. With raised port cylinder heads, the sky is the limit
Power: Power depends on what you have to start with, or what else you plan to do to the engine. If you have low compression (9.5:1 or less) and are not going to change pistons or mill the heads to restore the cylinder pressure, save some money and go with the ported iron heads. If you are starting on a fresh engine with higher compression ratio pistons, want to lose some weight and the budget can handle it ---go ported aluminum. There is another power consideration; most of the aluminum heads have a closed combustion chamber which is far superior to the OEM heads with their open chamber design. However, if the piston is not at 0.000" deck, the chamber design has very little effect.

If all this sounds like we don't like aluminum heads, the truth is quite the contrary. Aluminum heads are cleaner, easier to port and they look trick next to an iron head. If you make a mistake on an aluminum head, it is easy to fix. If you drop it on your toe it doesn't hurt as bad. Porting aluminum also keeps the shop cleaner, what's not to like? We just want you, our customer, to get the right cylinder heads, iron or aluminum.

Yeah, if aluminum heads were all that
revolutionary, they would be on my s/o. Iron heads with a small combustion chamber and a port job, the only way to go. IMHO

If heat transfer is your only problem with aluminum heads get the combustion chambers, valves, and piston crown coated with a heat barrier similar to what most of us use on our pipes. It's not that expensive.
Bill Stradtner