Edward R. Cozzi

If you're running in salt water, you're better off with cast-iron heads. I've pulled many aluminum heads that were junk after a few years.

PatriYacht

I have heard that aluminum heads, all things being equal, lose a few hp because of higher heat conductivity. They usually flow better and that's why they make more power. I think alum. is better in fresh water because they're lighter but in salt they corrode to fast.

DMOORE

The water jackets can be anodised to protect the aluminum. Remember, most every high performance intake, along with intercoolers are aluminum. Plus every jet ski motor made, and all outboards. Don't worry about aluminum in the motor. Just flush with salt away when finished.



Darrell.

Rage

I was only speaking to the impact to motor performance of aluminum metal versus cast iron metal as a head material. In other words the exact same heads except one made form aluminum and the other cast iron.

BenPerfected

Rage,
I doubt you are going to find many/any on OSO that have made two idenitical sets of heads (except for the metal type ) and then done back to back dyno testing/comparisons. as the engine is an air pump, it doesn't care what metal is used in the heads. The power should be close to the dsame if all else was equal. Aluminim is lighter (faster) and cast iron is more corosion resistant. Power? ...same.

Revelocity

Here's a related question that if I had a Desk Top Dyno program - I woudn't have to ask. Given that aluminum heads can tolerate a higher compression ratio for a given fuel grade, is there any rule of thumb that says if one increases the compresion ratio from say 8.75:1 to 9.75:1 (an 11% increase) and ALL ELSE REMAINS THE SAME, that horsepower will increase x %? I'm sure the relationship tails off with higher compression ratios but for THIS range can anyone offer an estimate of % HP increase? I'm trying to figure what higher compression potentially delivers in extra horsepower. Thanks.

Rage

Oh yes it does. You are missing the point. The higher the combustion temperature the more power, the lower the combustion temperature the lower the power on a given engine. This is where the better thermal condutivity of aluminum versus cast iron can reduce power. Conversely that same characteristic can reduce potential of detonation thus allowing aluminum heads to be designed with higher effective compression ratios which can gain back power. I have no idea if it is a wash or if the increased compression ratio capability produces more power gain than is lost to quenching of combustion temperature or the opposite.

There is no limit of things to take into account in head design differences and material choices. The comment above was intended to discuss only one, aluminum versus cast iron and its effect on power all things being equal.