MILD THUNDER

iTrader: (3)

Something I would like to talk about, and hear some thoughts, as well as share mine.

Everyone talks about "aluminum" being superior to Iron, in a supercharged marine engine, or even any marine engine. They say you can run more timing, more boost, more compression, because of the heat dissapation. While it is no secret, alum does dissapate heat better, but, I believe there is more to it.

Its always the HEAT issue. I am assuming we are talking about combustion chamber HEAT. Lets say we have an engine, that is running cold water temperatures. Say, 100, 120, 140 Degrees, whatever it may be. You have an engine, that is consuming anywhere from say, 500, to 2000 cubic feet of air per minute, depending on power level, rpm, etc. The combustion process, at higher engine speeds, is measured in the nanoseconds, from the time spark ignites the charge, to the time the charge is expelled out the exhaust. In reality, how much "TIME", is there for the air charge to become heat soaked? The exchange rate of air, at higher engine speeds, is immense.

Now, a car, idling in hot traffic, iron heads, 200 deg water temps, heat soaking the entire engine, intake manifold, stagnant air sitting in the manifold at low engine speeds, I can see that becoming an issue. A marine engine buzzing at 5000-6000rpm? Idk.

Then there's the concept of reducing combustion chamber heat and valve heat. Back in the 60's and 70's, engineers combatted this , via camshafts with more overlap. This aided in cooling the valves and chambers, and in practice, is still done today in certain applications. By allowing some of the intake charge to be blown out the exhaust, it greatly aids in keeping things cool, at the expense, of economy. Sort of how the intake valve runs cooler, due to the constant fresh air moving past it.

Of course then there is also valve seat widths. A marine engine, especially a supercharged one, should not have narrow seat widths, or valve margins. The majority of valve cooling, is done when the valve contacts the seat. So, widths and margins play an important role here. Valve seat concentricity, as well plays a part. If the valve is not seating concentric, or sealing against the seat well, this also can cause valve overheating. Valve seat material, also plays another role. Not only, for conducting the heat to the water jacket, but overall durability as well. A seat that transfers heat well, but doesn't last, and needs frequent valve jobs, may not be the best choice. A seat material that lasts long, but doesn't transfer heat well, also may not be the best choice.

Then we have water jacket design. Some heads, simply have a much improved water jacket design, which also, can improve overall cooling and heat transfer. On my new heads, the entire chamber backside is surrounded by water. Unlike a few other heads I've seen, where only partial areas of the chamber backside, are in water.

As far as airflow gains between iron and aluminum, all things being equal, there are none.

The reason I bring this up, is I recently decided to remove my 18 year old dart castings, and buy new heads. I decided to go with iron, not because of material, but because of the cost, airflow, and overall design, of the new iron heads I purchased. With that being said, I have heard it all. How Im going backwards, how I wont be able to run as much boost, I wont make any more power, I'm gonna have to back timing down, and so on. I had my old Dart heads flowed back to back against the new heads, and the new heads simply outflowed them, right out of the box. The Darts I had, had been treated to a hand valve job, some blending, and a little porting work. The new heads are currently in the process of getting some hand work done to them, and when finished, I will post the results of the flow numbers. Realizing flow numbers aren't everything, I also plan to re-dyno the engines.

While I enjoy the theories, I also like to look at results. Offshoreexcurision Kevin, had 500EFI merc's, with prochargers. Stock iron headed 8.8 or whatever compression, 7-8lbs of boost, and ran the chit out of them for many many hours, and no issues. Merc's 525sc/575sci/600sc/800sc , ran iron heads, and were very reliable engines. Strippoker was running iron heads on his 500's with whipples for many years with success. There are tons of success stories with guys running iron headed combos.

Overall, I think the majority of guys who have had failures running iron heads on supercharged stuff, liked blaming those failures on the cylinder heads material, rather than the other issues at hand. In no way am I suggesting Iron is a better choice than aluminum (unless in salt of course), but I think most hear the word "cast iron", and skip right past them, to aluminum, because of what they "heard" or "read" on the internet.

I have yet to see anyone confirm these theories, with hard data. There's data out there for everything these days, and still, nobody ever really does a back to back iron vs alum test, to see what each setup can tolerate as far as boost, timing, compression, cam, and so on. If there is, I would enjoy seeing it. Imo, just because you slapped aluminum heads on, isn't a free ticket to the golden land of high boost, high compression, worry free boating, even if you did stick an "inconel" valve in there.

Tinkerer

If you damage an iron head you will be buying a new head, the aluminum one can usually be repaired. CNC'd heads are NOT cheap.

rexcramer1

Aluminum pulls the combustion chamber heat to the cooling water in the head faster than iron. Aluminum is not just a little better at transferring heat, it is MUCH faster. Thus if at 5500 rpms your chamber temps are running 1500 degrees for example, with aluminum heads they may be 1425. That may be the difference betweven precognition and smooth running on some configurations. Add in the weight savings and the other benefits you mentioned, plus a reasonable price and you have a winner.

I am surprised no one is running aluminum blocks yet

Full Force

iTrader: (5)

I like the weight difference alone, when you blow things up as much as I do it's easier to remove aluminum in the boat LOL

phragle

iTrader: (3)

And as an added bonus, when you take the blown up aluminum heads to the recycling place, they are worth more!!!

MILD THUNDER

iTrader: (3)

Good point. Icdedppl had his ignition rotor come loose, and his timing went way off. Enough heat to melt the straps off spark plug, and severley tulip super alloy exhaust valves. The iron dart head itself, had zero damage. Our cylinder head guy, who has been doing cyl heads for 30 years in all forms of racing, pretty much said that IF he had aluminum, the heads would more than likely have suffered major damage.

Iron heads can be repaired as well to some extent, as well as aluminum. Personally, if I destroy either one of those heads bad enough, I'd want a new casting myself.

Mr Maine

When you yank heat out of the combustion chamber, you're taking usable power and putting it into the cooling water.

I think it's a cool topic, and I certainly don't think cast iron is better, but there are some points worth dicussing. Many people are under the impression that aluminum heads flow better that iron which has nothing to do with the material itself.

MILD THUNDER

iTrader: (3)

I always assumed thats why some racers coat the chambers, pistons, and valves. To reflect the heat back into the chamber, rather than let it be absorbed , turning heat into power. Could coating the chambers, also promote detonation then, since less heat is being pulled from the chamber?

Mr Maine

I think because of the heat absorbtion of aluminum you can run more compression or less octane. But the iron will make more power with less compression because the heat is staying in the chamber creating pressure on the piston.
Coatings probably do the same thing.

I remember taking thermodynamics and heat transfer classes and a nerdy professor discussing this regarding gas turbines and power production.

mike tkach

iTrader: (3)

imo,coating the chamber in the head would be a bad thing in a marine endurance engine.it can heat soak the rest of the chamber and start pre ignition.what might make a quarter mile drag car a tenth quicker could rapidly burn pistons in a half mile.it is also my understanding that coating the valves and piston tops slows the heat transfer into those parts and into the head to transfer the heat into the cooling water.