Iron VS Aluminum heads
 

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.

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.

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

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

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

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.

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.

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?

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.

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.

Also I've noticed less expansion in valve lash when dealing with oe .. World etc cast heads as opposed to dart Brodix.. ( on adjustable setups)

Maybe less fear of rocker stud breakage with iron when no shaft or girdles are added..

Aluminum is become easier to mass Cnc .. Plus it looks cool

I like the weight savings of an aluminum head, but one thing I think about is the expansion rates of aluminum on an iron block vs iron on iron. I have no idea what issues it causes but the rate of expansion between the two are huge, could be a non issue, just throwing it out there. What does it do to head gaskets with the differential?

Good thing about aluminum transferring heat faster is the exhaust valve.

Agreed. Point in my original post, was that there's more to cooling an exhaust valve, then the cylinder heads material. Things like seat widths, stem clearance, water temps, seat materials etc.

Its like the GM truck and RV engines. For years, they powered huge motorhomes, tow rigs pulling heavy trailers, up mountains. Heat was enough of an issue, that they installed inconel valves in these engines, which were cast iron headed. These engines ran 200+ degree water temps, and even saw 230+ pulling heavy loads, on hot summer days, ingesting 100 degree hot desert air. While they were only maybe making 400-450 ft lbs of torque, there exhaust temperatures had to be extreme. Many of these engines went 200 plus thousand miles in those conditions. They made quite a bit of low rpm cylinder pressure, with tiny camshafts as well. Tons of stock mercury engines running around in boats, everything from iron 4 cylinders, to merc racing supercharged engines, that proved to be extremely reliable.

I've seen some exhaust temperatures from N/A engines making half the power of supercharged , or even other N/A engines , be the same or greater.

aluminum heads on iron block has been done for 50 years so me think it is ok.

A little of topic, but coating a chamber won't cause "heat soak" and pre ignition. Coating valves and piston tops does help keep the heat out of them as you said - this is a good thing.

haxor,if the head gets coated would that make it retain heat and hinder the transfer of heat to the cooling water flowing through the head?

Coating piston tops is designed to reflect or transfer heat.. We have coated skirts to help with scuffing that occurs with short skirt piston. Helps not to scuff cyl walls..

The coating is designed to reflect the heat back in to the chamber to help from losing the energy. It is not designed to retain heat. Transferring excess heat in to the actual head material is often why aluminum heads require more timing advance.

i understand that but my question is----will coating the head in the chamber impede cooling of the chamber?example,throttle,s pinned for 5 minutes in a 42 foot fountain.

the coating on the skirt is not for heat transfer.

No, the coating allows more of the energy from combustion to be used for making power rather than heat loss/ thermal transfer. Same reason an Iron Head will make more power than an aluminum head. This also holds true for Aluminum vs Steel blocks.

That is correct. It is used for scuffing against the cylinder walls as stated. The word scuffing was used instead.of rubbing. scraping etc. more or less a non metallic contact barrier.

For what it's worth, being a old school racer from way back, I remember seeing a long engine tech talk with Bill Jenkins and he said that iron heads make more power as they retain the heat in the chamber, down side was weight and harder to port...

MT if you said it,I missed it ....What iron heads did you buy

Engine quest 320cc. They are basically the old pro topline/RHS stuff. Still cast in New Zealand foundry by masport. My head guy used to really like the old RHS/pro topline stuff, and had a pair of them to in his shop to compare. We actually saw some things they have changed for the better with the engine quest castings, although, they are for the most part, the same basic casting. I bought them bare, and installing all my own hardware.

There was an article a long time ago about aluminum heads and their ability to reduce preignition and ability to run higher compression. I can't remember who wrote the article but I think they quoted that you could run roughly 2 points of compression higher with an aluminum head than cast iron. What I think is more important with the aluminum heads is the CNC programs they have which give us superior chamber designs and optomized runner designs over cast iron. To me, that's the biggest difference between the two so you get a lot better designed head.

For instance; 4 years ago I got rid of my Merlin Grumpy Jenkins heads and installed AFR 357 CNC heads. I did not change a single thing on the setup other than bolting the heads on and I gained 3-400 rpms and the boat went from running 87mph to 92.3mph GPS verified. Then last year when I did my builds I optomized the camshaft over what I had previously and the boat went from 92.3 mph to 95.4mph GPS verified. All the while the boost levels stayed roughly the same.

Here's another article; http://www.performanceracing.com/mag..._aluminum.html

I was thinking about using those Engine Quest heads on a 509 MPI build I'm doing. The prices are really good, like $500 per bare casting.

In my case I had so much heat in my chambers aluminum heads would have been melted. All my Iron eagles needed was a valve job and clean up and back in service.
Aluminum is lighter that`s the biggest advantage to racers and why aluminum head is so popular.. extra 150 lbs in a boat makes no difference. That`s a cooler full of beer.

Marketing makes the iron head seem like old technology when that couldn`t be further from the truth.It`s not that you can run more timing with aluminum it`s that you have to.
At higher horsepower I`d rather have the strength of the Iron head.
Expansion/contraction is a whole nother story.

*edit.. I should have read all the post , looks like it`s already been covered.oops

Yes, they are. I payed a bit less than that. Actually they were 425 each to my door. They are a favorite in the truck pulling class that mandates iron head per their rules. There are quite a few guys making over 1000hp on motor with these heads, ported of course. Out of the box, they flowed 370cfm at 600 lift, and 388 at .700, .391 at 800. Keep in mind this is an as cast head, 320cc runner, with a 2.25 valve.

Ive talked with quite a few head specialists and engine builders prior to buying them, and read a bunch of posts over on yellowbullet and speedtalk, and couldn't find one negative about them. Once i got them, looked them over, had my head guy give me his opinion, he really liked them. Then once he pulled our darts off the flow bench, and started flowing them, he liked them even more.

I have thought about going to iron heads just because salt water eats the living **** out of aluminum. Who wants to spend 10 grand on heads every 5 years?

There are literally hundreds of aluminum head choices on the market these days and they go from basic stock replacement design levels, to raised runner, spread port full competition heads. The only draw backs I see to iron is 1) the weight, and 2) there isn't the selection and performance design upgrade choices available like the aluminum heads, but they're getting better. I've heard a few people mention "CNC" options for aluminum heads. Well CNC machining is not limited to aluminum. Any port can be digitized and CNC machined in any head. There are lots of iron heads out there with CNC machining done. If you start looking into some racing classes that have iron-only head rules you'll start seeing some pretty darn nice iron heads with a lot of time and effort into their development. The EQ320 is a good head to start with for the BB Chev. The Dart Iron Eagle 330 is a fully CNC ported iron head. There are some aftermarket BB Ford iron heads that are some very serious competition heads. The shapes and designs of the ports and chambers are what really matters, not the material. One of the design "flaws" in the BB Chev conventional head is the size of the chamber, not only in volume, but also surface area. It transfers way too much heat and making the head out of aluminum only makes things worse. The real benefit the aluminum chamber has over most iron heads is it's design and shape which up until just recent years was a huge improvement over OEM iron heads. It wasn't the material that made it better.

Apples to oranges. An ok casting compared to a full CNC head I would expect some very nice gains.

Couldn`t agree more, especially the chamber design. I have A LOT of hours into chamber work on my heads which translated into 134cc and lowered my compression to 7.5:1 .Now that I have a chance to raise that back to 8.4:1 with flat top pistons and knowing my flow numbers tailor the cam I`m hoping for some good numbers.

Coating the pistons other than the skirts ever notice the underside of the piston crown. What is that browish build up ..burnt oil. Have experimented with coating that side with a heat barrier which reduced oil temps. Have also painted my aluminum heads to help retain some heat. Some clam just pant the front and rear cylinder areas and not the center cylinders to keep heat temps more even between middle and end cylinders.

BBC has issues with the combustion chamber width vs the bore size they were really designed for a 5.00 bore back in the 427 days.
Some engines iron factory heads ported will flow better than some of the aftermarket stuff.

I think you should join the iron head club, especially in saltwater.

Not an expert, what effect does fuel have on this debate? The reason for my question, I have some old small block chevy stuff I will be throwing together for a drive around fun car, and have debated old good iron heads versus aluminum. If running e85, does that make the fuel burn cooler? Taking some of the heat detonation problems away? I've heard you can run more compression on e85.

What detonation problems ? What heat problems ? Im still not understanding how mercury has tens of thousands of iron headed marine engines out there for several decades now, and all of a sudden theres a heat/detonation problem if you use iron lol :cartman:

I would imagine ethanol would burn cooler though?

That is a good question. I see companies like AFR advertising how "thick" there decks are, and how that is great for forced induction engines. Theres no question iron is stronger when comparing them at the same thickness level. Is it possible an iron head has a better clamping force and less chance of distorsion under high pressures ? Maybe why high compression, high cylinder pressure diesel engines are still running iron heads ? I know a diesel engine can have extreme pressures and extreme exhaust temps. What do they do to keep their exhaust valves in one piece with their iron heads ?

WAG - less rpm (less power strokes per minute and more valve on the seat time), smaller valves, less cam duration (more time on the seat), etc,etc ???

I don't know diesels well, thus the WAG.