Horsepower advantage of Steel Heads Versus Aluminum.

We are debating using steel heads, instead of aluminum. I know heat=HP, and because steel would allow for less heat loss, they should make more HP.

Steel, however, is not as friendly to machine. Does anyone know of tests done on this subject? I'm curious to see what the actual HP would be, in comparison.

Thanks in advance!

 

All things being equal, I think the only difference is the weight. Thinking about newer engines, the Chevy LT1 came in aluminum head (corvette and F-body) and ironhead (Impala). The output of the iron head engine was slightly less but that was blamed on the exhaust design.

Aluminum can absorb heat faster than iron, so in modern engine design the compression ratios are higher with aluminum heads, that's were the extra power is made.

 

Our local flathead hill clmber racer etc has said for years with all his testing that the steel heads make the most power on the flathead ford engines.
Aluminum is easier ( like you mentioned) to machine and work with etc.....AND they look some damn cool....:>)
Let me know if i can help the "project" in any way ......ignition wise etc......

 

Of course, steel weighs more, too...much better characteristics in most out of the box aluminum heads...I'm not a thermodynamics expert, but, I'm sure a couple will come along soon, with opposing viewpoints, and heaps of information supporting their positions and this will get interesting.

I'm thinking that heat=horsepower is a DRASTIC oversimplification of the situation, however.

After all, cooler has advantages a plenty, too, such as deterring detonation, keeping under hood temps down, denser fuel/air mix, higher compression, etc...yes???

I can't wait to check back in on this argument...err, umm...debate.

I also suppose on a Flathead it might be all kinds of backwards and upside down to regular logic.

 

The advantage is better heat transfer = less detonation and higher compression.

 

So, anyone have any emperical data?

 

As I said I'm no expert, I'm just really curious, too, because I hear all about the advantages of aluminum heads all the time in my circles, and I find engine dynamics and concepts fascinating, but, I'm an admitted novice, and a total stranger to Flatheads. I'm just very interested in hearing the expert responses, too...which I expect, as always, will be divided into camps

As far as heat equaling horsepower, I say misguided because, though it is comparable, btu's and hp, I'd say it is obviously not just as simple as add heat = gain power, since heat can rob power, if it is not in the right place at the right time. It inhibits allowable compression, timing advance, and closes up tolerances, enhancing friction when applied to the entire engine ( and, even though we are talking about only cylinder heads here, still, the fact is that they are still attached to the same engine )

Now the buildup of heat, I suppose is a non-issue in a B-ville blast though, as you said.

I'm not arguing, because I'm not an engineer or a scientist, I am a student...but I am very interested. I just know what I have been told, and am always curious about the physics of engines and drive trains.

 

It's all good! I was just explaining the scenario.

Obviously, if I knew the answer, without doubt, I wouldn't need to post this!

 

Different topic, but one I was going to call you about- Can you run a magneto off of a crank sensor?

 

Smokey was an advocate of pouring water gl*** in the cooling p***ages to restrict heat transfer. Much has changed in the couple decades since then and i would think a thermal barrier coating in the combustion chamber would be better.

 

Anything that keeps combustion energy inside the combustion chamber where it can work, is a good thing.

As a material, the steel will absorb less heat and will therefore make "more power" if everything is apples to apples. But there are a LOT of other factors in play. If you keep the tuning the same between both, then more heat will soak into valves, rings, and pistons in the steel-headed version since it's NOT leaving via the heads. If you have top-notch parts here then you will probably be fine, and possibly make more power with steel heads than aluminum.

But it's hard to say. I've had iron race heads that made good power. I'm convinced the proliferation of aluminum heads is due to ease of casting and machining, ease of repair, lighter weight, and some efficiencies in cooling, but not necessarily in the ability to make power.

 

There was a test done recently by a magazine (I will have to figure out which one) in which they took two Dart heads - Iron Eagle's and Pro 1's with Identical port and chamber design and did back to back dyno testing on a 500+ h small block.

They made identical power. I think that shows that the port and chamber design is far more important than the material.

 

In spite of what some people say on TV, blocks and heads are cast from iron, not steel. To make them tougher and stronger, the iron that blocks and heads are made of is usually alloyed with one thing or another, or sometimes processd after casting to make them tougher, but it's still iron.

As has already been said, all things beine equal, aluminum is lighter. Iron doesn't conduct away as much heat from the combustion process...... Because of that, an engine with aluminum heads will put more heat into the cooling system than iron. Iron heads are also more tolerant of overheating and detonation than aluminum.

 

Buddy; Why not look into Plasma spraying a ceramic heat reflecting coat on to your aluminum combustion chambers? Best of both worlds. When I was running in XOB/GAlt with cast pistons it was the only way I had any hope of running all week. That's a long time ago now but I think I remember that I was using Metco 601 for my coating. Worked good.

 

You had better luck with that, than iron Rich?

 

Those coatings don't have a good long term track record on street engines.

 

I'm with Rich on this. The poor man's version would be a mirror polish on the piston tops and chambers. Coating is easier.

 

It is all about flow, the head material is immaterial - ***anium if you want. Once the engine is up to temp, there is no difference. The heat issue is dealt with the spark plug heat range not head material. And cast iron is easier to port/machine than aluminum, well the porting is easier and milling is about the same. Aluminum tends to gall the carbide cutters when porting so you have to take frequent breaks to dip the cutter into a lubricant (i like beeswax), cast iron is actually softer than the tempered aluminum head materials and won't gall the cutter, you can wade right into cast iron.
The real advantage to alumnim is repairing a misshap, you can weld up an aluminum head no problem. Cast iron is a bit touchy (esp between cylinders).

 

I'm ***uming we're talking flathead engines here, and further, never having seen the inside of a flathead Caddy, I'm ***uming a somewhat similar layout to a Ford flathead.
On a Ford, especially with race gas or alcohol, with or without nitro, the limiting factor isn't detonation, it's airflow over the transfer to the cylinder from the valves. Too tight of a chamber and it cant breathe at high rpm. So heat retention may well have something to do with it on a flathead!
What I do know is that around the ATL area, all the top oval track engine builders of the day used iron heads, Called "81sb" heads, as these were the number stamped on them and some called them "Denver heads".
Even after Weiand came out with their "Cheater Canadian Heads" which were non finned aluminum that the tracks allowed, the top engine builders stuck to the iron heads.
In fact I watched the late, legendary Jack Smih take a '34 Ford Coupe with a flathead, 4 carbs, alcohol and iron heads and outrun all the big overhead Cads, Olds, Hemis, etc. in about '54. This was @ Lakewood Speedway, a 1 mile dirt oval in ATL. The engine builder, IIRC was the also legendary Harvey "Bones" Jones, who is still living and still close mouthed about what was in his engines that were so ****ing fast!
Dave

 

All things being the same, an iron head will actually make more power than an identical aluminum head. That is not my opinion, it is a well know, and well do***ented fact. The physics are obvious but can be argued or disregarded. Real world experience on the other hand..... is what it is. For similar reasons, and contrary to what many believe, when an engine doesn't have a water heated intake a higher temp t-stat will result in moere power than a lower one.

 

True. Torque was more on the Impala LT1. I always thought that the Impala LT1 was "tuned" for such a heavier car.

 

Never tried an iron piston. My head was iron. I agree with all who say that keeping the heat in the combustion chamber will make more power for a given fuel burn than letting the heat escape into the water. PS I have cut a bunch of aluminum and I'll take it over cast iron any day. But today I am cutting iron. Dirty stuff. PS when I coated my pistons I was working as a tool maker for a shop coating Pratt & Whitney and GE turbine engine hot section parts. These things racked up plenty of miles, lots of which were over water. Neither my pistons nor their burners had any failures that I ever heard of.

 

"All things being equal" is leaving HP on the table, as far as the aluminum heads are concerned. A primary advantage is that you can typically run higher compression than you could get away with using iron heads. I ran 12.3:1 on a street LT1...granted, part of the ability to do that was being reverse cooled, but the motor was 10.4:1 stock.

 

The iron LT1 heads were designed later than the aluminum ones (they came out in '92, on the Vette), and had the advantage of more R&D time. The ports are essentially the same as the later Vortec head, and in stock form they will outflow the aluminum heads. The aluminum heads are easier/cheaper to port, though, and any advantage of the iron heads goes away at that point.

 

Pro
http://www.swaintech.com/store.asp?pid=10321
Con from enginebuildermag
Thermal coatings keep heat from spreading down into the pistons and rings, which may be counterproductive if the heat persists for a long period of time. That’s why several piston manufacturers do not recommend a thermal barrier top coating on pistons for naturally aspirated engines (without nitrous) or ones that are built for endurance racing. On these kind of applications, you’re probably better off without it.

 

I think if you really spent a lot of time and money you could find out that there are positives for iron heads for short time period racing purposes. I know that the Winged Express and some other Nostalgia TF cars run iron heads on aluminum blocks... I know another guy who machined iron combustion chambers into aluminum heads. Both these were for nitro drag purposes. I think with the ability to m***age aluminum heads easier. The cost always coming down on them. The weight savings. The cooling efficiency. Coatings available they are the way to go. Don't forget aluminum can be repaired a lot easier after being damaged too.

 

That is interesting. Buddy, i am not trying to steal this thread but if anybody can wade in and school me on the above statement - is there certain conditions that make it a true statement? I am a racer, my engine makes power for a few seconds and for the life of me i cannot see where cylinder head material will make many difference.
Thanks for the oil pump Buddy, i appreciate it.

 

Ok, lots of onfo here, thanks guys!

To clear up a few things: We have to make the heads anyway. Rich, in this instance would you coat the aluminum, or go with the iron heads?

The heads will be cnc cut, after flow testing is complete. There should be very little m***aging, if we plan right. Will we? Who knows!

Compression is not a problem, The engine will be 8:1, with a blower, and a superchiller intercooler.

3 mile track, so short runs. We can control temps.

Aluminum looks cool, but I don't need cool, i need Hp!

 

To me it sounds like you are leaning towards steel. I would probably lean that way too from what you are saying you are trying to accomplish. How much boost are you planning to run? Blowers can make up for mediocre heads!!! Steel will seal better (less likely to push out a head gasket). You can run just as much compression in an iron head as an aluminum head... for a while. The difference is after the engine has built up heat is it takes longer for the heat to escape from iron. The head gets hotter and stays hot for a long *** time. Aluminum heads shed heat like **** through a goose so they don't get the heat 'creep' allowing you to bump the compression a bit more. If you are not building a daily driver or a roundy round engine you should be fine. Are you running alcohol or gas? Alcohol would help a lot too.

 

Interesting thread...
I definitely think that it is a bit of a different game for a short run flattie, too, than a standard valve in head engine.
More issues with other variables offsetting the gain through combustion chamber heat I can see on a longer running motor, or, in the case of high rpm ( thus, more close-shave timing ) motors. Do you guys racing these motors use any mechanical or vac*** advance in these things anyway??? I know nada in the ways of the Flattie, but, my next coupe is looking like it might be getting one, so, I'm intrigued. Of course, I don't know how much you guys can really spin a flathead anyway, maybe yours does turn pretty good???
Ahhh..."All things being equal"...if that was only just ever once the case...

It sounds like the coatings or iron combustion chambers in easily repairable/modifiable alloy heads is a good deal.