Aluminum heads

-
For all of you none science folks that don't like math....this is for you......

upload_2019-11-8_12-58-32.png
 
yellow rose said:
So you are saying you'd tell someone with aluminum heads they can run 11:1 on pump gas but the exact same engine with iron heads you tell the guy to only be 10:1? That's wrong and crazy and the science and experience don't prove that out.
Click to expand...

No, I think you missed the word "not" in my post.
In fact, my oldest son has 11:1 with aluminum heads in his valiant. I just helped his brother build a 10.7:1 iron head motor. Its going in his 1/2 ton, which is heavier than the valiant.He is also using a cam with 10 degrees at .050 less than his brother in the valiant.

If I believed the aluminum/ iron controversy, I would kept the truck motor at 9:1. My personal daily driver, and only family car for years was a j headed 360 with a little over 10.5:1. Drove it daily all year round and the only time it detonated was a load of bad gas.
If you re-read my post, I said iron is Not the enemy of compression.
 
Here's a thought. If, for the purposes of this argument, that we agree that an aluminum headed engine can resist detonation better than an iron headed engine thus allowing higher cylinder pressures (after all, isn't that what we're really talking about?)- could the difference be that of the materials themselves, aluminum vs. iron, and not how fast heat can be dissipated?
 
dart_68 said:
Here's a thought. If, for the purposes of this argument, that we agree that an aluminum headed engine can resist detonation better than an iron headed engine thus allowing higher cylinder pressures (after all, isn't that what we're really talking about?)- could the difference be that of the materials themselves, aluminum vs. iron, and not how fast heat can be dissipated?
Click to expand...

The only meaningful difference between the materials is strength and hardness. Iron is harder and stronger. Alum is softer, and weaker (lower modulus).

So, if there IS a difference between the two heads when it comes to compression performance, it would have to be from some intrinsic property of the material - deformation can account for some lost power due to greater deformation, but any decently designed alum head won't deform enough to impact performance noticeably and this would not help much with detonation (pre ignition) resistance.

If deformation isn't the difference, then it has to be down to heat. But none of the math or reality supports there being much difference in the thermal performance either.

The only place that may have an effect would be the ability for the alum head to draw heat from the exhaust valve slightly faster. I think there's better ways to deal with that than changing compression.
 
dart_68 said:
Here's a thought. If, for the purposes of this argument, that we agree that an aluminum headed engine can resist detonation better than an iron headed engine thus allowing higher cylinder pressures (after all, isn't that what we're really talking about?)- could the difference be that of the materials themselves, aluminum vs. iron, and not how fast heat can be dissipated?
Click to expand...


I don't agree with any of that. Nor will I so we can't even have a reasonable discussion about it if you hold your fallacies as truth.
 
Mopar Sam said:
No, I think you missed the word "not" in my post.
In fact, my oldest son has 11:1 with aluminum heads in his valiant. I just helped his brother build a 10.7:1 iron head motor. Its going in his 1/2 ton, which is heavier than the valiant.He is also using a cam with 10 degrees at .050 less than his brother in the valiant.

If I believed the aluminum/ iron controversy, I would kept the truck motor at 9:1. My personal daily driver, and only family car for years was a j headed 360 with a little over 10.5:1. Drove it daily all year round and the only time it detonated was a load of bad gas.
If you re-read my post, I said iron is Not the enemy of compression.
Click to expand...


I need to go back and look at my post. I thought I quoted 66dart or something like that. It certainly wasn't directed at you.
 
Mopar Sam said:
No, I think you missed the word "not" in my post.
In fact, my oldest son has 11:1 with aluminum heads in his valiant. I just helped his brother build a 10.7:1 iron head motor. Its going in his 1/2 ton, which is heavier than the valiant.He is also using a cam with 10 degrees at .050 less than his brother in the valiant.

If I believed the aluminum/ iron controversy, I would kept the truck motor at 9:1. My personal daily driver, and only family car for years was a j headed 360 with a little over 10.5:1. Drove it daily all year round and the only time it detonated was a load of bad gas.
If you re-read my post, I said iron is Not the enemy of compression.
Click to expand...


Did you actually post that quoted I quoted? I thought it was someone else.

There are too many threads going on this topic and I'm getting punch drunk from all the forum hopping.

I knew what you were saying. I just got crossed up. I apologize.
 
yellow rose said:
Did you actually post that quoted I quoted? I thought it was someone else.

There are too many threads going on this topic and I'm getting punch drunk from all the forum hopping.

I knew what you were saying. I just got crossed up. I apologize.
Click to expand...

Posts 224, 225. Sometimes I glance through posts too quickly, and have to go back and look, because I missed the persons point. You actually agreed with post 224, and then post 225 made me think you missed the "not" .

I am not the most eloquent poster, that is for sure.

No apologies necessary, I forget what thread I am in half the time, and lately it doesn't even matter.... aluminum/iron/rubber/ketchup its all good!
 
yellow rose said:
It has been done and there is no way that the cores can be the same with aluminum and iron.

You'd either have an aluminum head that was so thin a baby fart would blow it apart, or a CI head that was so heavy, and the water jackets so small it would weigh a ton and couldn't be cooled.

Again, I read the Hughes post and he didn't give any "science". It just regurgitated the same old fact that aluminum dissipates heat faster. So what? Refer to my post in the racers forum.

Let me see if I can sum it up without typing a book.

The rate of change in increase of temperature of combustion is so fast, that the rate of change of temperature of the coolant can't accept that temp increase.

IOW's, no matter how fast the head materiel can reject or dissipate heat, the coolant can only take so much of an increase. And coolant accepts heat much slower.

And then, we can discuss how many BTU's the coolant can reject, at what load does heat dissipation become relevant?

For example, you have an 11:1 CI headed engine and cruising down the road, temp and load stabilized, and when most detonation occurs is right here...when you transition into tip in. The load goes straight up, the engine rattles and you either mash on it to get through it or back off the throttle to stop it.

Explain to me, with science, how an aluminum head can conduct heat so quickly as to remedy that.

I can also tell you this observed fact. Detonation almost never occurs at WOT. Almost never, and to get that your tune up has to be so jacked up that nothing will fix it except correcting the underlying issues and head materiel won't do that.

Low RPM, high load detonation is the real enemy, and an aluminum head ain't going to fix that.
Click to expand...
As said, 100% apples to apples is not going to happen due to the casting.

However, IMHO the above is missing a crucial and vital point about the heat conduction. It is correct that once the combustion process starts, the head material does not do anything, since the heat generation is so fast that the head material does not matter. But what is being missed is that the peak temperature and pressure (which is what we are interested in for managing detonation) is NOT ONLY due to the heating during the combustion process. It is a result of the temperature/pressure of the gases immediately prior to the start of combustion plus the heat added during combustion.

There is no arguing with this matter... The research that established this was done 80-90 years ago, in the 1930's, that cooler engines and mixtures are less prone to detonation. You can find the papers out there if you look. (And I don't believe that the laws of physics have changed any since then LOL.)

It is the gas temps just prior to combustion where the cylinder/chamber materials can make a difference. The thermal resistance of AL is 3/10ths that of cast iron. So, as long as the other thermal resistances are similar or the same (the chamber gasses into chamber wall, chamber wall to coolant, and then the whole effective thermal resistance of coolant to air) then aluminum lowers the overall thermal resistance from chamber surface to air. The aluminum chamber will be cooler when you need it to be: during the intake and compression time prior to the start of combustion. If that can be used to keep the gases cooler prior to the start of combustion, you have succeeded.

How much of this is a factor? IDK.... Hard to separate it all out. I will not say the YR's results are in any way wrong.... but my opinion all along it is due to other things he is doing, and other factors in the combustion process and operation, that makes the materials appear equal in his tests. (And we don't know how extensive those tests really are to be able to judge if they indicate a broad result.)

As for the 'going through the detonation conditions at tip in by mashing the throttle', that mashing is changing other combustion conditions to get away from the detonation. But that says zip, zero, nada about the chamber material's contribution to the detonation when it does occur. So that is not a proof of anything about the materials. I can only say what's indicated above.... that other factors are more important overall in YR's testing. But a different engine, setup, operating, may benefit more clearly from the materials difference.

Noting new or bad about any of this..... Research work goes to great lengths to try to contrive tests to separate out all the different effects, but sometimes, the papers confess that it just cannot be done in their particular testing setup, and all they can draw is probable conclusions. So no surprise that it cannot be done in the field.

BTW.... If you had an accurate steady state dyno, and the AL was actually pulling out more heat to keep the chamber temps lower, then the coolant temps wold rise.
 
Phreakish said:
More fuel for the never ending fire:
Comparing Aluminum And Iron Cylinder Heads - Car Craft Magazine - Hot Rod
Click to expand...
I've read this article before, and the writer agree's with my take on their data.....that it is NOT definitive at all. This single point test really was just filler (like Freiburger said in the last sentence). The cam was big, which bled off cylinder pressure, making it so that there was really no danger of the engine detonating. A proper test would have involved changing variables that actually may have had some bearing on the hypothesis (like using lower octane fuel, smaller cams, etc).
 
HughesEngines said:
Compression ratio and cylinder pressure are not strictly results of mechanical factors.


Confusing compression ratio and cylinder pressure is a common mistake and problem for amateur engine builders. They are related, but not the same, as commonly thought. Compression ratio is strictly a result of mechanical influences such as bore, stroke and combustion chamber volume. Cylinder pressure is pressure inside the combustion chamber when the engine is running. Cylinder pressure is influenced by compression ratio along with several other factors – for example:

1. Altitude – The higher the altitude, the lower the cylinder pressure: resulting in reduced performance like lowering the compression ratio, but the compression ratio remains the same.

2. The material the cylinder head is made of effects pressure too. The aluminum cylinder head will dissipate (that means draw off) heat from the combustion chamber much faster than cast iron with no effect on the compression ratio. But it will lower the running cylinder pressure. Lower temperature means lower pressure, and lower pressure means less power. That is why you should increase compression ratio when switching to aluminum heads, or you can leave it alone and reduce your power, all other things being equal.
Click to expand...

I am good with most of this until the part that I bolded above. The power result is not directly the result of peak pressure. It is a result of the pressure changes over the volume changes in the cylinder. Anyone who is interested in this needs to look up and start to understand what is called a 'P-V' diagram. Here is a good example; look at figure 2 halfway down the page:
Four stroke engine - Energy Education

The energy output is the area inside the curve (the larger upper part of the curve). You can have a higher peak pressure (the highest point on the curve), but a smaller area, like if you open the exhaust valve earlier and the right hand section of the enclosed area shrinks. Thus the energy per cycle will be lower despite a higher peak pressure.

So there is no direct, automatic relationship between cylinder pressures and power output. It has to be examined as pressure changes versus volume changes. Higher compression ratio means higher peak pressures, but the end pressures will be higher too, so, again, it is pressure changes versus volume changes.

Which gets into other effects of higher CR but we'll leave that alone for now....!
 
nm9stheham said:
BTW.... If you had an accurate steady state dyno, and the AL was actually pulling out more heat to keep the chamber temps lower, then the coolant temps wold rise.
Click to expand...

More heat into the coolant would mean more fuel burned too. OEM's all using aluminum heads suggests that there must be other reasons to use aluminum (hint: it's cost and weight savings).

nm9stheham said:
If that can be used to keep the gases cooler prior to the start of combustion, you have succeeded.
Click to expand...

True, cooler at the start will be far less prone to preignition - that's a fact.

The question then is whether the air coming into the chamber is a different temperature than if the head were made from iron. In a water cooled engine there's going to be little difference. I would argue the exhaust valve has more effect on charge temperature than the chamber itself (still trying to find the ASME paper on the subject), and that an aluminum head cools the exhaust valve slightly better but not enough to have a tremendous impact on compression ratio choices.
 
Very good point on the exhaust valve since it sees more heat and is normally harder to keep cool. During the over lap period, how much heat comes back in due to the hot valve as well as the gasses themselves is a interesting point to look at. This would be a constant variable due to the amount of engine material combinations of parts used, compression ratio, and cam timing/dynamics of moving the gasses effectively or not.
 
Phreakish said:
More heat into the coolant would mean more fuel burned too. OEM's all using aluminum heads suggests that there must be other reasons to use aluminum (hint: it's cost and weight savings).
Click to expand...
Not at all. (Though I won't argue at all with that being the OEM reason to use it ...)

If the head chamber surfaces are truly cooler, it is because the thermal resistance of the heads is lower, and thus overall thermal resistance from gases to air are also lower. That means the heat flow through the heads and through the coolant, through the rad, and into the air will increase..... because the whole heat flow path, from chamber gases to outside air, has a lower overall thermal resistance. But the thermal resistance from coolant through rad to air is the same. So the higher heat flow raises the coolant temps.

I know it seems wrong to say that. How it changes:
  • Temp drop from gases to head material is higher (which absolutely says that heat flow will be higher)
  • Temp drop through the head itself is lower (due to much lower thermal resistance despite the higher heat flow)
  • Temp drop from head to coolant is higher (due to the higher heat flow)
  • Temp drop from coolant to air is higher (due to the higher heat flow)
There are a whole lot of 'all things being equal' in there.....like coolant flow rate, and surface finishes, which have a big effect on thermal resistances.
 
nm9stheham said:
Not at all. (Though I won't argue at all with that being the OEM reason to use it ...)

If the head chamber surfaces are truly cooler, it is because the thermal resistance of the heads is lower, and thus overall thermal resistance from gases to air are also lower. That means the heat flow through the heads and through the coolant, through the rad, and into the air will increase..... because the whole heat flow path, from chamber gases to outside air, has a lower overall thermal resistance. But the thermal resistance from coolant through rad to air is the same. So the higher heat flow raises the coolant temps.

I know it seems wrong to say that. How it changes:
  • Temp drop from gases to head material is higher (which absolutely says that heat flow will be higher)
  • Temp drop through the head itself is lower (due to much lower thermal resistance despite the higher heat flow)
  • Temp drop from head to coolant is higher (due to the higher heat flow)
  • Temp drop from coolant to air is higher (due to the higher heat flow)
There are a whole lot of 'all things being equal' in there.....like coolant flow rate, and surface finishes, which have a big effect on thermal resistances.
Click to expand...

I get all that, my statement was with the assumption that power output remains the same (and I almost typed it too.. I should have). If there's more heat extracted from the chamber, and power output remains the same, fuel consumption has to go up. If fuel consumption were steady, then power output has to go down.

Same 'all things being equal' in my original statement ;)
 
Here's a decent lecture I found on heat transfer:
http://web.mit.edu/2.61/www/Lecture notes/Lec. 18 Heat transf.pdf

Without the accompanying notes, it's incomplete. However, there are useful bits there. In-chamber temperature is lower on an aluminum head (slide 22, page 11). This makes sense. But the amount of energy removed won't be any greater with the aluminum head. The greater conductivity and lower resistance means that for the same energy 'wicked' away, the resultant temperature of the chamber walls will end up being lower.

The lecture also points out that convection is the main means by which heat is conducted, and that until ignition happens, there's little convection going on and so little heat transfer.

One of the slides also lists the exhaust valve and the spark plug as the hottest items in the chamber - which would suggest that proper mixture and spark plug selection matter more when it comes to pre-ignition than cylinder head material.
 
Phreakish said:
One of the slides also lists the exhaust valve and the spark plug as the hottest items in the chamber - which would suggest that proper mixture and spark plug selection matter more when it comes to pre-ignition than cylinder head material.
Click to expand...
This, IMO, is in a word, “BINGO”
 
nm9stheham said:
As said, 100% apples to apples is not going to happen due to the casting.

However, IMHO the above is missing a crucial and vital point about the heat conduction. It is correct that once the combustion process starts, the head material does not do anything, since the heat generation is so fast that the head material does not matter. But what is being missed is that the peak temperature and pressure (which is what we are interested in for managing detonation) is NOT ONLY due to the heating during the combustion process. It is a result of the temperature/pressure of the gases immediately prior to the start of combustion plus the heat added during combustion.

There is no arguing with this matter... The research that established this was done 80-90 years ago, in the 1930's, that cooler engines and mixtures are less prone to detonation. You can find the papers out there if you look. (And I don't believe that the laws of physics have changed any since then LOL.)

It is the gas temps just prior to combustion where the cylinder/chamber materials can make a difference. The thermal resistance of AL is 3/10ths that of cast iron. So, as long as the other thermal resistances are similar or the same (the chamber gasses into chamber wall, chamber wall to coolant, and then the whole effective thermal resistance of coolant to air) then aluminum lowers the overall thermal resistance from chamber surface to air. The aluminum chamber will be cooler when you need it to be: during the intake and compression time prior to the start of combustion. If that can be used to keep the gases cooler prior to the start of combustion, you have succeeded.

How much of this is a factor? IDK.... Hard to separate it all out. I will not say the YR's results are in any way wrong.... but my opinion all along it is due to other things he is doing, and other factors in the combustion process and operation, that makes the materials appear equal in his tests. (And we don't know how extensive those tests really are to be able to judge if they indicate a broad result.)

As for the 'going through the detonation conditions at tip in by mashing the throttle', that mashing is changing other combustion conditions to get away from the detonation. But that says zip, zero, nada about the chamber material's contribution to the detonation when it does occur. So that is not a proof of anything about the materials. I can only say what's indicated above.... that other factors are more important overall in YR's testing. But a different engine, setup, operating, may benefit more clearly from the materials difference.

Noting new or bad about any of this..... Research work goes to great lengths to try to contrive tests to separate out all the different effects, but sometimes, the papers confess that it just cannot be done in their particular testing setup, and all they can draw is probable conclusions. So no surprise that it cannot be done in the field.

BTW.... If you had an accurate steady state dyno, and the AL was actually pulling out more heat to keep the chamber temps lower, then the coolant temps wold rise.
Click to expand...


The only place I know of other than marine stuff where en engine is in steady state is Talladaga or Daytona. Everything else is transient RPM so a steady state measure is kinda worthless for what we are considering.

Again, an aluminum head is at the same temperature as a cast iron head when running. It's not any cooler because it's aluminum.

Want to prove that? It's easy. You can measure a cast iron intake and record the temps. The swap on an aluminum intake and the temps will be the same. Or so close it's not worth considering.

I do nothing special to my engines other than not buying some cookie cutter junky assed off the shelf cam. But I do that regardless of what the head casting is made of.

Been doing it for decades and all brands. Had a BBC street strip deal come into the shop from another builder local to us. It came in at 555 CID on pump gas and the calculated CR was a paultry 9.25:1. Rediculous.

Then we got the cam card (engine came in because it was down on power and stuck a piston) and it was some off the shelf hydraulic roller. First things first, the cam went in the resale pile and the lifters followed the cam.

Then we changed Pistons to get the CR to 11:1 with yes, you guessed it, iron heads. Of course the owner was wetting his panties because he was a forum surfer and all the key board builders assured him it was grenade with the pin pulled.

Ordered a CUSTOM cam from CamMotion and it looked nothing like all the keyboard heroes said it should. A HR lobe with solid lifters. Again the interweb went wild claiming disaster and explosion on the first dyno pull.

That was the summer of 2006. My brother ran into the guy at a car show this summer. 13 years later, about 55k on the engine, all on pump gas and still going, detonation free.

One example of doing it again.

The facts are simple. Detonation almost always occurs at high load, low speed throttle positions. There is no way on Gods green earth that an aluminum head can reject heat so much faster, and the coolant can accept the heat so fast as to correct this.

I say the biggest issue people have is they don't understand cam timing enough to pick the correct cam so they end up with off the shelf junk cam with the Comp de facto LSA which is almost always wrong. So they give up CR (which is HP) and they give up HP because the cam timing is wrong.

Then, they believe the lie that a wide LSA makes the idle so much better that they have to have it. I used to say unhook the tach. The fact is this. If the cam timing is correct for you combo, then the LSA is what it is, and is almost always much more narrow that the keyboard builders think it should be.

Again, I'm 340 inches, 11.08:1 measured and my cam is 255 at .050 on a 105 in at 105 and my junk will idle right down to 750. I don't let it idle that slow, ever but it will. With full timing (36 total) and zero detonation on pump gas. Premium pump gas but that low grade junk is just that...low grade junk.

Does it lope? Yes. Is it miserable to drive and sit at a stop light? Nope. It's doesn't idle any rougher that a cam much, much smaller. Why is that?? Because the lobes were selected for my combo. It isn't magic. It's called preparation.

One last thing. If all the proponents of the silly idea that head materiel makes a difference believe what they say, I should be able to go to 12:1 or even 12.5:1 and change nothing but the heads, just because the aluminum rejects the heat so much faster and better.

Only a fool would do that. I'd bet everything I have and a bunch of stuff I don't have that not a single proponent of the aluminum advantage so called would ever be willing to attempt that change on their own engine. I wouldn't do that. That much CR would require a totally different cam. Regardless of head materiel.

In fact, I've never ever had a single cam grinder tell me I needed aluminum heads for detonation resistance.

The reason why the OE's love aluminum is because it's light (think CAFE standard stupidity), cheap (mo profits), and much easier to machine and easier on tooling (again...show me the money).

Never once was there a consideration of detonation in that decision.

Here's a largely unknown fact. When Honda came out with their aluminum framed dirt bikes the entire off road motorcycling world was in awe of this magical, engineering wonder.

The fact of it was, 4130 chromoly was getting scarce and expensive over on Dai Nippon. Way too expensive. They have no natural resources there and have to import everything. So they opted for the much cheaper aluminum.

It was all profit and availability motivated. I have zero issues with that. I have issue with the myths perpetuated by Honda and the media about why the change was made. It wasn't for any special, secret go fast anything. It was $$$$$.

That's why KTM, GasGas, TM and probably more still make them chassis from 4130. They can get it. And they get it cheap enough to not compromise with aluminum.
 
rumblefish360 said:
Very good point on the exhaust valve since it sees more heat and is normally harder to keep cool. During the over lap period, how much heat comes back in due to the hot valve as well as the gasses themselves is a interesting point to look at. This would be a constant variable due to the amount of engine material combinations of parts used, compression ratio, and cam timing/dynamics of moving the gasses effectively or not.
Click to expand...


Especially on cylinder heads with paired exhaust valves. The localized temps there are much higher. But again...I spent a shitton of time and money on my W5 headed engine moving water around, pulling it from between the exhaust valves of 3-5 and 4-6 and didn't see any measurable power increase. Or loss.

Plugs didn't look any different. Nothing. You can test this stuff until you go broke and not find anything. And I've tested this way more that I should have. It just doesn't matter what the head is made of when it comes to detonation resistance.
 
Phreakish said:
Here's a decent lecture I found on heat transfer:
http://web.mit.edu/2.61/www/Lecture notes/Lec. 18 Heat transf.pdf

Without the accompanying notes, it's incomplete. However, there are useful bits there. In-chamber temperature is lower on an aluminum head (slide 22, page 11). This makes sense. But the amount of energy removed won't be any greater with the aluminum head. The greater conductivity and lower resistance means that for the same energy 'wicked' away, the resultant temperature of the chamber walls will end up being lower.

The lecture also points out that convection is the main means by which heat is conducted, and that until ignition happens, there's little convection going on and so little heat transfer.

One of the slides also lists the exhaust valve and the spark plug as the hottest items in the chamber - which would suggest that proper mixture and spark plug selection matter more when it comes to pre-ignition than cylinder head material.
Click to expand...


Exactly. Spark plugs have been around since the invention of the IC engine, and yet way too many are woefully ignorant of how to select and read a spark plug.

The information has been out there for decades. With the web, it's become even easier to find the information and learn how to do it. All the EFI whatever and such means nothing if you can't read a plug. There is no one size fits all A/F ratio for all engines. Get the plugs correct and happy and THAT is what YOUR A/F ratio should be.

In another thread I talked about CR, pump gas and tune up. That's another reason I know I can run more CR than the nattering nabobs love to prattle on about.

And you'd be surprised how many people I've offered to teach plug reading and only two took me up on it. Guys want a plug and play, fast food, convenience store build but they also was 580 HP and a butter smooth 500 RPM idle like their boring assed Camry. But they don't expect the Camry to make 580 HP.

It's just plain mental and experimental laziness.
 
You must log in or register to reply here.
-

Back
Top