Aluminum heads
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.
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.
