A few more bits of info from engine builders-



From Darin Morgan (was at Reher-Morrison now I believe BES)

"A cast iron block with cast iron heads will make more power than any other combination.
A cast iron block with aluminum heads will make less power.
An aluminum block with aluminum heads will make even less power."



From Larry Meaux (pipemax creator)

"a back-to-back Dyno test on SBC
cast-iron Bowtie Block -vs- alum Block
everything exactly the same, just blocks were swapped
there was 30 HP difference at 600 rpm/sec

another back-to-back Big Block Chevy test = approx 40 HP

another back-to-back SS Hemi test on Cylinder Heads only
with cast-iron -vs- aluminum = 12 HP more w/cast-iron
same flow numbers + port vol CC's

i did another similar test with my own personal SBC dyno test engine
..on the small block Chevy, it was a solid 8+ HP gain with
cast-iron over aluminum head.

the above were actual Dyno tests,
for theoretical HP/TQ differences between alum -vs- iron Blocks
by using FlowBench CFM Numbers -vs- what HP the different
block materials made on the Dyno =>

the results were=> for the same Flow CFM numbers,
i have yet to see an aluminum block engine make
the same HP/TQ that the cast-iron Block engine makes.

so far in all my Data,
the cast-iron Block always 100.0 % PerCent of time
makes more HP/TQ than an aluminum block

since Heat=HP/TQ
i think most of it might have been lost
to aluminum block acting like one big Heat-Sink
and some of it to ring blowby cfm w/alum.

very good discussion guys ! i am learning things as well as confirming things i have thought about for many years.
i have always liked higher engine temperatures [200-205f] than most, but sometimes i have difficulty getting the correct distributor curves [mechanical as well as vacuum advance] for the particular application.
having said that, i realize today's factory high horsepower is all fuel injection computer controlled, as well as using higher engine temperatures, but if using carburetor[s], a knock sensor [or two] plus a retard box is the correct way to go, correct ?
please help me understand how these retard boxes work with knock sensors. the only one i'm even slightly familiar with is the MSD box with the dial on the face, and as i understand it, that unit just pulls timing at a preset rpm ? can it even work with knock sensors ?
my foggy old brain needs some assistance here. TIA !

I don’t disagree with any of that. In fact, I whole heartedly agree that an aluminum block won’t make the power an iron one will. I know this from back to back testing and found it the same every time. I’ve never tested the same with heads, but Morgan and Meaux are two of the smartest, most experienced guys in the field, so I don’t doubt their results with head materiel changes.

What I’m not seeing is how this relates to detonation resistance. IMO it doesn’t, because the transient response time for detonation to occur is so fast the head materiel is of no consequence. I was running higher than orthodox pump gas compression ratios clear back in 1984. And never have I seen an aluminum headed engine take more compression (or an iron head taking less compression) before detonation sets in.

Yes and it was mentioned but just to reiterate, I also don't think all of the power loss from iron to aluminum block is solely from thermal loss but also to a great extent stability/ring seal. (which they also touched on)

[/color]I agree. Some of that power loss is ring seal.


As far as detonation resistance, I think we need to look at it in terms of the title of this thread for starters. The engine masters video was an attempt but I don't think really getting down to where it matters. I think you would need to start with an aluminum headed engine on the edge of pump gas usable then switch to iron to see if it will take the same ignition lead on the same fuel then compare power. At a more realistic/stable coolant temp if we are trying to figure this out for street driven vehicles vs just a drag car. (and I would think that would be the goal)

[color:#FF6600] I agree. As long as the chambers between the two heads are the same, as well as quench etc. then that would be a good test. Who knows, when I get my dyno up and running I may try it if someone wants to pay to do it. As far as coolant temperature I keep all my street/strip stuff at no hotter than 180 and prefer 160. If you can get it down below 160 (which is near impossible in a street car) you won’t have much of a heater/defrost. At that point, you no longer have a real street/strip pump gas deal. But 160 is easily doable and it reduces detonation tendencies by an order of magnitude.


When they start with an under 10 to 1 engine and high 130's coolant temp and a decent bit of cam, you're miles away from being detonation sensitive no matter what the head is made of.

[/color] I agree.

Yes of course you can transition into detonation instantaneously, I just have a different viewpoint of how heat conduction can affect this, regardless of how fast this can occur.

As a different example, I've calibrated hundreds if not thousands of supercharged GM vehicles with factory piston squirters. Replacement engines that delete these are notably more sensitive to detonation at both part and WOT and do not take as much lead at WOT compared to a stock shortblock. That being said, I don't think the amount of heat squirters could pull out of the piston compares to how much heat a combustion chamber could transfer, especially if we are comparing a material multiples more effective at doing so. (and transferring to a much larger completely surrounded volume of coolant much more efficient itself in heat transfer than oil)

[color:#FF9900] I don’t disagree with this. I think piston oilers are a big deal. I think every engine can use them, but most of the old junk I work on/with doesn’t lend itself to retrofitting piston oilers. If I could do piston oilers I would.

To that example, if the idea that everything is happening too fast for it to matter was true, I don't think you would see much difference with piston squirters, nor do I think manufacturers would bother spending money on them, if they didn't matter.

If you're on board with the idea that when approaching the edge of detonation on a particular combo, that heat can push it either way (safer or over the edge) and also don't dispute Morgan and Meaux's observations on HP output vs material differences, I think it's fair to conclude that if you had an aluminum headed engine on the edge of detonation on a particular fuel that switching to an equally capable iron head may put it over the edge due to it's lesser ability to transfer heat as efficiently.

[/color] I’m not sure about this one. There certainly is some power loss because you lose some heat through the aluminum, but IMO crap ring seal is the big power loss. I just cringed when a guy came in with a NA program and he was dead set on switching to an aluminum block. I knew it would lose power and I knew ring seal would be garbage after 5 or so heat cycles. The difference in surface area between a pair of heads and a block is huge. I’m sure someone on here who is good with math could calculate the number of BTU’s it takes to get an aluminum block from ambient to operating temperature, but I’d bet it’s significant. And then they could calculate how many BTU’s is required to keep an iron and aluminum block at the same operating temperature. Again, I’d bet it would take a significant of heat (power) just to maintain that temperature. And again, it would take less heat (power) to keep the iron block at temperature than the aluminum block. And that is a power loss.


Otherwise what would account for the power difference?

[color:#FF6600] Ring seal and the amount of heat it takes to retain operating temperature.

Just speculation but as far as your observations of never seeing a difference in what engine would take more compression (vs head material), is it possible that like the engine masters comparison, that the engine, whatever it was, was not on the brink of detonation vs the fuel used, with either cylinder head?

[/color] It depends on who you ask, but most would tell you I run everything on the edge of detonation. I spent the last weekend working with 4 different pairs of tunnel ram carbs, and according to the “gurus” standing around, I was going to send every one of them into detonation. The plugs agreed with me, and all four of the owners are happy today with how their tunnel rammed engines are performing on the street. As a reference, one of them is a 632 Chevy with Big Chief heads and a pair of 1600 CFM Twin Blade Dominators on it. A quick shout out to Trevor at Get’M Performance. A super sharp guy and he is willing to help. He pulled my chestnuts out of the fire twice last weekend.

Lastly, again, not trying to say there's a miraculous/huge difference, just in cyl head material difference, but I do think it's notable and measurable, for good reason. At least something to be considered, when planning a combination, including vehicle weight, trans type/converter/gearing, intended use (what kind of load it will see)/fuel/etc.

[color:#FF6600] I can’t disagree with this either. I think one mistake some guys make is they don’t think in terms of combination. Your last sentence sums it up pretty well, but one metric you didn’t mention was the driver. One guy I worked with last weekend didn’t drive in a manner that would cause me to build him an engine with more than about 10.5:1 ever. He had a 4 speed and he didn’t downshift near enough to warrant another point of compression regardless of what the heads are made of. He drives his street/strip car like he’s driving a Prius. In a corner where were I were driving I would have dropped all the way to first gear he just lugged it out of the corner in third. It doesn’t matter what you do, if you build an engine for a guy like that with unorthodox compression ratios he will drive it into detonation no matter what you do. You have to build and tune for the end user and how they drive. If you don’t, you can end up eating a poo sandwhich.

Drop your coolant temp 40 degrees, block of any heat to the intake manifold, use a quality annular booster and a relatively high compression pump gas engine will make way more power.

heat is always blocked no matter what intake is used. i have experimented with coolant temperatures between 180-210f, and it doesn't seem to be much difference. what i have noticed, however, is gas mileage is noticeably better at 205 than at 180. these are street/some strip engines. i know mileage means nothing in this discussion, but could that mean a better combustion process at elevated temperatures due to me NOT correctly putting a package together, or choosing wrong components ?
i have never asked anyone about choosing a cam, although i like around 240-270 duration @.050. just because that's the way i have always done it. also 3.90 to 4.30 gear sets with a 3000-4000 converter stall so the engine doesn't lug.
it now comes down to ignition timing, carb tuning, and exhaust experimentation. i realize when a guy can hear a "ping" inside, there is more happening inside the engine that is not good. this now brings this "old duma$$" to think about knock sensors, retard timing, and coolant temperatures.
thank you mr. mad scientist, for taking the time to help me get my head around the items i have been screwing up all these past years !