iron head vs aluminum head combustion heat

[seefour]

I have heard that a iron head will produce more power than aluminum all things being equal except the head material.
Is this true? the iron traps the heat and aids better in ignition<???
has anyone tried a thermal coating in combustion chamber to trap the heat with aluminum?

[TMSJoe]

I have read that many times but have never had the opportunity to prove it.

[pitts64]

I always thought aluminum was more for the weight savings then anything else...

[Cobra720]

Cheaper to make (cnc) easier to repair I would think.

[twl]

Yes.
Yes.
Yes.
Aluminum conducts heat faster and better than iron, so some higher amount of combustion heat is lost into the aluminum casting, vs iron.

The difference may be small, but it is often referenced when setting ignition timing.
Many people, including myself, have used thermal barrier coatings in aluminum heads to good effect. I can't say I recorded any measurable power differences which could directly be isolated to that coating alone, but the aircooled head runs cooler with the coatings.

[Schurkey]

I sort-of remember a magazine test where they took iron and aluminum castings from a certain manufacturer, which were "supposedly" identical in port shape, combustion chamber shape, etc.

They ran them on a dyno. The aluminum heads made more power than the iron heads, which was not the expected outcome.

This was a long time ago; I don't remember which magazine or what heads were selected. I'm sure it was SBC based.

[boiler man]

from a heat transfer standpoint common aluminum will pass 136 BTU per hour per square foot of surface, iron will pass 46.33 BTU per hour per square foot of surface. Iron will pass .12 BTU per pound, Aluminum .24 BTU per pound. The rate of transfer changes based on the alloys that are used. But aluminum basically passes 3x the heat to the cooling system that iron will. The reason why iron heads are not guaranteed to make more power with all things being equal is because all things are usually not equal.


Dave.

[racear2865]

This came up several years back with Smokey Yunick at a PRI seminar (I think). He said "all things being equal that cast iron would make more power. He then came right back and reminded us of the weight savings and repair ability of aluminum. He then said that in order to get more heat retention in aluminum--he poured sodium silicate in the water ports of the aluminum head and then rotated it on a rotisserie for 24 hrs or sumtin to that effect. It also helped to seal any porosity problems. He especially did it after he welded the heads. I have never tried this, so me dont know
reed

[PackardV8]

That cast iron heads make more power is proved by the fact every race engine in the world today, F1, Top Fuel, Pro Stock, NASCAR uses iron heads. Oh, wait, no one races iron heads . . . . .

[racear2865]

That cast iron heads make more power is proved by the fact every race engine in the world today, F1, Top Fuel, Pro Stock, NASCAR uses iron heads. Oh, wait, no one races iron heads . . . . .

I totally agree. Used to there was quite a large difference in cost of aluminum versus cast. Not any more. So why would you go to cast unless tied by rules
reed

[wyrmrider]

go to cast iron
or
go to cast aluminum
?
vs billet ?

[groberts101]

I use coatings on all my personal stuff and have often seen greater cooling temp reductions with AL vs Cast. Not much overall difference in final temps when the coatings are used on either or.. but slightly greater percentage of change when coatings are used on AL. That alone tells me there must potentially be greater heat transfer occurring between the two materials and coatings are effectively closing the gap differential between the two materials.

I've found coatings will allow more aggressive tunes while also simultaneously improving safety margin/hotspot reduction/burndown time.

Either way you go here... the splitting of fine hair will be required to weigh such small differences. And those hairs get even finer when we're talking moderately powered street stuff rather than full race duty.

[MadBill]

This came up several years back with Smokey Yunick at a PRI seminar (I think). He said "all things being equal that cast iron would make more power. He then came right back and reminded us of the weight savings and repair ability of aluminum. He then said that in order to get more heat retention in aluminum--he poured sodium silicate in the water ports of the aluminum head and then rotated it on a rotisserie for 24 hrs or sumtin to that effect. It also helped to seal any porosity problems. He especially did it after he welded the heads. I have never tried this, so me dont know
reed

I followed that procedure, which was in one of his books, circa 1978 with my ZL-1 aluminum BBC heads. AIR, it went like this:
1. Clean the water jackets out ultra-well.
2. Bolt sealer plates onto head surface and all water outlets save one, which is fitted with a quick-connect air fitting.
3. Heat the head to 250° F. for at least an hour.
4. Pour a quart of water glass (Sodium Silicate) into the open port, cap it off and apply 100 psi air pressure.
5. Slosh the head around for a few minutes to distribute the liquid, then let sit for 30 min. or so, turning occasionally.
6. Release air pressure, remove plates and allow solution to drain.

I don't know how effective it was, but my then ~ 650 HP 495" all-aluminum BBC never gave a hint of overheating in my stock system '70 -1/2 Z28.

[BOOT]

I'm surprised no one has mentioned what I always hear bout alum heads and that's how they will tolerate more compression with the same octane(heat dissipation). I like iron because it's stronger.

[140Air]

This came up several years back with Smokey Yunick at a PRI seminar (I think). He said "all things being equal that cast iron would make more power. He then came right back and reminded us of the weight savings and repair ability of aluminum. He then said that in order to get more heat retention in aluminum--he poured sodium silicate in the water ports of the aluminum head and then rotated it on a rotisserie for 24 hrs or sumtin to that effect. It also helped to seal any porosity problems. He especially did it after he welded the heads. I have never tried this, so me dont know
reed

I followed that procedure, which was in one of his books, circa 1978 with my ZL-1 aluminum BBC heads. AIR, it went like this:
1. Clean the water jackets out ultra-well.
2. Bolt sealer plates onto head surface and all water outlets save one, which is fitted with a quick-connect air fitting.
3. Heat the head to 250° F. for at least an hour.
4. Pour a quart of water glass (Sodium Silicate) into the open port, cap it off and apply 100 psi air pressure.
5. Slosh the head around for a few minutes to distribute the liquid, then let sit for 30 min. or so, turning occasionally.
6. Release air pressure, remove plates and allow solution to drain.

I don't know how effective it was, but my then ~ 650 HP 495" all-aluminum BBC never gave a hint of overheating in my stock system '70 -1/2 Z28.

Bill, what did you think was the mechanism of the benefit? You had overheating before?