What Is the Ideal Cylinder Head Material for Maximum Horsepower?

[SHARKBITEATTACK]

I'm trying to understand the relationship of thermal conductivity and power in an ICE. I've heard that if you have 2 identical cylinder heads only one was cast from aluminum and the other iron, the iron one would produce more power. (Assuming there is no pre-ignition) I guess this is because the aluminum conducts heat better and as a result more energy is disapated into the cooling stystem during combustion -energy that should be used to force the piston down.

So is there a better material or coating that will allow higher compression without the energy "bleeding off" into the cylinder head?

[Tommy Cookers]

aluminium alloy heads gave more power than iron heads because their better thermal conductivity allowed a higher CR

similarly bronze was used (before valve seat inserts existed to allow aluminium), and one designer thought to use a silver alloy
today beryllium/aluminium 38/62 - 50/50 seems much better due to its remarkably high thermal conductivity (also strength at temperature, and SHC)
if valve cooling is correspondingly good
however, CR can only be as high as the valve clearance volume allows, eg in race engines with very high bore:stroke ratio

coatings primarily work by reflection of radiant heat and preventing carbon deposition ?

[riff_raff]

All other things being equal, and ignoring issues like detonation, it might be possible that the cast iron cylinder head would give better power than the cast aluminum cylinder head. However, you must also consider that the reduced heat load transferred to the coolant with the cast iron cylinder head will only result in higher exhaust gas temps if it is not used effectively.

[J.A.W.]

FE has great heat retention characteristics - for cooking a well-seared steak..

But for a high-performance racing cylinder head, unless it is deemed necessary by reg's - to use it..
..due to FE being the original production-based material.. it is surely best left to the stove top/BBQ..

As an example, check out the Chrysler Hemi design based heads used in 10,000hp top fuel dragsters.. they're not FE heads..

[PlatinumZealot]

FE, Fe, or cast Iron?

[J.A.W.]

FE, Fe, or cast Iron?

Sarcasm, or irony?

But technically, you are correct P-Z, ferrous metal-wise, so do kindly forgive my editorial crew - for not correcting my error..

Back on topic, although the original Chrysler 426 Hemi heads were cast iron..
..factory Al units quickly became available as an alternative for max-power/lightweight 'Super-Stock' SS/AA drag racing..

[PlatinumZealot]

FE, Fe, or cast Iron?

Sarcasm, or irony?

But technically, you are correct P-Z, ferrous metal-wise, so do kindly forgive my editorial crew - for not correcting my error..

Just wanted to be sure that you were talking about iron and not some new fancy material. Like, I dunno, Ferrous something another. So it was a genuine question.

[strad]

The weight-saving advantages of aluminum heads versus cast iron are obvious and widely accepted—especially in drag racing, where weight high up in the front of the car is especially undesirable.

“Cast iron has been used for making cylinder heads since the early days of the internal combustion engine,” noted Jack McInnis of World Products, Louisville, Kentucky. “Its primary advantages relative to aluminum are lower cost and durability. Aluminum’s significant advantages are light weight and relative ease of repair by welding.”

But could the thermal properties of iron offer a power advantage over aluminum? That question gets complicated.

“Thermal conductivity has been debated for many years,” said Kevin Feeney of RHS, Memphis, Tennessee. “Historically, an iron head was considered more durable, and able to make more power due to the fact that it would not dissipate the combustion heat as quickly. With everything else remaining equal, there exists some merit to this argument.”

Mike Downs of Trick Flow Specialties, Tallmadge, Ohio, pointed out that the thermal conductivity of aluminum is “four or five times that of iron. This means an iron head will usually operate hotter. On the positive side, this means the fuel is pre-heated in the intake runner and easier to ignite in the cylinder.

On the negative side, it means the preheated air/fuel mixture will expand, reducing the effective flow into the engine and increasing the risk of pre-ignition. A properly designed aluminum head will transfer heat more quickly to the coolant, leaving the intake runner cooler and therefore able to flow more air-fuel mixture into the cylinder. High-energy ignition systems easily compensate for the cooler intake charge and help achieve maximum fuel burn.”

“The greater thermal conductivity of aluminum is a great advantage,” agreed Chris Frank of Frankenstein Racing Heads, Joshua, Texas, “especially in power-adder applications. That ability to dissipate heat quickly allows for more aggressive tune-ups.”

“Aluminum heads dissipate heat quicker than cast iron,” echoed Torrance, California-based Edelbrock’s Smitty Smith. “This can be an advantage in elimination-style drag racing, keeping the head temperature consistent round after round.”

With aluminum, Tony Mamo of AFR (Air Flow Research), Valencia, California, concurred, “detonation is less likely in an engine on the ragged edge, as it won’t hold as much heat. But that also firms up the argument that a cast iron head on an engine without detonation issues would make more power for the very same reason!”

“You need to build more heat with aluminum to make the same power,” agreed Bill Mitchell Jr. of Bill Mitchell Products, Ronkonkoma, New York, “or compensate by coating the chambers to keep more heat in the cylinders.”

[J.A.W.]

While the 'heat soak' characteristics of Fe cookware works for a great steak..
..it is a disadvantage for racing mills..

Another exemplar of the classic U.S. pushrod race-mill is the XR 750 Harley Davidson..
The 1st iteration used the Fe top end of the then current production Sportster..

..& while champion roadracer Cal Rayborn was successful aboard his..
.. in the freezing conditions of the Easter Trans-Atlantic Trophy races over in Blighty..
..back in the heat of America.. ..the Fe jobs faded out, lost power, & had to quickly be replaced with Al..

[riff_raff]

For a lightweight high performance SI race engine cylinder head, aluminum has been shown to be the best compromise. But it's still interesting to compare aluminum to cast iron for a cylinder head material.

Aluminum does have much better thermal conductivity than cast iron. But cast iron has better elevated temperature fatigue strength capability than aluminum, which means the structure around the combustion chamber can be made thinner using cast iron. This partially offsets the much greater density of cast iron.

For commercial high power turbo diesel engines where weight is not a concern, the heads are cast iron and the pistons are forged steel. With this type of engine the extreme combination of combustion gas pressure and temperature preclude the use of aluminum. By the time an aluminum cylinder head deck or piston crown structure is made thick enough to give adequate fatigue life for the extreme peak cycle pressures involved, it cannot provide the necessary heat transfer rate thru the heavy sections to keep surfaces exposed to high combustion gas temps within acceptable limits.

[gruntguru]

Interesting. Current F1 engines are almost certainly running peak cylinder pressures in the upper range for diesel engines. Of course life expectancy is far lower.

[J.A.W.]

There have even been examples of steel combustion-chamber 'skulls' - being cast into Al cylinder heads..

I'd suggest though, that BMEP/efficiency notwithstanding, the noted large industrial CI mills..
.. are not nearly in F1 territory - specific output-wise, let alone power-to-weight, either..
..so do not have such major heat-soak/component stress-cycle/fatigue issues - to contend with..

[J.A.W.]

One of the engines that featured the steel 'skull' cast into an Al cylinder head was Yamaha's 650 twin..

This mill was race developed to enable Kenny Roberts to win & retain the AMA No 1 plate in the mid `70s..
..however.. despite being a later OHC design than H-D's XR 750, Kenny found himself being out-powered..
( & so Kel Carruthers built a 2T road-racer TZ 750/4 powered dirt-bike for him, but that's another story.)

The race-spec Yamaha XS 750 head mods deleted the cast-in 'skull' combustion-chamber.. see below..
https://thexscafedotcom.wordpress.com/2 ... w72-heads/

[Tommy Cookers]

@ r_r's post

Gilles Simon predicted (for current F1) that part-steel pistons were likely (but not iron or steel heads)
as in car diesels
there is no point in having the head or valves cooler (detonationwise) than the piston crown (as NACA showed wrt the sleeve valve)

regarding heads, modern bronze combines high conductivity with greater strength than iron at any temperature (so might not be heavier)
ie beryllium bronze which these days seems to be called copper beryllium (98% Cu, 2% Be)

we could stop limiting ourselves to cheap casting methods and materials
(castability and strength at elevated temperatures being mutually antagonistic properties)
plenty of engines have had forged aluminium alloy or fabricated heads (detachable or otherwise)

Simon also suggested that optimal CR might be sacrificed for valve size
both fast aircraft and current F1 have of course substantial propulsion compensations for loss to crankshaft power from sub-optimal CR

@ JAW's time-travelling posts

the Ariel VH pioneered and sustained in road-use production a 'spectacles'-type iron valve seating cast into an alloy head
full (bronze) skulls eg Norton's 1934 racer attempts having been quickly superceded (due to seat recession/non-reparability)
though it allowed a 10:1 CR on the 80 octane fuel of the day
the (1935) Mk V KTT Velocette seems the first to have seperate shrink-installed and replaceable valve seats as today

of course alloy heads were then in widespread use in aircooled sidevalve (flathead) motorcycle engines for the CR benefit
(and Lycoming pioneered the aircraft flat 4, made cheaply as a 1 piece (iron) sidevalve block/cylinder casting with alloy heads)
earlier liquid-cooled aero engine designers (eg Napier Lion type) also tried hard with alloy, before insert valve seat technology was viable

[gruntguru]

Slightly off-topic. Can anyone confirm whether all teams use a bolt-on cylinder head? The high cylinder pressures and near-detonation operating point may benefit from an integrated head/cylinder design.