MILD THUNDER

iTrader: (3)

It is true, that aluminum, does dissapate heat much faster than iron. The problem with "iron" heads, heating the air charge, stems from car days. You take a car, that has 200+ degree coolant temps, insane underhood temps, idling around town, the air in the intake manifold track, can certainly become preheated. You then crack open the throttle from a red light, and bam, you just shoved some hot crappy air down the engine.

Now, in a boat, we aren't running 200+ degree coolant temperatures. My personal engines, aren't even running a water thermostat. My engines metals, aren't getting very hot at all. I have water jacketed exhaust, that also isn't adding heat to the engine room.

At 3000, 4000, 5000+ rpm, the engine is taking in, and expelling, ENORMOUS amounts of air. The air being drawn in, has very little time spent, in the intake port. We are talking nano seconds. The air may be traveling at a rate of 300 feet per second! The combustion event, takes nano seconds, from ignition to completion at higher engine speeds. The combustion chamber surface temperatures, can range from 250-500 degrees. When SAE engineers did many studies with temperature probes at various locations throughout the cylinder heads combustion and valve areas, it did in fact, have a cooler surface temperature, with aluminum. The simple fact, the aluminum transferred heat into the water jacket better. Keep in mind, the actual peak temperatures during combustion, are much, much higher. Well over 2,000* F. and exhaust temperatures, in the 1200-1500+ range.

IMO, the advantages of aluminums cooling benefits, have more to do with cooling system sizing needs, than it does with combustion quality. Matter of fact, today, some are using specialty coatings, on pistons and combustion chambers, to help KEEP the heat in the chamber, and out the exhaust, rather than the energy be absorbed into the radiator.

Most of the guys who tell you aluminum heads are better because they cool things down, usually have the deer in headlights stare, when you start questioning them about the cylinder cooling effects from camshaft overlap, EGR valve function, mixture swirl, exhaust scavenging, and so on.

Theres a million things that play a factor into what is "safe" , things much more critical than the cylinder heads material. I know of quite a few marine engines, running around with cast iron cylinder heads, making 800, 900, 1000+hp with zero issues.

Offshoreexcursion had a set of stock 8.75:1 500EFI's, with 8.5lbs of boost , that went 300+ hours. I certainly wouldn't recommend him switching to alum heads, and raising the static to 9.75:1 and running the same boost. Tons of other guys have supercharged those engines, as well as HP500's and ran the crap out of them. Icdedppl, had dart iron heads, that had no issues non intercooled running 6-8lbs of boost and 34-35* of timing with 8.5:1 static.

sutphen 30

mild,,you have knock sensors on your engines?

MILD THUNDER

iTrader: (3)

I do not, but Icedppl does

SB

iTrader: (1)

Don't forget, Until Dart and then a little later Protopline (which RHS picked up and hich EQ picked up RHS) made cast iron heads, the factory and Merlin heads combustion chamber leaves a lot to be desired in unported form. Combustion chamber design has lots to do with both timing requirements and detonation tendencies.

Aluminum aftermarket heads where designed with better, more modern combustion chambers way before cast iron's where.

MILD THUNDER

iTrader: (3)

Absolutely.

MILD THUNDER

iTrader: (3)

thought this was interesting . They did an iron vs aluminum comparison on the dyno, and found really no change in anything. What I did find interesting, was that the engine made more power when running coolant temp at 110*, vs 185*. Quite a bit more power as well.

http://www.hotrod.com/articles/ccrp-...er-heads-test/

css19

as far as I know is not good that the engine is running at low temperatures
ideal operating temperature otto engine is 90 Celsius
why not put intercooler, water to air? will reduce the inlet air temperature, and add a little power
I really do not know how much belt driven blower raise the temperature of inlet air

css19

for me it is somehow logical that there is little difference between the two heads on the same engine
and this with the operating temperatures is somewhat a surprise to me, but I'll put on my engine thermostat

Baja Rooster

iTrader: (1)

I see a big advantage of aluminum over iron primarily being it's a lot easier to take a grinder to them. If you have a nice clean set of iron heads I would lean that way just because I *believe they are more stable in the long run.

*Im not an engine builder and can barely even google.

tommymonza

Why not use a 250 blower? You already have the 177?