Heads Iron Vs aluminum
 

Not reinventing the wheel,just making a basic 525 sc. A lot of things have improved since it was designed, The 731 cam is supposed to be a nice improvement and I have one of those. Using a merc mag bottom end freshened up. A lot of posts and discussion has stated the original compression ratio was exceedingly low and that something around 8.5;1 would work a lot better so I am aiming in that direction. (making about 5 psi boost on top of that)

Now the heads. I have some mag heads, but head tech has changed dramatically. With heads like EQ cast irons and Promaxx aluminum not being a whole lot more that completely going thru my old heads.

What are the pros and cons of each? Assuming that properly sized either would outperform oem.....

your thread title confused me as i have never seen a steel head then i figured you might have meant aluminum.anyway,i am one of the dumb guys who still feels that their are advantages to using an aluminum head other than the weight saving.i do believe that the eq head is a lot of bang for the buck espically for the budget builds.i am building an engine right now that is going to have a set of them.i know nothing about the promaxx but we have a guinnie pig[getrdunn] experimenting with some so we will get some good information about them soon,the are looking like they may be ok but time will tell.imo a crane 731 cam,8.5-1 c/r eq heads would be a good combination for a 177 blown deal.i will be watching your build and i hope it makes good power.

Fixed, thanks Mike...

Getting closer on the title. If you give it just one more shot, I bet you nail it. :whistle:

Isn't that 177 a tiny blower that needs to be Overdriven?

How much power you looking to achieve? 731 is a good cam for that 177 combo but are you going to run intercooler? I see there was a couple for sale on swap recently. That actually raises a question though that I personally have no experience with. But just shedding some light on the subject. Intercoolers are used to lower air temps/charge correct. So in a sense would aluminum heads help keep the temps down as well. Another scenario what if you have both aluminum heads and intercooler. I'm just pondering this but it does make sense if you just think about a little. I know MT did a bunch of temp testing so and recently post but I'm not so sure about intercooler with aluminum heads. Again what's mercury doing on their sc builds. Their R&D has to be astronomical.

No intercooler. Powerwise, Somewhere slightly north of 550.

From what I understand on what I have read, on the 177 an intercooler adds some restriction, so you need to speed up the blower even more to compensate creating more heat. So my mind sees that as somewhat of a wash. Also by raising the static compression about a point over what merc ran in the 525sc, I can run the same boost and make more power

While we are thinking of such things, the alum head will take a point more of compression from what I am told. Now would alum heads allow me to run run 91 vs 93? I have a 60 gallon tank and would like to be gas dock friendly if possible,

Yes true on intercoolers. Would definitely wanna research what one to get if you did. Your goal of 550 plus will be achieved easily with cam and static comp bump. They run extremely fat also if your running stock 525 sc 1050 carb. You'd have to tune a bone stock 525 sc to come close to actually 525.

the merc 525sc makes 525 at the flywheel according to mercury marine.with a static c/r of 7.5.1they still required premium fuel.imo,with a good tuneup 89 oct would work just fine.i never understood why they wanted premium fuel,maybe old school thinking,maybe to get it past the warranty period.

DAve said the ones in the Donzi would ping on 89 but only if you really leaned into the boost for a stretch. His opinions on the motors after running them for several trouble free years has been one of the deciding factors going that way. Also why I not trying to get more out of them per say, just updating them with the tech thats avail today. A lot has changed in 15-20 years.

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.

mild,,you have knock sensors on your engines?

I do not, but Icedppl does

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.

Absolutely.

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/

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

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

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.

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

Already have a 177 and manifold both sets of pulleys etc on the shelf. It's easy to get caught up n the bigger blower make more power deal.! But there are 2 things holding me back...

1. I don't want to start eating drives

2. I have a 22 foot boat and a heavy hand, I don't want to get dead......

Fixed it. :poopoo:

Hopefully drives aren't a big deal on the light weight single. The dead part though, that makes since. Are you going to have to modify your hatch? My main reason for not sticking with a 525SC build.

Understand having the 177. Just thought the 250 is so much more efficient , less heat more power.

Work with what you got .

Drive it like you stole it

yep, gonna have to modify or build new hatch. from rough measurement I need about 4 inches more room.

Rob, not to sidetrack your thread, but are you planning on upgrading the drive somewhat?
I was / am in the same boat as you are.
Steel tower, hard shim, blueprinted and so on?

Most likely, after the first time I blow it up..if its fixable,,,,

Your drive will be fine. What I don't get is #2 I don't want to get dead?

You've seen me run a boat with 300 hp...now double that.....

Is alunimum like awuminum ? :evilb:

:Score-101010:

Only after several capt and cokes....

I think we messaged about my build.

454 bored .060 over
L2399 pistons- 8.75 compression
Crane 134561 Cam Style: Hydraulic flat tappet

Basic Operating RPM Range: 3,000-6,000

Intake Duration at 050 inch Lift: 236

Exhaust Duration at 050 inch Lift: 246

Duration at 050 inch Lift: 236 int./246 exh.

Advertised Intake Duration: 296

Advertised Exhaust Duration: 306

Advertised Duration: 296 int./306 exh.

Intake Valve Lift with Factory Rocker Arm Ratio: 0.553 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.571 in.

Merc HP500 heads. 2.25 intake 1.88 exhaust

525sc/177blower
dominator carb

Made 572@5600 on the dyno. That was with the engine on the cool side. After the blower got warm, the pulls flattened out to 550-552hp on the later pulls. I have 60 hours on the setup. Runs great all the time, runs even better on cool days. I suspect a chiller is needed on a 177.

Those cams sound good on 454/468. Get as much air in and out of there as possible. You have scoops or enough clearance without. Install extra vents if need be. Intercooler pros and cons.

Howsmit running with that static compression? what kind of fuel?

Runs perfect. I have been told that is what merc should have used with the small blower. I also run 34* of timing. I use 91 non-ethanol. All marinas and many stations have it.

The small or big upper pulley?

I don't know if my pulley is small or big. I do know its 1/2 the diameter of the crank pulley. Makes about 4.5psi to 5psi of boost.

Im full of questions tonight...since I am looking at a 242 without motor... how well does it fit back there?? hatch clearance etc....??

Pm endeavour32
He had one years back and was in and out of the bilge I know that for sure.

My 242 is an 86. It has about 2.5 inches of clearence. If your boat is an 87 or newer, the hatch is a few inches taller than the 86 and older boats.