Issues with using Aluminum heads on Iron Engines

[Bigdave196]

Ok, were in a discussion in a different thread and one of the ideas to bring up HP was to change the factory cast iorn heads/intake manifold over to an aluminum heads and intake. I know that in a auto setup where your running a sealed cooling system that this helps with power and weight, but I have had several marine mechanics and the guy who rebuild my motor tell me that this causes some kind of electric charge that over time magnitizes the block due to a reaction between the water flowing thru the different metals. This is supposed to be on a normal Lake supplied cooling system and not a sealed system.

Was I mis informed by an "urban legend" or did I just mis understand?

Thank you.

 

[greenwell001]

Re: Issues with using Aluminum heads on Iron Engines

big dave read my reply on the other thread

 

[180shabah]

Re: Issues with using Aluminum heads on Iron Engines

Just how mouch powr are you looking to make?

 

[JustJason]

Re: Issues with using Aluminum heads on Iron Engines

electric charge that over time magnitizes the block due to a reaction between the water flowing thru the different metals

Well it doesn't magnatize the block.
But if you put 2 dissimilar metals (such as cast iron and aluminum) and an electrolyte (water is an electrolyte, saltwater is a better one) you make a battery. Batterys make electricity and electricity speeds up corrosion/galvanization.

 

[mkast]

Re: Issues with using Aluminum heads on Iron Engines

Was I mis informed by an "urban legend" or did I just mis understand?

In non destructive testing, one form is magnetic particle inspection.
The most common method of magnetic particle inspection uses finely divided iron or magnetic iron oxide particles, held in suspension in a suitable liquid (often kerosene). This fluid is referred to as carrier. The particles are often colored and usually coated with fluorescent dyes that are made visible with a hand-held ultraviolet (UV) light (sometimes referred to as black light). The suspension is sprayed or painted over the magnetized specimen during magnetization with a direct current or with an electromagnet, to localize areas where the magnetic field has protruded from the surface. The magnetic particles are attracted by the surface field in the area of the defect and hold on to the edges of the defect to reveal it as a build up of particles.

To magnetize the part, in this example use a crankshaft, considerable direct current is required to magnetize the crankshaft, way more than can be generated through galvanic corrosion or electrolysis. The crankshaft is demagnetized with alternating current after testing.

There are other considerations when using aluminum in a marine environment, magnetizing the engine isn't one of them.

 

[mylesm260]

Re: Issues with using Aluminum heads on Iron Engines

Couple things:

#1. Yes, there is truth to this. I believe the term is called electrolysis.

Generally speaking, two different types of metals + and electrolyte (in this case salt water) = corosion

Different types of metals react differently (some worse than others)
Having a current go through them also make this worse (for example, the - side of the alternator going through the bracket, through the head, through the block, and to the battery via the ground cable on the starter)

Having said all that, If you boat in fresh water only, or if you have a heat exchanger, I woudn't worry about it.


Also, be very careful when choosing aftermarket heads.

Remember that GM itself offers two grades of heads already, vortec and non vortec.

Pretty much all the available aftermarket heads will be better than the gm non vortec heads, but many of the aftermarket heads perform about the same as vortec heads.

To get any kind of real improvement, you have to go with the pricey aftermarket heads like air-research.


And remember, any improvement you get from better head flow is going to be in the "top end" it will not help you make more bottom end torque. So if you find you need a bigger prop to hold you're rpms back, you will be sacrificing hole-shot.


I personally think aluminum heads on their own is not worth it. However, if you used it as a piece of a build, they can help significantly.

The 383 guys have got it right. They get more displacement, more compression and better flow (with good aftermarket heads)

This gives them more power across the board.



You know though.... for the money you're considering spending, you would be much much better off to marineize an LY6. I plan on doing this in the offseason.

LY6's are 100% aluminum already (block and heads), and the GM production vortec 6000 they put in their trucks is already pretty much marineized (minus a couple things of course)

I've already tracked down manifolds, and all the other necessary parts are available from GM.

I was hoping to get a couple guys together on this forum, and we could go through it simultaneously, and make a "how to"

 

[n2ostroker]

Re: Issues with using Aluminum heads on Iron Engines

And remember, any improvement you get from better head flow is going to be in the "top end" it will not help you make more bottom end torque. So if you find you need a bigger prop to hold you're rpms back, you will be sacrificing hole-shot.

This is untrue to say the least.
Anytime you increase low, mid, and high lift flow you will increase hp and torque across the board. That's like when someone said porting only gives top end power. Very untrue..
Aluminum heads are great. You can get a good port and combustion chamber in iron. But the weight and combustion chamber efficiency will never be there.
They are more expensive but you gotta pay to play and I'm guessing far less than trying to adapt a whole new engine to a marine environment that has never been mass produced to do so. If you're going to look at that there are companies that make LSX motors for marine use.


The corrosion being talked about is galvanic corrosion. It is where your motor basically turns into a battery and eats itself from the inside out. On freshwater or a closed cooling system the boat will be worn out before you eat through the aluminum. It's the same reason Merc uses zinc anodes. The zinc gets sacrificed before the aluminum does.

 

[mylesm260]

Re: Issues with using Aluminum heads on Iron Engines

This is untrue to say the least.
Anytime you increase low, mid, and high lift flow you will increase hp and torque across the board. That's like when someone said porting only gives top end power. Very untrue..
Aluminum heads are great. You can get a good port and combustion chamber in iron. But the weight and combustion chamber efficiency will never be there.

You need to read up on volumetric efficiency.
http://en.wikipedia.org/wiki/Volumetric_efficiency

Here is a link to an actual dyno compairison between aftermarket aluminum air-flow research heads and stock heads.

Notice how the aftermarket aluminum heads make the same (actually slighly less) torque bellow 2700 RPMS?


So in fact, saying that aftermarket heads don't give you more bottom end torque is absolutely true. The volumetric efficiency of a small block chevy is already pretty much maxed out in the lower RPMS. The flow restrictions of the stock heads don't become an issue until higher up in the RPM range.


Now, if the heads resulted in a higher compression ratio, that would be different.

And yes, the same is true of a port and polish, it does NOT give you more bottom end torque.

In fact, it takes AWAY from bottom end torque. Why are heads not ported and polished from the factory? Production engines are built for torque and fuel economy, not balls out top end power.


If he goes with aftermarket heads, he will make more power in the upper RPMS.

In order to make that power usefull, he will need to prop higher.

Propping higher will sacrifice hole shot.

 

[180shabah]

Re: Issues with using Aluminum heads on Iron Engines

It's the same reason Merc uses zinc anodes.

Merc hasn't used zinc in about 15 years. All aluminum from the factory.

 

[n2ostroker]

Re: Issues with using Aluminum heads on Iron Engines

You need to read up on volumetric efficiency.
http://en.wikipedia.org/wiki/Volumetric_efficiency

Here is a link to an actual dyno compairison between aftermarket aluminum air-flow research heads and stock heads.

I know what volumetric efficiency is.....
No, a stock small block head is not near 100% efficient. Not even close.
You can't compare an LS motor to any older Chevy motor vortec or non. Not the same motor. You also can't compare a 205cc LS-1 head or any 205cc head to any Gen 1 or 2 stock head of 155-165cc totally different animal. You don't have to have a huge port to make power.

I'm not bench racing on the internet but I think you need to go and do a little more research to find out what works and what doesn't.

 

[n2ostroker]

Re: Issues with using Aluminum heads on Iron Engines

In fact, it takes AWAY from bottom end torque. Why are heads not ported and polished from the factory? Production engines are built for torque and fuel economy, not balls out top end power.

Really...
I could have swore it was because they made millions of them and they had work on numerous applications.

 

[AZSenza]

Re: Issues with using Aluminum heads on Iron Engines

Aluminum heads will corrode-eventually. As long as you arent going crazy with a 3 grand set, you'll be fine. The weight saved with aluminum heads and intake (and I would also recommend aluminum exhaust manifolds and risers) will wake your boat up as much as the horsepower. There are heads out there for 1K$ a set. You can also raise your compression a full point due to the better heat transfer of aluminum. They do warp easier and dont take the abuse cast iron can. If I had the money, I'd be doing it.

 

[jaxnjil]

Re: Issues with using Aluminum heads on Iron Engines

Merc hasn't used zinc in about 15 years. All aluminum from the factory.

true but every one still calls them as zinc anodes; and doesn't mercruiser still use two different metals for anodes? one for fresh and one for salt.
also OP is from provo utah. while there are some fresh water lakes over there, theres nothing saying boat wont end up on the great salt lake




any way for the original poster. no not a urban legend; your getting sound advice.

in fact quite doable. doable and practical are; to some people the same thing.
you might want to look up 470 mercruiser and get more insight on mixing block head material.

 

[mylesm260]

Re: Issues with using Aluminum heads on Iron Engines

I know what volumetric efficiency is.....
No, a stock small block head is not near 100% efficient. Not even close.
You can't compare an LS motor to any older Chevy motor vortec or non. Not the same motor. You also can't compare a 205cc LS-1 head or any 205cc head to any Gen 1 or 2 stock head of 155-165cc totally different animal. You don't have to have a huge port to make power.

I'm not bench racing on the internet but I think you need to go and do a little more research to find out what works and what doesn't.

I spent 20 minutes looking for a dyno comparison of a stock 350 vs 1 with aftermarket heads, that was the only one I could find, and yes, I know it's an LS1.

Same concept though. You're increasing the flow of the head.


Some info about VE.

At lower RPMS, smaller runners and smaller valves will give you more VE. This is because you get a higher port velocity.

Going to Bigger valves and bigger runners gives you better flow in the higher RPMS.


The VE of a gen 1 small block is already pretty close to the limit for an NA engine in the lower RPMS.

The only real way you could increase the VE of a gen 1 small block in the lower RPMS is to have longer intake runners or longer exhaust runners (headers) with the correct aspect ratio (diameter vs length) or an even more conservative cam profile.

In a marine application, this isn't possible.

If you would like to go on google and find a link to a dyno that shows aftermarket heads making more bottom end torque on a gen one small block to prove you're point, then go for it.

Link to AFR's Dyno page

All AFR's dyno's are for packages. And notice WHERE the engines are making peak HP? 5500-6000? Not really usefull in a boat.


Also, look at the two dyno graphs.

The one on the left is a 383. They START their dynos at 2500 RPMS (for a reason)

at 2500 RPMS, the 383 is making 460 ft/lbs of torque.

At 2500 RPMS, the 350 is making 360 ft/lbs of torque.

Also notice the angle of the curve. the 383 has a flat ish torque curve at 2500 RPMS, you can tell its going to make good torque even at 1500 or 1200.

The 350's torque curve is on a steep angle @ 2500, you can tell that at 1500 it is going to be making SIGNIFICANTLY less torque.





Hey don't get me wrong, There is a LOT of room for improvement on the stock heads, but don't be fooled and think that by simply bolting on a new pair of heads, that you're going to have more power across the entire band, it simply isn't true.

 

[mylesm260]

Re: Issues with using Aluminum heads on Iron Engines

Here.
Look at these.

The official specs for a GM marine 5.7L

So at 2500 RPMS, a BONE STOCK GM MARINE ENGINE is making 360 ft/lbs of torque (FROM GM MARINE'S WEBSITE)

AFR's DYNO website

This is a custom built 350 using the pretty much the most expensive and best regarded aftermarket aluminum heads for the CSB.
And at 2500 rpms, the engine is making *drum roll please* 360 ft/lbs of torque.

SO. Using links to GMmarine, and AFR, I have proven that aftermarket heads do NOT give you more bottom end torque.

In fact, if you look at the angle of the dyno graphs, at 1500 RPMS, the bone stock gm marine 5.7L would be making MORE torque.

torque @ 1500 RPMS is basically you're hole shot.

I would argue that at 1500 RPMS, the AFR heads are marking 20% less torque than a BONE STOCK GM MARINE 5.7.

Why do you think GM posts their dyno graph almost down to idle, and AFR STARTS their dyno graph @ 2500 RPMS?

Really...
I could have swore it was because they made millions of them and they had work on numerous applications.

Again, LOOK AT THE DYNO GRAPHS, a chev pickup truck will spend 95% of it's life bellow 2500 rpms.

The STOCK heads are clearly better bellow 2500 rpms. If they ported and polished their heads, or if they ran aftermarket heads, then the engine would have a LOWER VE below 2500 rpms, and would make less torque and get worse mileage.

I know what volumetric efficiency is.....

You obviously don't.

Here, maybe this explanation will help.

Atmospheric pressure is 1 bar (14.7PSI)

Let's use a garden hose and a garbage can as an example.

Let's say you had 4 minutes to fill a garbage can with a 1" hose.

Would you get it full? Of course you would, 4 minutes is a long time.

Now, let's say you had 30 seconds to fill the garbage can with the same 1" hose. Would you get it full? probably not. a 1" hose doesn't flow enough water to fill it up in that amount of time.


Now, using the same 4 minute example, what if you had a 2" hose, flowing 3 times as much water.

IF you can fill the garbage can to 100% with a 1" hose, then will a 2" hose fill it any more? of course not, the garbage can can only be filled to 100%

But, if you tried to fill that same garbage can in 30 seconds, then the 2" hose would make a huge difference.


Filling you're cylinders with air at low RPMS is like filling a garbage can with water in 4 minutes, you've got plenty of time to get it full.

Filling you're cylinders with air at HIGHER rpms is like filling a garbage can with water in 30 seconds, or 15 seconds or 5 seconds. The flow of the water (or the CFM through the head) makes an enormous difference.

remember, as RPMS increase, the "window of time" (intake duration) decreases. There is less and less time for the air to flow into the cylinder.

How "full" you're cylinders get with air is you're volumetric efficiency.

If your piston is all the way down, and you're cylinder pressure is 1 bar, than you're VE is 100%.

If you're engine moved at 1 RPM, you could have 100% VE while breathing through a tiny pin hole.

So when I say there is no room for improvement without longer intake runners, exhaust headers, or different cams, I'm basically saying that bellow 2500 rpms, the cylinders are already getting "filled" to 100% (14.7PSI absolute)





You may also ask how do the after market heads make LESS torque @ 1500 RPMS?


Think of it this way.

if you had a 1/2 HP water pump pumping water into a 1" hose. When you turn the pump on, it may take 2 seconds for the hose to fill and the water to start flowing.


If you took the same 1/2 hp water pump and pumped water into a 3" hose, when you turn the pump on, it may take 5 seconds for the hose to fill and the water to start flowing.


So if you turned the pump on for 6 seconds:

The 1' hose would fill for 2 seconds and flow for 4
The 3" hose would fill for 5 seconds and flow for 1


So in an engine, it's a trade off. Smaller valves and smaller ports will yield higher port velocities and will result in MORE bottom end torque.

 

[jtybt]

Re: Issues with using Aluminum heads on Iron Engines

As has been addressed, aluminum heads don't increase HP/torque where it's needed in a marine application. What it does do is have a cooler combustion chamber temps which lowers the chance of detonation under load. This may let you use lower grade gas or run a bit leaner fuel/air ratio or increase compression during build.

Your biggest plus is probably the weight loss.

 

[mylesm260]

Re: Issues with using Aluminum heads on Iron Engines

As has been addressed, aluminum heads don't increase HP/torque where it's needed in a marine application.

That's not entirely true.

at 4400 RPMS, the aluminum heads will flow much better and make much beter HP than a stock engine.

That's kind of usefull.


Because boats don't have transmissions though, when you increase their power, you REALLY need to increase it from idle to ~5000 RPMS.

If you increase power from 2500-6000 rpms, without increasing it from idle to 2500, then you're going to have a lop-sided torque curve.

Like I pointed out earlier, those aluminum heads used in part of an over-all build are fantastic (just ask the 383 guys)

 

[n2ostroker]

Re: Issues with using Aluminum heads on Iron Engines

mylesm260-
I guess all aluminum heads have big ports and are only made for high rpms...
You brought in a dyno example showing 205cc heads on a 350cu in motor. No it might not make as much torque down low for a few hundred rpms on that example. But save for those less than 500 rpms where it falls a whopping 5-8 ft-lb less even that motor would feel a lot better all around with the big heads with ~20ftlb more torque the whole rest of the powerband. Not too mention the weight savings and better heat transfer.

Again your assuming they all use a huge, large valve lazy ports. They don't.

You do realize that the highest VE happens around the torque peak or slightly before, right? So by going on what you're saying a 350 hits its peak torque long before 2500rpms? It won't happen. Now you posted a graph for a new Vortec motor. Yes the Vortec is a great head and very efficient. Even on that motor torque peaks at 3200rpm. I'd bet even a Vortec motor out of the box runs around 85-87% VE. Not even close to 100%. Throw an old set of open chamber wedge heads on like they used up til the Vortecs and see how much worse it gets.

So are you one of the guys that thinks a turbo or supercharger increases VE?

Have fun with your stock parts.

I'm done you win. Stock is where its at!

 

[mylesm260]

Re: Issues with using Aluminum heads on Iron Engines

If you want to see a fantastic motor, look at this:

http://www.gm.com/experience/techno...s/specialized/marine/2010_6000_LY6_Marine.pdf

That's an LY6.

You can get one used out of a chev pickup truck for 1300 bucks, complete with wiring harness and ECU.

No matter WHAT you do to a gen 1 350, that LY6 would be 1000 times better.

Better Volumetric Efficiency across the board (variable valve timing)
Better Thermal Efficiency
A rotating assembly RATED for 5600 RPMS in a marine application
6 Bolt Mains


Good after market 350 heads are like 1500 bucks.

For 2500 bucks, you could buy and marineize an LY6.

Same bolt pattern as Gen 1 350's
You can use PCM manifolds with custom risers to work with Mercruisers


It will make more power, more torque, get better milage and last longer than anything gen 1. (a wild 383 build MAY make more peak HP, but it would be lacking in many other areas)

 

[n2ostroker]

Re: Issues with using Aluminum heads on Iron Engines

That AFR chart is a motor built for a car not a marine engine.... What heads are they, cam, intake, carb...? How can you compare the two?
Apples to Apples.
You didn't prove anything except you can search the internet and make long post.