Are aluminum heads worth it? Which ones? Here are some answers.

[YoungPerformance]

It seems I have been asked these questions a lot recently. I will try to help answer these questions with some data. I recently did some flow testing on some stock cast iron heads that were both stock, as cast, and ported, a set of Brodix BB-2Xtra CNC that had also been hand ported and some AFR 357 CNC heads. This is by no means a scientific experiment. However, I did try my hardest to keep all of the variables the same. These test were done on the same flow bench with the same fixture, using the same operator.
The first thing I was trying to see is how much my port work helped. Next, how much better are the aftermarket heads then a set of stock cast iron heads. Finally, were the CNC heads maxed out or was there more to be found with porting.

Disclaimer!!!
This is not a scientific test. These numbers will be on the low side as compared to published numbers. I was looking more for a comparison then all out max flow. Several factors will cause my numbers to be low.....I used a 4.5" bore fixture instead of a 4.600" that most manufaturers use. That larger bore fixture will help flow by unshrouding the valves. Next, I did not use a pipe on the heads. I never have used one in the past, so I wasn't going to start now since I would have no way to compare to previous tests. The pipe will not only increase flow, but it will also represent more realistic conditions since there will be a pipe on the heads on the engine. These two factors alone could account for 30 -40 cfm or more. Again, I am not looking to see what the max flow is as much as I am looking to compare the heads and see if porting will help.
Here are the numbers:

Stock GM cast iron head (188 casting)

Exhaust stock ported

.200 117.3 117.3
.300 149.8 150.6
.400 174.4 180.0
.500 183.9 191.8
.600 187.0 197.0
.650 187.0 197.0

Intake stock ported gain
.200 149.0 150.1 .9
.300 197.0 203.8 6.8
.400 232.6 246.4 13.8
.500 258.1 277.8 19.7
.600 279.6 303.5 23.9
.650 287.0 311.4 24.4

This was not a full port job. I only did the chambers and the bowls, since they were the worst. I did not touch the runners at all. So with a little more work these heads can really be improved. The bowl area was really bad. The seats did not match up with the head at all, so there was a large step left in the head when it was cut for seats. This is where I did most of the work ( along with the area around the valve guides)

Now for the aftermarket heads. First up are the Brodix heads. They are the BB-2Xtra 355 CNC . I flowed one of the heads right out of the box and one that I did some port work to. I didn't really do a bunch of aggressive cutting. I spent more time on polishing and cleaning it up. Now you may say why do you have to do any work to a CNC head. Well, you don't have to but the numbers show that they can certainly be improved upon. It really depends on what you are looking for in terms of hp if it is nesseccary. I haven't done any work to the AFR heads yet. I'm not sure if I will. They really look nice and I was expecting them to really outflow the Brodix heads. They did in the lower lift, but not in the upper lift ranges.

Brodix BB-2Xtra 355CNC:

Intake: stock ported gain
.200 148 148 0
.300 220 224 4
.400 282 292 10
.500 323 335 13
.600 354 370 16
.700 375 394 19
.750 383 403 20

Exhaust: stock ported gain
.200 128 128 0
.300 165 168 3
.400 227 231 4
.500 255 257 2
.600 271 277 6
.700 281 286 5
.750 285 289 4

AFR 357 CNC:
Intake exhaust
.200 159.0 141.1
.300 235.2 190.2
.400 289.2 237.8
.500 326.1 248.8
.600 355.1 252.0
.700 378.6 254.2

Like I said, I haven't done any port work to the AFR's yet. When I do, I will post those flow numbers. Again, these numbers are going to be low compared to the published numbers for the reasons listed above. I hope this may help someone make a decision as to which route to go. Thanks for looking.
Eddie

[LIVE WIRE]

Hey Eddie , This question is sort of related, but compared to cast iron heads . How reliable are alumium heads as far as longevity & durability goes . Thanks again for all your help .

[YoungPerformance]

The only longevity problems I have seen are due to guys not flushing them out after running in salt water. Other than that, I haven't seen any problems.
Eddie

[LIVE WIRE]

Thanks Eddie, Your a true professional

[PatriYacht]

In some ways they are more reliable than iron factory heads. They don't crack by the exhaust valve like the stock ones sometimes do. And if they are damaged, aluminum heads are easy to weld and machine. Guides and seats can always be replaced.

[Geronimo36]

The corrosion around the water ports that are very common on aluminum heads can be repaired if they're not too bad. I've even seen alum heads with half the valve punched thru it welded back together. :eek:

I religiously flush my engines after every run, even if it's 5 minutes but still have to have my intakes fixed every 2-3 years and see the same on other boats I work on that don't have brass inserts. It's like a service item...but since it's aluminum it can be fixed. :)

If you run in salt I highly recommend investing in FW cooling if you're running alum heads!

[Chris]

There are a number of factors that are important to look at when selecting a head.

Flow is nice, but anyone can cast a big hole on either side of the valve. Maintaining flow velocity is a big factor. And you can't get good velocity in a gaping cavern of a port. Just like putting a Dominator on a small block, there's an RPM that the setup will work well, but it's not going to be anywhere really usable. Take a look at the AFR 315CNC head. Smallish port volume but really good flow. And in it's size range, fantastic velocity. They make great power across the RPM range.

Another one is intake to exhaust port ratio. Having a braod selection in aluminum heads allows you to select what you need, and tyhis is an important consideration. Blown engines need more relative exhaust flow. The intake charge being more dense is putting more into the cylinder. Add to it that supercharging is a more efficient process, not requiring the piston to draw the charge in. So taking the same port on a NA engine and putting a mere 6lbs boost on it puts alot more into the cylinder. It has to go somewhere. Common sense tells you that you need a larger exhaust port than you typically would with a NA engine.

Aluminum heads are more thermodynamically efficient. They draw heat away from the combustion chamber much more efficiently than iron does. In the real world, this gives you the margin to run a little more timing, a little more compression or a little more boost than you could get away with running iron heads. Free horsepower.

Lastly there's cost. Anyone can make the holes larger. Doing it and ending up with an engine that has a powerband maximized at every point in the RPM band takes knowledge and talent. That costs $$. And frankly, with such a broad spectrum of off-the-shelf heads available, it's more and more becoming a lost art. But even if you find someone that can do the job in the ideal fashion you're seeking, most likely the expense of finding a pair of good castings, seats/guides/surfacing and then the porting services... you're looking at the cost of a new set of proven, bolt-on heads.

[ROGUE]

[QUOTE=Chris;419615]
Aluminum heads are more thermodynamically efficient. They draw heat away from the combustion chamber much more efficiently than iron does. In the real world, this gives you the margin to run a little more timing, a little more compression or a little more boost than you could get away with running iron heads. Free horsepower.

Well, just to clarify that point. Plop a comparable (flow+velocity) aluminum head on an iron headed engine and do nothing else and you will lose horsepower due to the loss of heat. You will have to increase compression or something to stay equal.

[YoungPerformance]

You're right. Heat is horsepower, but to much is the enemy. The trick is to be able to control the heat.

Great post Chris. This is what I want to do with this thread. I want to get people talking and sharing their experience and knowledge. I can also learn from it. I am definetly not a cylinder head expert. I just wanted to share some of my findings. This is not all that needs to be considered when picking heads. I really wanted to show the difference between the stock cast iron and aftermarket alum. heads. I have been getting that question a ton lately....."Do I port my stock heads or replace them with alum." I wanted this to show that the cast iron heads can be improved upon, but they still will not equal the larger aftermarket cnc heads. However, not everybody needs a head like that. If you are looking for a small to moderate increase in hp, then some porting of the stock heads may be a good option.
Anyway, lets keep it going. Share your setup and hp.
Eddie

[Chris]

This is a piece of information I stumbled across a few yers back. I took the big block Chevy stuff out of it and pasted it into an Excel file with headers. It made it easier to use...

http://users.erols.com/srweiss/tablehdc.htm#BBChevy

It gives you the specs and such on virtually all of the heads out there. You can look for yourself at the differences between port volume, flow and velocity.

Like Eddie, I'm no expert. But I am interested in knowing why sometimes people bolt on "better" parts and their boats slow down. This is a big one. When I get this one figured out, I might tackle cams ;)

[tunnelvision69]

This is a piece of information I stumbled across a few yers back. I took the big block Chevy stuff out of it and pasted it into an Excel file with headers. It made it easier to use...

http://users.erols.com/srweiss/tablehdc.htm#BBChevy

It gives you the specs and such on virtually all of the heads out there. You can look for yourself at the differences between port volume, flow and velocity.

Like Eddie, I'm no expert. But I am interested in knowing why sometimes people bolt on "better" parts and their boats slow down. This is a big one. When I get this one figured out, I might tackle cams ;)

that is unbelievable chris!!!