efficiency aluminum vs iron cyl heads?

[HankL]

Has anyone seen any real hard numbers
on what the efficiency (BSFC) changes are
between identical cast iron versus aluminum cylinder heads?

Are there any weblinks to BSFC graphs?

Although I am interested in BSFC
I am guessing that high Torque in the 2000-3000 rpm range
will match up to high BSFC.

I am also guessing that the old rule of thumb:

"Aluminum cylinder heads need a compression ratio one point higher to make the same power as cast iron heads"

Means that the efficiency difference is about 2 to 3% or so,
since a 10 to 1 compression ratio
is about 2-3% more efficient than 9 to 1 ?

For the Commando and Magnum aluminum cylinder heads are there any dyno graphs comparing them to their cast iron cousins in any magazines or old MP catalogs?

It would seem that the newer Edelbrock aluminum Magnum head is very similar to the Mopar Performance RT cast iron head.
Combustion chamber on the Eddy is 58 cc and RT is 60 cc.
Inlet port on Eddy is 177 cc vs 180 on RT.

Does anyone know of dyno results where those two heads have been tried out on the same short block ?

I know on the MP Magnum aluminum they dropped the combustion chamber cc to 53 from about 60 cc but the intake port cc's was enlarged too.

Did Chrysler test any prototype cast iron 5.7 Hemi heads against the production aluminum 5.7 heads?

Same question for 426 Hemi cast iron heads vs aluminum heads?

I have been able to find out that General Motors contracted out a dyno evaluaton job a few years ago to a company called McLaren Performance comparing the two versions of the cast iron 'Vortec Bow-Tie' small block chevy cylinder heads to aluminum 'Fast Burn' heads, based on this magazine article:

http://www.superchevy.com/technical/...0511sc_vortec/

Apparently McLaren Performance did over 100 dyno runs comparing the various heads.

Anyone know someone who works at McLaren Performance who they could ask? They have a web site at:

http://www.mclarenperformance.com/eportal/

but there is not much there.

Here's Hughes Engines view of aluminum vs cast iron heads:

http://www.hughesengines.com/general...icleID=1000002

Any help, info or opinions appreciated....

[rumblefish360]

Hank, your asking a set of tuff questions here. And there worth looking into. But I couldn't answer on the BSFC of these heads. If I had a ton of info and data to look at, I could come up with a theroy based on history. But that doesn't mean what was par for the past will remain current on the present.
Build up dependent (?)
Apples to apple comparo ?

Do we have any dyno room operaters here or fellas that have done comparos between heads?

[sanborn]

Hank, you are just "up the road" from someone who can answer your question. Years ago, Nascar mandated the use of factory cast iron heads(That is the reason for the existence of W2s, GMs "Turbo" and Fords race Cleveland heads). They were allowed to fully port the heads---which most shops did---and created a lot of cracked iron heads! It was not unusual to replace a set of GM heads after each race. The teams were screaming about the cost of replacing heads after each race. So Nascar let them use "factory like" aluminum heads instead of cast iron. All of this occurred about 1980(my memory may be off a year or two).

There was a lot of dyno comparisons made in the Charlotte area during this time of the cylinder head changover. If you can find someone who was involved during this era, they probably could be of help. I've lost most of my contacts that would have been involved in the comparisons---so I can't be of help. You might contact Automotive Specialists in Concord, they probably did more heads during that era than anyone else---Keith Dorton is the person to talk to. Robert Yates was involved, as was Waudell Wilson, as was Mike Fryar, as was Maurice Petty. The list was pretty long, others were involved during that time.

On an "apples to apples" comparison, the iron would produce about 3-4% more HP than aluminum. But, that was before racers learned about thermal barriers. Today, the aluminum heads will perform at about the same level if they have enough extra mass to keep the heat inside the combustion chamber.

Hope this helps!

[Crank]

the thing with nascar is they run really high compresion ratio's and alluminum will cool at a much faster rate . Car craft did a spred on aluminum vs iron just resently and the end result was they preferd the iron head because their wasn't much difference in performance.i'm not really sure what your looking for .could you be a little more spacific in what you are looking for.

[sanborn]

Not that this has much to do about the question but Nascar MAX compression allowed is 12 to 1.

[HankL]

thanks for the replies so far

i wonder if any magazines had articles in the early 1980s during the NASCAR change from cast iron to aluminum ?

anyone have a pretty good collection of old articles?

is it true a good whiff of old race gas improves memory,
or is the opposite true....can't remember


This link has come up from a responder:
------

http://www.chevyhiperformance.com/te...38/index3.html

sample quote:
"One of the most frequently asked cylinder-head questions is, “Is aluminum that much better than iron?” CHP performed a test using a 383ci small-block with a Crane PowerMax roller cam (232/240 at 0.050 with 0.525/0.543-inch lift) fitted with a pair of almost-identical World Products Sportsman II iron and Sportsman II Lite aluminum heads. The heads offered almost identical port configurations and intake port volumes (200 cc), valve sizes, and chamber sizes. In fact, the only difference was that the aluminum heads used CNC-machined combustion chambers while the iron heads were as cast.

Accepted cylinder-head theory contends that iron heads do not conduct as much heat away from the cylinder as aluminum does, so the iron heads should make more power—everything else being equal. Surprisingly, in our test the aluminum heads made more power than the iron heads by an average of 4.6 hp throughout the entire curve. The iron heads made a peak of 407 hp and 449 lb-ft of torque, while the aluminum heads made 408 hp and 454 lb-ft of torque. We attributed the difference to the aluminum’s CNC-machined chamber, which improved combustion efficiency. We still believe that given true identical iron and aluminum heads, the difference would have been 1 or 2 percent in favor of the iron heads.

The more important question is not really iron versus aluminum, but rather the airflow potential of the heads in question relative to their price. Given this criterion, the best head would be the one with the most intake and exhaust airflow for the least amount of money. Aluminum weighs less and is generally much easier to repair. Iron is less expensive but weighs more. The choice is up to y