Cast Iron versus Aluminum Heads
 

I am currently running a Merlin VR Marine345cc Rect Port cast iron head and have been told if I wanted to make more power via increasing boost that I should first switch to an Aluminum Head? Motors are 540's 8.2:1 compression dynoed ar 905 HP with Littlefeld Blowers and SuperChillers! I guess what I am asking is what are the advantages of Aluminum Heads and what is the effect on current setup of switching? Also any recommendations on which Aluminum Heads are the best?

I've been told that using aluminum heads allows you to run 1 point higher compression on n/a engines since they get rid of heat more efficiently. In your case you could probably run more boost without fear of pre-ignition. Best heads? I like AFR best, canfield second best, but there are lots of good ones out there.

that could be true, on a n/a engine iron heads make more h/p vs aluminum on a same head, from retaining heat in the combustion chamber, so that being said with the heat loss of aluminum that should work...Rob

I have always been told that there isn't really any power advantages by going from a steel head to an aluminum head. However, I have also been told the steel head may make a little more torque because they retain the heat a little more vs the aluminum head.

Also, I agree with what Nova 26 has said in his post. "I've been told that using aluminum heads allows you to run 1 point higher compression on n/a engines since they get rid of heat more efficiently....."

There are some good aluminum head companies out there....Dart, AFR, Brodix, Canfield, etc. are all very close in how they perform. AFR may have the edge as it stands now---but products are always changing. A good head and cam combination is what you need. RMBUILDER/Bob Madara of Marine Kinetics in N.Y. 585-654-8583....he can set you up with heads---he is a wealth of knowledge and has helped many guys on here over the years with situations like yours.

You should be using aluminum heads in a blown application. Gives you a larger margin of safety by better controlling cylinder temps that can lead to detonation. Detonation can take out a motor in a few seconds if you are in full boost.

Other then the weight savings and tolerence to more compression switching to aluminum heads because of material alone isn't a good reason to neccesarily go from iron to aluminum. The real reason to look at the modern aluminum heads over cast iron is the fact that a pair of cnc'd aluminum heads (if they are in your budget) are going to outflow your current heads by a mile unless they are already ported.
The Merlin vr heads (and the dart equivilants) have near stock exhaust flow,the 345's have the same exhaust port as the 310's essentially and are stones,in stock form they only flow 220 to 230 cfm which gives you a terrible intake to exhaust ratio. you end up with a I/E ratio of around 65%,a good set of cnc'd aluminum heads will flow closer to 300 cfm exhaust and you will see a big hp gain with the right cam. I had a set of merlin vr's,it took ALOT of exhaust porting to get them to work well at all. With a ton of boost I could barely make 750 hp,when I switched to afr 315 cnc's I made 950 hp and with a even better cam and components I made over 1100 hp, Look hard at the flow numbers before buying a set of heads,your pushing air in the intake port but it still has to get out and a restrictive exhaust port isn't doing you any favors,Smitty

To save some significant $, consider having Jim Valako (JimV)rework the Merlin exhaust ports an do minor fluff on the intake ports and chambers. It can also rework the chambers for the ideal CR. He can send them back ready to bolt on.

true he will do a nice job. the merlins are better for salt water to.