Iron vs. Aluminum 21 stud heads - which is better?
 

Hello. My 21 stud 1935 V8 has Iron Cylinder Heads. I see I have developed a water seep from a hairline crack in the passenger side head. I am considering now replacing the heads and want advice on aluminum or iron heads. Thoughts appreciated. Take care!

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

Just found this thread from 2015: https://www.fordbarn.com/forum/showthread.php?t=165514

Any other thoughts?

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

From my experience, serviceable aluminum heads are much harder to find and a lot more expensive if you do.

The post quoted was about four cylinder engines. From what I know, there are a several sources for replacement four cylinder heads, but at present, none for the early V8's (stock style heads).

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

Aluminum cools a little better than steel. Worth the additional cost? Probably not.
Cast iron heads are plentiful and rather reasonable in price. Figure out if you need a head for flat or domed top pistons prior to purchasing any replacement head.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

I appreciate the information more than you know. I may have a source for original aluminum heads for the 21 stud V8... price seems reasonable too. If they are in decent shape i may pull them in and give them a go.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

I be leave new Aluminum heads are available in Australia ,I ditched my stock Al heads due to corrosion .Some anty freeze speeds up this when left in to long ,After welding and surfacing some years later remove them because of water in the oil most of the weld was eaten out .
I now run one cast dome and one flat top motor runs strong it was a experiment that i tend to do to see what happens ,The edison effect i guess . Ted

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

This the result of "Galvanic Corrosion". A little knowledge of chemistry and some sacrificial magnesium anodes goes a long way to minimize this.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

yes fair comment , =testing the PH every so often may help ,

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

pros and cons;
Aluminum heads are original to your engine
Aluminum heads are higher compression
Aluminum heads require far more care in fitting and in use; need to be fitted with non copper head gaskets, anti seize applied to all studs to prevent galvanic corrosion, additives to coolant to prevent the same...
Also care needs to be taken fitting spark plugs; use more anti seize!


Cast iron heads expand/contract at same rate as the block.

Cast iron heads are quieter.

Although they are lower compression, because they hold the heat more than ali, the 'effective' compression is much the same.
So, all round they are less worry...


Strange you've found the cast iron rh head to be cracked...my experience is that the lh heads seem to be the ones that crack for some reason?



Take your pick....

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

If your into originality the aluminum head is it. Look through the V8 club addendum for corrections to the 35-36 restoration book they are on their web site. Good description as to what the heads should look like.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

Where do they most commonly crack?

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

Mine has a small crack from base of a plug port down towards the bottom about two inches... all external... only way i see it is a rust line... and a bit wet after driving.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

The truck Iron heads I plan on using on my current build have combustion chambers with a steep ramp down to the valves ,they CC the same as Aluminum flat top heads .There chamber shape is like a Durant head that was popular for boat racing in the day ,Ted

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

I had one with a vertical crack between 2 cylinders, I thought that was a real odd place to crack without any others.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

I have a pair like that too, made me question the specs that say iron heads are larger than aluminum.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

Yeah ,you would think more power is required on a truck ,my odd head car from memory was the same ,

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

One more ? on Aluminum Heads. I have found two sets that look good and appear to be original. Any reason I should not purchase one of these sets instead of a more recent head?

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

In my opinion, there is no reason to not purchase the best of the sets you'd found.
When installing, be certain to use composite gaskets. Also, I'd suggest you coat each stud with Anti-Seize®.

Before purchasing be certain what heads you need. Flat top pistons? Domed pistons? Lots of things may have been altered since your car was new.
I'd feel bad for you if you'd purchased a set of heads and found out later, they are not correct for your application.

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

I appreciate the reply. All good information. I rebuilt my engine almost two years back and it has flat top pistons so I feel good about these heads. They also have the same Ford part numbers on them as my iron headsl. I will find some composite gaskets and use anti seize on studs and plugs. Thanks!

Re: Iron vs. Aluminum 21 stud heads - which is better?
 

Don't lubricate the spark plugs. They require a good ground.