[DeTomaso] Stock 4V Heads vs alloy
John Taphorn
jtaphorn at kingwoodcable.com
Tue May 11 21:53:04 EDT 2010
While aluminum heads allow you to run higher compression, they forfeit much
of the advantage by withdrawing heat energy from the combustion cycle. As I
recall, Dan's dyno testing revealed little advantage over iron quench heads.
I concluded they were superior in lightening the car and your wallet. I can
appreciate the former.
JT
----- Original Message -----
From: "LS" <lashdeep at yahoo.com>
To: <JDeRyke at aol.com>; <DeTomaso at realbig.com>
Sent: Tuesday, May 11, 2010 1:35 PM
Subject: Re: [DeTomaso] Stock 4V Heads vs alloy
Thank you for the responses.
You've offered a compelling argument for the Aluminum heads and something to
seriously think about.
So, the next obvious question is...which ones?
Thanks,
LS
________________________________
From: "JDeRyke at aol.com" <JDeRyke at aol.com>
To: lashdeep at yahoo.com; DeTomaso at realbig.com
Sent: Tue, May 11, 2010 2:12:18 PM
Subject: Re: [DeTomaso] Stock 4V Heads vs alloy
As you mentioned, the 35 lb per head weight-savings is one big advantage-
both in physically handing the castings and for the car's improved center of
gravity. Along with the intake manifold, the heads are the heaviest
high-mounted parts in your Pantera.
A second is infinite repairability; I've heard of alloy heads BROKEN IN HALF
that were successfully rewelded.
Third: the most desirable head configuration is the closed-chamber Boss type
and all alloy heads come this way. Converting any common iron heads to Boss
specs will cost close to the price of alloy heads. Reproducing the
high-efficiency alloy head exhaust ports in any iron head is impossible.
Fourth, iron heads- even closed-chamber Boss heads- aren't very stiff;
during the '69-'72 period when 351-Cs were being professionally raced,
NASCAR shop mechanics developed a number of internal braces for the
combustion chambers to keep them from flexing at high rpm/high compression
running. All Cleveland cylinder heads are thin-wall construction just like
the blocks; some heads flexed enough to reverse the flow of cooling water
through the engine! This led to unexplained overheating and head cracking.
The required mods called 'posting' are outlined in Waddell Wilson's racing
engine prep book; Jr Johnson also had similar brace techniques.
Finally, the cooling characteristics of alloy heads are far superior to any
iron heads; so much so that one can usually run 1/2 to 1 full point of
compression HIGHER than even a fully modified iron racing head. In these
days of low octane tractor fuel being sold as premium gas for many dollars
per gallon, being able to run pump gas without engine damage is certainly
worth consideration! The only time iron heads should even be considered is
if high-boost turbocharging is in your future. Iron heads retain more heat
and boost than alloy heads- if you can keep the rest of the engine
together....
My 2¢- J DeRyke (with SVO heads on the street since 1990)
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