Depending on what you read, the 452 heads were the best RB heads ever made (other than Max Wedge) for flow. However, it is a relatively minor ( ca. $120-$150) expense to have hardened valve seats added to any head if the heads are already being refurbished anyway. I always wondered how deep the hardening was on the "hardened heads" and for example if the heads had one or more valve jobs would the hardening still be effective. If you put the hardened seat inserts in, the valve seat can be cut exactly where the machinist wants it and is not dictated by wear etc. Also, you get a better than original hardened seat. I personally don't worry about it with my 1969 440. If at some time the heads need to be rebuilt, I may swap to the set of 452's which I have or put hardened seats in the original 906's. The hardened seat inserts are better (more durable) and the original heads are "better" so I would probably go that way.
----- Original Message -----
From: "Rob McCall"
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: RE: IML: Unleaded or Leaded gas
Date: Thu, 9 Mar 2006 17:42:05 -0500
> From what I've read, the unleaded heads were being phased in for the '72
model year, along with the lower compression ratios. By '73 everything
should have been unleaded. I believe cat converters were phased in during
'74, and unleaded was mandatory for the cats to live.
Rob McCall
'67 LeBaron, lead-head (but I do have a pair of '452 casting heads on the
shelf if necessary at a future date).
----- Original Message -----
From: clgilleland@xxxxxxxxxxxx
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: IML: Unleaded or Leaded gas
Date: Wed, 8 Mar 2006 00:36:57 -0600
Hi, I was wondering When did Chrysler start putting hardened valves in
engines so they could br ran on unleaded? I have a 74 Imperial with a build
date December of 1973.
Fred Joslin
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