1972 LT-1 cylinder heads
Has there been a determination as to when or if 3973487X heads were replaced with 3998993 heads on late 1972 LT-1s?
-
-
Re: 1972 LT-1 cylinder heads
My June '72 built LT1 has the 3973487X heads. -
Re: 1972 LT-1 cylinder heads
A very late 72 LT1 had these on it. 26,4xx car. Engine is stamped 0627 for a build date.
Another car I worked on built almost the same time, engine stamped 0629, had heads dated E 19 2.
So, before that?
Gary B
Gary BComment
-
Re: 1972 LT-1 cylinder heads
Thanks for the replies. It seems to me with a second week of June production date that either casting could be possible. I have spoken to a number of engine builders and they all told me that they cannot remember seeing 487X dated after late April. With a 5-20 block casting and a 5-26 engine assembly six weeks or more between castings seems a bit of a stretch. I know the exterior of the heads are the same, but I need different heads so I might as well try and find the proper ones.Comment
-
Re: 1972 LT-1 cylinder heads
For what it is worth and if you have available Alan Colvin's "Corvette by the numbers" he claims on page 157 the 3973487X was only used in late 1972 model year cars.
I believe the 3998993 heads had a valve size of 1.94/1.50 (intake/exhaust) and therefore not heads for a LT1. The LT1's heads had valve sizing of 2.02/1.60. The 3973487X had this valve sizing.Comment
-
Re: 1972 LT-1 cylinder heads
Jerry------
I believe there were some 3998993 heads that were originally machined for 2.02/1.60 valve sizes.
The primary difference between the 3973487X and 3998993 is that the exhaust valve seat area was slightly redesigned to support induction hardening of the seat. Induction hardening of the exhaust valve seats was introduced for the 1973 model year but, I suppose, some late 1972's might have had it. Or, at least, they had the redesigned seat whether induction hardening was actually done, or not.
There's an "upside" and a "downside" to induction hardening of the exhaust seats. The "upside" is that induction hardening makes for a longer lasting exhaust valve seat and resists recession. The "downside" is that it makes the valve seats more susceptible to cracking. The latter is why these heads and other induction hardened seat heads are not too popular.In Appreciation of John HinckleyComment
-
Re: 1972 LT-1 cylinder heads
Thanks Joe.
Do you agree with Colvin that the 3973487X was only available in the late 1972 model year cars?
Apparently the 3973487X heads were configured with the LT1 valve size, but also for the smaller 1.94/1.50 valves. Is this a correct assumption?Comment
-
Re: 1972 LT-1 cylinder heads
Yes Jerry I have alan's book, but on page 159 he also states that 3998916 heads with 2.02/1.60 valves may use 3998993 casting #. I would like to here from someone that has later dated 487X heads to make me believe they were used until end of the 72 model year. You know i'm nit-picking this thing, but to me that is one of the things that make this hobby fun. I also have a 1963 coupe which also has many early and late parts of which early and late are all different times of the model year
Comment
-
Re: 1972 LT-1 cylinder heads
Jerry------
It's very possible that the 3973487X was used only for late 1972. This is some sort of variant of the 3973487 cylinder head and I do not know what the differences are.
I believe the 3973487X heads were manufactured in both 1.95/1.50 and 2.02/1.60 valve size. Actually, this was common for very many cylinder head castings.In Appreciation of John HinckleyComment
-
Re: 1972 LT-1 cylinder heads
Hi Just found this thread. I had started a new thread because my May car has a 487X and a 993 on it. They are supposed to be original to the carComment
Comment