I have noticed different GM p/n's for 1970 LT-1 cylinder heads and am curious which/what is the deal? Alan Colvin identifies GM p/n 3927186, 3947041, and 3973414(LT-1 only) as legitimate p/n's. I have a Jan '70 build date with 186 heads date coded L 1 9..!! Are these heads (186) correct, or should all '70 LT-1s have 414 heads? Tks, Jeff B.
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Re: 1970 LT-1 cylinder heads
Jeff-----
Any of the cylinder head casting numbers you mentioned could have been originally installed on a 1970 LT-1 and any would be "correct". However, I think that the 3927186 was probably the most common casting utilized for 1970 LT-1 applications.
By the way, do your heads have screw in studs and guide plates? Most, if not all, 1970 LT-1s should have these.In Appreciation of John Hinckley -
Re: 1970 LT-1 cylinder heads
Joe: Yes, both are present. In looking at the most recent issue of Vette Vues where Alan further identifies 1970 cylinder head cast numbers, and combined with the fact I am installing a new camshaft(heads most exposed), I found most curious that the 186 head was used for 350/300 applications. My date code mates perfectly, I have the build sheet, etc. that authenticates the RPO code, but was left with a bit of an empty feeling when comparing GM p/n for 1970 LT-1. Under what applications was the 3973414 head used? Most appreciative for your reply..Tku, Jeff B.Comment
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Re: 1970 LT-1 cylinder heads
Jeff-----
I don't think that there were any particular circumstances that were involved with respect to which cylinder head castings were used for a particular engine. I think that the 3 different castings used for LT-1 were used more-or-less randomly or, perhaps, during particular segments of the model year.
As I mentioned, the 3927186 cylinder head is, by far, the most common. It was used for BOTH 1.94"/1.50" AND 2.02"/1.60" valve applications for both the 1969 and 1970 model years. In other words, the castings were the same and only the final machining (and, consequently, finished PART number for the head which appears nowhere on them) was different for the 2 different valve sizes.
I believe that the reason for the 3973414 casting was this: both the 3927186 and the 3947041 cylinder heads required significant engine plant machining to install the screw-in studs and guide plates. So, a different cylinder head casting was developed that was designed around the installation of screw-in studs and guide plates. This minimized the amount of machining that had to be done at Flint Engine. I expect, but don't know for sure, that the '414' castings were used later in the model year. That's because I don't see why the Flint plant would have continued to use the '186' and '041' castings for screw-in stud heads after they had the '414' castings available. Of course, there may have been a "ramping up" period when there weren't enough '414' castings available for engine build needs. I doubt that too many molds were ever produced for the '414' cylinder head considering its limited application and one-model-year-only useage.
Keep in mind that the "1970-1/2" Camaro Z-28 came out in the spring of 1970, after the 1970 Corvettes. The Corvette LT-1 production requirements weren't so great that Flint Engine had too much trouble machining '186' and '041' castings for screw-in studs. Only 1287 cars were built with an engine with this requirement. However, after their introduction in the spring and culminating in the fall, almost 9,000 Z-28s were built and sold for the very short 1970 model year. So, it was this requirement that may have prompted the '414' cylinder head's introduction to ease Flint's machining operations.
Due to their 1970-only useage, the 3973414 castings are quite rare. In fact, I don't think that I've ever seen one. However, keep in mind that they are FUNCTIONALLY and, except for casting number, VISUALLY IDENTICAL to the '186' heads. You could only discern the difference if you had one of the RAW CASTINGS and, I expect, no one has any of those. Unless, of course, Mark Gorney can come up with some.In Appreciation of John HinckleyComment
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Re: 1970 LT-1 cylinder heads
"Thank you, Joe" for a wonderfully detailed reply. My '70 runs so well/strong, and the casting date mating perfectly for a very early build(Jan)on a car that is well-preserved, I found it odd that a base motor cylinder head p/n would be found; this is a CA NA9 car with the correct 4189 Holley carb. Tku, Jeff B.Comment
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Re: 1970 LT-1 cylinder heads
Jeff-----
The cylinder block casting for the 1970 LT-1 is the same as the base engine block, so why not expect the same for the cylinder heads? The '186' cylinder heads are quite common, but used to be a very sought after item. These days there are MUCH better cylinder heads available for performance purposes so hot -rodders aren't too interested in the '186' anymore. But, they're just about as good a cylinder head as GM ever used on any PRODUCTION small block engine. Ever.In Appreciation of John HinckleyComment
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