C1 - 1958 and 59 Block Casting

[Jimmy J.]

Is a 283 block with casting # 3737739 correct for a 1958 and 59 Corvette and why was there 2 different casting numbers? Thanks in advance. Jimmy

[Rod K.]

Re: C1 - 1958 and 59 Block Casting

I'm not an expert, but the NCRS Spec Guide shows the 739 block for '58 and early '59. The 3756519 block was mid-late '58 through late '61. Why two?? Just a guess, but '58 was the first year for "thin walled" block castings. Maybe there were issues resolved with the 519, phased in to use up the 739's. I recall there was the possibility of core shifts which made boring the thin walled blocks 1/8" an adventure (ask me how long they might last under race conditions). Hope you get a more expert answer.

[Loren L.]

Is there ANYONE out there who can

document a "739" casting in a 1959 outside of possibly the first 20 cars?

[Joe L.]

Re: C1 - 1958 and 59 Block Casting

Jimmy-----

There is an important and significant functional difference between the GM #3737739 block and the GM #3756519. The former uses a rope-type rear main seal and the latter uses a neoprene rear seal. For the most part, all Chevrolet small blocks changed to the neoprene-type rear seal for the 1959 model year. I would say that IF any GM #3737739 blocks were used for the 1959 model year that it would have had to be only VERY early ones.

[Jimmy J.]

Thanks to all of you that responded. *NM*