Block 3855962 for 1965, question about changes during the production year
The 396 engine block casting for the 65 is 3855962 for the full year. Early 65 corvettes have a "PASS" emboseed bell housing flange, while later 396's that year had a "HI PERF" cast lettering. But are there any real differences in these early and later year blocks other than this embossing ? (Past threads do not seem to indicate any real differences?...from what I am reading) Thanks Tony
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Re: Block 3855962 for 1965, question about changes during the production year
Tony . I have not been able to find any difference in early and late "Corvette" Pass. or Hi perf. blocks. All Real 962 Pass. Corvette blocks had front and rear ribs . All real Corvette 962 HI Perf. blocks had ribs . BUT not all 962 HI Perf .blocks had ribs. I have two late HI Perf . 962 blocks cast in 1965 (I dont remember the date) that are 4 bolt with all the correct oil holes etc but have no ribs . These were 66 Chevelle blocks . My question has always been how can they change the blocks "Pass to HI Perf" and 962s with or without ribs and use the same casting numbers ? I always thought when you changes a mold you had to change the casting numbers . Why did they change from pass. to HI perf. and why were the ribs dropped for all 66 BBs and came back in 67 ? -
Re: Block 3855962 for 1965, question about changes during the production year
I was told "back in the day" by the guys from Tonawanda that the High-Perf blocks had thicker cyl walls and would overbore to "427" specs where the "pass" version had thinner walls.Bill Clupper #618Comment
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Re: Block 3855962 for 1965, question about changes during the production year
..interesting..that means they used completely different pistions too...Comment
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Re: Block 3855962 for 1965, question about changes during the production year
All 396 Corvettes used 11.1 pistons . Chevelles had less compression . They were all the same bore .Comment
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Re: Block 3855962 for 1965, question about changes during the production year
Pass car also used a low compression (10 to 1) as I remember for the 325 hp version of the engine. That was the two-bolt block that used the thinner wall casting.Bill Clupper #618Comment
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Re: Block 3855962 for 1965, question about changes during the production year
All the 962 blocks with the ribs over the timing chain cover used the same water jacket cores as 427s and can be bored out to at least 427 + 0.060. I think the thin wall 962 blocks for 1966 Chevelles (without ribs) began around August 1965. It makes no difference whether they are marked "PASS" or "HIPERF".Comment
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Re: Block 3855962 for 1965, question about changes during the production year
Wow -- a lot of info being discussed here. Let me go slightly off-topic by bringing in the '65 passenger 396 block, the 3855961, which, other than having 2-bolt mains, may or may not (depending on opinions above) be similar (or otherwise identical). So let me throw the similarities out for discussion.
Both the casting words HI PERF and PASS appear in 3 places (see first 3 thumbnails below) on 3855961's and early (maybe later ?) 962's (and even '66 942's ?). These are found under the timing cover, under the bellhousing [I held a mirror], and above the oil filter. . PASS appears again on the bellhousing flange [opposite the block casting number] of early 962's, and HI PERF at same location on later (dated 'E' casting or later months, per '65 TIM&JG). Truck appears once, under the back, hidden by the bellhousing (I believe this continues into 1966 MY ?).
The 4th thumbnail shows the 961 casting date E_14_5 (was assembled T0607LF), and the distance between the two cylinder cores. I measure 0.372"; maybe 0.370" if the casting surface wasn't so rough. Would really appreciate if someone would do the same on a 962 block, so we could put this wall thickness topic to bed.
The two big pictures are to show the two front and two rear ribs.
cComment
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Re: Block 3855962 for 1965, question about changes during the production year
Wayne: I have 2 Feb 65 and 1 April 65 962 blocks. I will get a measurement on the water jacket clearance of them and some 427s. Also I will note whether all of them say PASS or HIPERF on the bellhousing flange. I should have the info by Thursday. I didn't know that 65 961 blocks also had ribs over the timimng chain cover.Comment
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Re: Block 3855962 for 1965, question about changes during the production year
Patrick I dont remember if I asked you before , what are the vin numbers on your 962s Im still missing my original for 17346 built today may 12.Comment
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Re: Block 3855962 for 1965, question about changes during the production year
i've had a couple 961 pass car blocks that lacked the pair of gussets or ribs. mikeComment
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Re: Block 3855962 for 1965, question about changes during the production year
Wayne: Don't bore that 961 block to 427 even though it has the ribs. I was surprised that a ribbed 961 block existed and I am surprised again that its wall thickness is not the same as an early 962 block with ribs.
I looked at three 962 blocks: B 4 5; B 20 5 and D 24 5. All were marked "PASS" on the bellhousing flange and had the same combinations of Hi Perf and Pass on the other locations as your block. Both February blocks had already been bored to 427 and had been used for years. I did not remove their freeze plugs. I had had the D 24 5 block decked, grained and cleaned years ago and the freeze plug holes were open. The largest drill bit I could insert in the water jacket between the bores was 13/64 (0.203) on the fluted end and only by rotating it. I estimate the water space between the bores as 0.200 inch. I tried the same drill bit on a 67 427 block and the water jacket space was identical. The picture below is the D 24 5, 962 block. Since the same space on your early 961 block was 0.372, cylinder wall thickness of the 65 962 and the 427 is about 86 thousandths greater, allowing a bore 0.172" greater.
I have long wondered why the 961 and 962 blocks are the only big blocks bearing different casting numbers for the 2 bolt and 4 bolt versions. Your ribbed 1965 model year 961 block is identical in external appearance and markings (except for the last digit of the casting number) to the 1965-model year-only 962 block. In this case, the difference in casting number appears to designate the difference in wall thickness. Unlike the 961, the 962 seems to have been actually designed as a 427. Was this a secret gift to hot rodders or a last minute change of policy? I once heard a quote attributed to Zora Duntov about the 66 427 being a weight saving measure for the Corvette, saving 31 cubic inches of cast iron. This was received as a joke, but we see it was literally true.
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Re: Block 3855962 for 1965, question about changes during the production year
Bill: Two of the blocks were coded for a Z-16 Chevelle and a full size Chevy (like a cool 396-425 Biscayne). The other was lightly decked and only "511" was remaining of the Corvette vin. At one time I had the block from 5117811 (cast 4 24 5) built T0511IF) but that is the closest to your car I have seen.Comment
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Re: Block 3855962 for 1965, question about changes during the production year
Patrick -- thank you for a very informative post. My 961 block is currently 30 over (TRW piston pic thumbnails) and very little wear according to the cylinder bore honing pattern, so I won't be going to 60 thou
. The rod journals are all STD and the mains are all .001 undersize, which might have even been factory (except mine are all Federal Mogul). So I'm hoping that my teardown for inspection will require little or no work. You can see immediately by your photo that the gap between cylinder cores is less than what I showed for my 2-bolt (3rd thumnail).
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