brucep

A recent admirer of my 66 L-79 said that it had 2 bolt mains, but the higher horsepower 327 Corvettes, like his 63 with 365 HP had 4 bolt mains. Is this true? I thought the cam and lifters were the only differences for the earlier 365 HP motors. Then there were the FI engines with 375. Were the blocks different too?


[Modified by brucep, 1:54 AM 5/12/2003]

achapman

The C2 327 were all two bolt mains for all the HP ratings. There may have been some one off engines with 4 bolt for GM testing purposes, but that's all.... :cheers:

SWCDuke

Admiration does not equate to expertise!

The only OEM 327s with four bolt mains was 1968, which was also the last year of 327 production. GM did this to use common blocks and bearing sizes for all 4" bore SB displacements. The main and rod bearing sizes were increased to restore crankshaft journal overlap because of the 350's longer stroke, and extending these to other displacments meant that blocks could be common with varying strokes ( for 302, 307, 327, and 350 CID displacements) accomodated by crankpin radius and piston compression height.

Though early 350s were four bolts, in later years only SHP versions had four bolts. Four bolt mains are not really necessary on a street small block and are not worth the additional weight.

All '63 - '65 Corvette engines were built from the same two-bolt "870" block, but late in '65 the "180" block came into use. Two other block numbers were used in '66 and '67, but all were two bolt and essentially interchangeable.

Duke

66427-450

Duke -

you sure the 68's had 4 bolt/big crank blocks? my cousin bought a new 68 Z-28, and it had the 2 bolt/small crank setup?......... maybe they put a 67' 302 in it?. (he still has it by the way.....)

Mike
PS: I would have bet $1000 that the 4-bolts blocks started te same year as the 350 (69)
:seeya


[Modified by 66427-450, 11:10 PM 5/11/2003]

SWCDuke

Now that I think about it, you are right. The big bearings were standard on all SB displacements in '68, but the four bolt block with thicker bulkheads did not come online until the '69 model year. I was used on the 302 Z-28 and the L-46 and LT-1. Of course, the LT-1 was delayed and didn't debut until '70, though it was originally planned for '69. I won't take that $1000 bet, but you are wrong on the 350. It debuted (with the larger bearings) in '67 - on the Camaro, I recall, but in a mild state of tune, and the Corvette didn't go 350 until '69.

Duke

P.S. Searching my metal archives for this 30+ year old trivia is good brain excercise. So why can't I remember what I did yesterday. ;)


[Modified by SWCDuke, 9:14 PM 5/11/2003]

clem zahrobsky

all 67 were small journal and 2 bolt except the 350 camaro engine,68 327 were big journal but still 2 bolt

62fuelie

Duke, Ah, s**t, now I can't remember what it was I was going to say. I Do remember something about some bad mushrooms when I was younger.... :D

Goodname4ID

If you are planning to build a really high HP small block, there is a 2 bolt to 4 bolt main conversion that can be done. I recently read an article about it. I will look up the article and give details if anyone is interested.
cheers,
Lee

66427-450

[QUOTE]........ but you are wrong on the 350. It debuted (with the larger bearings) in '67 - on the Camaro, I recall, but in a mild state of tune, and the Corvette didn't go 350 until '69. [QUOTE]

I guess my mind was stuck on Corvette engines (1st year: 69). I clearly remember, when working at the chev dealership back then, driving a dark green '68 327/350...... then a blue '69 350/350

MasterDave

Here's another one, I could have swore that my '67 RS SS Camaro had a small journal 350 in it. Or was it a large journal 327? I do remember something different about the crankshaft mains though. No, I'm sure it was the first year 350. :crazy:

wallyknoch

1967 SS Camaros came with two basic engines, the 350 ci and the 396 ci. No 327`s in a SS option Camaro. :cheers:

MasterDave

OK, it must have been a small journal 350 then. Man that was a long time ago. :yesnod:

JohnZ

Yup - all 327's, regardless of journal size, were 2-bolt blocks, and there were no 327's in SS Camaros - all were 350's or 396's; the 327/350 was never offered in a Camaro, but it was available in the Chevy II/Nova. :thumbs:

66427-450

Yeah, I had a red/blk 66 Nova SS, with a 327/325 (same as the 350hp vette engine), it was a screamer... all I added were: headers, hurst shifter, sun tach, small traction bars, and slicks (at least initally).

PS: I think they also offered the vette 327-300 in that car (but they called it a 327/275).

SWCDuke

The '67 350 was large journal, but all other '67 SBs were small journal. In '68 all SBs went to the large journals to standardize on bearing inserts, and in '69 the four bolt block with thicker bulkheads showed up for the 302 Z-28 and SHP 350s for the Corvette.

As I menttioned earlier, the reason for the journal size increase was to restore lost journal overlap because of the longer crank throw radius (1.74" for a 350). The increase in journal size was not required from a bearing design consideration perspective. Back in that era, F5000 engine builders preferred small journal cranks because they didn't need the increased journal overlap with only a 1.5" throw, and the smaller diameter bearings meant reduced engine friction.

Duke



[Modified by SWCDuke, 2:02 PM 5/12/2003]