394–Big Block, Yes or No?
July 17th, 2022, 08:25 AM
#1
FourDoorGlory.com
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Location: North Texas
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394–Big Block, Yes or No?
There are a lot of posts out on the ole interwebs calling the 394 a Big Block engine. Most of these references seem to come from current owners, or dealers looking to sell a car. Do we have any former Oldsmobile powertrain engineers here on the site that can provide an independent take on this?
Wikipedia:
The 260 cu in (4.3 l), 307 cu in (5.0 l), 330 cu in (5.4 l), 350 cu in (5.7 l) and 403 cu in (6.6 l) engines are commonly called small-blocks.[1] 400 cu in (6.6 l), 425 cu in (7.0 l), and 455 cu in (7.5 l)[1] V8s have a higher deck height (10.625 in (27.0 cm) versus 9.33 in (23.7 cm)) to accommodate a 4.25 in (108 mm) stroke crank to increase displacement. These taller-deck models are commonly called "big-blocks", and are 1 in (2.5 cm) taller and 1.5 in (3.8 cm) wider than their "small-block" counterparts.
My personal take has always been that the only Oldsmobile big blocks were the 400, 425, and the mighty 455.
Let the debate begin, but again, hoping that a former Oldsmobile engineer chimes in with some objective information
Wikipedia:
The 260 cu in (4.3 l), 307 cu in (5.0 l), 330 cu in (5.4 l), 350 cu in (5.7 l) and 403 cu in (6.6 l) engines are commonly called small-blocks.[1] 400 cu in (6.6 l), 425 cu in (7.0 l), and 455 cu in (7.5 l)[1] V8s have a higher deck height (10.625 in (27.0 cm) versus 9.33 in (23.7 cm)) to accommodate a 4.25 in (108 mm) stroke crank to increase displacement. These taller-deck models are commonly called "big-blocks", and are 1 in (2.5 cm) taller and 1.5 in (3.8 cm) wider than their "small-block" counterparts.
Let the debate begin, but again, hoping that a former Oldsmobile engineer chimes in with some objective information
July 17th, 2022, 08:34 AM
#2
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Join Date: Aug 2011
Posts: 3,060
Small block vs.big block is the comparison between the size of different engine blocks made by the same company/division line. Olds division of GM in the 394 era didn't make other blocks at that time so there isn't anything to make a comparison with. It's neither a SB or a BB IMO, it is an Olds 394.
I guess one could compare it to the aluminum V8 offered but I wouldn't.
I guess one could compare it to the aluminum V8 offered but I wouldn't.
Last edited by Sugar Bear; July 17th, 2022 at 08:36 AM.
July 17th, 2022, 08:37 AM
#3
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Location: St. Paul Minnesota
Posts: 4,053
If its on the internet, it must be true ?
The engineers didn't didn't coin this terminology. I thought this very same question came up on here and one of the members explained it quite well.
The engineers didn't didn't coin this terminology. I thought this very same question came up on here and one of the members explained it quite well.
July 17th, 2022, 12:40 PM
#5
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,467
There is no legal definition of "small block" or "big block". In Oldsmobile land, the distinction has been applied to the second gen motors that come in two different deck height configurations although at Chrysler the B-motor (383) and taller deck RB-motors (440) are both considered "big blocks". Ironically, the first gen Olds V8s were made in three different deck height configurations.
July 17th, 2022, 01:18 PM
#6
Running On Empty
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July 17th, 2022, 05:05 PM
#7
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Some of y'all know this stuff like the back of your hand - I don't. It isn't like I've never pulled an engine, had a deck milled, etc. etc., but keeping up with BOP, Chevy & Caddy was never in my calling w/ regards to which GM engine was the predecessor &/or which was "commonly" referenced as a small block or a big block except in bar-room parlance (chatter).
I tried to find this information once before (about the time I joined CO) but it was like getting blood from a turnip for me & I gave up on Gen 1 engine designs.
So, this is where I'm at attempting to find out the answer to my question regarding Joe's answer - there were three different deck height configurations in the Gen 1 engines.
Realizing all Gen 1 engines were 90° bank angles, I started examining bore & stroke. Not really caring if it was called a sbo or bbo since my original question above (directed towards Joe) was which three deck heights were used in the Gen 1 engines.
303 - bore = 3.750"; stroke = 3.4375"
324 - bore = 3.750"; stroke = 3.4375"
371 - bore = 4.000"; stroke = 3.6875"
394 - bore = 4.125"; stroke = 3.6875"
I hate assuming (since you know where that will get me), but if I employ some deductive reasoning I might "suggest" an answer based solely upon bore & stroke - possibly?
303/324 - same deck height (Deck Height #1 - shared)
371 - (Deck Height #2 - not shared)
394 - (Deck Height #3 - not shared)
Am I close, warm, cold, freezing?
I tried to find this information once before (about the time I joined CO) but it was like getting blood from a turnip for me & I gave up on Gen 1 engine designs.
So, this is where I'm at attempting to find out the answer to my question regarding Joe's answer - there were three different deck height configurations in the Gen 1 engines.
Realizing all Gen 1 engines were 90° bank angles, I started examining bore & stroke. Not really caring if it was called a sbo or bbo since my original question above (directed towards Joe) was which three deck heights were used in the Gen 1 engines.
303 - bore = 3.750"; stroke = 3.4375"
324 - bore = 3.750"; stroke = 3.4375"
371 - bore = 4.000"; stroke = 3.6875"
394 - bore = 4.125"; stroke = 3.6875"
I hate assuming (since you know where that will get me), but if I employ some deductive reasoning I might "suggest" an answer based solely upon bore & stroke - possibly?
303/324 - same deck height (Deck Height #1 - shared)
371 - (Deck Height #2 - not shared)
394 - (Deck Height #3 - not shared)
Am I close, warm, cold, freezing?
Last edited by Vintage Chief; July 17th, 2022 at 05:09 PM. Reason: sp 234>324
July 17th, 2022, 05:27 PM
#8
Phantom Phixer
Join Date: Dec 2011
Location: Apopka, FL
Posts: 4,699
You are getting warm.
There are only two deck heights in the first generation line of engines.
The 303 and 324 shared the same deck height. Just different bores.
When the 371 was introduced in 1957, the deck height was raised and the 371 and 394 differed in bore.
There are only two deck heights in the first generation line of engines.
The 303 and 324 shared the same deck height. Just different bores.
When the 371 was introduced in 1957, the deck height was raised and the 371 and 394 differed in bore.
July 17th, 2022, 05:34 PM
#9
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,467
Charlie, I've always understood that the 1957-58 371s had a 1/8" taller deck than do the 303s and 324s and the 1959-64 blocks (both 371s and 394s) have a 1/4" taller deck. J2 manifolds won't fit 303s or 324s without machining because the shorter deck, and they won't fit 59-64 motors without spacers because of the taller deck.
July 17th, 2022, 08:55 PM
#12
Phantom Phixer
Join Date: Dec 2011
Location: Apopka, FL
Posts: 4,699
Charlie, I've always understood that the 1957-58 371s had a 1/8" taller deck than do the 303s and 324s and the 1959-64 blocks (both 371s and 394s) have a 1/4" taller deck. J2 manifolds won't fit 303s or 324s without machining because the shorter deck, and they won't fit 59-64 motors without spacers because of the taller deck.
The block deck height was raised again in 1959 because they used longer rods.
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