A 1964 383 two barrel was given a factory hp rating of 305 with a two barrel carb, .390 lift cam and single exhaust.
A 67 A body 383 was given a 280 hp rating with 516 heads and 1.60 exhaust valves, a 256/260 duration cam with .425/.437 lift, low rise intake and a small AFB four barrel plus DUAL EXHAUST.
A 68 A body 383 got a higher rise intake, AVS carb, 906 heads with 1.74 exhaust valves, same cam as 67. HP rating was 300.
A 69 A body 383 got all the 68 stuff plus the hi-po 383 and 440 cam with 268/276 duration, and .450/.465 lift. HP rating was 330.
A 69 A body 440 got essentially all of the 383 A body stuff only with 57 more cubic inches. HP rating was 375 - same as B body hi-po 440s.
A 67 B body 383 was given a 325 hp rating, same engine as in the A body except for the exhaust manifolds. Want to see how much better the 67 B body manifolds were? Here you go (A body top, B body bottom):
View attachment 1716481118
By the way, here is an A body 383 driver's side manifold compared to a 340 driver's side manifold. Remember, the 383 got a 2.25 inch pipe coming off it, the 340 got something like an inch and 7/8, PLUS is had a huge dent in it to clear the torsion bar.
View attachment 1716481119
Now, because the early A body 383's had fewer rated hp than the later ones, many assume the later A body manifold was better. Well, I have one of each. The later A body manifolds were designed to clear power steering, not gain horsepower. Look at them side by side. The late manifolds are flatter (narrower) than the early ones to go around the steering box. The late manifolds also make a sharper turn to go down to the exhaust pipe flange.
Here, late top, early bottom.
View attachment 1716481121
Here, early left, late right.
View attachment 1716481122
I haven't flowed these two manifolds, or dyno tested them on a running engine, but the early ones sure look to me like they would flow better.
One more thing, the non-hi po B body 383s were rated at 325 hp in 67, 330 in 68-69. None had the hi-po cam. Note that the B body 330 horse 383 is NOT the same as the 69 A body 383. The non-hipo B body 383s in 68-69 had the standard cam, the A body 383s in 69 got the good Road Runner/GTX cams.
Note also, that the big cam was supposedly only 5 horsepower better than the standard cam in the 383 (330 vs. 335), but 25 hp better in a 440 (350 vs. 375) and 30 hp better in an A body 383 (300 vs. 330)
One more thing about that 280 hp rating in the 67 A body 383s. Hot Rod Magazine put a B body 383 on an engine dyno. Supposed to have 325 hp; they got 280.
And while most contemporary road tests showed the 383 A body running low fifteens in the quarter, Super Stock and Drag Illustrated got theirs to run 14.70s just by shifting manually at 5500 instead of letting it shift at 4200 in drive. (Nothing special about the governor in A body 383 Torqueflites.)
All of the contemporary road tests were skeptical of the 67 A body 383's hp rating or the claim that it lost 45 hp because of the so-called restrictive exhaust system. And really - is there any way its exhaust manifolds could be that bad? Or so bad that they lost 25 hp compared to a 64 single exhaust, two barrel, dinky cammed, single exhaust 383?
C'mon folks. Back in the fifties and sixties, the manufacturers all played games with their horsepower ratings. A 58 Ford FE 352 that was supposed to have 300 gross hp but only made 200 on a dyno? A 67 Mopar 383 that was supposed to have 325 gross hp, but only made 280 on a dyno? And there are many more examples. FACTORY RATINGS IN THIS ERA WERE NOT GOSPEL
OK, rant over.
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