Chrysler ball-stud hemi

The ball-stud hemi (known internally as A279 and affectionately as the BS Hemi)^[1] was an automobile engine designed by Chrysler Corporation in the late 1960s.^[2] It never entered production.^[3]

Intended to deal with the troubles created by the low-production 426, of which only about 9,000 were built from 1966 to 1972),^[4] as well as the different architectures of the higher-volume 383 cu in (6.3 l) and 400 cu in (6.6 l) B and 440 cu in (7.2 l) RB V8s, the ball-stud hemi was to be suitable for high-volume manufacture at low cost while generating high performance.^[5] Chrysler hoped to replace three block and two head designs with the ball-stud design.^[6] It was to be based on a low-deck block and available in 400 cu in (6.6 l) (4.32 by 3.38 in (110 by 86 mm))^[7] and 440 cu in (7.2 l) 4.32 by 3.75 in (110 by 95 mm))^[8] displacements^[9] (and Chrysler considered a 444 cu in (7.3 l),^[10] which could have used stock 4.32 in (110 mm) 400 cu in (6.6 l) pistons),^[11] while the new valvetrain would cut both weight and cost,^[12] as well as making it possible to fit it in a greater variety of models.^[13]

The A279 initially used the B-block head bolt pattern, which "badly hampered" its exhaust ports,^[14] forcing the use of a serpentine flow around some of the outer bolts^[15] This was changed late in development,^[16] but not before some tooling based on the original design had already been created.^[17] This meant the head was not truly hemispherical, but had more intake port area than exhaust (3.575 sq in (23.06 cm²) versus (2.488 sq in (16.05 cm²)).^[18]

Its intake valves were nearer the intake manifold, exhaust valves nearer the exhaust pipes.^[19] The staggered "poly" arrangement improves airflow by "reducing valve shrouding and eliminating the sharp runner turns" of inline valve arrangements.^[20] It also had equally-spaced intake ports (similar to the 428SCJ), thereby achieving "more consistent mixture distribution" than the Wedges.^[21] Chrysler used a 14 mm (0.55 in) spark plug, rather than the typical 18 mm (0.71 in), in an effort to fit it as centrally as possible in the combustion chamber.^[22]

The intake and exhaust valves were the same size as the 426's,^[23] the 2.25 in (57 mm) intake canted at 15° from the bore centerline, the 1.94 in (49 mm) exhaust at 6°.^[24] By contrast, the B-block's were 2.08 in (53 mm) and 1.74 in (44 mm).^[25]

Compared to the wedge, the ball-stud block had two additional clean-out holes to remove casting sand, because the large bore made coolant in the water jacket very significant,^[26] and an additional oil drainback hole at either end of the block, due to demand for lubrication of the rocker arms.^[27] Suggestions to increase the size of the oil pump pickup to 3/8 in (9.5 mm) (compared to the 426's 1/2 in (12.7 mm)) never passed the endurance testing stage.^[28]

Pistons were to be cast aluminum.^[29] Compression ratio was targeted as 10.5:1; on the surviving engine, it was measured at 9.8:1.^[30] Forged conrods used the Wedge's 3/8 in (9.5 mm) hardware, as opposed to the Hemi's 7/16 in (11.1 mm), but would nonetheless have been considered high-performance parts.^[31]

The intake was to be a single Carter ThermoQuad, of greater flow than any previously used, on a dual-plane intake manifold,^[32] while dual four-barrels were never even considered, in the face of toughening emissions standards.^[33] A split-level (vertically split, rather than horizontally divided) intake was also experimented with.^[34]

Chrysler hoped to have the ball-stud in production sometime between 1971 and 1973.^[35] In testing, it proved able to outperform the single four-barrel carburetted A134 440, and lagged behind the eight-barrel A102 426 Street Hemi.^[36] About one year of development was put in before the project was stopped, in late 1969.^[37] It wa a victim of increasing demand for emissions controls and a reduction in emphasis on performance, as the "horsepower wars" wound down.^[38] Moreover, Chrysler was suffering "severe financial stresses" that nearly brought the company down,^[39] so the new production tooling and facilities were now uneconomic.^[40]

Estimates of the number built vary from three to twelve.^[41] Only one is known to survive.^[42]

Notes

1. ^ Kirschenbaum, p.72.
2. ^ Kirschenbaum, Al. "Mopar Mystery Motor", in Hot Rod, 3/86, p.71.
3. ^ It should not be confused with Chrysler Australia's 245 cu in (4.0 l) Hemi slant 6. Kirschenbaum, p.72.
4. ^ Kirschenbaum, p.71.
5. ^ Kirschenbaum, p.71.
6. ^ Kirschenbaum, p.71.
7. ^ Kirschenbaum, p.78.
8. ^ Kirschenbaum, p.78.
9. ^ Kirschenbaum, p.71.
10. ^ Kirschenbaum, p.71.
11. ^ Kirschenbaum, p.78.
12. ^ Kirschenbaum, p.71.
13. ^ Kirschenbaum, p.71.
14. ^ Kirschenbaum, p.72.
15. ^ Kirschenbaum, p.72.
16. ^ Kirschenbaum, p.72.
17. ^ Kirschenbaum, p.72.
18. ^ Kirschenbaum, p.72.
19. ^ Kirschenbaum, p.72.
20. ^ Kirschenbaum, p.72.
21. ^ Kirschenbaum, p.72.
22. ^ Kirschenbaum, p.72.
23. ^ Kirschenbaum, p.74.
24. ^ Kirschenbaum, p.74.
25. ^ Kirschenbaum, p.74.
26. ^ Kirschenbaum, p.74.
27. ^ Kirschenbaum, p.72.
28. ^ Kirschenbaum, p.74.
29. ^ Kirschenbaum, p.74.
30. ^ Kirschenbaum, p.72.
31. ^ Kirschenbaum, p.72.
32. ^ Kirschenbaum, p.78.
33. ^ Kirschenbaum, p.72.
34. ^ Kirschenbaum, p.78.
35. ^ Kirschenbaum, p.71.
36. ^ Kirschenbaum, p. 71.
37. ^ Kirschenbaum, p.71.
38. ^ Kirschenbaum, p.71.
39. ^ Kirschenbaum, pp.71-2.
40. ^ Kirschenbaum, p.71.
41. ^ Kirschenbaum, p.71.
42. ^ Kirschenbaum, p.71.

Sources

• Kirschenbaum, Al. "Mopar Mystery Motor". Hot Rod, 3/86, pp.71-8.