"Tech Papers" by panic
Are American V-8 Motors That Bad?
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    The myth is that American V-8 motors are fun, patriotic, valuable, but inefficient and obsolete. They appear to produce much less horsepower per inch than an equivalent foreign (Japanese, German, Italian, etc.) motor, and are therefore technically backward, retrograde and inferior.

    This is not true. Horsepower per cubic inch absolutely cannot be “scaled” up or down; cylinders of different sizes and proportions behave quite differently. Larger cylinders are (generally) more efficient as to ring seal (this is physics, not quality control), and also thermal efficiency (surface to volume ratio). However, due to mechanical stress limits, they are only more efficient than smaller cylinders until they reach their piston acceleration limit (125,000 f/s/s with 1mm rings), at which point the higher potential speed of the smaller cylinder begins to have the advantage.
    A fair evaluation cannot be made solely on the basis of displacement (3000cc, for example, regardless of motor type). Dr. F. W. Lanchester, one of the earliest true geniuses of the internal combustion engine, analyzed this problem over 90 years ago, and correctly decided that comparing motors on the basis of size only gave an unfair advantage to motors with more cylinders, and favored those with larger bores and shorter strokes. He devised a formula to allow motors with different numbers of cylinders, and different proportions to compete on a fair and equal basis, with the superior product to be determined by the execution of its individual design & construction, regardless of bore and stroke. His original formula needed only slight modification to be accurate today:

HP = B1.65 × S.5 × N × C

    In plain English, the horsepower of a motor is equal to the Bore taken to the 1.65 power, times the Stroke taken to the .5 power, times the Number of cylinders, times a Constant representing the quality of material available, type of fuel, barometric pressure, temperature, etc. I've arbitrarily chosen to value “C” at 4 for a race motor, and 60% of that, or 2.4 for a street motor, to return a realistic number. For those of you who've forgotten their math, I've used superscript to indicate powers: “B2” is “B squared”, or multiplied by itself; “B.5” is “square root of B”. Today's pocket calculators make easy work of this.

    Watch what happens to a 340 as the stroke is increased, using the same bore size:

340 Power with Stroke as Variable

Bore

Stroke

Type

Race Factor

Street Factor

HP, Race

HP, Street

Engine Size

HP/Cubic Inch

4.04”

2.960”

Trans-Am

4

2.4

551 HP

331 HP

304”

1.81

3.310”

340 std.

583 HP

350 HP

339”

1.72

3.580”

360 stroke

606 HP

364 HP

367”

1.65

3.790”

Stroker

624 HP

374 HP

389”

1.60

4.000”

Stroker

641 HP

384 HP

410”

1.56

4.125”

Stroker

651 HP

390 HP

423”

1.54

4.250”

Stroker

661 HP

396 HP

436”

1.52

    Here's a 400 B motor used as the basis:

400 Power with Stroke as Variable

Bore

Stroke

Type

Race Factor

Street Factor

HP, Race

HP, Street

Engine Size

HP/Cubic Inch

4.34”

3.000”

De-stroke

4

2.4

625 HP

375 HP

355”

1.76

3.375”

400

662 HP

397 HP

399”

1.66

3.750”

451

698 HP

419 HP

444”

1.57

3.900”

BBC rod

712 HP

427 HP

462”

1.54

4.000”

Stroker

721 HP

433 HP

473”

1.52

4.150”

Stroker

735 HP

441 HP

491”

1.50

4.250”

Stroker

743 HP

446 HP

503”

1.48

    The following table is a series of hypothetical motors of the same displacement: 122” or 2000cc (2 litres). All are built with the proportion of bore to stroke fixed at 4-3 (such as 4.00” + bore 3.00” stroke = 302”), to remove this as a variable. The number of cylinders is the important variable. Note the huge difference in maximum power for V-12 engines.

2000cc Motors, Bore/Stroke Ratio: 4-3, Variable: Number of Cylinders

Number of Cylinders

Bore

Stroke

Race Factor: 4

Street Factor: 2.4

V-12

2.585”

1.939”

320 HP

192 HP

V-8

2.960”

2.220”

286 HP

171 HP

6

3.255”

2.441”

263 HP

158 HP

4

3.730”

2.798”

235 HP

141 HP

2

4.700”

3.525”

193 HP

116 HP

    The following table is a series of hypthetical motors with varying numbers of cylinders, built using the same piston size (4.25”), with the stroke varied to achieve the same engine size: 454”.

454” Motors, Bore: 4.25”, Variable 1: Number of Cylinders, Variable 2: Stroke Length

Number of Cylinders

Bore

Stroke

Race Factor: 4

Street Factor: 2.4

16

4.25”

2.000”

985 HP

591 HP

12

2.665”

853 HP

512 HP

8

4.000”

697 HP

418 HP

6

5.335”

603 HP

362 HP

4

8.000”

493 HP

296 HP

2

16.00”

348 HP

209 HP

    Notice that the stroke increase has very little effect on maximum power; this strongly favors motors with short strokes. The V-12's power is the result of physics, not better quality, as the formula shows!!

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