Back to Durango Deuce ProjectCalculating Horsepower at Altitude
Variables:
PSI = atmospheric pressure (see table)
CR = compression ratio (10.6)
HP = Horsepower
VE = Volumetric efficiency (.95-1.05)*
CID = cubic Inch displacement (335)
RPM = revolutions per minute (6000)
(PSI x CR x VE x CID x RPM) ¸ 5252 ¸ 150.8 = HP
Example: 14.70 x 10.6 x 1.05 x 355 x 6000 ¸ 5252 ¸ 150.8 = 440 HP
|
Altitude |
PSI |
283 CID .80 VE @ 5,252 rpm |
335 CID .95 VE @ 5,252 rpm |
335 CID 1.0 VE @ 6,000 rpm |
335 CID 1.05 VE @ 6,000 rpm |
|
0 |
14.70 |
233.94 |
328.84 |
395.45 |
415.22 |
|
1,000 |
14.17 |
225.50 |
316.99 |
381.19 |
400.25 |
|
2,000 |
13.66 |
217.39 |
305.58 |
367.47 |
385.85 |
|
4,000 |
12.69 |
201.95 |
283.88 |
341.38 |
358.45 |
|
6,000 |
11.77 |
187.31 |
263.30 |
316.63 |
332.46 |
|
8,000 |
10.90 |
173.46 |
243.84 |
293.23 |
307.89 |
Notes:
Volumetric Efficiency = actual volume of air used by the engine ¸ the CID.
335 ¸ 335 = 1 or 100% VE
100% VE means the cylinders are completely filled with air.
Less than 100% means less torque is produced.
Peak torque generally occurs at peak VE.
Torque and horsepower are equal at 5252 RPM
Supercharged engines force more air into the cylinder and have VE over 100%
Normally aspirated race engines can have VE over 100% because of inertial ram effect.
Edelbrock tech page says:
Stock engines have around 60-80% VE
Performer engines 75-90% VE
Torker engines have 90-100% VE
Performer RPM engines have 95-105% VE
Victor Jr. engines have 105-115% VE
Victor engines have 110-122% VE
Must have the complete engine package for these numbers to be valid.