Desktop Dyno Calculations

 

Mopar Factory Engines

 

Stock 1968 383 Magnum                      Stock 1968 440 Magnum

(335 HP / 425 TQ factory rated)                       (375 HP / 480 TQ factory rated)

                                                           

RPM     HP        TQ                                            RPM     HP        TQ

2000     134       350                                           2000     155       408

2500     172       360                                           2500     197       414

3000     218       381                                           3000     246       430

3500     257       386                               3500     289       434                

4000     290       381                                           4000     325       426

4500     316       368                                           4500     353       412

5000     331       347                                           5000     371       390

5500     335       320                                          5500     372      355

6000     322       281                                           6000     359       314

 

Peak HP: 335HP @ 5500-RPM               Peak HP: 372HP @ 5500-RPM

Peak TQ: 386 ft/lb @ 3500-RPM             Peak TQ: 434 ft/lb @ 3500-RPM

 

These are the factory engines for 1968.  I tried to get all of the specification as perfect as I could.  As I entered the data, I was able to calculate where the biggest gains were.  I’m most concerned with the Torque (TQ) of an engine rather than the Horsepower (HP).  Torque makes a street car easier to drive.  Notice how the Factory Torque Numbers are about 40 ft lbs greater than what I could do on Desktop Dyno.

 

 

Stroker Designs (Exhaust Manifold Comparison)

 

383/431 Stroker #1                                383/431 Stroker #2

HP exhaust manifolds                                        HP exhaust manifolds

OEM Camshaft  @ 0 degrees                         OEM Camshaft @ 4 degrees Advanced

 

RPM     HP        TQ                                            RPM     HP        TQ

2000     155       407                                           2000     158       415

2500     198       417                                           2500     203       427

3000     250       437                                           3000     256       448

3500     293       440                               3500       299     449

4000     330       433                                           4000     333       438

4500     357       416                                           4500     359       419

5000     372       391                                           5000     372       390

5500     376       359                                          5500      368       352

6000     359       314                                           6000     345        302

 

Peak HP: 376 HP @ 5500-RPM              Peak HP: 372 HP @ 5500-RPM 

Peak TQ: 440 ft/lb @ 3500-RPM             Peak TQ: 449 ft/lb @ 3500-RPM

383/431 Stroker #3                                383/431 Stroker #4

HP exhaust manifolds                                        HP exhaust manifolds

MP 280 Camshaft @ 0 degrees                        MP 280 Camshaft @ 4 degrees

 

RPM     HP        TQ                                            RPM     HP        TQ

2000     148       388                                           2000     149       392

2500     193       405                                           2500     196       412

3000     244       427                                           3000     249       436

3500     290       435                                3500     295     442

4000     328       430                                           4000     331       434

4500     359       419                                           4500     359       419

5000     375       393                                           5000     370      389

5500     375       358                                          5500      363       347

6000     356       312                                           6000     337        295

                                                           

Peak HP: 375 HP @ 5000&5500-RPM     Peak HP: 370 HP @ 5000-RPM 

Peak TQ: 435 ft/lb @ 3500-RPM                Peak TQ: 442 ft/lb @ 3500-RPM

 

Stroker #1 and #2 made more TQ and HP than the 440 Magnum from 2000-RPM to 5500-RPM.  They basically had 400 ft/lbs of TQ from 2000-RPM to 5000-RPM.  That is a fairly flat torque curve.  Stroker #2 had the Factory Camshaft centerline set to 4 degrees advanced.  This brings the HP/TQ curves into play sooner.  It probably has about 400 ft/lbs at just above 1500 RPM.  But Stroker #2 will run out of steam a little early.  Notice how Stroker #1 gains ground on Stroker #2 from 4000-RPM up to 6000-RPM.

 

Stroker #3 and #4 used the Mopar Purple Shaft 280 camshaft.  Its HP curve was flat at the peak, which would designate the shift point of 5500 RPM.  However, the camshaft didn’t really perform as well as the OEM Magnum.  Both TQ and HP were down in the comparison.  With the Factory Intake and Exhaust Manifolds, the MP 280 didn’t get a chance to breathe.

 

 

Stroker Designs (Ceramic Coated Header Comparison)

 

383/431 Stroker #5                                383/431 Stroker #6

Ceramic Coated Headers                                    Ceramic Coated Headers

OEM Camshaft @ 0 degrees                              OEM Camshaft @ 4 degrees advanced

 

RPM     HP        TQ                                            RPM     HP        TQ

2000     171       448                                           2000     174       457

2500     218       458                                           2500     222       466

3000     263       460                                           3000     269       470

3500     311       466                                 3500     318     476

4000     357       468                                          4000     362       475

4500     392       458                                           4500     396       462

5000     414       435                                           5000     415       436

5500     421       401                                           5500     413       394

6000     402       352                                           6000     388       339

6500     372       301                                           6500     350       283

 

Peak HP: 421 HP @ 5500-RPM              Peak HP: 415 HP @ 5000-RPM 

Peak TQ: 468 ft/lb @ 4000-RPM             Peak TQ: 476 ft/lb @ 3500-RPM

 

383/431 Stroker #7                                383/431 Stroker #8

Ceramic Coated Headers                                    Ceramic Coated Headers

MP 280 Camshaft @ 0 degrees                           MP 280 Camshaft @ 4 degrees advanced

 

RPM     HP        TQ                                            RPM     HP        TQ

2000     165       434                                           2000     167       439

2500     211       444                                           2500     214       449

3000     257       449                                           3000     262       459

3500     309       464                                           3500     315       473

4000     357       469                                          4000      361       474

4500     397       463                                           4500     399       465

5000     419       440                                           5000     415       436

5500     421       402                                           5500     410       391

6000     399       349                                           6000     380       332

6500     364       294                                           6500     334       269

 

Peak HP: 421HP @ 5500-RPM               Peak HP: 415 HP @ 5500-RPM

Peak TQ: 469 ft/lb @ 4000-RPM             Peak TQ: 474 ft/lb @ 4000-RPM

 

 

 

For Stroker #5, I added a set of Ceramic Coated Exhaust Headers to the OEM camshaft.  For the Desktop Dyno calculations, I used Small-Tube Headers with Mufflers.  It was a huge gain in both HP and TQ.  Stroker #4 made 45 HP more and 19 ft/lb peak TQ more than without the headers.  Stroker #5 made 450 ft/lbs of TQ from 2000-RPM to 4500-RPM and comes close to making 400 ft/lbs TQ at IDLE!!  Horsepower was way up, by letting the engine breathe.  Stroker #6 picked up much earlier in the TQ curve and really produced the numbers I like.  I set the OEM camshaft to 4 degrees advanced on the centerline.  Which moved the HP/TQ curves lower.  It lost a little HP but still gained 39 HP over exhaust manifolds.  However, it gained 27 ft/lbs of TQ.  It probably makes more TQ at idle than Stroker #1, #2, #3, and #4 made through the entire power-band.

 

Stroker #7 and #8 had the Mopar Performance 280 camshaft installed.  Now that the engine could breathe a bit better, the camshaft performed much better.  Both the HP and Torque numbers were very similar, with the MP 280 edging the OEM Magnum in the 4000-RPM to 5000-RPM range.  However, the Stroker still didn’t breath well enough to use the MP 280 to it’s potential.  Intake and cylinder head modifications would need to be made.

 

These are just basic Desktop Dyno numbers, not real life.  These were done to help understand where the possibilities may lie in building good, useable horsepower and torque in the Stroker 431.

 

Mark Jackson

February 14, 2005