Dyno Testing the SBC
 
The purpose of this page is to show you the power output results of adding performance parts.

 

You will see that most improvements that increase the amount of air an engine can draw in will increase the horsepower, but reduce the torque at the lower RPM levels. However the maximum torque is increased, being produced at a higher RPM. This is because improvements to airflow slow the incoming air velocity at slower speeds, but increase the air volume at higher speeds. 

 

You will see that the CompCams XE268H cam improved every level of the power curve.

This is partly due to the improve design over factory of these Xtreme Energy cam.

Using a shorter duration XE cam will most likely provide a greater increase in torque at the lower speeds. However in the "real world", engines don't always respond as expected.

For example the 1-3/4" headers should have reduced the low speed torque, yet they improved it. Using these bigger headers on a stock motor would surely reduce the torque.

Additional, two identical motors will most likely produced differing power output numbers, never the less they will be close. This is because there are so many subtle variances in a motor, from port shape and size to ring sealing.

 

You will also see that the now famous GM Vortec heads only increased torque above 5000rpm,

but this increase becomes substantial. For an engine turning at 6000rpm (the numbers in blue are at 5800rpm) there was a 33ft/lbs increase and 45ft/lbs with the ported heads. The horsepower was increased 38bhp and 51bhp respectively.

These are significant numbers, but the increased cost of using these heads, typically requiring a valve spring upgrade and a special intake manifold, as is the case with most performance parts is only worth it if you plan to "rev" the motor up.

A slower running truck motor for example will not benefit from these heads.

Never the less a Vortec motor also uses a hydraulic roller cam, which will also improve overall performance, and was the staple for GM pickup trucks through the nineties.

 

If you are replacing a later model vehicle motor the Vortec is a good choice.

If it is an older vehicle, or you don't plan to rev it beyond 5000rpm, or you don't want to spend any more money than necessary, then the early GM Goodwrench motor can serve you well.

 

One last word on Vortec heads. They are cast very thin and are fragile if overheated and will crack serious, well beyond repair. However these heads will out flow Dart S/S, World S/R, (to.550 lift) GM LT1, Corvette L98, Dart Iron Eagle 180cc (however their better ex. flow will likely result in greater power production).

Pro Topline makes a much stronger Vortec head, and Edelbrock makes two sizes of aluminum Vortec heads.

Pro Topline's Torker head will out flow both their own and Gm's Vortec head.

 

A word on 383 conversions. With no other changes except the longer stroke, theoretically a 383 will make 30ft/lbs more than a 350 below 3000rpm, but begin to loose this advantage as the RPM climbs.

This is due to the increased friction of dragging the rings further up and down the cylinders.

We have found that in the "real world” the horsepower lost to fiction is not quite as serve.

However because the 383 is larger, using a slightly longer duration cam will produce a similar idle quality and vacuum as a smaller cam in the 350 and improve the upper RPM power.

Overall a 383 will accelerate more quickly in a street driven application, but a 350 will begin to catch up eventually. It is unlikely to make up the difference within a 1/4 mile.

 

Finally a roller camshaft will improve the overall power output, although it may no be as much as illustrated here, See CompCams Testing.

 

We have found that if available for an application using 1/6" rings in place of 5/32" improves power due to less fiction lost to ring drag. Lighter weight pistons and rods also promote more rapid acceleration, be the results in a street curser do not justified spending too much money on exotic parts.

 

I hope this information helps you determine where and how to spend your money.
 

RPM 355 TQ
2500 405
3000 402
3500 392
4000 367
4500 325
5000 277
5500 231
. BHP
2500 193
3000 230
3500 262
4000 280
4500 279
5000 264
5500 242
CR 9.0:1  XE256H 212/.447 218/.454

RPM 383 TQ
2500 435
3000 426
3500 407
4000 366
4500 310
5000 257
5500 207
. BHP
2500 207
3000 243
3500 271
4000 278
4500 265
5000 245
5500 216
CR 9.0:1  XE256H 212/.447 218/.454

RPM 383 TQ
2500 416
3000 414
3500 407
4000 384
4500 342
5000 294
5500 239
. BHP
2500 198
3000 236
3500 271
4000 293
4500 294
5000 278
5500 250
CR 9.0:1  XE268H 218/.462 224/.469

RPM 383 TQ
2500 441
3000 436
3500 433
4000 409
4500 362
5000 310
5500 262
. BHP
2500 210
3000 249
3500 289
4000 312
4500 311
5000 295
5500 274
CR 9.0:1  XE270HR 212/.495 218/.502

 

                          Mr Goodwrench 383s

Mr Goodwrench 350s  

 

Engine 

2000

2600

3000

3600

4000

4500

5000

5500

6000

Peek Torque   

Stock 350 8:2  Ex Manifold  & mufflers

 

---

 272

283

 320

311

 227

 238

 ---

---

324/3700

1-5/8 headers turbo mufflers

 

---

283

303

349

330

296

248

---

---

349/3600 

Edelbrock Performer manifold

 

---

267

274

350

338

306

259

---

---

350/3600

Raise CR 8.7:1 Pocket Porting

 

---

268

285

362

354

 326

282

---

---

362/3600

CompCams XE268H 224/.477 230/.480 

 

---

262

367

373

373

368

350

---

---

377/3800

Corvette L98 10:1 CR Alum. Heads

 

---

354

358

380

373

361

347

333

---

380/3600

Edelbrock RPM Holley 750 Carb

 

---

350

381

402

389

383

362

337

---

402/3500

GM Vortec Heads Edel. Performer RPM Holley 750 9.2:1 CR

Estimated  AFR 195

New AFR 195

---

347

 

348

348

381

 

393

396

398

 

422

431

395

 

441

461

389

 

452

472

374

 

445

465

352

 

418

438

---

400/3500

455/4700

475/4600

GM Vortec Pocket Ported

 

---

345

385

401

395

395

384

363

---

401/3600

Raise CR to 9.6:1

 

348 346 382 409 405 403 391

366

---

406/4300

Change to 1.6:1Rockers

 

348 346 396 416 412 414 396

372

---

415/4400

Change to 1-3/4 Headers

Estimated  AFR 195

New AFR 195

357 

 

357

357

341 

 

342

343

397 

 

409

409

428 

 

452

470

422 

 

468

488

413 

 

476

496

402 

 

473

493

378 

 

444

464

---

430/3700

476/4500

499/4700

 .

. . . . . . .

.

. 

Engine 

2000

2500

3000

3500

4000

4500

5000

5500

6000

Peek Horsepower

Stock 350 8:2  Ex Manifold  & mufflers

--- 132 162 193  237  237  227

---

---

239/4100

1-5/8 headers turbo mufflers

 

--- 127 173 204 251 254 236

---

---

255/4400

Edelbrock Performer manifold

 

--- 121 157 231 257 265 247

---

---

265/4300

Raise CR 8.7:1 Pocket Porting

 

--- 124 163 239 270 279 269

---

---

280/4400

CompCams XE268H 224/.477 230/.480  

 

--- 161 209 254 284 315 333

---

---

336/5300

Corvette L98 10:1 CR Alum. Heads

 

--- 168 204 251 284 309 331

348

---

348/5500

Edelbrock RPM Holley 750 Carb

 

--- 166 217 268 296 328 345

353

---

355/5400

GM Vortec Heads Edel. Performer RPM Holley 750 9.2:1 CR 

Estimated  AFR 195

New AFR 195

---

165 

 

165

165

217 

 

224

226

265 

 

281

287

301 

 

336

351

333 

 

387

404

356 

 

423

443

369 

 

438

459

---

396/5500

453/5600

478/5800

GM Vortec Pocket Ported

 

--- 165 220 267 300 339 366

380

---

384/5700

Raise CR to 9.6:1

 

134 156 218 279 308 345 372

384

---

396/6000

Change to 1.6:1Rockers

 

134 157 226 276 314 355 377

390

---

402/6000

Change to 1-3/4 Headers

Estimated  AFR 195

New AFR 195 

136 

 

136

136

162 

 

162

163

226 

 

234

234

285 

 

301

313

321 

 

356

372

354 

 

407

425

383 

 

450

469

396 

 

464

486

---

396/5500

472/5600

500/5800

 .

. . . . . . .

 .

. .

383 AFR 180cc Heads CR 9.8:1

CompCams XE268 Hyd. Flat. 224/.477 230/.480 

Edel. RPM Holley 750cfm

000

_____

 000

385

_____

 191

408

_____

 233

428

_____

277

434

_____

330

430

_____

377

416

_____

396

400

_____

412

364

_____

416

434/4000

____________

416/6000

383 TrickFlow 195cc Heads 9.5:1

CompCams Mech. Roller Cam 242/.570 248/.576

Edel Victor Jr. Speed Demon 750cfm 

 000

_____

 000

000

_____ 

 000

427

_____

 245

446

_____

297

454

_____

346

455

_____

390

444

_____

422

421

_____

441

394

_____

450

458/4600

____________

450/6000

383 TrickFlow 195cc Heads 9.5:1

CompCams Mech. Roller Cam 242/.570 248/.576

Edel Victor Jr. Speed Demon 750cfm

000

_____

 000

000

_____

 000

412

_____

237

428

_____

285

442

_____

337

440

_____

377

446

_____

424

424

_____

444

397

_____

453

450/4900

____________

454/6100

383 9.6:1 236/242