| By the Numbers |
| Test 1: Stock iron 5.0 heads with 1 5/8-inch headers, Flowmaster 2 1/2-inch exhaust, 750-cfm carburetor, and Comp Cams XE274 hydraulic flat-tappet cam |
| Test 2: Same as above with Dart 170cc Wet Flow heads |
| Test 3: Same as above with Dart 195cc Wet Flow heads |
|
| TEST 1 | TEST 2 | TEST 3 | DIFF |
| RPM | TQ | HP | TQ | HP | TQ | HP | TQ | HP |
| 2,200 | 276 | 116 | 266 | 112 | 271 | 113 | -5 | -3 |
| 2,400 | 275 | 125 | 262 | 119 | 280 | 128 | -5 | -3 |
| 2,600 | 282 | 140 | 277 | 137 | 292 | 145 | 10 | -5 |
| 2,800 | 292 | 156 | 295 | 158 | 305 | 163 | 13 | -7 |
| 3,000 | 303 | 173 | 311 | 178 | 317 | 181 | 14 | -8 |
| 3,200 | 312 | 190 | 323 | 196 | 327 | 199 | 15 | -9 |
| 3,400 | 321 | 207 | 331 | 213 | 336 | 217 | 15 | 10 |
| 3,600 | 328 | 224 | 337 | 231 | 342 | 235 | 14 | 11 |
| 3,800 | 330 | 240 | 343 | 248 | 347 | 251 | 17 | 11 |
| 4,000 | 334 | 255 | 348 | 266 | 350 | 267 | 16 | 12 |
| 4,200 | 334 | 268 | 352 | 282 | 351 | 281 | 17 | 13 |
| 4,400 | 332 | 278 | 354 | 296 | 351 | 294 | 19 | 16 |
| 4,600 | 327 | 287 | 353 | 309 | 350 | 306 | 23 | 19 |
| 4,800 | 321 | 293 | 350 | 319 | 348 | 318 | 27 | 25 |
| 5,000 | 314 | 299 | 346 | 329 | 345 | 329 | 31 | 30 |
| 5,200 | 307 | 304 | 341 | 338 | 343 | 340 | 36 | 36 |
| 5,400 | 300 | 309 | 337 | 347 | 339 | 350 | 39 | 41 |
| 5,600 | 293 | 312 | 334 | 356 | 335 | 358 | 42 | 46 |
| 5,800 | 284 | 313 | 328 | 362 | 329 | 363 | 45 | 50 |
| 6,000 | 271 | 310 | 317 | 362 | 320 | 365 | 49 | 55 |
| 6,200 | 256 | 302 | 301 | 356 | 308 | 364 | 52 | 62 |
| 6,400 | 242 | 295 | 291 | 355 | 298 | 364 | 56 | 69 |
| |
| Avg | 303 | 246 | 324 | 268 | 328 | 270 | 24.5 | 24.0 | |
| Peaks | 334 | 313 | 354 | 362 | 351 | 365 |
|
| Note: The DIFF column calculates the power difference between Test 1 and 3. The average power numbers were generated from data taken every 100 rpm, while we limited this chart to every 200 rpm. |
With all this power potential, we knew we'd need a decent ignitionsystem, so we plugged in one of Pertronix's new billet plug-'n'-playvacuum-advance distributors along with a set of Pertronix 8mm wires. Theaddition of the vacuum advance will also help part-throttle performanceand also give a positive nudge to fuel economy, if you care about stufflike that. Then for the exhaust side, we bolted on a set of Hooker15/8-inch Super Competition coated headers and plumbed the 3-inchcollector into a 21/2-inch exhaust system using a pair of FlowmasterSuper 40 mufflers.Testing, 1-2-3
The heads use standard Ford small-block valvetrain parts, and our headscame with 1.437-inch single springs, 10-degree retainers, 3/8-inchrocker studs, and Comp Cams guideplates.
To begin our test, we decided to use the base set of iron '89 5.0L headsalong with the Performer RPM intake, 750-cfm carb, headers, and exhaust.The engine spec'd out at 9.2:1 compression, running on paltry 92-octanepump gas. This would give us a solid baseline with the bigger Compcamshaft that we could use for our power evaluation. After carefullybreaking in the camshaft, the little 306ci small-block churned out 313hp at 5,800 with at 334 lb-ft at 4,000. Now it was time to bolt on thefirst of the Dart heads.
We decided to test the smaller, 170cc heads first. It was a simple taskto bolt on the heads on the Digilog dyno. We did not see a huge gain intorque--peak torque improved by 20 lb-ft--but it also moved up the rpmband from 4,000 to 4,400, which would explain part of the increase.Where these 170cc Pro 1 Dart heads really shine is in the horsepowerdepartment. From 4,400 rpm on up, the Dart heads were worth an averageof 43 hp, while peak power surged from 313 with the stock iron heads toan impressive 362, for a gain of 49 hp. Average horsepower throughoutthe entire rpm span also improved from 246 to 268, for an overallaverage horsepower gain of 22. Remember, all we did was bolt on a set ofheads.