We don't have to tell you that other than a nitrous kit, the best bang for your horsepower buck will always be with a set of good cylinder heads. Dart recently upgraded its lineup of aluminum Pro 1 Ford castings with two sets of redesigned Pro 1 heads that have benefited from Dart's work with a very sophisticated wet flowbench.
This bench has allowed Dart to massage the ports to improve wet-flow performance, which means that the company now takes into consideration not just how the air flows through the intake ports and into the combustion chambers, but also how the heavier fuel is transported into the chambers. The theory is that by tweaking the intake ports and the chambers, these heads will make more power. It sounded good to us, so we decided to test the idea on a conservative little 0.030-over 302 Windsor Ford we put together for "Build Your First Engine" in the July '04 issue.
The only significant change we made to the engine was to swap in a larger cam to take better advantage of these new Pro 1 heads. Right about now, you're probably thinking that while these heads made great power, they're also probably close to $900 each. Would you change your mind if we told you these heads sell through Summit Racing for $456 each, complete and ready to bolt on? That's just a touch over $900 for the pair.
Head GamesDart offers two new Pro 1 wet-flow aluminum heads for the Windsor Ford-a 170cc intake port and a 195cc version. The smaller heads come with 1.94/1.60-inch valves. The larger heads are blessed with a bigger, 2.02-inch intake valve, while the exhaust remains at 1.60. Both heads feature 62cc chambers with a modern, kidney-shaped configuration to improve combustion efficiency. The heads lock into the standard Ford 20-degree valve angle and intake-face configuration, but to improve the exhaust side, Dart raised the exhaust ports 0.135 inch, although the stock header-flange bolt spacing remains. This means there may be some clearance issues between the chassis and headers in some applications.
The heads were assembled with 1.437-inch-diameter springs set up with130 pounds of seat pressure at an installed height of 1.800 inches. If you desire bigger springs, Dart can also equip either of these heads with 1.550-inch-diameter springs that pump up the seat pressure to a stout 195 pounds at a 1.900-inch installed height for more valve-lift clearance for the valve-stem seals.
Test ConfigurationTo complete our 306ci little-block, engine guru Ed Taylor bolted in a more aggressive Comp Cams Xtreme Energy 274 camshaft (see "Cam Specs" sidebar). While hardly a daily driver kind of cam, if you're going to build a serious small-block Ford, you have to screw a little camshaft into the engine. At a touch over 0.500-inch lift for the intake and exhaust, this cam and its longer duration seemed to be a good match for the Dart heads.
To complete the induction side, we retained the Edelbrock Performer RPM Air Gap intake manifold but added a larger Holley 750-cfm, 0-4779 mechanical-secondary fuel mixer to ensure the induction side would not present a restriction. We could have converted to a single-plane like an Edelbrock Victor Jr. 302 to pump up the top-end power, but we felt that the midrange torque advantages of the RPM Air Gap were well worth the small sacrifice.
With all this power potential, we knew we'd need a decent ignition system, so we plugged in one of Pertronix's new billet plug-'n'-play vacuum-advance distributors along with a set of Pertronix 8mm wires. The addition of the vacuum advance will also help part-throttle performance and also give a positive nudge to fuel economy, if you care about stuff like that. Then for the exhaust side, we bolted on a set of Hooker 151/48-inch Super Competition coated headers and plumbed the 3-inch collector into a 211/42-inch exhaust system using a pair of Flowmaster Super 40 mufflers.
Testing, 1-2-3To begin our test, we decided to use the base set of iron '89 5.0L heads along 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-octane pump gas. This would give us a solid baseline with the bigger Comp camshaft that we could use for our power evaluation. After carefully breaking in the camshaft, the little 306ci small-block churned out 313 hp at 5,800 with at 334 lb-ft at 4,000. Now it was time to bolt on the first of the Dart heads.
We decided to test the smaller, 170cc heads first. It was a simple task to bolt on the heads on the Digilog dyno. We did not see a huge gain in torque-peak torque improved by 20 lb-ft-but it also moved up the rpm band 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 horsepower department. From 4,400 rpm on up, the Dart heads were worth an average of 43 hp, while peak power surged from 313 with the stock iron heads to an impressive 362, for a gain of 49 hp. Average horsepower throughout the entire rpm span also improved from 246 to 268, for an overall average horsepower gain of 22. Remember, all we did was bolt on a set of heads.
With this kind of gain, we were excited about testing the 195cc heads to see what kind of power we would see with the larger intake. We anticipated that the low and midrange power probably would not improve, since the 170cc Pro1 heads would have the velocity advantage over the larger 195cc heads. The larger heads did perform better compared to the smaller Dart heads in the midrange from 3,000 to 4,000 rpm, generating more torque than the smaller Dart heads. Had we spent more time on tuning the smaller heads, it's possible we could have made more torque in this range since the air/fuel ratio was a bit lean in the midrange area with the 170cc heads.
Looking at the peak numbers, the 195cc heads cranked out a serious 365hp achievement at 6,000 rpm and continued to carry only a minor drop in peak power all the way through 6,400 rpm, which told us that had we bolted in a bigger cam or perhaps a set of 1.7:1 rockers, we might have made even more power. But let's not downplay a solid 52hp increase over the stock iron heads with these out-of-the-box Pro 1s. If we're allowed to play "what-if" games, it appears that the larger 195cc heads would do better yet with a larger camshaft and more valve lift to take advantage of their greater flow potential.
Evaluating either of the Dart Pro 1 heads against the iron baseline, it's obvious that Dart has scored again for the small-block Ford fans with a great selection of heads. Anytime you can bolt on 50-plus horsepower with a pair of heads that cost less than $1,000, that's a bull's-eye where we come from.
By the NumbersTest 1: Stock iron 5.0 heads with 151/48-inch headers, Flowmaster 211/42-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 365Note: 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
Cam Specs Adv. Dur. @ Lobe Camshaft Dur. 0.050 Lift Sep. Comp. XE274, Int. 274 230 0.519 in 110 Flat-tappet hyd., Exh. 286 236 0.523 in Parts List Item Source Type PN Price Camshaft Comp Cams XE 274 31-246-3 $105 Lifters Comp Cams Hydraulic flat 832-16 86 Rocker arms Comp Cams Aluminum rollers 1043-15 301 Pushrods Comp Cams Heavy duty 7831-16 28 Dart 170, Pro 1 Dart Aluminum 13100080 456 Dart 195, Pro 1 Dart Aluminum 13200010 456 Carburetor Holley 750 0-4779 398 Intake manifold Edelbrock RPM Air-Gap 7521 231 Valve Covers {{{Ford}}} Racing Black {{{M}}}-6582-F302 n/a Water Pump Edelbrock Aluminum 8840 145 Main studs ARP Stud kit 254-5501 58 Head-bolt kit ARP Black oxide, 6-pt. 154-3605 91 Engine-bolt kit ARP Black oxide 554-9801 117 Pulley set March Single V-groove 01614 n/a Headers, coated Hooker 151/48-inch 6222HKR 380 Mufflers Flowmaster Super 40 952546 {{{80}}} ea. Distributor Pertronix Billet plug 'n' play D130710 191 Plug wires Pertronix 8mm 808390 50Note: All prices were pulled from www.summitracing.com so you have a realistic idea of what the parts cost.
