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