Drag Illustrated Issue 150, November 2019

tional cylinder sealing bolts. One potential weak- ness with all LS engines is the factory four-bolt cylinder head pattern. Assuming that this head will see both aggressive normally aspirated ad- venture and power-adders such as nitrous, su- perchargers, or turbochargers, the Dart head is equipped with a 6-bolt pattern. These extra bolts are intended to be used with a matching Dart LS Next block that offers the additional cylinder clamping option. This allows pushing the cylinder pressure envelope while minimizing the danger of pushing out the head gasket. Accompanying these additional fasteners is a thicker 0.750-inch deck surface that is com- mon among all Dart LS head packages and also promotes gasket sealing. Along with high cylinder pressure is the promise that these heads will also see higher engine speeds. Addressing this concern is Dart’s option of using either the standard LS7 rockers with a Dart billet rocker bar or with optional machining that will ac- commodate a Jesel shaft rocker arm system. Dart also offers a range of different valve spring options from a street-oriented beehive to an aggressive dual spring combo for hydraulic roller lifters all the way up to a larger 1.310-inch diameter dual spring for mechanical rollers that will require adjustable rockers for lash. These sturdier springs place the maximum valve lift at 0.650-inch. A stock LS7 chamber comes in around 70cc, but the Dart Pro 1 version enjoys a much more enhanced fully-CNC machined chamber that measures 66cc. This may not seem like much, but this slight change is worth almost exactly a half ratio of compression, depending upon your configuration. This tighter chamber also makes it much easier to create compression in a competi- tion engine without resorting to obtrusive domes that negatively affect flame travel. The larger, 285cc intake ports also enjoy the advantages of complete CNC porting that exactly matches the design as opposed to as-cast ports that may suffer from slight variations due to cast- ing variables. All this points to enhanced flow as evidenced by the accompanying flow chart that reveals this head is capable of 381 cfm of airflow at 0.800-inch valve lift. These are equivalent big-block Chevy flow numbers but delivered in a far lighter and more efficient overall package. A recent Dart dyno test on a 427ci Dart SHP short block with the LS3 style 15-degree Dart heads destined for Drag Week cranked out 759 hp at 7,300 rpm with 600 lb-ft of torque at 5,900. With the obvious flow advantages of this latest PRO1 12-degree head, higher horsepower num- bers are certainly possible. The 285cc PRO1’s taller valve angle and valvetrain enhancements all point to positive top-end horsepower possibilities. As an added benefit, Dart also offers a LS7 style intake manifold to complement the new heads. The 4150 style carbureted manifold comes as a split design where the manifold is split vertically in the center to allow custom porting or in-house CNC porting by Dart. -JEFF SMITH FLOW CHART These numbers were generated on a SuperFlow bench using the standard test depression of 28 inches of water and a 4.125-inch cylinder bore. VALVE LIFT DART INT. DART EXH. 0.200 0.300 0.400 0.500 0.600 0.700 0.800 162 233 293 334 361 380 381 118 164 208 230 244 252 263 The exhaust side of the 12-degree Dart head maintains the stock LS7 port location and bolt pattern which makes converting these heads easy. These Pro 1 exhaust ports are a substantial improvement over the stock versions, which is an area often overlooked but crucial to top-end horsepower. PART NUMBERS DESCRIPTION Dart Dart Dart Dart Dart Dart Dart LS7 12-deg. C-Core bare casting LS7 12-deg. Bare, Dart rocker bar LS7 12-deg. Bare, Jesel rocker bar LS7 12-deg. 1.290” beehive, hyd. roller LS7 12-deg. 1.295” dual, hyd. roller LS7 12-deg. 1.310” dual, solid roller Pro 1 LS 12-deg. single plane carb intake manifold MAX LIFT PN N-A N-A N-A 0.625 0.650 0.650 N-A 11060000 11060080 11060080J 11061182 11061183 11061184 45311021 The heads are available bare or assembled with hydraulic or solid roller valve springs. They can also be configured for a Dart rocker bar compatible with stock LS7 rockers or fitted for a Jesel rocker set up. The LS7 uses an intake pattern that is different from the more common LS3 rectangle port layout. Dart anticipated this and offers five different carbureted or EFI configured split plenum manifolds that can be used for a specific high-horsepower application. Dart’s 285cc rectangle port LS7 style head is near the peak of potential for a hot street cylinder head. It sports fully CNC ports and combustion chamber using massive 2.20 / 1.625-inch valves. This head must be used on a 4.125-inch or larger bore in order to clear the valves. November 2019 DragIllustrated.com | D r a g I l l u s t r a t e d | 63

Drag Illustrated Issue 150, November 2019 | Page 63