October '19

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38 THE SHOP OCTOBER 2019 BUILDING THE Nighthawk II LS PRECISION ENGINE finalized at 192 grams and big ends at 444 grams (x2). Rod bearings x 2 weighed in at 86 grams, ring packages (including support rails) were at 61 grams, and a pair of spiral locks at 4 grams. Total bobweight was set at 1,714 grams. With the addition of 4 grams for antici- pated oil cling, each bobweight half was set at 861 grams. During the initial spin, the crank was heavy at the front by 38 grams and the rear was heavy by 42 grams, which was great— no need for adding weight. To accommo- date the light weight of the Icon pistons and the subsequent bobweights, material was easily removed from the front and rear counterweights (via Holtrey's balancing machine's drill press), finalizing at -1.5 grams front and -1.7 grams rear. Thanks to SCAT's excellent raw balance setup of this crank and Holtrey's exper- tise, this was a relatively straightforward balance job. After balancing, I installed a GM 12561513 key into the SCAT crank's rear key slot and a Pioneer PK9 short key into the front slot (for the Fluidampr balancer). After applying a thin film of Royal Purple Max Tuff assembly lube onto the crank snout, I then heated the Cloyes crank gear in my convection oven to about 350 degrees and gently tapped it into place using an aluminum tube as a driver. This was followed by installing the Cloyes oil pump drive gear (heated as well to ease installation). An ARP crank bolt and washer secured the balancer, requiring a straight torque of 235 foot-pounds. This eliminated the multi-step installation of a one-time-use GM OE bolt and provided a re-usable feature in addition to offering vastly superior durability. The 428-ci build managed 631 hp at 6,300 rpm and 563 foot-pounds of torque at 4,800 rpm during a rather limited time on the dyno. The potential is there, with more ponies to be had with further tuning. But, considering that this build was planned as a totally streetable LS platform, 631 hp is nothing to sneeze at as our initial baseline. COMPRESSION RATIO OF OUR 428 CID: CYLINDERS 8 BORE 4.131" STROKE 4.000" ROD LENGTH 6.125" GASKET BORE 4.200" HEAD GASKET THICKNESS 0.051" DECK HEIGHT 9.240" TOP OF 1st RING TO PISTON TOP 0.180" COMBUSTION CHAMBER 69 cc PISTON DISH + 3 cc DECK TO PISTON 0.000" TOTAL VOLUME 962.87 cc CYLINDER VOLUME 8878.57 cc HEAD GASKET VOLUME 11.57 cc COMPRESSION RATIO 11.42:1 CAM BEARINGS & CAM The Dart LS Next block requires 55mm bearings with all bearings featuring the same O.D. So, instead of using LS cam bearings (MAHLE SH2125S), we needed to obtain Dart bearings P/N 32210101-5. These bearings are PTFE-coated and designed for use in the Dart block. Each bearing features three oil holes and a cir- cumferential oil groove. Read the Dart block instructions and be aware of this prior to ordering your cam bearings. After bearings were installed using our Goodson cam bearing installer tool, the COMP hydraulic roller cam was coated (journals and lobes) with Royal Purple Max Tuff lube and carefully inserted. The cam slid in smoothly and rolled effort- lessly, with no need to perform any bearing scraping. Dart's precision cam bores (along with our previous careful deburring of all cam bore edges) made bearing installation a breeze. With the cam fully inserted, the spe- cial Dart cam retainer plate was installed, with the two button-head screws coated with Loctite 242 and torqued to 106 inch- pounds. A total of about eight spins were performed as Jody Holtrey crept up on the target weight. Our lifter bodies measured 0.842 inches. Lifter bore clearance measured 0.0015 inches with bores at 0.8435 inches. Our COMP hydraulic roller cam features lobe lift of 0.367/0.367 (0.624 w/ 1.7 rockers), duration of 243/251 and LSA 114. Rated at 2,400-7,200 rpm.

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