9 Our test motor featured a forged crank and rods from Procomp Electronics and forged pistons from Probe Racing. The 18cc domed pistons produced a static compression ratio over 10.0:1 with the smallest chamber heads.9 Our test motor featured a forged crank and rods from Procomp Electronics and forged pis 10 ARP supplied the necessary head studs and bolts, while we relied on Fel Pro head and intake gaskets during the test.10 ARP supplied the necessary head studs and bolts, while we relied on Fel Pro head and i 11 To properly test the heads, Comp Cams came through with an XR300HR hydraulic roller cam and lifters for our test motor. The XR300HR cam offered a 0.560/0.580 lift split, a 248/254 duration split, and a 110-degree LSA.11 To properly test the heads, Comp Cams came through with an XR300HR hydraulic roller ca 12 Comp Cams also supplied the necessary timing chain, pushrods, and two-piece (aluminum) front cover for our test mule.12 Comp Cams also supplied the necessary timing chain, pushrods, and two-piece (aluminum) 13 Induction chores were handled by an Edelbrock Victor Jr. intake and Holley 950 HP carb.13 Induction chores were handled by an Edelbrock Victor Jr. intake and Holley 950 HP carb 14 Fire for our fuel was supplied by an MSD billet distributor and Digital 7 ignition amplifier. Timing was adjusted to maximize power, but most heads ran best near 40 degrees of total timing.14 Fire for our fuel was supplied by an MSD billet distributor and Digital 7 ignition amp 15 Prior to the dyno test, each head was run on the flow bench to determine not only peak flow numbers, but flow through the entire lift range.15 Prior to the dyno test, each head was run on the flow bench to determine not only peak 16 The intake ports and combustion chamber volumes were also verified. The port volumes for the various heads varied by over 45 cc, while the chamber volumes varied by as much as 11 cc.16 The intake ports and combustion chamber volumes were also verified. The port volumes f 17 It was also necessary to mock up each head to determine pushrod and ARP head bolt/stud lengths. Spring pressure was also a critical issue, as insufficient pressure limited available engine speed. Despite what manufacturers tell you, BBC heads need between 180-200 pounds of seat pressure and near 400 pounds of open pressure when running a hydraulic roller cam.17 It was also necessary to mock up each head to determine pushrod and ARP head bolt/stud 18 It was necessary to adjust the valves after each head/pushrod swap. The hydraulic roller cam made valve adjustment a snap.18 It was necessary to adjust the valves after each head/pushrod swap. The hydraulic roll 19 The stock valve springs on the peanut-port heads were obviously not going to get the job done with our hot hydraulic roller cam, so they were upgraded to a set of 26120 beehive springs from Comp Cams. Comp sold the entire upgrade, including the 0.300-thick rotator eliminator spring cups.19 The stock valve springs on the peanut-port heads were obviously not going to get the j 20 The heads run in the test varied greatly with some offering as-cast combustion chambers.20 The heads run in the test varied greatly with some offering as-cast combustion chamber 21 A couple of the manufacturers opted to supply CNC'd combustion chambers. The chamber volume varied from a low of 110 cc to a high of 121 cc.21 A couple of the manufacturers opted to supply CNC'd combustion chambers. The chamber v 22 Intake port prep also varied, from as-cast to simple port matching. 23 Companies like AFR (shown) and Edelbrock offered full CNC intake porting.23 Companies like AFR (shown) and Edelbrock offered full CNC intake porting. SOURCES Dart Machinery 353 Oliver Street Troy MI 48084 248-362-1188 www.dartheads.com Edelbrock 2700 California St. Torrance CA 90503 310-781-2222 www.edelbrock.com Airflow Research 661-257-8124 www.airflowresearch.com Brodix 301 Maple P.O. Box 1347 Mena AR 71953 479-394-1075 www.brodix.com Trick Flow Specialties 1248 Southeast Avenue Tallmadge OH 44278 330-630-1555 www.trickflow.com Holley/Hooker 1801 Russellville Road Bowling Green KY 42101 270-782-2900 www.holley.com Comp Cams 3406 Democrat Road Memphis TN 38118 800-999-0853 www.compcams.com L&R Automotive 13731 Bora Drive Sante Fe Springs CA 90670 562-802-0443 www.lnrengine.com Dr. J's Performance 436 S Montgomery Street Orange CA 92868 714-808-9780 www.j-performance.com Procomp Electronics 605 S. Milliken Avenue Unit A Ontario CA 91761 909-605-1123 www.procompelectronics.com « | 1 | 2 | 3 | 4 | 5 | View Full Article By Richard Holdener Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
