Cylinder Head Development
Precision Race Components was founded in 2004 to satisfy a need in the market for quality, affordable ported GM cylinder heads. Fresh factory castings are utilized and all machine work is done on premises using state of the art CNC machinery. According to Jason, "In 2004 we purchased a Haas 5 axis CNC machine and a Newen Countour BB CNC seat and guide machine and embarked upon an extensive R&D effort to develop a street port that would flow over 300 cfm while still retaining the excellent swirl and velocity characteristics of a stock head. Modifications include port work to the intake, exhaust and bowl area. The combustion chambers remain stock, except for the 5.3-based heads that are reworked to flow to the LS6 capacity. Optional to the customer is a performance valve job (retail $100) that we offer for all of our Stage heads. The Newen CNC machine and our proprietary valve angles really improve the low and low-mid flow characteristics of the head." Various GM castings are available including the LS6 (12564243), LS1 (12564241), 5.3 (12561706) and 6.0 LQ9. With combustion chamber sizes ranging from 61.15 cc on a 5.3 casting to 71cc on a 6.0 variant, the enthusiast has a wide range of available compression ratios, depending on their application specific needs. Stage I heads are shipped using the stock valves which feature 2.00-in intake and 1.550-in exhaust valves. Stage II and 2.5 heads are recommended for power adder or larger cubic inch applications and feature increased intake and exhaust flow (318 cfm at .625 lift versus 310 cfm for Stage I) due to increased port volume and oversized stainless steel valves. The investment in stainless valves from either Manley or Rev increases flow and is a critical longevity enhancer when the valves are subjected to boost and/or elevated temperatures from nitrous oxide or forced induction.
Dyno Configuration AIT HP RPM Torque RPM +/- HP/TQ
Stock 93 400 5,600 411 4,900 N/A
Camshaft Only 84 482 6,400 439 5,100 82/28
PRC Stage 1 heads/Cam 88 530 6,600 464 5,200 48/25
PRC plus Bolt-Ons 97 551 6,600 476 5,600 21/12
Total 551 476 151/65
Key Engine Parameters: Maximum values noted, *unless otherwise noted
Cylinder Head Flow-
All flow numbers quoted at 28" test pressure. Components SuperFlow SF600 flow bench. LS1 heads are casting number 12559853, LS6 and all stages of PRC heads tested are casting number 12564243.
Head .100 .200 .300 .400 .500 .600 .625
Stock 853 (Intake) 67 122 178 215 219 227 227
Stock 853 (Exhaust) 52 97 133 156 170 180 180
PRC Stage 1 (Intake) 72 149 205 255 287 307 310
PRC Stage 1 (Exhaust) 63 121 154 191 214 220 228
PRC Stage 2 (Intake) 75 151 209 260 293 315 318
PRC Stage 2 (Exhaust 66 124 160 194 217 227 234
PRC Stage 2.5 (Intake) 75 151 209 260 293 315 318
PRC Stage 2.5 (Exhaust) 66 124 160 194 217 227 234
Head Combustion chamber Intake Exhaust
LS1 cc 66.7 cc 200 cc 70 cc
LS6 cc 64.5 210 cc 75 cc
PRC Stage 1 cc 64.5 cc 237 cc 75 cc
PRC Stage 2 cc 64.5 cc 238 cc 75 cc
PRC Stage 2.5 cc 64.5 cc 238 cc 75 cc
Valve Sizes Intake Exhaust
LS1 2.00 1.550
LS6 2.00 1.550
PRC Stage 1 2.00 1.550
PRC Stage 2 2.02 1.570
PRC Stage 2.5 2.04 1.575