4.8/5.3/5.7 - RLD Performance LS1 head has slightly less average and peak flow than a stock LS3 cylinder head. This is an outstanding small displacement cylinder head. However, this is the same price as the LS2/LS6. This head series is a stage III street/strip/race head for smaller bore engines. The heads are sold as new GM castings or on an exchange basis. These heads are built to order with proprietary upgraded CNC ports, customer specified valve train parts and specified valves. Our standard 4.8/5.3/5.7 heads all flow the same and have the same valve size and runners after machining. The main difference is the exhaust port which is round rather than a "D" shape. The round port actually has less flow loss through the exhaust manifold or header when tested but LS2/LS6 enthusiasts insist on the "D" port regardless of the flow. Another advantage is that we use new or exchange factory castings and the part numbers are not ground off like some of our competitors. Polishing the runners add between 6-7 CFM at each lift point. The flow is comparable to the AFR 205 head.
CombC= 62 67
RunnerCC= 217 200 70 200 70
Valve =2.0 1.55 1.89 1.55 2.0 1.57
RLD CNC VS Stock 4.8/5.3L VS Stock 5.7L
Lift I E E/I I E E/I I E E/I
.200 132 109 83% 128 93 73% 122 97 74%
.300 187 147 79% 179 121 68% 178 133 75%
.400 238 175 74% 210 145 69% 215 156 73%
.500 274 193 70% 218 163 75% 219 170 78%
.550 281 202 72% 221 168 76% 223 176 79%
.600 281 206 73% 226 174 77% 227 180 79%
AVG 232 172 74% 197 144 73% 197 152 77%