Small Bore LS3
RLD Performance LS3 CNC cylinder head has more velocity, average flow and peak flow than a stock LS7 cylinder head. This new casting is designed for engine sizes of 6.0L or bore size of 4" and larger. However, we produce a small bore version of this cylinder head. This head utilizes a smaller intake valve to prevent cylinder bore impingement. In stock form, this head could create the characteristic dip in the lower rpm area. We have designed the correct camshaft to work with this combination. The small bore LS3 may be an inexpensive solution to a high RPM small bore engine. CNC versions of this head can add up to 20cc's to the intake port volume. Poorly designed CNC ports can kill port velocity and should be utilized on engine sizes over 370 cubic inches. Our Port design does not kill low lift flow.
We have found the L92 ports to not be sensitive to valve shape, valve cosmetics or brand. So, a factory valve does flow as well as a Manley Race Master. As Manley Race Master valves are approximately 23% heavier than a factory hollow stem valve, we do not advise using them. The new Factory Hollow stem valve for the LS3 Corvette may be the best choice for weight and price point for a performance L92/LS3 head. When making valve train determinations for the L92, valve weight is very important.
These heads are currently sold as new GM castings which are further CNC modified per the customers needs. LS3/L92 heads can be modified in several ways. Valve sizing can go up or down. A smaller intake or exhaust valve would be more appropriate for engine sizes less than 6.2 Liters. However, standard valve sizes can be utilized for engines of 6.0 liters and up. Finally a LS7 large valve version is available for large bore combinations. The combustion chambers can be CNC machined or left alone, depending on application. We see no need to CNC the combustion chamber except for small bore applications. It should be noted that in the stock form, we have found the L92 to have more average flow than the a stock LS7 under .600 lift. Our CNG LL3 has more average flow than the stock LS7 and only 18 CFM shy of our highly modified LS7 head.
For performance applications with this big valve head, we feel that a conical or beehive spring is inappropriate and should not be used. We sell an ideal spring kit for these heads. This head assembly can be built with premium hydraulic roller cam springs for increased lift and rpm range.
All airflow data is corrected data (Temperature and Atmospheric Pressure) at 28" of water. Intake is measured with a shaped entry and the exhaust is measured with a stub pipe. Polishing the runners add between 6-7 CFM at each lift point.
CombC =68-69 68-69 68-69
RunnerCC = 277cc 280cc 260cc
Valve = 2.16 1.59 2.16 1.59 2.16 1.59
RLD CNC LS3 VS GM CNC LS3 VS GM Stock LS3
Lift I E E/I I E E/I I E E/I
.200 144 124 86% 150 105 70% 151 111 74%
.300 224 179 80% 222 140 63% 208 152 73%
.400 276 198 72% 260 168 65% 256 174 68%
.500 313 223 71% 298 190 64% 294 183 62%
.550 328 240 72% NA NA NA NA NA NA
.600 338 248 73% 332 201 61% 316 189 60%
.650 350 254 73% NA NA
.700 347 255 73% NA NA
AVG 290 215 74% 252 161 64% 245 162 66%
Note - Max flow thru intake =322 M/E avg.=215 E/I avg. =69%