Hemi Heads

The RLD Performance 6.1 Hemi CNC cylinder head has more velocity, average flow and peak flow than the GM Corvette LS7 CNC cylinder head.  The Late Model Hemi program includes the most highly developed Hemi cylinder heads on the market with stage 1, 2 and 3 intake manifolds, a custom camshaft line, custom pushrods, a new shaft rocker arm system, custom racing spring kits and custom titanium valves.  We build parts that fit and stand up to the abuse of racing.  

Maximum factory valve lift is .550.  Cylinder head development included a complete work up of both the 5.7 and 6.1 i.e., analyzed, installed, modified and flow tested.  The combustion chambers were CNC quench pad qualified, both valves and seats were analyzed for shape and size.  Intake valve and seat ranges were tested from 2.055"-2.200".  Exhaust valve and seat ranges were tested from 1.5" -1.7".  Six valve seat angles as well as four valve head angles were included.  Valve length is critical and GM valve are not advisable. For performance applications a single groove bead lock is far superior to a factory triple groove rotating lock. Valve train improvements were identified including fitment.  Concepts like piston to valve clearance, valve length and valve guide stability for maximum performance were explored.

Several competing aftermarket heads were baselined for comparison.  Several intake port shapes were developed for CNC replication.  Certain combinations emerged as superior, the most practical and the most economical to utilize.  In the end, a new machining process, Trade Named from US Patent Office as  "Flowline Machined", emerged as the best flowing port.  Simply put, we outflow the competition.

A custom shaft rocker arm system was developed in conjunction with PRW to stabilize the valve train.  A complete custom camshaft line was developed for maximum performance.  Conical and dual racing springs were developed up to .875 lift.  More about camshafts and valve train can be found (here...).  Learn about maximum horsepower for this platform (here...).  Dyno sheets can be found (here...)  By looking at the flow data below it is too bad that you cannot use a 5.7 head on a 6.1 for added compression or a 6.1 intake manifold on a 5.7!

CombC=73                         70

RunnerCC=188cc 58cc     270cc 85cc

Valve= 2.080/1.60          2.200/1.61

     RLD CNC 6.1         VS   6.1 Stock Head    VS   RLD CNC 5.7 Head

Lift      I      E    E/I           I       E     E/I              I      E     E/I      

.100   84    52   62%         71     62   89%            73    60    82%  

.200  171  100  58%         158   132   84%           154   122   79%

.300  250  133  53%         228   175   77%           225   167   74%   

.400  310  179  58%         278   200   72%           275   196   71%

.500  355  215  61%         299   213   71%           305   216   71%

.550  369  237  64%         303   216   71%           316   222   70%   

.600  377  246  66%         307   217   71%           316   226   72%

.650  381  255  67%         307   216   70%           319   226   71%

.700  382  257  73%         307   220   72%           312   225   72%

.750  383  262  68%         309   220   71%                   

AVG  306  194  63%         257   187   73%           255   185   72%


RLD CNC 6.1             VS         GM LS7 

Lift      I      E    E/I           I     E    E/I      

.100   84    52   62%        71   50   70%     

.200  171  100  58%        145  120  83%  

.300  250  133  53%        222  158  71%       

.400  310  179  58%        271  192  71% 

.500  355  215  61%        315  207  66% 

.550  369  237  64%        332  214  64%     

.600  377  246  66%        348  219  63% 

.650  381  255  67%        350  220  63%   

.700  382  257  73%        352  221  63%  

.750  383  262  68%        NA   NA                     
AVG  306  194  63%        276  178  64%   



 RLD Performance, P.O. Box 890066, Temecula, CA 92589 (951) 676-4948, 9am-5pm Pacific Standard Time M-F, stan@rldperformance.com