Mangum Racing CNC Ported MR275 11° LS3 Cylinder Heads
Built from the Mangum Racing 6-bolt 11° LS3 casting featuring a massive .750” deck surface, the MR275 is designed for maximum-effort naturally aspirated and boosted LS combinations where airflow, strength, and valvetrain stability are non-negotiable.
This casting was engineered for builders who want every available advantage, valve angle, deck thickness, port efficiency, and piston-to-valve clearance, all optimized to support serious compression and high cylinder pressure environments.
Each set is fully CNC machined in-house on brand new Centroid 5-axis machining centers and finished on Newen seat & guide equipment. Every head is hand blended, inspected, and assembled in small batches to ensure repeatability and precision.
Airflow Performance
Tested on a SuperFlow bench with a 4.125” bore plate
Intake (Radius Entry)
.200” – 143 CFM
.300” – 221 CFM
.400” – 283 CFM
.500” – 330 CFM
.600” – 358 CFM
.700” – 381 CFM
Exhaust (No Pipe)
.200” – 112 CFM
.300” – 161 CFM
.400” – 202 CFM
.500” – 232 CFM
.600” – 242 CFM
.700” – 248 CFM
With a 275cc CNC intake runner and optimized 98cc exhaust port, the MR275 delivers exceptional mid-lift efficiency with dominant high-lift airflow. The 11° valve angle significantly improves piston-to-valve clearance, allowing aggressive cam timing and higher compression strategies without compromise.
Premium Hardware & Construction
- 6-bolt Mangum Racing 11° LS3 casting with .750” deck thickness
- Optimized 11° valve angle and revised valve locations
- 2.185” hollow stem stainless extended-length intake valves
- 1.600” stainless extended-length exhaust valves
- Bronze guides
- Choice of PAC 1207X, 1208X, or 1209X dual spring packages
- Titanium retainers
- Viton seals
- 1.250” steel spring seats
- 70.5cc fully CNC chambers (milling available at no charge)
- Chamber softening options for 4.000”, 4.065”, and 4.125” bore sizes
- Flat milling at .006” per cc
- Substantial piston-to-valve clearance for advanced camshaft profiles and
- compression increases
- Minimum bore: 4.000”
Built for Maximum Effort Combinations
The increased deck thickness supports extreme cylinder pressure in large displacement and boosted applications. The revised 11° valve angle enhances airflow efficiency while providing additional mechanical clearance, a critical advantage in high-rpm, high-lift camshaft programs, or builds where smaller combustion chambers are required.
These heads have supported combinations exceeding 2,000 horsepower and 200+ mph in competition environments, making the MR275 a proven solution for serious LS3-based builds.
If you are building a no-compromise LS3 combination, naturally aspirated or power-adder, the MR275 was designed for exactly that purpose.
