Deck Milling Available (Contact us prior to ordering)
If selecting Chamber Softening, please note on your order if you want it for a 4.000", 4.065" or 4.125" bore
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 a 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.
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” hollow stem stainless extended-length exhaust valves
- Bronze guides
- PAC 1208X dual spring package (1207X or 1209X springs optional)
- Titanium retainers
- Viton seals
- 1.250” steel spring seats
- 70.5cc CNC chambers (milling available at no charge)
- Chamber softening available ($50)
- 1/2" head stud hole upgrade available ($50)
- Flat milling at .006” per cc available
- Substantial piston-to-valve clearance for advanced camshaft profiles and compression increases
- Requires longer than stock pushrods
- Minimum bore: 4.000”
- Sold/Priced as a Pair
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.
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
