Ecotec Intake Valve Size Guide: 35.6 mm Heads, Stems & Fitment
The HF35.6 Size Reference
The BK HF35.6 intake valve has a nominal 35.6 mm head and approximately 5.97 mm main stem diameter. Its head is approximately 0.5 mm larger than the commonly published 35.1 mm OEM-size reference. Confirm the actual parts in the head being built; do not assume every Ecotec service valve shares identical dimensions.
The intake set contains eight valves. The 16-valve package contains eight intake and eight exhaust valves. Exhaust dimensions are different and should be recorded independently.
Measure More Than Head Diameter
Record actual head diameter, main stem diameter, guide bore, overall length, keeper-groove location and tip height. Compare the seating face and the finished contact pattern with the seat in the cylinder head.
Guide clearance is the measured relationship between the valve stem and guide. Neither a nominal 5.97 mm stem nor a valve that slides through the guide establishes that the clearance is suitable for operation. Have the machinist set the assembly to the relevant component requirements.
Stock Tip and Oversize Head Describe Different Features
Standard / Stock Base Circle refers to the tip configuration intended for a compatible stock-base-circle camshaft. It does not reduce the HF35.6 head to the OEM-size reference.
Reduced Base Circle / Regrind refers to the extended-tip configuration. Added height above the keeper should not be used as a substitute for measuring keeper position or spring installed height. Read the tip guide before comparing overall lengths.
Cylinder-Head and Clearance Checks
A normal professional valve job establishes the finished seat relationship. Check available seat material, concentricity, contact location, chamber clearance, valve-to-valve clearance and piston-to-valve clearance. Increased diameter does not mean every seat needs major reconstruction, but seat condition must be assessed rather than assumed.
The retainer, locks, spring and seal arrangement then determine other assembled relationships. Use the installation checklist to record the measurements for each position.
Frequently Asked Questions
Can I choose by vehicle model alone?
No. Identify the exact engine, head and camshaft combination.
Is an exact overall length published here?
No. This guide does not assign an unverified overall length to both tip versions. Obtain the current specification for the version being ordered.
Start With the Complete Intake Valve Guide
GM Ecotec Intake Valves: Stock vs Performance, Sizes, Materials & Fitment brings the sizing, geometry, testing, tip selection and installation topics together.
Related BK Racing Products
- HF35.6 intake valves — set of eight
- Complete intake and exhaust valve set
- Ecotec performance exhaust valves
- 83 lb Ecotec valve springs
- Ecotec titanium retainers
- Solid lash adjusters — L61/LSJ version; verify fitment
- Solid lash adjusters — later-generation version; verify fitment
- Extra-clearance spring seats and Viton seals — add-on for BK 83 lb springs