Join Date: Nov 2006
Location: North Channel Lake Huron
Re: Big Block Chevy Piston to Valve Clearance
Valve to Piston Clearance depends mostly on Size of Valve reliefs and Dia of Valves and Inversely Proportional to Duration of the Cam - That is the longer the duration the tighter the Valve to Piston Clearance. Basically do not worry about Valve to Piston Clearances with Cams under 300 Advertized Duration Degreed per Specks in STK OEM Specked Engines as Cam and Piston Manufactures take this into account. Ensure when Clay Modeling that you have enough Piston Valve Relieve Diameter when running Large Dia Valves.
Valve to Piston Clearances are closet when the Intake 1st Opens and the Exhaust Valve Closes - Advancing or Retarding the Cam by 2 Degrees generally changes the clearance by .010" respectively.
Head Gasket thickness, Milling either Deck or Heads change the Valve Seat Height and affect Valve to Piston Clearances - Generally Lobe lift has very little affect unless you running extreme (310+) durations.
Pending Cam, I've run .080"/.100" Int/Ext Clearances with 2.19/1.9" Dia Valves and TRW or Speed Pro Domed Pistons to over 7000rpm in SR BBC Mills without issues. Some will run clearances as tight as .060"/.080" (Not uncommon in SBC's).
As Darrel mentions Check Intake Valve to Cylinder Bore Clearance especially when running a 396 Bore and Large Dia Intake Valves in which case one may have to Fly Cut Clearance in the upper Edge of the Cylinder Bore around the Intake Valve above the Combustion Ring Stop Position.
Last edited by Z15CAM; May 20th, 12 at 05:05 PM.