A turbocharged, eight cylinder, two-stroke/cycle diesel engine has a swept volume of 5160.31 cubic inches, a 9 1/16 inch bore, 10 inch stroke, and a compression ratio of 14.5 : 1. If during an overhaul, each cylinder head is to be trued by milling off .024 inches thereby losing 1.55 cubic inches from its clearance volume, what will be the resultant swept volume and new compression ratio?
• Definition of swept volume vs clearance volume in a cylinder • Formula for compression ratio: CR = (Swept Volume + Clearance Volume) / Clearance Volume • Effect of milling the cylinder head on which volume actually changes
• Decide whether changing the cylinder head height affects the swept volume, the clearance volume, or both, given that bore and stroke stay the same. • Use the original compression ratio and total swept volume for all 8 cylinders to back-calculate the original total clearance volume, then the clearance volume per cylinder. • After subtracting 1.55 cubic inches from the clearance volume of each cylinder, recalculate the new total clearance volume and then the new compression ratio.
• Confirm whether the swept volume per cylinder changes when only the head is milled and neither bore nor stroke are altered. • Carefully convert between per-cylinder and total (8-cylinder) volumes so you don’t mix them up. • Re-check your final compression ratio calculation: CR = (Total Swept Volume + Total Clearance Volume) / Total Clearance Volume, using consistent units throughout.
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