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SMALL BLOCK PISTONS

SMALL BLOCK PISTONS

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SMALL BLOCK PISTONS

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  1. SMALL BLOCK PISTONS • “Production” Design Basics • Pistons must handle many different requirements: • Transfer combustion pressures to pin/rod. • Seal combustion gases (with rings) from crankcase. • Seal lube oil (with rings) from combustion chamber • Be durable using aluminum. (200k miles) • Be quiet during all operation conditions (low & high temp & rpm) • Skirts are NOT straight or round. • Vertical shape is typically like a barrel. But, thrust side is different shape vs. non-thrust side. (0.010” barrel on dia) • Circumferential shape is oval (0.025” on dia) • Pin holes are NOT straight (0.0003” ‘trumpet’ shape to inside) • Ring grooves are NOT flat (0.12 degrees uptilt) • Top groove is hard anodize for durability • Skirts are polymer coated to allow tight fit for noise (0.001” interference fit) Halka – 09 SE 11

  2. SMALL BLOCK PISTONS 2011 6.2L L99 (CAMARO AUTO) Halka – 09 SE 11

  3. SMALL BLOCK PISTONS • Supercharged Pistons • Supercharged pistons must handle higher combustion temperatures / pressures – along with higher tendency for detonation: • Crown is much thicker. • Ring lands are much thicker. • Pin hole bearing surface much longer. • Higher strength / scuff resistant rings. • Cast vs. Forged? • ALL pistons are designed / validated to meet engine specific requirements. • It then depends on marketing advantages, aftermarket ‘headroom’, cost (forgings 2X to 3X cost of casting). • Forgings also have lower ‘chance’ of material processing defects (inclusions, cold shuts, etc.) • 6.2L LSA S/C is cast, while 6.2L LS9 is forged – for marketing & ‘headroom’. Halka – 09 SE 11

  4. SMALL BLOCK PISTONS 2011 6.2L LSA (CADILLAC CTS-V) Halka – 09 SE 11

  5. SMALL BLOCK CONNECTING RODS • PM and TITANIUM • PM • All Small Block ‘high volume’ rods are Hot Forged Powdered Metal (PM). • This material (with hot forging process) is as good as standard steel. Sections / widths are designed to meet specific engine requirements – whether 4.8L V8 or a 6.2L S/C LSA V8. • Very consistent shape control – no weight pads required. • Titanium Rod • First used in production on the 2006 Corvette 7.0L LS7 V8. • Required on 7.0L LS7 due to bearing film pressures and crank balance. • Required on 6.2L S/C LS9 due to bearing film pressures and marketing. • Putting titanium rods in a production engine was difficult – many new ‘learnings’ Halka – 09 SE 11

  6. SMALL BLOCK CONNECTING RODS • Titanium • ‘Learnings’ • Titanium rod material is very ‘tough’, but sensitive for fatigue. Due to lower thermal expansion rate than steel, we found the steel backed bushing had to have lower interference fit to eliminate pin end fatigue failures. • Titanium does not ‘like itself’. Meaning, rod-to-rod side face wear has to be controlled by addition of a coating (PVD Chrome nitride or similar coating) and oiling slots. Without these features, rods could wear 0.080” in a just a few hours. • A special rod bolt was required due to crankcase clearance (short bolt and short head height). Also, special moly grease is required for the threads and underhead (see #2 above). • Titanium is expensive. Production cost has doubled since start of 7.0L LS7 in 2006. Engine cost today for a set of rods is many hundreds of dollars. Halka – 09 SE 11

  7. SMALL BLOCK CONNECTING RODS 2006 7.0L LS7 Titanium Rod Development ‘Spin Test’ Halka – 09 SE 11

  8. SMALL BLOCK CONNECTING RODS 2011 5.3L/6.0L/6.2L PM 2011 7.0L TITANIUM Halka – 09 SE 11

  9. SMALL BLOCK PISTONS 2011 7.0L LS7 (CORVETTE Z06) Halka – 09 SE 11