Gen III vs Gen IV
09-03-2012, 08:08 AM
#11
New ones are 8.8:1, not 9 anything as I said.
Stroke is the difference. Hence the word "compression ratio". It's less on a 4.8 than a 5.3. So since the piston is travelling less distance you don't compress the a/f mixture as much. Stroke on a 5.3 is 3.62" and a 4.8 is only 3.27". On the older 5.3's you had dished pistons with flat tops only in the 4.8.... Then with the same heads they were roughly about the same compression ratio. Now that is no longer the case as the 5.3 has flat tops.... and 243/799 heads have larger cc chambers than the old 706/862's ( 64 vs 61 cc). So that is why a 4.8's CR is in the ******* like some turd Gen 1 from the 70's. No wonder they are so doggy, lol.
Right from GM powertrain for RPO L20 4.8's.....
Stroke is the difference. Hence the word "compression ratio". It's less on a 4.8 than a 5.3. So since the piston is travelling less distance you don't compress the a/f mixture as much. Stroke on a 5.3 is 3.62" and a 4.8 is only 3.27". On the older 5.3's you had dished pistons with flat tops only in the 4.8.... Then with the same heads they were roughly about the same compression ratio. Now that is no longer the case as the 5.3 has flat tops.... and 243/799 heads have larger cc chambers than the old 706/862's ( 64 vs 61 cc). So that is why a 4.8's CR is in the ******* like some turd Gen 1 from the 70's. No wonder they are so doggy, lol.
Right from GM powertrain for RPO L20 4.8's.....
Type: 4.8L Gen IV V-8 Small Block
Displacement: 4807cc (293 ci)
Engine Orientation Longitudinal
Compression ratio: 8.8:1
Valve configuration: Overhead valves (2 valves per cylinder)
Valves per cylinder 2
Assembly site: Romulus, MI
St Catherines, Ontario
Valve lifters: Hydraulic roller
Firing order: 1 - 8 - 7 - 2 - 6 - 5 - 4 - 3
Bore x stroke: 96.01 x 83mm
Fuel system: Sequential fuel injection
Fuel type: Applications:
Regular unleaded Chevrolet Express ( Cutaway ) , GMC Savana ( Cutaway )
Regular unleaded and E85 Flex Fuel Chevrolet Silverado, Express ( Passenger, Cargo )
Regular unleaded and E85 Flex Fuel GMC Sierra, Savana ( Passenger, Cargo )
Maximum Engine Speed: 6000 RPM
Emissions controls: Catalytic converter
Three-way catalyst
Positive crankcase ventilation
Bore Center (mm) 111.76
Engine Mass TBD
Applications: Horsepower: hp ( kW )
Chevrolet Express > 10,000 lbs 260 hp ( 194 kW ) @ 4600 rpm SAE CERTIFIED
Chevrolet Express < = 10,000 lbs 280 hp ( 209 kW ) @ 5200 rpm SAE CERTIFIED
Chevrolet Silverado 302 hp ( 225 kW ) @ 5600 rpm SAE CERTIFIED
GMC Sierra 302 hp ( 225 kW ) @ 5600 rpm SAE CERTIFIED
GMC Savana > 10,000 lbs 260 hp ( 194 kW ) @ 4600 rpm SAE CERTIFIED
GMC Savana < = 10,000 lbs 280 hp ( 209 kW ) @ 5200 rpm SAE CERTIFIED
Applications: Torque: lb-ft. ( Nm )
Chevrolet Express > 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
Chevrolet Express < = 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
Chevrolet Silverado 305 lb-ft ( 414 Nm ) @ 4600 rpm SAE CERTIFIED
GMC Sierra 305 lb-ft ( 414 Nm ) @ 4600 rpm SAE CERTIFIED
GMC Savana > 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
GMC Savana < = 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
MATERIALS
Block: Cast iron
Cylinder head: Cast aluminum
Intake manifold: Composite
Exhaust manifold: Cast nodular iron
Main bearing caps: Powder metal
Crankshaft: Cast nodular iron with undercut and rolled fillets
Camshaft: Hollow steel
Connecting rods: Powder metal
Additional features: Electronic throttle control
E85 Flex Fuel
Variable Valve Timing ( VVT )
Extended life accessory drive belt
Extended life coolant
Extended life spark plugs
Oil Life Monitor System
Displacement: 4807cc (293 ci)
Engine Orientation Longitudinal
Compression ratio: 8.8:1
Valve configuration: Overhead valves (2 valves per cylinder)
Valves per cylinder 2
Assembly site: Romulus, MI
St Catherines, Ontario
Valve lifters: Hydraulic roller
Firing order: 1 - 8 - 7 - 2 - 6 - 5 - 4 - 3
Bore x stroke: 96.01 x 83mm
Fuel system: Sequential fuel injection
Fuel type: Applications:
Regular unleaded Chevrolet Express ( Cutaway ) , GMC Savana ( Cutaway )
Regular unleaded and E85 Flex Fuel Chevrolet Silverado, Express ( Passenger, Cargo )
Regular unleaded and E85 Flex Fuel GMC Sierra, Savana ( Passenger, Cargo )
Maximum Engine Speed: 6000 RPM
Emissions controls: Catalytic converter
Three-way catalyst
Positive crankcase ventilation
Bore Center (mm) 111.76
Engine Mass TBD
Applications: Horsepower: hp ( kW )
Chevrolet Express > 10,000 lbs 260 hp ( 194 kW ) @ 4600 rpm SAE CERTIFIED
Chevrolet Express < = 10,000 lbs 280 hp ( 209 kW ) @ 5200 rpm SAE CERTIFIED
Chevrolet Silverado 302 hp ( 225 kW ) @ 5600 rpm SAE CERTIFIED
GMC Sierra 302 hp ( 225 kW ) @ 5600 rpm SAE CERTIFIED
GMC Savana > 10,000 lbs 260 hp ( 194 kW ) @ 4600 rpm SAE CERTIFIED
GMC Savana < = 10,000 lbs 280 hp ( 209 kW ) @ 5200 rpm SAE CERTIFIED
Applications: Torque: lb-ft. ( Nm )
Chevrolet Express > 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
Chevrolet Express < = 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
Chevrolet Silverado 305 lb-ft ( 414 Nm ) @ 4600 rpm SAE CERTIFIED
GMC Sierra 305 lb-ft ( 414 Nm ) @ 4600 rpm SAE CERTIFIED
GMC Savana > 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
GMC Savana < = 10,000 lbs 295 lb-ft ( 400 Nm ) @ 4600 rpm SAE CERTIFIED
MATERIALS
Block: Cast iron
Cylinder head: Cast aluminum
Intake manifold: Composite
Exhaust manifold: Cast nodular iron
Main bearing caps: Powder metal
Crankshaft: Cast nodular iron with undercut and rolled fillets
Camshaft: Hollow steel
Connecting rods: Powder metal
Additional features: Electronic throttle control
E85 Flex Fuel
Variable Valve Timing ( VVT )
Extended life accessory drive belt
Extended life coolant
Extended life spark plugs
Oil Life Monitor System
Last edited by 1994Vmax; 09-03-2012 at 08:20 AM.
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