Why so "low?" Sherman wanted to see if with the Comp Cams roller cam, the engine could run on his dyno using Chevron 91-octane unleaded gas and make big power. It did. It remains to be seen what octane number the 408 will need in actual competition.
The thing to always remember about Cometic gaskets is this: They offer a gasket for your engine in "any bore and any thickness."
It is much more cost effective to dial in the final compression ratio with a Cometic head gasket rather than taking the block back to the machine shop for more milling of its decks.
Aftermarket Block RecommendedThere are a lot of 350 blocks and it is general racing knowledge that all stock iron block wall thicknesses are not the same. Call it "production casting irregularity." Regardless of what anyone else says about stock factory blocks, Sherman emphatically told us, "I recommend a beefier, clearanced aftermarket block (example: Dart) for my 667hp hybrid 408. It weighs 45 poundss more due to its beefiness. It costs $1,995 or so more, but they will never cause a problem.
Complete flow bench results are listed in the technical sidebar. Suffice to say, the intake ports measure 316 cfm flow at 0.700-inch valve lift. This is huge. The exhaust port flow spec is 233 cfm. The biggest 408 small-block engine produces over 500 lb-ft of torque from the mid-4,000 rpm on up to 6,800 rpm. This is huge.
Horsepower output measures over 500 from 4,800 rpm to 5,600 rpm then over 600 hp from 5,700 rpm to 7,200 rpm. Big torque and horsepower numbers at every measured rpm is how Joe Sherman won the inaugural Engine Masters Challenge seven years ago. A ballpark price for this custom-built engine is $12,000. That's $17.99 per horsepower. Being internally balanced, the engine could be painted stock Chevy orange and look like a warmed over 350 to most onlookers.
Sherman's Tamer HybridJoe Sherman's other hybrid 408 is referred to as "Jr." It has a smaller camshaft, a 750 cfm Speed Demon carburetor, smaller heads, an Edelbrock RPM Air Gap intake manifold, and a 10.5:1 compression ratio. It produces 568 hp at 5,800 rpm and 568 lb-ft of torque. It's ballpark price is $10,500 to $11,000.
667 HP 408 Engine SpecificationsCamshaftManufacturer/Type: Comp Cams RollerDuration @ 0.050-inch: 270 degrees intake280 degrees exhaustLobe Separation: 109 degreesCamshaft Lobe Lift: 0.454-inch intake0.438-inch exhaustIntake Valve Lift (1.6 ratio rocker arm)0.726-inchIntake Valve Lift (1.5 ratio rocker arm)0.681-inchExhaust Valve Lift (1.6 ratio rocker arm)0.657-inchExhaust Valve Lift (1.5 ratio rocker arm)0.645-inchValve Events @ 0.050-inch Lift:Intake Opens-30 degrees BTDCIntake Closes-58 degrees ABDCExhaust Opens-69 degrees BBDCExhaust Closes-29 degrees ATDCValve Lash: 0.013-inch intake (cold)0.017-inch Exhaust (cold)
Cylinder HeadsAFR 1100 Eliminator 210 ccCombustion Chamber Volume: 65 ccIntake Valves: 2.080 -inch dia. x 5.020-inch longExhaust Valves: 1.600-inch dia. x 5.030-inch long
Valve SpringasManufacturer: Comp CamsModel: 26115Closed Valve Seat Pressure: 255 psi @ 2.00-inchOpen Valve Seat Pressure: 663 psi @ 1.25-inch