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A 409 cu in (6.7 L) version was Chevrolet's top regular production engine from 1961 to 1965, with a choice of single or 2X4-barrel Rochester carburetors. Bore x stroke were both up from the 348 cu in (5.7 L) to 4.31 in × 3.5 in (109.5 mm × 88.9 mm).
The head is machined flat, with recesses only for inlet and exhaust valves, spark plugs, injectors and so on. The combustion chamber itself is contained within a dished depression in the top of the piston. The Heron head is suitable for petrol and diesel engines, for ohv and ohc valve-gear, and for small and large engine displacement capacities.
All MEL engines had wedge-shaped combustion chambers formed between a flat head surface and an angle milled block deck (10 degrees off square with the bore axis), with the piston top determining the compression ratio and combustion chamber shape, similar to the Chevrolet Big-Block 348 combustion chamber, also introduced in 1958, and the later 409 and 427.
These were wedge-head engines with a unique combustion chamber that resulted from a valve angle of only 6°. This was much flatter than the 23° of the small-block Chevrolet and 20° of the Ford small-block wedge heads. This very open and flat chamber was fuel efficient and had lower than average emissions output.
Common shapes for the combustion chamber are typically similar to one or more half-spheres (such as the hemi, pent-roof, wedge or kidney-shaped chambers). The older flathead engine design uses a "bathtub"-shaped combustion chamber, with an elongated shape that sits above both the piston and the valves (which are located beside the piston).
The LB1 used in trucks and vans was referred to as Vortec in Chevrolet literature (named after a combustion chamber design known as a swirl port which twists the fuel mix from the intake ports as introduced with the Cavalier's 2.0L engine), and this name continued to be used with all truck and van 4.3 L (262 cu in) V6s until 2014.
A hemispherical head ("hemi-head") gives an efficient combustion chamber with minimal heat loss to the head, and allows for two large valves.However, a hemi-head usually allows no more than two valves per cylinder due to the difficulty in arranging the valve gear for four valves at diverging angles, and these large valves are necessarily heavier than those in a multi-valve engine of similar ...
The Vortec 5700 L31 (VIN code "R") is a 5.7L V8 truck engine. It is Chevrolet's last production first-generation small-block. The cylinder heads feature combustion chambers and intake ports very similar to those of the LT1 V8, but lacking the LT1's reverse-flow cooling and higher compression.