styling of the Austin Allegro, which was originally intended to sport a much sleeker appearance until it was decided by BL management that it would use the E series in its largest engine variants. A higher compression version of the 1.7 was developed utilising a twin carburettor set up with increased valve lift and flat-topped pistons. As fours and sixes shared production tooling, the four also had a long stroke and siamesed cylinder liners, even though it did not need the reduced width. This was especially true in later designs of transverse-engined BMC and BL cars, when the side-mounted radiator was moved to fit across the nose of the car reducing overall width of the engine considerably. The lack of water jacketing caused considerable development problems when the 1.5 L in the Austin Maxi needed an optional larger engine size. The 1.5 L four-cylinder E series could not be readily bored out, the placing of the gearbox directly underneath the sump made stroking the engine more difficult, and the Maxi was too narrow to accommodate a large-capacity six-cylinder. Overcoming these problems meant that even a modestly increased displacement, to , did not appear until 1971. The engine was originally envisaged as a 1.3 L and 1.5 L four-cylinder, with a 2.0 L six-cylinder created by adding two cylinders to the 1.3 L block. However, as development continued it appeared the 1.3-litre E series would not have any huge benefits over the 1.3 L A series being developed at that time from the existing 1.1 L, so the smaller E series was dropped. The result was a saving in development capital for BMC, but also meant the six-cylinder had to be developed from the 1.5 L block, creating its unusual engine size of . Later derivatives The four-cylinder E series was effectively discontinued when the Allegro went out of production in 1982. However it was substantially redesigned into the R series, and later the S series in the mid-1980s. The R series was effectively a stop-gap solution for the Austin Maestro, and is all but identical to the E-Series, the main difference being modifications to take an end-on transmission, in place of the BMC 'transmission-in-sump' arrangement. The S-Series was a more thorough redesign, featuring a belt-drive camshaft in place of the E-series chain and a completely new cylinder head. The six-cylinder version was not directly replaced. Engine sizes 1.5-litre engines The