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I suspect as the Sprint motor was designed in very early 70s,its actually designed to run on 5 star rather than 4?
The conversion of the slant-4 to 2Ltr 16-valve config. was designed around 1970 by Coventry Climax (Harry Mundy), under the oversight of Charles Spencer King for the Specialist Division of BLMC. That was specifically so they could take the Dolomite racing in Group-1 (Series-Production Touring Cars), which needed 5000 in a year to qualify. Group-1 homologation only allowed/demanded modifications from the production spec. for safety.
So I reckon it was designed with little regard to what was sold in pumps, but only to what was available in the pit lane for group-1 use, and timing on the race cars set to whatever that would allow. That, careful assembly, blueprinting, and a bit of engineering to spec. limits, etc., presumably, accounts for how they got well over 150bhp on HS6s and a standard spec. cam and pistons. I believe there's a figure of 175 quoted somewhere, but I can't find it at the moment.
As I understand it, the Group-2 use (Touring Cars with "modifications aimed at making them better suited to competition"), which allowed different carbs, inlet and exhaust manifolds, and other mods from production spec, came later. I understand there were a couple of external firms developing the Group-2 (and Group-4 TR7) engines, and they gave around 250 bhp. That's stunningly close to what Costain-Duckworth's twin cam BDG engine gave, which was developed from the Kent, presumably on a much bigger budget (alloy block and such). But, as I understand it, Ford/Cosworth never made enough to gain Group-1 approval - the RS1800 was a Group-2 car, but re-homologated into Group-4 in 1977 as the 2ltr Escort RS, because of the changes the FIA made to the rules in Dec. 1975, with Appendix J to the International Sporting Code for 1976. That was mostly dropping the 100-off rule that had got some Group-2 modification approved on 100 kits of spares made available to buy, not production of homologation specials like the TR7 Sprints of 1977.
Graham