In the case of Vauxhall, I think they committed the sin of winning an argument: The Lotus head and I think the triple plate clutch and ZF gearbox used on the rally version of the Chevette HS were actually approved for the Magnum homologated before the end of 1975, though the HS was homologated in 1976 (backdated from 1977).
From what I can piece together, what happened was that Vauxhall (DTV) managed to argue with the FIA/CSI that they could use those parts on the HS because, when the FIA removed the 100-off rule, they’d given the following allowance: “Mechanical elements recognised in Group 2 before 31.12.75 as well as the authorised modifications according to the prescriptions of Art 260 of former Appendix J can be used until 31.12.77 for rallies."
That article 260 included the 100-off rule, including a list of “Optional equipment which may be recognized with a minimum production of 100 units per year to equip 100 cars”, and the list included heads with different numbers of cams and valves, gearboxes, overdrives, rear axles, and a shed load more (which is how BL got approval for the 16-valve Group 4 TR7 with the Doly Sprint overdriven gearbox in October 75, without having made any). But that rule did not require that any cars had to be modified to get authorization, just that kits for a “bolt on option”, containing all the parts, had to be freely available for anyone to buy and had to be listed for the car.
However, the extension for their use till the end of 77 doesn't say that the parts and mods should have been authorized and approved for the same car they were being used on, it just says authorized parts, etc., can be used. Now I can't imagine the FIA intended that teams would be able to use parts from other cars because of that allowance, but Vauxhall (DTV) were able to argue successfully that they could.
Assuming it was a mistake by the FIA and DTV used it as a loophole, I have to wonder how the FIA/CSI felt towards them about that. I also wonder how they felt when they discovered in early 78 (ultimately from an article by Graham Robson) that DTV weren’t going to stop using the Lotus head, etc. They sent in the inspectors (Neil Eason-Gibson was one of them), but somehow DTV got the impression from that inspection that they had an extension till May 78, and issued a press release to that effect - though they’d got nothing in writing for it – and sent the car, with the Lotus head, etc., to the 1978 Rally Portugal. The CSI, however, sent a telex to the scrutineers there, ordering them not to allow the car to run unless those mods had been removed.
So Vauxhall had to withdraw from rallying until the differences between the rally and production HS were acceptable to the FIA/CSI. Oddly, it’s said that Blydenstein went on to make the GM 16-valve head better than the Lotus one, at least by the time the 50 (some say 10 percent of the full requirement for a new homologation = 40) HSRs were used to homologate the evolution of the HS into Group 4. And that’s another interesting story.
Graham
_________________ The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.
Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).
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