Had to do this reply in two parts due to a forum text length restriction
Make no mistake about it, the Jaguars were very good naturally aspirated touring cars. Most people would assume with the 1400KG weight penalty they had to run due to being in the 5-6L class that they would never be dominant, and possibly struggle to be competitive, but in the end they were very successful. But in fact, they should not have been as good as they were. When Walkinshaw homologated the big cats in 1982 the V12 had just over 370 HP. The lighter 280HP BMW 635s could run with them, especially on the twistier tracks. By the end of 1983 after a lot of engine development the cats had 390 HP, but the BMWs were giving them a very hard time. In the first round of the 1984 ETC, the cats all of sudden had 450HP on tap. Why? The restricting factor for the pre84 engines was the "may type" heads. These heads were developed for the road to give better fuel consumption and driveability, but ran out of puff approaching 7000RPM. Walkinshaw turned up in 84 with the pre "may type" heads, which were better suited to racing, developing power right up to 7500RPM. Now the Europeans had a different attitude to rules and cheating to us here in the pacific (or rule interpretation as they prefered to call it), and they had a lot of "if you dont protest us doing X we wont protest you doing Y" gentlemen agreements between the major players, and most of the time it all evened itself out. But FIA was not impressed as these clearly were not the heads homologated on the road cars. When told, Walkinshaw threatened to pull all his cars out from every championship. FIA caved in, and gave the heads a tick of approval. This except for the M3 non standard air box in 1987 was the only example I know of when FIA approved a regulated part that was supposed to be fitted to the road cars but wasnt, (ignoring Eggenbergers blatant wheel arch modifications on the 87 Sierras, in that case they didnt give it a tick, they just turned a blind eye to it). At least FIA fixed the M3 air box fiasco in 1988. My point? How well would the big cats have gone if they turned up at bathurst with the "May type" heads and "only" 390HP instead of 450HP? I suspect they would have still been on the front two rows of the grid, but the faster cars, especially the Volvo, would have given them a very hard time.
The two Zakspeed cars were built to run in the 1984 DTM. The first car to be finished was raced by Klaus Ludwig, I remember he qualified well and finished second or third? I dont know who the second car was built for but after that one race both cars were shelved, never to race again in the DTM for reasons only known to Zakspeed, most probably relevent marketing and hence sponsorship reasons.
I concur. What killed Group A was the inadequate weight factoring for turbo cars, which the volvo and nissan took advantage of and later the Sierra and Godzilla made a mockery of. When FIA drew up the rules the current turbo cars werent the potential weapons they became a mere five years later. Poor hindsight we can say now, but back then look at what was on the market, eg the Ford Escort turbo, hardly world beating stuff.
Now further on the point of the rules, it was amazing that the Holden Commodore and the big Cat was as succesfull as they were. FIAs rules were specifically made to keep those pesky yanks with their big low tech V8s from being competetive, the last thing they wanted was for the yanks to come and spoil the party, hence the rules were drawn up to favour small capacity cars like mostly sold in Europe and a 6L limit to keep out those big blocks or woe forbid turbocharged/supercharged V8s! But with the power that was potentially available to the small block larger V8s, they had to make them uncompetetive as well, (at the time I dont think FIA had any inkling anyone would want to homolgate the Jags, indeed there is still doubt to this day whether 5000 XJS's were made in the homologation year) so they hit the top two capacity classes with two hammers, extra large weight (which as you know not only affects speed but has an effect on tyre wear) and not much bigger tyres than the smaller cars were allowed to run. For example, 4,501 cc to 4,999 cc - 1,325 kg, over 5,000 cc cars - 1,400 kg, yet a typical sporting touring car sold in europe, 3,001 to 3,500 cc – 1,110 kg, was allowed to be nearly 300KG lighter than the expected capacity class most V8s would be in!
And the most common type of touring car sold in Europe, ie 2L cars, 2,001 to 2,500 cc - 960kg a whopping 440KG lighter! Under this formula a 2L turbo that had a potential of say 360 HP only had to weigh only 1035KG! (2,501 to 3,000 cc – 1,035 kg) A potential rocket ship compared to a 370HP V8 weighing 1325KG or 390HP V12 that had to weight 1400KG! Even with the 1987 turbo factor of 1.7, a 2L turbo such as the Sierra Cosworth only had to weigh 1100KG, and the RS500 had a potential of over 500HP! (3,001 to 3,500 cc – 1,100 kg in 1988) yes that's right, FIA LOWERED the weight limit for this class but raised the weight for the 4.5-5 and 5-6 classes! The poor old commodore got a weight INCREASE in 1987 (4,501 cc to 4,999 cc - 1,340 kg in 1987) and as a double whammy 1" smaller width tyres. And you wonder why with this sort of shenanigans with the rules Group A was dominated by turbos? And then came the 600+HP 4WD Skyline to make a complete mockery of the formula. Enormous power, medium weight, big tyres.
And now a hypothetical question. What would have Group A racing been in Europe if Brock had the hindsight to homologate a sporting evolution VH Commodore to compete in the 1983 ETC? Assuming the follow on model VK was also homolated in 1984, how would this have affected the 1985 Nissan Sport series at Wellington & Pukekohe in late January 1985, and the ATTC in 1985? One can only wonder what if. geeze I wish I had a time machine