reinforcing of chassis, tuning of engine and transmission parts etc. Weight restrictions were applied on a scale in relation to the engine cylinder capacity. The minimum weight was 580 kg for engine below 1000 cc, to 1,300 kg for engines over 5,000 cc. The final specific rule applied to wheel sizes, which were similarly applied in a scale related to engine cylinder capacity. Resulting builds Ultimately there were few restrictions on technology, design or materials permitted. For example fibreglass bodywork was used in the case of the Ford RS200, a car without a commercially available counterpart, though silhouette race cars using space frame chassis were still common even when consumer car equivalents were mass produced, for example in the case of the Peugeot 205 T16 or Lancia Delta S4. The rules provided for manufacturers who wanted to compete in rallying with mid-engine and RWD or 4WD, but their RWD production models had been gradually replaced by FWD counterparts. By reducing the homologation minimum from 400 in Group 4 to 200, FISA enabled manufacturers to design specialised RWD or 4WD rally car homologation specials without the financial commitment of producing their production counterparts in such large numbers. There were no restrictions on boost, resulting in the power output of the winning cars increasing from 250 hp in 1981, to there being at least two cars producing in excess of 500 by 1986, the final year of Group B in rally. Turbocharged engines weren't common in commercial cars and had only been introduced since the mid-1970s, but in the early and mid-1980s engineers learnt how to extract extraordinary amounts of power from turbo engines. Some Group B manufacturers went further, Peugeot for example, installed an F1-derived Turbo Lag system to their engine, although the technology was new and not very effective. Lancia twincharged their Delta S4, adding both a supercharger and turbocharger to their engine. When the Group N, A and B rules were decided, the weight/engine displacement restrictions were thought the only way to control speed. Nowadays, the power of turbo engines is limited by mandating a restrictor in the intake, and the Groups Rally hierarchy for example, each have limits on weight/engine power (kg/hp). Within all the groups, there were 15 classes based on engine displacement with a 1.4 equivalence factor applied for forced induction engines. Each class had weight limits and wheel sizes. Notable classes for Group B were