On that note, what common technical regs/formula would you say would there be if that happened?
almost none since CART like today's Indy used the system of single supply of the chassis or almost ( at the beginning it was dominated by the Lola chassis with some competitors like Peske, Penna, Rahal trying to hinder it from 2002 onwards it became a single brand with use a the Panoz - DP01, the only real difference is the engine manufacturer which ranged from the ever-present Cosworths to Chevrolet, Ford and Honda ) to reduce prices and bring the competition closer ( giving the drivers the same initial conditions more or less the same for everyone )
the differences between the two categories are actually significant :
The cars ran mostly on street circuits, were heavier and longer than those of F1 ( as well as using different types of fuel )
the minimum weight reached 700 kg without a driver, against the 640 kg ( with driver ) of the F1
The Champ Car was looking for the use of ground effect, a limited element in F1 to slow down the increase in performance and for safety reasons
furthermore, driving assistance devices were forbidden, with the exception of the semi-automatic gearbox on the steering wheel, which is very common in the maximum formula
the starts in Cart ( with the exception of the last season of the category in 2007 ) were launched in F1 starting from stationary
The Champ Car exploited the Push to Pass, a mechanism by which the driver supplied his turbo with a greater supercharging which allowed the use of 50 more horsepower by pressing a button, the cars were provided, by regulation, at most 60 seconds of supercharging . this idea was introduced in F1 with some teams in 2009 and only in a stable way from 2011 to 2013, commonly called KERS it was further developed with the advent of hybrid engines from 2014 onwards
now for example let's compare three qualifying flying lap times between F1 and CART / Indy car on the same track and in the same year ( we use 1993, the year in which a certain Nigel Mansell tested both cars ) the track we use for the the comparison is the Detroit racetrack ( used by F1 until 1989 ) Nigel sets the fastest lap in 1:48:08 against his own time on the same track ( driving a Williams - Judd ) of 1'42"897 a 2.2 seconds behind to Ayrton Senna fastest lap in the race
these are the differences that come to me at the moment, however if we want to talk about a merger between the two categories I would suggest a small change at the dawn of the Indy 500 and associates ( since Otl until the end of the 1960s the race was considered an integral part of the F1 championship, even if none of the main participants took any part ( except for rare dazzling appearances, such as Ferrari and Ascari or the Lotus with Jim Clark, it must be emphasized that the situation was similar in the opposite sense ( few Americans took part in a GP that was not Indy in the first 20 years of the world championship )
or make real the threat made by Enzo Ferrari during the fight between FIA - FOCA in 1986 to grind formula one and compete in Indy ( Ferrari had already prepared a car the F - 637 to participate in the following year's championship ) I doubt that Ferrari will really do it ( but it can very well do as nowadays with participation in F1 and WEC )