Tuning is allowed. I ran this two or three times in
@ZOPPO GT s Thunderclub, and it was great. The fast guys mostly went for Gr3 cars , then a bunch were is Class 4 in Classics.
About multi class racing.
The BOP for my former multi class series worked pretty good. Feel free for using it for your Ring Rats races if you want. Here it is:
Class 1 (Racecars Gr. 2 + 3 + 4 only) ------ 544 hp (400 kW) / 2602 lbs (1180 Kg)
Class 2 (Group N cars only) ----------------- 374 hp (275 kW) / 2602 lbs (1180 Kg)
Class 3 (Group N cars only) ----------------- 238 hp (175 kW) / 2425 lbs (1100 Kg)
Class 4 (classic cars <1974, all groups) --- 374 hp (275 kW) / 2602 lbs ( 1180 Kg)
All cars wich was made 1974 or before have to start in class 4 only. The BOP for class 2 and class 4 is the same and it looks they can race in just one class. But I devided them, because the performance between classic cars and modern cars is too different.
Kind regards and speed safely!