While I am not able to own or race one, the simple answer is HONDUH--in all of the ITC, ITB and ITA classes.
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If you're looking to build a new(er) car, I'd suggest a 88-91 Civic STD Hatch in ITC, a 88-91 Civic DX hatchback in ITB, or a 88-91 Civic/CRX Si in ITA. All are viable options for their respective classes depending on how fast you want to go