I believe they are . Regulations link is on the top left of the website but not on the left hand tabs. It seems to 2017 regs and not updated for 2018 which is not ideal, hopefully someone can clarify.
- PROTO CLASS
5.7.4 A production based naturally aspirated 4 cylinder car engine having a maximum swept volume of
2000cc and with maximum 200 240 bhp at the flywheel and a maximum engine speed of 8500
rpm.
5.7.5 A production based naturally aspirated 4 (maximum) cylinder motorcycle engine having a
maximum swept volume of 1600 1300 cc and with maximum 200 240 bhp at the flywheel.
You will find the 2018 regs on the BARC website. Look under the championship and click on downloads.
Let me know if these don’t answer the questions.
Pete.
