Board Thread:Game Discussion/@comment-33721000-20180523173941/@comment-32672384-20180523175225

In endurance champions, if you are using the Nismo to complete, either the Audi or the Porsche will need to be upgraded to 93PR to 100% the series. This can be done without gold upgrading. You will also need to own the Audi to attain 100%

So no, unless you're gunna use it in time trials, the porsche only needs R$ upgrades. You could also upgrade it so it can farm LeMans races while the Nismo is servicing, if you really wanted to.