Just wanted to let you know that Instant Build (Design) cheat is making things built faster however there are no performance boosts from those parts. When you review the part itself it shows that it is suppose to have more performance, but when you review the graphs and compare it to second car, it has no boost. In fact sometimes original parts show up to have more performance.
Also disabling the Instant Build/No Cost(Design) cheat, has no effect. Seems to be a permanent Cheat.
This is mostly likely not possible. All the cheat does is setting the time it takes to produce to zero. It does not modify anything else. Unless the days are linked to the performance boost effect it is impossible for the cheat to have an impact on it.