I’ve been building a fleet of custom cars starting in the early eighties, and I’ve managed to get their performance comparable to cars of the era. Barring maybe fuel economy, there is one big disparity I’ve noticed between the engines I’ve created and the real ones I drew inspiration from, and that is the compression ratios. All of my engines have needed much lower compression ratios verses their real-life counterparts in order to run comparably.
I considered this could just be an issue of my design methods, so I decided to put the engine designer to the test. I decided to replicate the infamous Pontiac Iron Duke Tech IV (specifically, the post-83 version with a 9:1 compression ratio), an engine which was not exactly a precision-built work of mechanical art. The engine designer, however, completely choked. In order to get the in-game engine to match the real engine’s power outputs, I had to set top end and fuel delivery system quality levels to +10 and had to retard the timing all the way to 0 in order to keep the engine from knocking, among other things. Once I turned the compression ratio down to around 7.4:1, I was able to get comparable performance to the real Tech IV while keeping the various engine parameters realistic.
I understand there’s a lot of factors at play here, but everything I’ve been seeing designing my own engines and replicating real ones seems to point to this relationship between compression ratio and fuel octane being off.