The following dyno charts were recorded at APR during the tuning of the APR Stage 3 software on my S4.  The car was tuned on 91, 93, 100, and 104 octane fuels.  In addition APR made a water/methanol injection tune using 93 octane gasoline.

With the consistency of having the same tuner and the same car setup being recorded on the same dyno equipment it makes for a good illustration of what differences high octane fuel has in comparison to lower octane fuel aided by water/methanol injection.

The chart below compares the base 93 octane tune with the 93+water/methanol tune.

APR uses a Dynapack dyno so calling it wheel horsepower is not completely accurate since the measurement is made at the hub, but the horsepower increase is about 25 whp, increasing from 385 to 410.

The next chart shows the results of a tune using 104 octane fuel and no water/methanol injection.

The dashed line was the baseline performance of the previous version of the 104 octane tune, and the solid line represents the new 104 octane tune performance.  The 104 octane tune produced a peak horsepower rating of approximately 468.

Comparison

With the 93+water/methanol tune peaking at 410 and the 104 octane tune peaking at 468 it is clear that the higher octane fuel produced more horsepower, nearly 60 “whp” more.

Caveats

Water/methanol injection involves multiple variables and if time had permitted to evaluate alternative configurations it might have been found that another combination of factors resulted in higher performance from the 93+w/m fueling setup.  Water/methanol ratio, volume of injected fluid, location of the w/m nozzles, fineness of spray, all could have been changed.  Additionally, how aggressively APR tried to tune the water/methanol setup could have closed the gap between the two options.

I am doubtful that any of those changes would have bumped the 93+w/m numbers up from a 25 hp gain to 85 hp so that the two alternatives were equivalent.