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You are goign to lose power if go from a good non-knocking pump gas tune to a C16 without changing anything. To get the most out of C16 you usually need to raise the effect compression or run a lot more timing plus lower your fuel output.
C16 is a denser fuel than pump gas so more of it gets injected in the same pulse width time. A pump gas tune that is running around an 11.5:1 A/F will usually turn into an 10.8-11.0:1 mixture when you switch to pure C16. So you need to remove some fuel one way or another, like going farther negative on an AFC. You aren't really leaning out the mixture, your just trying to get it back to the same air/fuel you started with on pump gas. However, you can usually goto a leaner mixture than you were able to run on pump gas and start picking up some additional horespower.
The easiest way for us to raise the effective compression ratio and make the C16 happy is to raise the boost. Along with the boost comes more horsepower. If you don't want to raise the boost for some reason, then your going to need to run a little more timing on the C16 to get the fuel to ignite at the right time to keep making the same old power. You can sometimes run a fair amount more timing and try to make some extra horsepower, if you aren't using up all the octane already in boost, lean A/F, poor intercooling, etc. Don't worry a lot about getting crazy high timing numbers though. The power gains are usually minimal once you reach a certain point.
Mara's power on her 1G compression usually stopped sees gains at all at 24 degrees. That is with the base timing advanced and the ECU running off of the final max flow timing map(the one that gives 22-23 max then goes down to 19 degrees around 7000). The advanced base would give a little power in the mid range and topend range past 7000 area where the ECU wasn't running as much timing. Peak HP wasn't really help at all, just in a few areas. On Andy Nash's car we went from a base of 0-1 degrees to an advanced base of around 8-10 degrees and saw a gain of about 5whp. Not a huge gain for a car running a retarded base timing going to advanced. It's usually better to just run more boost than try to push the timing to the limits.
If you want to run a lot of boost on pump gas and make decent power that way then run as little timing as you can get away with. With higher compression, you usually need even less timing. If you can get 20 degrees out of a 2G compression then I wouldn't spend too much time trying to go any farther. Stock without any AFC fooling going on the 2G ECU only wants to run 16 degrees of timing max on its highest airflow map versus the momentary 23 degree peak timing max on the highest airflow map in a 1G ECU.
On C16 you can usually push the limits of stupidity and still not knock. On Mara's car we did just about everything to the extreme edge of tuning and the C16 would take it. We ran high boost on a shitty intercooler, so a lot of the octane was used just to compensate for the high heatsoaked intake charge air temps. We shot for an airfuel close to 12.5:1 and we often upped the base timing from the stock of 5 to 8-10. We didn't always do the timing though because we knew that it did next to nothing and wasn't worth the effort and risk. Boost equals power, timing doesn't.
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