[Adger Smith]

Tony,
What I mean is that you should give the engine what it wants to make power. Don't say it needs to have (as example) 13.2 AF ratio. Do like MJ says. Tune for best power. That might change going from Dyno to car, too.
I have run into customers that will tell me:
1. It has to have ---- A/F ratio to make power
or others that have an EGT meter and tell me:
2. It has to have ------ EGT... Usually they find out real quick they are off base with their assumptions if they want the engine to make the best power.
I have found that, Usually, lower compression engines make more power on a little richer mixture.
They can also like a degree or two more timing than the same combo with hi compression. Some times that changes in the car. (gearing/converter/Load in the car being different than dyno)
My guess it has to do with the charge density in the combustion chamber.
The richer mixture may increase the C/R a little and make the mixture molecules pack tighter and burn better. Isn't it said that Combustion is just a chemical reaction where heat is extracted from the A/F mixture? Just as a side note, some of the guys I know that run Comp say they can't see much with the merge collectors on the Dyno, but the car usually goes down track faster. I'm with MJ on how the merge collectors might help on the fuel curve, esp in a car going down track.
I might suggest you go back and check your tuneup with both collectors at different acceleration rates on the Dyno. You might find that w/ the merge collectors there is a real difference in the faster rates. (back to that signal at the carb booster)