Dyno tune ?

How much you gain is anybody's guess.

1. The factory specs are obtained at near ideal conditions. If you habitually drive in other conditions - high heat, extreme cold, high altitude - having the engine tuned to those conditions can gain some power.
2. Your engine may not be performing as designed. Injector pulses may not be timed right, the advance curve may be off a little. A good dyno tuner should be able to correct that.
3. The factory tune is extremely conservative. Made for the average driver, in average conditions, to meet emissions requirements, and to allow the engine to last forever on cheap pump gas. If you're willing to run premium all the time, there's lots of power to be had.

Can you clarify what you mean by that? I *always* run premium, in everything I drive. So what would I do on an EFI engine to improve performance?

Thomas

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1965 Ford Mustang fastback 2+2 A Code 289 C4 Trac-Lok Vintage Burgundy w/Black Standard Interior Vintage 40 Wheels 16X8" w/BF Goodrich Comp T/A Radial 225/50ZR16

EFI engines have knock sensors and the 'puter takes out timing advance when pre-ignition is happening. So the lower the octane, the less timing advance you're getting. All else being equal, all three grades of the same gasoline will burn the same and provide the same amount of power. But with a computer varying the timing according to the octane, you'll get a little more power with higher octane.

180 Out

You may always run premium, but if the engine is stock, you probably don't need to. Check the owners manual. You can get good improvements by increasing the ignition curve, and increasing the injector pulse. More fuel + more spark = More power. The simple way to do it is something like a hypertech tuner, which does exactly that. A dyno tune with a custom chip will test your engine, and alter those two factors for optimal performance across the power band with the aftermarket parts you've already installed.

10-12 rwhp if tuned correctly.

Ed