[MJN]

Don't forget the drivetrain inertia effect on a dynamic dyno such as the Dynojet. This is never really accounted for in any of the previously quoted losses it's just 'part of the percentage'. You can very nicely lower your 1/4 mile ET by reducing your drivetrain mass/inertia by using a lightwieght reciprocating assembly, aluminum flywheel and driveshaft and lightweight wheels and tires. Making these changes would show up as a gain in HP on a Dynojet even though no HP was actually added to the engine. For a car with a heavy drivetrain, with say a jag rear end that has the extra U/J's and driveshafts, the mass to be accellerated is much higher than for a live axle and should show lower HP numbers on a Dynojet and slower acceleration times, all else being equal.

By the way 15:1 A/F ratio is waaaayy too lean under load. For a lean burn cruise it may be OK. You will burn up something in very short order running with that A/F ratio. 13.6:1 is probably ideal for a N/A engine. The power changes you are seeing are certainly not due entirely to the A/F ratio. Be carefull.