Engines with knock sensors can adjust to lower-grade fuel. How much power is lost when coming down from, say, 92 octane to 87?
A lot depends on the engine. Many of the new cylinder head designs-the GM Vortec (4.8, 5.3, 6.0, 8.1), the newer Fords (4.6, 5.4), and the DaimlerChrysler engines (3.7, 4.7, 5.7 Hemi) for example-have had combustion optimized to the point that we crank in much less timing advance than we did previously. On these engines, the change is minimal with stock calibration. On older engines, either a factory fuel-injected engine with an "old-tech" combustion chamber, or add-on fuel injection on a previously carbureted engine, the effect might be more pronounced. More aggressive fuel and spark mapping would change all of that in both cases.
The number one problem with EFI conversions is fuel delivery. Fuel shearing, a.k.a. aeration, is the result of inline pumps, improper fuel-line routing, and certain types of fuel filters. The sure cure is an in-tank fuel pump like this. Use a stock one from an EFI rig if it will fit your application, or use an aftermarket pump that can be adapted to many types of tanks. Note the large-capacity replaceable suction filter at the bottom that stays submerged.
Are there any negative effects in day-to-day driveability with going to a larger-bore mass air sensor on a MAF system?
We have not done any quantification in our labs to authoritatively answer this question. I doubt it would make any difference unless the feed to the ECM is altered. If the larger sensor uses the same 5-volt reference and signaling, I would suspect little difference.
What are the common pitfalls to converting carbureted engines to EFI, both aftermarket kit and home-built?
Fuel delivery is the number one problem, particularly the placement of the fuel pump. In my experience, over 80 percent of the problems are fuel-delivery related. In my opinion, only an in-tank pump should be used. Why? "Fuel shear"-that's an engineering term for aeration. Air in the fuel lines in anything but tiny amounts can have a major effect on driveability and performance. Erratic low-speed performance, vapor-locking, and lean conditions under load are just a few possible symptoms. On a typical EFI conversion, an inline pump is installed with a filter between the pump and the tank. The flow through the filter shears the fuel, which can also cause problems with the pump. The pump should be protected by a filter, but it's better placed in the inlet of a submerged pump. If an inline pump must be used, a submerged fuel "sock" is a better idea than an inline filter in front of the pump. We've also found that certain types of fittings will cause fuel shear. Just like optimizing intake or exhaust flow, all bends in the fuel line should be gentle ones, and transitions inside the lines as smooth as possible. After fuel problems, poor electrical connections are the big problem. Wires connected by the "twist and tape" or "Scotch Lock" methods are inadequate.
Precision Automotive's programmable Delphi ECM is adaptable to almost all EFI systems in four-, six- or eight-cylinder applications. It will require some mods to the EFI electrical harness to install. This is the way to go when your engine is modified beyond the stock ECM's ability to compensate. TO program, you need only a modest laptop with Windows 95 of up, a special program that's available from Precision, and patience.
What is the major key to performance improvement in an EFI engine?
It's simple: Optimum fuel and spark for the particular application. In milder cases, that can come from an aftermarket chip or programmer. Many of these are emissions-legal. If you want serious increases, combine internal and external engine mods with new calibration. If you want calibration that will give you driveability comparable to OEM, in most cases you need a stand-alone programmable ECM, some dyno time, and a laptop with programming software. With time, effort, patience, and thought, it's possible to do that without the dyno. If the calibration is optimized for the engine, you should get optimal results.
Any specific calibration tips for trucks and 4x4s?
Traditionally, with a heavy load, we add fuel and subtract spark. This keeps combustion-chamber temperatures in the safe zone and allows for reliable engine power. For four-wheeling, we might devise a more aggressive acceleration enrichment calibration to allow the throttle response to be more positive.