Paper or plastic? Credit or cash? Sweet or unsweet? Oh, the questions of the ancients have perplexed us so. Yet we continue to argue points for each side with equal validity and fervor. An argument closer to our hearts that seems to come up regularly is whether a carburetor or electronic fuel injection is the superior form of fuel delivery in a high-performance engine.
The debate usually goes something like this: "Carburetors cool the engine and injectors let hot air in."
"Yeah, well injectors are more precise and can shoot the gas right into the combustion chamber."
"Yeah, well carburetors are cheaper."
"Yeah, well injectors can run even if the car is vertical or upside down!"
"Yeah, well where is the oil in your engine if the car is upside down?"
"Yeah, well my dad can beat up your dad."
Patrick at Pro-Systems set...
Patrick at Pro-Systems set up the Holley 950 HP carb for MME. Mark McKeown then modified the throttle shaft to attach it to a TPS sensor.
Since the beginning of internal combustion time, basic carburetors have been taking advantage of the Bernoulli effect as their primary method of delivering atomized fuel to the awaiting engine. Though visually quite different from what we see today, the design first patented by Karl Benz in 1896 showed the basic simplicity by which a carburetor could properly meter fuel based on the load and rpm of the engine. In a nutshell, low pressure in the manifold (open throttle) would invite a rush of air through the carburetor. As the high-velocity air passed through, it would draw fuel through carefully placed holes in the carb bore and send it down into the combustion chamber. Tuning is done primarily via fuel jets and air bleeds that are swapped out to richen or lean out the engine, and acceleration enrichment is accomplished usually through the use of an accelerator pump and adjustable or replaceable actuators like accelerator pump cams. There are entire books on the theory and function of carburetors that we won't go into on the next few pages, but in essence, the carb is a fairly basic device that can be tuned fairly well by anyone with a little bit of patience and a good carb book.
Sixty-pound injectors set...
Sixty-pound injectors set at 42 psi were overkill, but dialing them back was not an issue with the C-Com software.
Crude forms of fuel injection have also been used as far back as the late 1800s, mostly in diesel engines, and later adapted for use in airplane engines in World War II. Planes with simple carburetors would simply empty the bowls and starve for fuel in a negative g or inverted flight situation where the injected planes had no trouble with those maneuvers. It wasn't until 1954 that Mercedes-Benz brought commercial gasoline mechanical fuel injection into the public domain. Though Robert Bosch is usually credited with being the father of electronic fuel injection, EFI, it was actually Bendix that released the first EFI system, the Electrojector, on a '57 AMC Rambler Rebel. Yes, an AMC. Bosch later snapped up the rights to the Bendix design and modified it for the famous D-, K- and later L-Jetronic systems. EFI systems typically use sensors to measure coolant temp, air temp, manifold air pressure (MAP), and throttle position at a minimum and compare these against fuel maps created by the tuner to get the engine running at peak efficiency. As with carburetors, EFI systems can be tuned fairly well by anyone with a little bit of patience, a good tuning book, and a laptop. In both cases, an oxygen sensor, a good long stretch of road, and/or a dyno make the task much easier.
Both fuel delivery systems have had many face-lifts over the years, but the question remains: Which is better? While building an engine for the 2009 Engine Masters Challenge, Mark and Heather McKeown of McKeown Motorsport Engineering decided to tackle that question once and for all.