For those of you who didn't bother to follow all the links posted by RacEoHolic330, here's a little story about EFI & CARB. Maybe not as entertaining as madmike1157, but very informative...
Let’s take the race to Pikes Peak and expand it a bit…
One of the important things is consistency: that’s why automatic transmission cars are so good at bracket racing. With a little effort on the driver’s part, they get off the line the same every time. Transport that idea to EFI and carbs: the EFI system is like the auto trans, and the carb is like the 5 speed. It can be much more difficult to get consistent 60 foot times with a 5 speed than an auto trans.
Large changes in temperature or barometric pressure can affect power output due to the change in air/fuel ratio in carb systems. EFI takes care of that problem by getting input from the sensors and adjusting the injector pulse duration .
Sample examples:
Carb: You take your new hotwheels 351 with a carb, fancy heads, hot cam, built C4, etc., etc. to the local tuner whiz. He’s a little peculiar, one of those hair on fire, can’t stand still kind of guys, but he gets results. He also gets $100 an hour plus $300 for dyno usage, so wasting his time isn’t healthy for your wallet. It’s 60 degrees and dry as dust as you pull into the dyno shop. The first pull is terrible, and he shakes his head and makes some insulting remarks about your hat size. Out come the tools and 15 minutes later he’s ready for another run. This one is better but flattens out near the top. He’s thinking a different power valve is the fix. More tool turning, another 15 minutes and he’s ready to go at it again. Next run looks really good on top end power, but the mid range torque is down and isn’t what he wants. Time to change more parts… Out comes the jet kit and he finds the proper size, along with another 15 minute slice of your wallet. Fire up the engine, re-adjust the idle and accelerator pump linkage and run it up. This one makes him smile – a little. He tells you that this isn’t the ultimate, but it is good. Pleasantries are exchanged, along with $400 of your money. Weeks pass and spring turns to summer, along with several trips to the track. The track results have been good, but the times seem to increase as the temperature rises. Today it’s 95 and so humid that everything has a layer of sweat. First run, power is down, the car seems to bog, the trap speed is down and the ET is up. You check the timing, tire pressure, fuel pressure, all OK. Second and third runs produce similar results. Another run and you do a clean cut at the last light. Coasting into the return lane, your pit crew buddy meets you with a plug wrench and some extra bodies to push the car out of the way. Plugs come out, inspection is done and you conclude that the engine is running rich. A call to the tuner guy results in him digging out the dyno sheet and looking at his notes. More insulting remarks follow, and he asks you if you expected the same tune that ran good at a dry 60 degrees to run the same at a sweaty 95 degrees. You say yes and then he tells you to get a life and some more education on how temperature and humidity affect engine performance. He offers a retune for the current weather at a discounted $300 flat rate. A sudden pain in your wallet springs to life as your credit card starts to throb like a stubbed big toe…
EFI: Your new EFI 351 is all ready to go, hot HCI combo,70 MM TB, 30 pound injectors, 80 MM MAF, built C4, stock computer and a lot of time and effort. A trip to the dyno is scheduled and it’s a fine day, 60 degrees outside and bone dry. You pull up to the dyno shop and are greeted by a little guy with frizzy red hair that looks like an explosion in a mattress factory and is wearing a T shirt that says “DynoGuys” on it. He seems a little weird, but he is supposed to be the best. Five minutes later, he has a laptop connected to the computer port and is ready to roll onto the dyno and prep for a run. Tires, timing, fuel pressure & idle are checked and pronounced acceptable. First run is a baseline and shows there is more on the table. “DynoGuy” shakes his head, mumbles something and does a tap dance with his fingers on the laptop keyboard. Two more up and down runs, and he smiles, showing the braces on his teeth. The engine returns to idle and it seems a little rough. “DynoGuy” dances on the keyboard some more and things smooth out. Another run up and down and he hands you the dyno sheet and asks if that was what you had in mind. You say yes, he shuts everything down, disconnects the laptop and heads for his office. Five minutes later he is back with a little black box that the plugs onto the car’s computer where his laptop was plugged in. He plugs in the black box, secures the loose pieces and kick panel. So far so good – then he hands you a bill for $475. You look and see $300 for the dyno, $50 worth of his time and $125 for the custom chip he just installed. Ouch! Well, at least your air miles on your credit card just went up.
Weeks pass and the miles go by. The car even passes the gas stations, something it never did before. Several trips to the track prove fruitful, the car just keeps getting better. You decide to make a July 4th bonus race, even though it is 95 degrees and so humid that even your cat is sweating. Off to the track: first run good, second, third and forth runs are good too. You look in the glove compartment at your previous time slips. All are tightly grouped with about a 1/10 of a second between the highs and lows. Bonus time comes up & you win $75 for the most consistent times for the season.
The point is EFI is a consistent performer, hot or cold, rain or shine. Differences in temperature and humidity are accommodated by the computer’s programming. No jets to change, no linkages to adjust, no power valves to tinker with. No getting stinky smelly from gasoline while playing with tiny parts that seem to want to run away and hide from you.
Consistent all weather performance, good gas mileage, and no failing the smog check because of non standard equipment are the pluses of an EFI car. Cars that were EFI and have been converted to carb will not pass smog testing. That may not be a problem now, but if you move or sell the car to someone in an emissions regulated are, it will be.
. Would like to go back to EFI one day, complete aftermarket maybe Megasquirt. I know it would improve millage with the EFI, but may lose some hp
. For now it will stay carbed for the few hundred miles a year it is just fine
he won't be walking because reliable FI
