Soooo, what you mean is you like my carbed engine then? Lol! You are right Mr. Richker, EFI is better even in my opinion.Cheap, fast, and street - pick any two of the three.
The first step is to decide what will be the primary function of the vehicle?
Where will it spend most of it's time?
Some basic thoughts about two very different approaches to making power in an internal combustion piston engine:
Carburetors are mechanical devices that depend on pressure differences to meter fuel. The venturi is common to all type of carbs, it is what creates the pressure difference that makes carbs function. The float bowl is vented to the atmosphere just above the venturi in most carbs. The fuel is sucked out of the bottom of the float bowl through a metering system that controls the gross amount of fuel delivered to the engine. That metered fuel is then delivered to the point in the carb where the greatest pressure drop occurs. In some simple carbs, it is the area of the smallest part of the venturi opening. More complex systems may use a booster venturi to aid in fuel delivery.
Notice the emulsifier tube in the diagram: it has two purposes: It helps break up the fuel into tiny droplets and it serves as a suction breaker when the engine isn’t running. That keeps the siphon effect from sucking fuel out of the float bowl when the engine is shut down.
Also present in carbs are separate circuits that meter fuel at idle, a power valve that opens up to provide extra fuel at high power settings, and an accelerator pump to provide extra fuel when the throttle is suddenly opened. All these circuits with the exception of the accelerator pump depend on a pressure drop to make them work.
The primary limitation of carbs is that they are a mechanical device, and have no way to compensate for changes in temperature and atmospheric pressure. These two items can limit the power of a carb’d car. A race to the top of Pike’s Peak on a hot summer day would be an example of how this will affect a race car. Or a trip down the drag strip at Denver, Colorado in the summer compared to one in Los Angles during the winter. Definite power differences would be seen & felt. Adjustments can be made, but it requires some small amount of wrenching to do.
EFI does not depend on a pressure drop to pull fuel into the intake or help atomize the fuel. The venturi and associated restriction of the intake airflow is eliminated. Instead EFI measures either air pressure or airflow along with air temperature, water temperature, RPM, and throttle position to calculate the amount of fuel needed. The calculation is much more precise than the simple mechanical process of a pressure drop across a venturi. Since a pressure drop across a venturi is not part of an EFI system, pressurized injection is needed. The injectors are capable of consistently breaking the fuel into tiny droplets that flash to vapor and distribute themselves evenly in the individual intake ports. Couple the precision of the air/fuel measurement along with timed, pressurized injection of the fuel directly into the intake port, and you have a superior system.
EFI expands itself into engine management: not only does it control fuel delivery, but ignition timing as well. The computer can add or remove timing advance while the engine is running, according to the need of the moment. Inputs from sensors can detect detonation and retard the timing, or add timing if the engine can handle it. With an aftermarket tuner and a laptop computer, you have an infinitely tunable machine that can make changes on the fly while you are racing. Consider the possibility of the computer detecting a sudden increase in RPM due to wheel spin. The computer could reduce the timing advance to the point that the wheel spin was minimal and then increase it as the car picked up speed.
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.
You missed something ...The Baro sensor on the A9x and later MAF engine control computers are designed to accommodate changes in density altitude and will compensate for any reasonable altitude a driver might encounter. Granted that lower density altitude can't really be compensated for, but the engine control computer will give the best match for current altitude density and temperature possible.jrichker is pretty good but I want to be a stickler.
Weather (density altitude) can and will effect an EFI car much more than 1/10 from perfect conditions to miserable... So that example is not so accurate... I saw over 4mph and nearly 7/10's from running on the north east coast in October to running in the desert in July.
Having said that, if the car were carb'd and tuned for the northeast coast, running in the desert in July would likely have been even worse... and drivability would have been terrible... the EFI maintained perfect drivability. For a carb'd combo to keep up you would need to swap jets/power valve and make mixture and timing adjustments. Assuming you know what you are doing you would be right back to running with the EFI car.
So, yes, the EFI accommodates for the conditions to keep the car running the best it can given those conditions, but it is not magically able to overcome density altitude... Carb, not so much, it'll require parts swapping and tuning and likely a bunch of throw away runs at the track getting it right.
Since I'm getting ready to run the fuel lines in mine, and I'm carbureted, I don't need a return line for that, do I?I drove for years with an edelbrock 650 carb on my car and an air fuel ratio gauge. My 89 gt convertible got 26 mpg on the highway with zspec t5 and 373 gears. I did no tuning to the carb other than idle screws and adjusting the power valve....even ran the stock efi distributor with the computer hooked up. I don't know how it ran at all but it did and I drove it all over. From Maryland to Alabama.
I don't know how or why it ran so good. I used an aeromotive return style fpr and a cheap Mr.gasket inline fpr before the carb. Also, I had a one inch spacer on the edelbrock intake. The injector harness was removed along with all the sensors accept the factory temp. sensor.
Easiest set up I ever had. Started every time. Just had to replace the Mr.gasket fpr every about 6 mos. the aeromotive would only drop the fuel pressure to 15psi...ran Mr.gasket at 6psi.
When I removed the efi I noticed the car would build power when smashing the gas...unlike the efi where it felt like it hit instantly.
Changed all over a shorted o2 sensor wire. Now I'm going back efi.....with a turbo [emoji106]
I agree, with my pint sized motor and not needing real high pressure, I was thinking I could get by with a single line. Just wanted to ask, I have found I don't know everything while building my car!You can do a dead head system. (no return)
As long as fuel demands are not crazy high.
Given a choice,a return is the better way.
The same argument could be made about points ignition over electronic ignition.Then there's always the one thing that no EFI guy ever seems to talk about if we have to consider a scratch build, or a aftermarket conversion.
Money. Lots of it.
A carburetor on an engine doesn't need the ECU that a F.I. engine does. It doesn't need the throttle body, the wide band O2 sensor, or any of the other required sensors (IAT, MAP, TPS). It doesn't require the 300.00 set of injectors, fuel rails or 250 LPH wet pump (minimum) either.
It only requires somebody with the ability to look at a spark plug who isn't color blind, and can read a vacuum gauge. And does not require some red headed wack job tuner to get the combination to make power.
What ever did we do before there were dyno shops?....Everybody worth the salt in their sweat could read a plug, and tune idle w/ a screw driver, and a vacuum gauge. Last time I checked, all of the classes in all of the top NHRA N/A classes still use one of those ancient dinosaurs to win the money.
The examples given make it seem like our subject is a jet setter, dashing from both sides of the country to race his car. I'm sure that there are those guys out there that are,..but would venture to say that most only care about the track they go to, in the city state, and region they live in.
So in hind sight,...how freakin hard is it to turn a screw driver, turn a socket wrench, and make a few adjustments in the spring, then change those same adjustments later when the weather changed?
A good race capable carb to power an 11.0 sec car can be 1000.00, but conversely, can also be had for half that that will work perfectly for the intended purpose.
My current project is injected. 400.00 worth of 42 lb/hr injectors, 400.00 ECU (from a scratch built kit) 300.00 Wide band, 300.00 fuel pump, 200.00 regulator, 200.00 throttle body,...150.00 in those "various sensors". and two fuel lines to make all that crap work.
That = 1950.00 and that is cheap considering there is no fuel rail configured, or intake manifold in the price
If it don't run right (which it currently doesn't) I have the same two choices that Joe Carb does....(And that is if it will even start).
learn how to tune it myself,.....or pay somebody to do it.
A brand new carb on a known previously running engine only needs to be bolted on, hooked up, fed fuel, and it'll start, I gaurantee it. Get out your screw driver and it'll idle. Sit down with one of the 50 various tuning books out there and you can completely disassemble make improvements/changes and then put the thing back together, and it'll run again.
Simple,....cheap,..and red headed wack job resistant.
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