9 replies to this topic

[sinister]

Source: http://www.pro-system.com/scoop92102.html

Carburetion Vs. Injection

One of the most oft asked questions is why do carburetors make more power then EFI and why do the car manufacturers use EFI if carburetors make more power?

A few years ago we used some contacts at General Motors to verify some simple facts from some dyno data we had received from a head to head comparison.

An engine was being constructed for Comp Eliminator style racing and the program was going to be electronically fuel injected. Well the system was giving the engine shop some questionable numbers. The shop removed the EFI system and installed some of our Pro Stock carburetors on the EFI manifold top so they could quickly compare systems.

The engine responded immediately with much faster acceleration rates and a 5 percent improvement in power.

The EFI designer was brought out to the site and try as he might he could not out perform those carburetors. When the session wrapped up carburetors were king by 24 horsepower.

I've heard similar stories and similar claims when comparing systems.

So when we analyze this information it really comes down to a simple fact. Carburetors and Electronic Fuel injection are two completely different systems. They share no concepts and each has a different theory.

EFI's claim is this: I will supply sprayed droplets of fuel at the proper air to fuel ratio all the time.

Carburetors claim: I will supply a pre-emulsed froth of fuel and air into the engine at a preset ratio.

The results proved the analysis of the concepts to be correct. In this case, the carburetor was supplying the engine in question with the proper air to fuel ratio, so the EFI's advantage was gone. Remember, EFI has a computer to tune the engine. You have you. If you know how to tune you'll have the advantage. Carburetors (at the risk of sounding chauvinistic) are a man's game. Guessing rarely works. You have to know how to actually tune an engine.

Remember a carburetor is an atomization/emulsion machine. An injection system is a proper air to fuel delivery ratio machine. Two different concepts. If a carburetor can be designed to supply the perfect air to fuel ratio all the time it should consistently outperform EFI. Its design lends itself to have an unfair advantage in atomization.

Obviously adiabatic expansion is the next question on the list. So if we take a good look at the carburetor we see its not only a perfect machine for atomizing fuel, it also has another advantage. The joule-thompson effect.

Tests performed using quartz plates and infra red sensors located in the plenum area beneath an NHRA Pro-Stock engine revealed an intake manifold temperature drop on a 85 degree day of almost 20 degrees as a result of the the carburetor creating this effect.

So when your neighbor with EFI is ingesting 85 degree air, your power-plant could be ingesting 65 degree air.

That's a nice advantage.

But let's not skip over the atomization advantage. In a high end designed carburetor the fuel is emulsed to lift it. Its a controlled froth. I won't kid you, it's very difficult to control. Its much easier to build a carburetor that operates on a vacuum to ratio concept. But the fogging advantage is gone. So when a customer asks, why is this carburetor more expensive than that builders carburetor as they look basically the same. Most of it is all in the emulsion package and the time spent flowing it and tweaking it to do its job. Remember in a high emulsion design .001 of an inch is a big deal. They're difficult to balance and require sophisticated equipment that many shops have never seen. Also, don't go poking things into the metering block passages to inspect them or look around. You might just lose 10 lbs of torque.

The disadvantage of carburetors used to be restriction. I remember back 20 years ago before booster technology really took off you had to size carburetors to operate on 1-2 inches of vacuum in the plenum at the starting line. The restriction alone was probably costing these engines a 2-3 percent power loss.

Tests we performed at Sonny's racing 5 years ago showed us numbers of about .6 in the plenum and spikes of about 1.1 to 1.3 in the runner at the finish-line. That's a pretty huge decrease and just for dynos sake when we built carburetors large enough to reduce this number by on average 40 percent we saw an increase of only about 3-5 horsepower on an IHRA Pro-Stocker. SO that advantage for EFI is now also gone.

Now that these same engines can operate on as little as .5 hg of vacuum at the starting line and only 1-1.2 at the finish-line, the restriction is nil. Really it all comes down to getting the air to fuel ratio correct. If a carburetor can do that, it should win the race every time. After all, by design, it's a superior emulsion machine.

Thanks for reading.

[MATTSS]

EFI thats all there is to it, in saying that carbys do have there plus'

[DEM82]

Some differences that make EFI ideal to manufacturers compared to carburettors are big No.1 Emissions. no.2 precise fuel ratio control, as stated in the original post. no.3 Drivability, carburettors can be difficult at times. Consumers don't want the inconvenience of using the choke on a cold morning, idling issues when Air con compressors are cycled, the list goes on. These key points and i'm sure many more are the core demands EFI is designed to fulfill. Power is somewhere down the list.

I happily sacrifice a 5% power loss with EFI for a 20-30% increase in fuel economy.

A small percentage power loss for a dramatic improvement in drivability when i'm in traffic on a 40 degree day and using A/C while still moving slowely with traffic and yet have no signs of detonation and/or fear of stalling a subsequent hard restarting cause the fuel is boiling in the bowl.

EFI is not Perfect, neither are carbs but everything has it's place and purpose. For a drag racing application on a big V8, carb it up. For a daily that dabbles in circuit/drag/drift and has forced induction, EFI please.

[protd]

most of the problems you list are from a poor fuel system, a correctly set up carby and fuel system do not have any of the problems you mention.. i also don't beleive thats a carb uses 20-30% more fuel unless it's pig rich and practically dribbling out the boosters once again just part of having it set up correctly, not many people these days even know how a carb works which is sad, because they can be very very good in most applications..

but for fuel econamy and ease of use (because you pretty much never have to touch it once setup) i agree i would have nothing else but FI,

they both have there place in the car world..

Edited by protd, 02 December 2009 - 06:00 AM.

[xdclevo]

protd, on 02 December 2009 - 06:00 AM, said:

.. i also don't beleive thats a carb uses 20-30% more fuel unless it's pig rich

A agree, actually most EFI type motors that are setup for full power with big cam(s) for racing etc probably use more fuel than a carby.

And i beleive an EFI and carby are probably on par with making power, its just that its so easy to set up a carby than EFI that some get confused and its actually the tuner that is to blame not gettin the most from EFI.

And this is a carby mob doing the testing, ofcose they are slightly biased

[7shades]

I hear banjos...

[Lights-Up]

Whats the source for this article.
Im a dumb-ass:unsure:

Edited by Lights-Up, 02 December 2009 - 04:47 PM.

[SiKnEsS]

jeesus, talk about grave diggers lol, musnt have anything better to do obviously haha a year old thread for christ sake and u only reply now rofl

[sinister]

First line of the post..... link to the source

[BPM]

180SEXX, on 02 December 2009 - 05:07 PM, said:

jeesus, talk about grave diggers lol, musnt have anything better to do obviously haha a year old thread for christ sake and u only reply now rofl

more useful information rite there, did you take notice when he joined??



Just to add, FI has a huge advantage over a SINGLE carb, but at WOT 2 or more carbs is on par

Brinks