EFI vs. carbs

Please excuse my ignorance on this issue. I am curious as to why some people go with EFI vs. carbs. I am assuming the people running carbs do so for authenticity and the money savings.

If one doesn't care about authenticity (at least in terms of fuel management) and money isn't a great issue, is there any reason not to have EFI?

 

[Steve Toner]

Let's see... How about:

<UL TYPE=SQUARE><LI>Slight additional weight<LI>Additional failure mode(s)<LI>Inability to run leaded race gas[/list]

These are because EFI (or at least modern EFI systems - I'm no expert on the evil things Bosch might have done in the past) requires an ECU to operate.

The box weighs a couple of pounds (

big deal right? but I once heard someone say "a pound is a pound is a tenth of a tenth of a second"). This may be offset by the need to carry a toolkit if you have a carb setup so you can make adjustments because you've driven from sea level to 2500 ft or whatever...

As far as failure modes go, I'll tell you about a problem that showed up with the Eagle Talon/Mitsubishi Eclipse ECUs. I owned one of these cars until someone tried to make a left turn in front of me on my way to work one morning

Anyway, the ECUs contained 3 electrolytic capacitors and after about 5 years, people started noticing that their cars wouldn't start and had a "rotten fish" smell. Turns out the capacitors would leak, the electrolyte would eat away the traces on the circuit board, and the car would be dead (and in need of a $300 repair). I managed to replace my capacitors before they started leaking because the word got around...

As far as leaded race gas, every modern EFI system that I know of has an oxygen sensor, and this will be destroyed by leaded gas. Removing the O2 sensor when running race gas is not really an option because then the ECU can't tell if you're running rich or lean and make its adjustments... You can of course use unleaded race gas or regular pump gas.

These are not really very big negatives. Carburetors are certainly more fiddly, so if you're not into fiddling or authenticity, EFI is probably going to be a better solution for you (if, as you also noted, you can afford it).

 

[Dave Wharran]

Most aftermarket ECU's don't necessarily require an O2 sensor unless you want to run them in closed loop O2 control. If not running closed loop, they either use a MAP sensor and/or throttle position sensor to regulate fuel. I'm using just throttle position and rpm on my engine with the option of closed loop O2 from idle to about 2K rpms just to make it idle smoother under all operating conditions.

Pros and cons can be argued for both systems.
Some benefits of EFI are:
-more accurate fuel/air ratios throughout the engine load ranges
-more equal fuel delivery to all cylinders (when using port injection as opposed to TBI)
-faster throttle response
-recording and printouts of all engine parameters monitored by the ECU- both real time and historic data
-ignition timing control is included in most ECU's nowdays (with the ability to do crank fired/direct fired ignition)
-can be monitored and tuned via the laptop and O2 sensor (while driving if need be)-more tunable

Some drawbacks are:
-more expensive to install
-requires more extensive tuning than a carb, ie you don't just change one or two jets, you change fuel delivery at many points based on engine load and rpm.
-introduces more electronics onto the engine although the electronics now days are pretty robust. Remember though that most all ignitions are electronic now days, even in NASCAR where they still use carbs, so in most cases, there are electronic on the engine anyway.
-requires a laptop and software to tune and maintain

Both these lists of pros and cons could go on and on, but the final decision is based on what you want on your engine. Carbs have been around since the first engines were built. They have seen lots of development and do a pretty good job. EFI has been around for 30 years or better. It too has seen lots of development and will see more given the fact that all automobile manufacturers are now using it. I would look for more revolutionary things to come from the EFI side in coming years, given current advances in electronics and computers.
Dave

 

[Guest]

Whoa, Dave you've over generalized EFI. You've obviously only looked at the aftermarket systems in Jegs or Summit that are conversion systems. That said, Dave is not all wrong: there are Speed Density systems out there as he described, BUT it doesn't have to be that way.

One of the beauties of Mass Air EFI is that it is self adjusting, to a point of course. But you can make a lot of changes to a lot of things and the computer will adjust accordingly. Once you reach about 80% IDC on the injectors, you simply put in larger injectors and recalibrate the airflow meter. (Speed Density systems do require a little more adjustment.) And it does not require a laptop! There are control systems you can buy that do require this, but to say that EFI in general requires a laptop is way off base. A stock Ford EEC-IV EFI requires only a check engine light to count codes on if something is wrong.

NASCAR is in the dark ages and the only reason they have not gone to EFI is that they can't figure out how to police it. (Being in North Carolina, I have talked to a couple of NASCAR insiders and know of which I speak. Who is going to download and analyse every control program these guys might come up with?) Just look at all of the 5.O draggers out there; these are every day guys doing all kinds of stuff to their Mustangs and having no problems dealing with the EFI contols on them.

IMHO, there is no comparison when it comes to driveability: EFI is the best, hands down, no questions asked.

 

[Dave Wharran]

Ouch Lynn.
Actually, I said at the start of my note "most aftermarket ECU's". The context of my reply was only refering to 3rd party EFI systems, the Motecs, Haltecs, Electromotive, and many others. While the end result is the same, they are much different than production EFI systems in the tuneability they allow...and require. The aftermarket systems all require some type of programming device be it a laptop or purpose made programmer.
The production car EFI's are programmed at the factory for 99.9% of the public where the program never changes. You used to have to buy a new EPROM if you wanted to play with fuel and timing. I believe that there are now PC programs out there that will allow you and I to change those parameters although I'll confess I don't know for sure becasue I've had no reason to look. I use Haltecs on two of my cars, one for over 10 years. The system couldn't have been put on the engines without a laptop to program it. Once tuned though, unless you change something, the laptop never has to be plugged in again unless you want to datalog or just monitor.

If you have a stock or near stock engine, the factory ECU is fine. When you start putting wild cams, independent runner induction, and the like on an engine, you reach a point where the stock ECU's design won't allow or compensate for the necessary changes. Things such as blow back in the intake from long overlap, fast idle speeds controlled by an IAC, etc. The original design of those type ECU's was a mass produced ECU for mass produced autos. The aftermarket ECU's are designed with enough flexability, bells, and whistles, that they "fit" many applications.
An independent runner system can't use a mass air flowmeter. There is even a lot of debate on how effective a MAP sensor is on this type of induction (by tying a small line from each throttle body to a central "log"). Electromotive says it works OK. Others say it filters the signal too much to get good throttle response.

As far as NASCAR, the only point I wanted to make was that electronics are used a lot in racing (even NASCAR where they still use carbs) and hold up fine if designed properly.

 

[Guest]

Maybe I was a bit aggresive in my answer, but I still think you are selling short the EEC-IV and later ECUs. EEC-IV was used quite affectively in racing by Ford which, bye the way, is where it came from. The maps were modified somewhat but the basic inputs and outputs were there. Granted that individual runners are problematic for a mass air system but it isn't insurmountable. There are limits on how far you can take the cam. But, for all intents and purposes, we are talking about street machines here. Granted some (well many for the lucky guys in England) get some light track time, but for the majority, these ECUs can compensate for a plenty on a reasonable street engine. There are guys running superchargers and nitrous and ton of aftermarket parts who have put 60lb/hr injectors and recalibrated mass airflow meters on 5.0L engines and maybe a sandwiched in mod chip and are going like crazy.

The thing that kind of through me though was your statement about requiring more tuning than carbs. "Throwing in a couple of jets" is a gross over simplification; especially if you are talking about 8 Webers (since you through in individual stacks ;-). Properly balancing and maintaining that balance on anyting over a single carb is a non-trivial, ongoing process if you want optimum performance.

One definite advantage of carbs though is lower fuel pressure requirements. But even on that note, while the impression is that EFI uses these huge, almost dangerous pressures, the fact is that it is very close to the pressure that is probably on the water system in your house.

A HUGE EFI advantage is with emissions. EFI will provide the cleaner engine, period.

 

[Steve Toner]

Lynn Larsen said:
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> Properly balancing and maintaining that balance on anyting over a single carb is non-trivial, ongoing process if you want optimum performance. <HR></BLOCKQUOTE>

Mickey Lauria says:
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> Once the unit is synchronized and the idle mixtures are dialed in to give you the smoothest possible idle, you can hang up your Unisyn and screwdriver til' next spring, because now it's set! And when it's set, it's set!! They will not suddenly "go out" on you and ruin your day at the picnic. <HR></BLOCKQUOTE>

I don't think Mickey is taking altitude changes into consideration (though he does also say "This carburetor was intended for serious tuners and performance enthusiasts who want the most that their engine can give them. Welcome to the Big Time!"), but I wonder Lynn if you're speaking from experience or if multi-carb Weber setups have gotten an unjustified reputation over the years?

 

Concerning EFI, I love it! I had a 88 5.0 Mustang that I heavily modified, mass air, headers,monster head work and a Vortec blower. It was a joy to drive (my wife loved it) and there were no carbs leaking in the spring after 5 months of storage.
My 427 Cobra has 2-4 barrel Holleys because I believe thats way it shoud be.
I have a new set of Webers on the shelf for when I get ready to build my 40.
But, my motto has aways been build what you like and what makes you happy. I received a lot of static from guys because I didn't put a roll bar in my Cobra. I didn't want one and at my age I don't plan on going fast enough to turn it over.
Victor

 

[Steve Toner]

I love it too...for a daily driver. But for me, fiddling with Webers is part of the GT40 experience so I will have Webers on mine. And if I do get tired of fiddling, I can always change over. I HAVE graduated to a breakerless ignition system - had enough of that with my '65 Mustang...

 

[Paul Thompson 'Hooligan']

Hi all,
Roy Smart's 40 runs Kinsler throttle bodies with Motec management and the balancing is probably as awkward to set as with webers. What we have found is that the balance is mainly critical for tickover and v-small throttle openings. If its not right, you either drop a couple of cylinders, or two or more cylinders 'carry' the rest of the engine at idle. This can be easily recognised by monitoring the header temperatures.

Once the chokes are partially open, say qtr inch or more, providing they are not miles out, balance becomes less of an issue.

Once set up though, the fuel injection configuration is far more reliable, easy to start (hot or cold), tractable (wild cams etc) and will give more power.

Done correctly, its looks great too!

Just my thoughts / experience.

regards

Paul Thompson
[email protected]
of
GTD40 Club Web Site
-------------
Alloy 348 (302)
Kinsler TB's
Motec M48 Pro

[ June 23, 2002: Message edited by: P Thompson ]

 

[Guest]

I wish to apologize publicly to Dave Wharren. I obviously overstepped propriety and made poor choices in language, which were taken as personal affronts. I truly did not mean to make a personal attack but meant to engage in lively technical debate.

I should have merely stated that I disagree that the alleged requirement for more tuning is a drawback on EFI systems. It is my opinion that some EFI systems require very little tuning; they can be tuned and, indeed, tuned very finely while some EFI systems do require more tuning. All things considered, I still see this as an advantage, not a disadvantage.

Again, Dave, I humbly apologize for not simply stating my opinions, as above, rather than stating it in such a way that it came off as a personal attack. If my wording made anyone else uncomfortable, I apologize also to you. To everyone, I commit to endeavor to avoid this type of incident in the future by making wiser choices in language.

Sincerely,
Lynn

 

[Guest]

This is my opinion on this subject. If you want to spend a lot of money, well thats OK with me. For three hundred dollars are less I will go with the carburetor, I have had no problem with getting them to run right. For road use I would use a 600 cfm holley with the electric choke, model 1850. Webers and EFI are costly, do you really need them ?.I happen to think there not worth the money that you can invest in them, and Im not interested in impressing people.

 

[Jim Glickenhaus]

My 2c. What ever makes you happy is fine. Carbs are more original and worked well enough to win LeMans but EFI will defineatly be easier to meet emissions. Webbers are cool looking do cost more but once set up work very well. The only problem I've had with carbs is hot starting. Without pumping
you have to put your foot to the floor crank and let go as soon as it fires. On my Lola I can shut off the fuel pumps and run the carbs down before shutting down. This helps a lot but my MK-IV is not set up to do this.I agree electronic ignition is much better and prevents fouling. I use this on all of my cars including my P4 which has 24 plugs. None of my cars have a choke and I've not needed one but the P4 which has mechanical fuel injection is complicated to cold start. You rotate a cam which richens the mixture turn on 2 electric pumps which brings the fuel psi to 125, squirt raw gas down the trumpets, see photo on P4 thread,have someone stand by with a fire extingusher, and let it rip. As soon as it warms up you advance the cam on the MFI to lean out the mixture. If your planning on driving over 200 you crank it up 2 knotches. Once it's warm it will start without the above. That's how they did it at LeMans...