Why go from EFI to Carbs?

[PrOxLaMuS©]

After some research on the net.. especially from this site

http://www.geocities.com/zgarage2001/engine.html

And it mentions under Part 3 - carburation page, it is basically saying that Carbs are better than EFI?

I have also read that on Zcar.com.....

Why would Carbs be better or more efficient that EFI?

[Mustard-Z]

Well, obviously EFI is better than carbs 'cause why would auto makers move to EFI if it wasn't the better choice?

As far as we(datsun owners) go, i would choose whichever you feel more comfortable working with. You will make nearly the same power with both EFI and carbs on the street, and only in racing applications will you ever see the difference, which even then would probably be up to the tuner of the engine.

Of course that's my opinion, though.

As far as my cars??

'70 240z all original, Original SU's

Because I like it stock.

'78 280z 3x weber 45's

Because i wanted to see what the rage was about!

[PrOxLaMuS©]

You will make nearly the same power with both EFI and carbs on the street, and only in racing applications will you ever see the difference, which even then would probably be up to the tuner of the engine.

So in an racing situtation, which would you see the most difference?

[beandip]

Fuel injection is the most efficent with out a doubt. Having said that I purposly bought a car with out it and dont want it. Mostly because of he complications involved with it . I like the simple carberated car that I can work on with out high teck equipment. Just for giggles go to the zcar.com web site and read the posts, for the early Z up to '75 . about 80% are about injection problems . There are plenty of Z drivers going vary fast with the SU Round top carbs. Even on stroker engines. There is nothing better than a muliti-port injeted engine running perfectly. With the electrical trouble on z-cars staying simple for me is the way to go. My 2c

[Mustard-Z]

If you are really in for a spirited discussion on EFI vs. Carbs go here:

HERE

I'm sure you will enjoy the discussion.

I personally had problems with stock EFI and now have problems with carbs.....so whatever. I am willing to take carb probs over EFI mysteries.

I firmly believe though, that on a race track a 240z/280z with EFI could be tuned to the same extent as the same 240z/280z with 2x su's. It's more a matter of preference.

However, I think you most always get a more streetable power with EFI, as opposed to carbs.

Aren

[baddriver]

I see this question on all the boards, and I am constantly wondering why EFI has such a bad rap. I think a lot of people just don't understand it.

Now I realize that it is completely possible to build a high powered engine using carbs, but why anyone would want to do so is beyond me.

The simple fact is that carbs operate on the venturi principle. In order to draw in and atomize fuel, the air must pass through a venturi. A venturi is a restriction, and from that fact alone, anyone should be able to conclude that EFI can produce more power. Why people spend $$$$ opening up every restriction in the intake and exhaust system, and then bolt a restriction on top of the intake manifold is beyond me.

Now, before people jump up and down pointing out that this has nothing to do with engine power, follow me for one more second.

The volumentric efficiency, which does determine in part the engines power, is determined by the absolute pressure of the source of air (intake manifold). There are more things going on here sure, you can tune the intake runner so that a compression wave enters the cylinder at the proper time and improves your V.E., but only at a particular RPM. This can be done for either a carbed or an EFI car equally well. The real differnce is that on an EFI car, the manifold can be slightly closer to ambient pressure, due to the absence of the restriction. The difference is slight, but it always works in favor of the EFI.

Further, if you have a multipoint system, the air charge entering the intake manifold is less dense (due to the absence of fuel), and therefor accelerates more quickly, improving the VE when the intake valve opens.

As far as reliability, I feel that a fuel injection system is every bit as reliable as carbs, and no more expensive to repair. Fuel pumps may be the exception to this rule. Injectors are more reliable than people think. I here a lot of people talking about replacing them, and usually it doesn't fix the problem becuase there was nothing wrong with the injectors in the first place. If you find that you are spending a lot of money on your EFI, it could be that you failed to purchase a critical part, the factory service manual.

[PrOxLaMuS©]

excellent write up baddriver....

Yeh I figured if carbs provided more power, why aren't they still in production for newer cars?

All viper's, corvertte's, ferrari's, lamboguini's, porche's, aston martin's, maserati's.... all the newer SuPeR cars have EFI.... and put out much much more power than any old muscle car with carbs.

I feel that EFI is much more efficient and powerful, my opinion

[JEFF]

I put Fuel Injection from a '78Z on my L24 block. That makes a very fast revving 2.4L engine.

- Jeff

[Walter Moore]

At least in the U.S. the real reason that nearly all cars have EFI is that it is almost impossible to meet the emission laws with a carb.

The wonderful unintended result of that is that the new cars are significantly easier to start and drive than the old ones were. (Particularly Ford products...)

Most of the people that I know who turn street cars into race cars convert them to carbs, but only to increase the airflow through the engine. The problem with that is that they have to have all sorts of instruments, like barometers, relative humitity gages, etc. because they have to constantly re-adjust the carbs for the current conditions. (Which is the original source of the Indy 500's "Carbration day" the Thursday before the race.)

Carbrators can actually only be adjusted to operate perfectly at one temperature, barometeric pressure, and humitity level. Which is the real reason that the older cars never seemed to run quite right, their carbs were set for a middle of the road setting and only sort of worked the rest of the time.

(Except Fords, which never worked right unless you yanked off the Motorcraft carb and replaced it with a Holly.)

As for the "restriction" of the venturi, all Otto cycle engines (Including fuel injected ones...) REQUIRE a restriction in the intake path to control the speed of the engine. That is the purpose of the throttle plate. (As opposed to Diesel engines that have no restriction in the intake.) It is still possible to buy huge carbs, like 950 - 1000 SCFM units that would absolutely flood a 2.8L engine. But what is the point?

If you really believe that EFI doesn't restrict the air flow, go pick-up one of the "Mustang" magazines at a book store and look at all the adds for "Oversized Throttle body" kits for the multipoint EFI that Ford put on those cars.

My opinon is that if you are going to run it on the street, and your car's electrical system is intact, you will be happier with the driveability of the EFI system. Mine is going to have the dual SUs that it came with when I get it running, because that is all I have. Besides, it isn't going to be a daily driver, and the funky carb based operation is part of the experience ;-)

[baddriver]

Really, I was expecting more angry replies from carb owners. You guys are very civil.

It's certainly true that the throttle plates are a necessary restriction on any car. One could not operate at part throttle without a variable restriction. So at any throttle position other than WOT, my argument is invalid. Really, though, how much time do you spend driving at part throttle?

I was also waiting for someone to point out that variable-venturi carbs (such as the Hitachi SU's and many other carb designs) can vary the flow capacity of the venturi to meet the demands of any engine. And that with turbo or other forced induction, one does not rely on atmospheric pressure to fill the manifold, so the minor pressure drop is negligable, one can simply increase boost a fraction of a psi to make up for it.

So whats better? I still hold that EFI is better. Several people have pointed out the superior emissions control and fuel economy that come from better mixture control are the real reason all modern cars have EFI. I think they are correct. I have also heard that the precise control of fuel mixture prevents engine wear by efficiently using up all the fuel in the cylinder, preventing it from washing off oil. I don't have any first had knowledge of this fact, however. I am just bringing it up.

Of course, I am from Iowa, and the biggest difference I notice between my fuel injected cars and the carbed cars I used to have, is that the FI cars start as quickly after sitting out in 0 degree weather as they do on a warm summer day, and if I want to, I can jump in and drive away with no hesitation or rough running without any warm-up time at all. I had a friend with a chevelle and a holley who had to start his car before breakfast and burn a gallon of gas every morning waiting for it to get up to temp.

Of course, carbs do their job, and do it very well. I wouldn't spend the money to convert to EFI if I had a carbed car. But you would never catch me tearing off my EFI to put carbs on either.

[mdbrandy]

In my younger days, I had a 71 240Z with SUs and then a 75 280Z with EFI. I had the normal fights with the carbs on the 240, and must say that the EFI on the 280 was WONDERFUL in the cold Illinois winters when it worked right. However, when problems ensued, they were MUCH harder to diagnose. Cost me $600 once (in 1981) to get someone to find a short circuit under the dash caused by a PO's wire rigging. Another time, while working on the car, I SOMEHOW managed to allow coolant to get sucked into the intake through the airflow meter. Filled up the bypass and it took me quite a while to figure that out. But when it worked (which was most of the time), it was nice!