EFI to carbs

Now that I have American V8s that I'm actually looking to modify (the daily driver LS2 doesn't need anything, but the 350 in the Roadmaster and the 4.6 in the P71 are crying out for attention), I've been paying a lot more attention to the Spike TV shows (don't know whether they really offer solid advice, but at least they are playing with engines like mine) and some (gasp) other magazines, like Hot Rod. In fact, I was just reading the Hot Rod Junkyard Jewels Ford 4.6 buildup and they replaced the fuel injection with a carb. Horsepower TV does carbs almost exclusively. I even recall some advice for powering up my Roadmaster that included ditching the TBI for a Quadrajet. Now, the Roadmaster is a '93, and is emissions-exempt here in IL. The Crown Vic is an '01 and still has to go in for the bi-annual OBD2 checkup. Basically I think I'm looking for what we all want: Cheap, nasty, easy, loud horsepower. Is swapping to carbs a good bet for me?

I seriously doubt that swapping to carbs will do anything for you. The TV shows go to carbs because: 1. The carb companies are paying them to. 2. They don't know anything about EFI. If you want to build up your motor, then you'll have to do something with the fueling. A megasquirt or other standalone system will give you a better, more HP, more driveable, more fuel efficient system than a carb. I used to like carbs, now I want EFI on everything as long as I have access to the fuel maps if I'm going to mod it.

EFI delivers exactly the right amount of fuel to a metered quantity of air at exactly the right time -- assuming that it is working propertly. With carburators, you sacrifice a lot -- going from idle to WOT, for example, can be an issue due to the instantaneous and temporary lean condition that is created when a vacuum gobbles down air and the fuel can't respond as quickly. Plus, they don't work right when they're cold and they're inefficient.

Like Dr. Hess said, go with Megasquirt or something similar. You can do so much more with a nice EFI setup.

My P71 dropped 2 seconds off of it's ET for less then the cost of a carb, let alone an intake, etc and is still a rock-solid reliable daily driver with good gas mileage. Spike (which is useless to watch because it's just a giant paid commercial) and the "traditional" car mags all go with carbs because the companies pay better and it's easier to engine dyno.

I'm not sure that easier is the word. I'd prefer to alter curves on a screen then turn a bunch of screws all the way in, and then back out X degrees out. And then fine tune them. Each affecting the others. At least with EFI you can see everything nicely on the screen at the same time. I'm sure that some old timers can tell you that turning this screw Y degrees means that you'll have to turn that screw Z degrees, but I'd rather not have to remember that. Especially with the number of carbs out there). Heck, a decent number of the EFI kits have a self learning function that will get you running fairly decently. Especially if you add a wideband.

You guys are totally wrong! Spike pushes carbs because everyone knows NASCAR uses carbs and it HAS to be the way to go!

Yes, FI can be thought of as the best carb you can buy/setup in ALL conditions at the same time (e.g. best for idle, best for economy, best for power). One of the only good reasons I could see going to carbs would be to have an entirely mechanical system (which might be useful if getting real wet is involved). It would be a good way to make a car that would survive a nuclear blasts EMP, but that's not usually a concern...

I dunno aircooled. I think if your going to worry about EMP survival, a MB 220D is what you should be going for, and it's injected too. Mechanical. Once started (needs glow plugs and starter), it'll run forever with no electrical input, or at least until it runs out of oil. I proved this several times as the alternator completely died and I drove home. Not even enough juice to power the radio. I'd bet that the glow plugs could survive an EMP, but I'm not sure about the starter. It might.

Dr. Hess wrote: I dunno aircooled. I think if your going to worry about EMP survival, a MB 220D is what you should be going for, and it's injected too. Mechanical. Once started (needs glow plugs and starter), it'll run forever with no electrical input, or at least until it runs out of oil. I proved this several times as the alternator completely died and I drove home. Not even enough juice to power the radio. I'd bet that the glow plugs could survive an EMP, but I'm not sure about the starter. It might.

there's a fantastic grm article idea in there somewhere. :omg::nice:

Horsepower TV lost all credibility with me after they found a way to claim they got more horsepower with a Fitch Fuel Catalyst. Carbs can be cheaper but usually only make sense if you can't get a good-flowing EFI manifold for the engine.

I would agree that the only way carbs can be viewed as an advantage for performance is if the EFI intake manifold is a totally crappy design....but then why not change the manifold AND go EFI?

I think the main reason some folks prefer carbs or claim they work better is that they don't have any experience with fuel injection setup. Presuming that both setups are optimized to a reasonable degree, fuel injection should STOMP carbs for all-around performance and driveability any day of the week.

I'd say leave the carbs to historic vehicles and vintage racecars.

The old diesel Land Rovers with mechanical injection were great. The engine would run underwater as long as the air and fuel supplies were kept clear.

TBI isn't the best fuel injection due to wonky fuel delivery, but at worst it's as good as a carb :)

ae86andkp61 wrote: I would agree that the only way carbs can be viewed as an advantage for performance is if the EFI intake manifold is a totally crappy design....but then why not change the manifold AND go EFI? I think the main reason some folks prefer carbs or claim they work better is that they don't have any experience with fuel injection setup. Presuming that both setups are optimized to a reasonable degree, fuel injection should STOMP carbs for all-around performance and driveability any day of the week. I'd say leave the carbs to historic vehicles and vintage racecars.

Actually...

The carburetor is the world's best Air/Fuel ratio meter because it self-adjusts. The fastest race cars in the world still use them for a reason (Bonneville, Pro Stock, Fastest Street Car, NASCRAP, etc, etc, etc especially aircraft!!). I'd still take EFI any day of the week for reliability, daily drivability, etc, but for all-out performance it's still a carb market. The blow-through setups for boosted cars these days is fascinating!

NASCAR uses carbs because it's required by the regulations. Aircraft development stopped in the 60's. I don't know about the regs for Pro Stock or the others, but I'll bet any time you find a race car with a carb it's there because it's required to be there.

For some reason, F1 hasn't used them for a while.

P71 wrote:

ae86andkp61 wrote: I would agree that the only way carbs can be viewed as an advantage for performance is if the EFI intake manifold is a totally crappy design....but then why not change the manifold AND go EFI? I think the main reason some folks prefer carbs or claim they work better is that they don't have any experience with fuel injection setup. Presuming that both setups are optimized to a reasonable degree, fuel injection should STOMP carbs for all-around performance and driveability any day of the week. I'd say leave the carbs to historic vehicles and vintage racecars.

Actually... The carburetor is the world's best Air/Fuel ratio meter because it self-adjusts. The fastest race cars in the world still use them for a reason (Bonneville, Pro Stock, Fastest Street Car, NASCRAP, etc, etc, etc especially aircraft!!). I'd still take EFI any day of the week for reliability, daily drivability, etc, but for all-out performance it's still a carb market. The blow-through setups for boosted cars these days is fascinating!

Explain? A lot of your examples are hindered by rules and tradition. Explain the self-adjusting bit too.

carbs do not perform well in a dive.

Carburetors run stoichiometric by design. The actual ratio is determined by the metering rods/jets/etc but once you have the proper amount of "fuel" dialed in to the engines CFM flow (which is actually quite easy) then it constantly maintains that ratio, even in humidity/weather changes (not extreme elevation changes like +-1,000Ft though). Mechanical injection systems run off of the same concept.

NASCRAP uses carb's because of the rules, yes. A few years back they did some testing on running an EFI setup on one at Daytona that didn't go so well.

NHRA Pro Stock uses carburetors because of the rules, however IHRA, AHRA, and others have similar classes where EFI and mechanical injection are allowed. The carb'd ones are still faster.

Bonneville doesn't have those kind of restrictions (in most classes) but there's hardly any EFI stuff in that field. At WOT perfect stoich can't be beat!

For aircraft look at the Reno Air Races and see what's used ;)

I'm just saying that calling EFI "better" then carb's for performance is a bunk idea. Some of the most powerful cars (blown "Fastest Street Car" drag racers) make soooo much power that their aren't injectors physically big enough to work. They're either mechanically injected or carb'd. In the classes that allow EFI and carb's both the carb's dominate. Give it another decade and that may change (especially with direct-injection) but for right now it's still true.

I've seen a couple of injected Nascar engines run in other series and they run just fine. It the rules changed most of the teams would have no problem changing. The only place where carbs are still competitve with fuel injection is drag racing where they are run wide open, and even there fuel injection is taking over as the computers and hardware become more affordable. The fastest drag cars are still injected, though it's mechanical injection. There are no carbed cars running as fast as the fuel cars anywhere.

P71 wrote: Carburetors run stoichiometric by design. The actual ratio is determined by the metering rods/jets/etc but once you have the proper amount of "fuel" dialed in to the engines CFM flow (which is actually quite easy) then it constantly maintains that ratio, even in humidity/weather changes (not extreme elevation changes like +-1,000Ft though). Mechanical injection systems run off of the same concept.

Yes and no. Carb stoichiometric values aren't exactly precise when compared to those of fuel injection. And most carbs are not capable of maintaining that throughout the entire rpm range. Many big block V8s run absolutely pig rich at idle.

EFI on the other hand monitors the O2 sensor (along with many other sensors), and can adjust constantly. It runs stoichiometric by design. More advanced systems can actually compensate for each individual cylinder.

Also, neither carbs nor EFI setups usually run perfect stoich at WOT. Maximum power actually comes in a hair below stoich - around 13.8ish. Not only that, but many tuners (especially on boosted setups) aim for values lower than that (~12 ish) to protect the engine during sustained high RPM WOT runs.

If a carb always outperformed EFI, then F1 would be using them.

The Cessna 172 that I fly is fuel injected. While starting it when it's hot sucks, its a great system. And you don't have to worry about carburator ice.

F1 should almost not be used as an example here. They don't even use camshafts. :twisted:

Nascar guys run at WOT pretty much all the time as well - carbs run pretty well like this. They don't have to idle for more than 11 seconds or so at a time.

I wish my R/C truck was fuel injected. That thing is a little demon when it's tuned right. The problem can be tuning it. I have seen those tiny things with little superchargers though . . .

Someone once posted it here and I think it was the best thing Ive ever read on the subject.

Carb vs. Injection is like baking a cake. If the gasoline is your sugar then the injection is using a measured amount, sampling and adjusting as needed. The carb is like throwing the sugar up in the air and saying whatever lands in the bowl is just about right.

As Ive learned to overcome my fear of electical stuff I have to admit that injection is just plain the way to go.

Hey confuZion3, Megasquirt that R/C truck. Or Microsquirt it. This is the one I built for the Sportster:

At WOT, sure, a carb can be tuned as good as EFI. But, EFI can also be tuned to idle that monster motor and provide decent fueling everywhere inbetween. Carbs are simple and that's an advantage.