Fuel injection VS carb. 500hp engine.

Efficiency is the only advantage I see in EFI. There is a ton more to tuning a Holley than jets and squirters and like Mr Hearne said timing is the cause of a lot of carb problems including efficiency. A lot of people take out the power valve and plug it and remove vacuum advance and wonder why they get 10mpg.

At a given rpm and throttle state in steady state conditions, the efficiency can be the same, but during transitional states will be very different. Efi will be trying to hit stoich and a carb will be doing god knows what.

And transitional conditions are where the majority of driving occurs.

phutch11 said:

At a given rpm and throttle state in steady state conditions, the efficiency can be the same, but during transitional states will be very different. Efi will be trying to hit stoich and a carb will be doing god knows what.

And transitional conditions are where the majority of driving occurs.

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I am definately not God, but I know were mine is in transition. It is not so bad, and it is a blow through. It would be much better if it did not have to flow so much fuel under boost.

brianj5600 said:

Efficiency is the only advantage I see in EFI. There is a ton more to tuning a Holley than jets and squirters and like Mr Hearne said timing is the cause of a lot of carb problems including efficiency. A lot of people take out the power valve and plug it and remove vacuum advance and wonder why they get 10mpg.

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pfft, if I got 10 mpg I'd be thrilled. LOL!!

phutch11 said:

At a given rpm and throttle state in steady state conditions, the efficiency can be the same, but during transitional states will be very different. Efi will be trying to hit stoich and a carb will be doing god knows what.

And transitional conditions are where the majority of driving occurs.

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So, there's really no difference between the two that you can feel in the "seat of the pants meter" Or in other words, you'd need to watch a dyno readout to see the tiny difference in the F/A ratio between one and the other.

Blown - Really? You can tell me with 100% confidence what your AFR is doing at 20% load, at a 10% throttle opening at say 3000 rpm? What if the temperature changes, or a high pressure weather front moves in?

D- You don't need a dyno to see efficiency differences between efi and carb, you need an odometer and a fuel guage and the ultimate seat of the pants meter, your wallet.
As I said in my first post, if I had to do it all over again, I'd go with a carb, because fuel mileage is not that important to me.

But guys, don't kid yourselves...in real world driving, not just cruise, not just one state of operation, but operations in many different conditions, efi is just plain more efficient.

Carbs are great for power, simplicity, weight, and cost - but they are not as efficient as efi.

Look at EZ-EFI from F.A.S.T.

Before I got into my (long story, 2-engine) debacle, I had planned to go Mass-Flo and was talked out of it in favor of EZ-EFI, a self-tuning TB EFI. Good reviews, easy to set up, great mileage, and without all of the tuning hassles of some of the SEFI setups out there. I figured that I could always tune my ignition by computer with the MSD 6AL-2, but I do understand the benefits of an EFI controller being able to control the ignition as well as the fuel-air mixture at the same time. It just seemed like too steep a learning curve, and while I felt that Mass-Flo would be as plug-and-play as could be, my engine builder had experience with it and felt otherwise.

Sooo, very long story short, that engine (408 stroker) is on the back burner and I had my 302 rebuilt as a 331 with a Holley HP 4150 750CFM carb. I'll have to wait to tell you how it performs on the street, with mechanical advance and no choke, but the dyno was at about 410hp, almost that much tq, and they said the carb was very plug-and-play. I bet it's a pig on gas, but it's a weekend driver at the very most.

phutch11 said:

Blown - Really? You can tell me with 100% confidence what your AFR is doing at 20% load, at a 10% throttle opening at say 3000 rpm? What if the temperature changes, or a high pressure weather front moves in?

D- You don't need a dyno to see efficiency differences between efi and carb, you need an odometer and a fuel guage and the ultimate seat of the pants meter, your wallet.
As I said in my first post, if I had to do it all over again, I'd go with a carb, because fuel mileage is not that important to me.

But guys, don't kid yourselves...in real world driving, not just cruise, not just one state of operation, but operations in many different conditions, efi is just plain more efficient.

Carbs are great for power, simplicity, weight, and cost - but they are not as efficient as efi.

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Well, not sure why you directed this at me but since you wanna be a smart ass. Yes, I know what my car does at all those situations since I have a wide band O2 that tells me what its doing. My car is 90% strip and a little bit of street driving hence the 9 second times if you look in my signature. Hell, my water temp gauge tells me more than most ppl since it goes to 60 degrees on up, and usually hit the burnout box at 100-120degrees engine temp. Pretty much fill the fuel cell, drive to the drags and make some runs and then drive back home.

Funny thing, I run the same jets in my car all season long and only change about a tenth of a second from heat to cold days. Mostly cause of the fuel I run.

I would never run EFI on my car unless it was a power adder car, simple as that.

I would recommend you take a trip to the local drag strip and see what everyone else is running. Using a non-tunable EFI will not help you in your endeavor. IMO, build the motor, put a carb on it, and if you decide on EFI later, go for it. I am building a 427 stroker (351w based) and using an Edelbrock Pro-Flo system I picked up on Craigslist on the cheap. My car will be a weekend cruiser, not a drag car. Build what you want, it's your money and time you are investing.

phutch11 said:

Blown - Really? You can tell me with 100% confidence what your AFR is doing at 20% load, at a 10% throttle opening at say 3000 rpm? What if the temperature changes, or a high pressure weather front moves in?

D- You don't need a dyno to see efficiency differences between efi and carb, you need an odometer and a fuel guage and the ultimate seat of the pants meter, your wallet. .

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It's plain to me that you're one of those guys who when they DO run a carb, they pick one that's too big for 90% of driving on the street. I used to do that, but now I pickem on the small side. This gives you EFI like throttle resonse and fuel mileage My 331 gets 16 MPG, cruising at 80 mph (that's turning about 3500 rpms) with a C4 auto and a 3.50 geared rear. Starts with very little babying of the throttle on the coldest days. The roller 5.0 in my 89 Ranger (also without overdrive) gets 18 mpg on the highway (same gearing as the 331's got) And it starts and idles at 20*F without a choke, using only one "pump shot" to prime the engine. That's in a truck that's got the areodynamics of a brick that weighs 3800lbs. The EFI'd 2.9 was only getting 19 mpg when I pulled it, and that was with overdrive and 3.45's. The other key to this is using an EFI cam grind. These work great with a carb. So you see, you DO need a dyno to see the difference between EFI and a properly tuned and sized carb, not just your wallet (which with an EFI system, unless it falls into your lap for free,) And is going to set you back a lot of moola, that could be better spent elsewhere

Phutch, don't get all excited, I already said EFI is more efficient. I am pretty sure you know very little about tuning a Holley. I too have a wideband and an A/F gauge in the dash. I can also data log so I do know what is going on with mixture. At cruise or light accel it is very easy to watch the gauge and see what is going on. I have learned tons from both the Innovate forum and the carb section of the turbo forums. I did not figure anything out on my own. If there is a problem area, I search for the fix and if I can't find out a fix I start a new topic. Most people never touch the idle restrictor, air bleeds, PVCR's, CCR's or E-holes. A lot of people don't even get the primary throttle plates right at idle. With a wideband it is easy to see what it is going on and make changes.

Blown- I apologize if that came off as smart, in all seriousness, I did not mean it that way, my point was just that with a carb, you have no exact idea what its going to do in any given transient state. Yes, you can monitor what it does with a wideband, but that is very, very different than knowing what it will do with certainty in advance.

In the operational state that I mentioned above, with an efi system, you know with certainty that in closed loop the engine will get the correct amount of fuel for a stoich burn, plus or minus some small amount.
Circling back to efficiency, this means that when you aren't getting on it the computer is constanly providing just enough, but not too much fuel... And it is checking and correcting itself many times each second.

In the same situation, a carb is adding fuel based on any number of mechanical controls you have tuned it with. While they can certainly be tuned to be optimal for many individual states of operation, in fact for many states, they will not be optimally for all.
D- I will not argue with your own experience as regards mileage on your vehicles. And while there certainly have been inefficient efi systems (alpha n, batch fire, most tbi), I still maintain that if you take an engine with a properly tuned, modern, multi point, sequential fire efi system and compare real world day in day out mileage against the same engine in the same vehicle, but with a carb, any carb you want, the efi system will win every time.

Back to our cars and our cobbled fueling together systems. I will grant you D that you can probably tune a carb that will be 80 to 90 as efficient as well tuned efi system. My point is, and has been, that for us hobbists that don't daily drive our cars, mileage doesn't really matter. Most of us lose more fuel to diurinal evaporation than to poorly tuned fuel systems.

For me specifically, my beef with my EEC based system is the weight and the cost. For the cost of everything I bought to get the system working (and I did 100% of the work), I could have had a 347 with nice alum heads, a great carb, and be 75 pounds lighter than I am today.

As is, I have a mild engine that gets great mileage and is much heavier than I would like for what I do with it.

OP - my point in posting all of my posts was to give you a different point of view on putting in an efi system, I am sure with all the posts and differing points of view, you will be able to make the best decision for you and your car.