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Old 01-23-2005, 01:53 AM
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Fuel Injection vs. Carburetion

It's obvious that you simply get more accurate fuel metering with fuel injection, but what I would like to know is if there is a significant power difference between fuel injection and carburetors. I have always used carburetors on my high performance motors, but this time I am thinking about using fuel injection for my next hotrod motor, and would like some basis to start on. I'm currently leaning to the more modern multiport sequential fuel injection, but I will have to check to see if this can be retrofitted onto an older SBC and if there are any good manifold choices that will accomodate this. Any input would be appreciated.

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Old 01-23-2005, 02:25 AM
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ON a motor like mine in the 650-700 HP range you can easily tune in 20 or so above a carb simply becase you can keep the fuel curve so tight off the fuel map, that and the feedback from the O2 sesor and not having to worry about distribution problems with the intake. To do that though you have to tune in the cylinders off of EGT's. I run a wide band O2 off the EFI system and two EGT's recording probes. I switch an EGT probe and dial in off my base cylinder. Much of the tuning should be done on the chassis dyno, it is far easier, much faster and safer.

The additional power though is minor compared to the ability to run a very wild motor on the street and HWY. It is much easier to get a big cam to work at low speeds with EFI and also attain excellent mileage on the HWY. When we did mileage runs on Power Tour this past year I got 18 on the Hwy cruising at 70, with an overdrive 200 4R and lockup 9X11 converter. Not bad for a motor that will hit 125 in the quarter and over 130 on nitrous.
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Old 01-23-2005, 07:32 AM
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I agree with Rick. There is just really no comparison. EFI wins hands down. People who tell you that a carb will make more power simply dont know WTH they are talking about. Of course you have to match the intake design to your power goals. There are alot of custom EFI manifolds available for wild engines. I can run my turbo engine with WBO2 feedback all the time. This allows constant tuning of the fuel curve to maintain a good lambda. EFI is the way of the future without a doubt.

Chris
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Old 01-23-2005, 08:32 AM
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I am also interested in looking at EFI as an option on my sbc and was wondering if there is any good printed info out there that anyone would recommend to get me started.

Scott
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Old 01-23-2005, 09:31 AM
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Generally speaking, a well matched sequential EFI produces up to a 20% increase in HP, torque, and fuel economy when used to replace the carb and intake on the same motor. An example of this was when I replaced the QJet and Edelbrock Torquer manifold on my Bud's mild 355 SBC. And this was done with the basic TPI from a 5.4L Camaro and a custom chip.

A good book to start with is a Powerpro Series, Fuel injection, Installation, Performance Tuning and Modifications by Jeff Hartman. (Call 1 800 826-6600 for ordering and ask for ISBN 0-87938-742-2 or go www,motorbooks, com). This is a late 90s publication and may have been updated. If not, the basics are there and will get you started into the 21st century of hot rodding.

Trees
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Old 01-23-2005, 12:12 PM
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a 5.4L CAMARO?
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Old 01-23-2005, 12:32 PM
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AKA 350

Trees
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Old 01-23-2005, 02:20 PM
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5.7 350
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Old 01-23-2005, 03:06 PM
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Personally, according to most of the crap I've seen (so take it with a grain of salt) for absolute max HP the carb will beat the EFI setup. I've read alot of magazine articles that lean this way (note I said max, not average). EFI would definitely lend itself to better mileage and driveability, but those aren't 2 things I'm too worried about in a hotrod. I don't think either is gonna make that much more than the other when properly tuned (I'd say the other posters number of 20HP would be about the biggest difference I'd expect), and if someone makes drastically more power with one over the other, they can't tune one of 'em worth a damn. Personally, after having both, I perfer the hands on tuning of the carb vs. farting with a computer for EFI, not to mention that IMO EFI motors are ugly. But if I needed one to start on a 30 degree day and get the absolute best MPG, the choice is much easier.
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Old 01-23-2005, 03:06 PM
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A 20% increase in HP and torque sounds a bit high on a conversion of apples to apples, same intake type and air body/carb design. No doubt taking a sub par intake carb combination and optimizing an intake and air valve combination can produce significant increases though at soem area of the power.torque curve. I certainly could see a TPI system boosting low end versus a torker style intake, I don't know if I buy that it would gain that amount on top though. Would be interesting to look throug the dyno sheets as to brake specifics, A/F ratios, CFM, and EGT's to see what changed.

That's not quite apples to apples though. Taking an EFI Vvictor Jr converted manifold and bolting on a carb will produce similar power curves as when run with an air valve and EFI control. Being able to sequentially tune in cylinders and spark advance over the RPM range though is what can give the EFI the edge. Even absent sequential control having the ability to just dial in the fuel curve overall on a much finer basis can be worth some power across the board.
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Old 01-23-2005, 04:00 PM
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In almost all instances, EFI is the superior choice in all around power, throttle response, idle quality, and not to mention keeping the fuel curve correct throughout the rpm range. You can do the same thing with a carburetor but you better be doing your homework.

There are a few instances in which a carburetor will deliver a better atomized mix of fuel and air. One example would be a tunnel ram type manifold with two properly set up 4 bbl carbs. The atomization of fuel and air on a set up like this probably cannot be matched with most injector type nozzles, which usually dump very close or actually into the head.
In this particular w.o.t condition, the carbs will win in the top end horsepower category.

EFI is today's clear choice to use for state of the art fuel delivery. Not to say that a master tuner with a carburetor cannot achieve some parody, because a carb is just a mechanical device, and it can be made to work quite wonderfully if the tuner knows what he is doing.

Once the programming and wiring is tackled on an EFI set-up, it becomes a no-brainer and very fool-proof.

I like carburetors because of the mechanicalness of the device, and my sentimental attatchment to old style hot rod equipment, but regardless of my fondness for old carbs, anyone can see that EFI is now, and carbs are the in the past.

The stand alone capability of a carb and magneto still appeals to me though.
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Old 01-23-2005, 04:28 PM
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Trees,

Thanks for the info, but maybe you know of another book. I got onto the web site you mentioned but they no longer have that book either by title or stock number.

Thanks,

Scott
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Old 01-23-2005, 05:28 PM
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INteresting that we've been getting so many of these threads lately, I've recently been interested in the subject myself. I've read many interesting arguments for EFI lately, and I have to say, as soon as I get a little more knowledge and experience about it under my belt, I'm probably going to start piecing together a system.

I think EFI, as with any other upgrade, has a benefits and drawbacks... the drawbacks really only being price, difficulty and sometimes an untidy engine bay. I think all three of those, however, can be bested by a savvy builder. I know a few guys who have pieced together systems and DIY units for under1500 bucks, a far cry from the 3000 you see in magazines.

The benefits, I've seen are awesome. Especially in places like Michigan. THe problem with a carburetor is that it only uses one variable to measure how much fuel to dump into the rushing air. Namely: airspeed (directly proportional to RPM). EFI, however, measures throttle position, load on the engine, ambient temperature and air density. Like I mentioned before, in a climate like ours, its a great feature to have (so much change in all of the above variables, unlike, for example, Arizona). I did a little figuring on air density the other day, and with the extreme changes in climate here in michigan through a normal season, your AF ratio could change an entire point. So if your carb is set to 12.5:1, you could go to 13.5:1 when the temp got cold right before you put the car away. On a demanding motor that's cutting the edge of pump gas with hot compression, I don't think that's really acceptable (not that it can't be countered).

Food for thought, anyway.

K
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Old 01-23-2005, 05:39 PM
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If EFI has one drawback it is the cleanliness of the engine bay that killer mentioned. I have not got through the effort to try to clean mine up, but I am going to have to one day. It is just screaming EFI when you open the hood. Some might like that, but I like a cleaner look. Just harder to achieve and takes something inventive. I have to get mine running consistantly before that project.

Chris
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Old 01-23-2005, 05:41 PM
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Carburetor vs. Injection

There is not a Black and white answer to this question, especially without more specific parameters. In most applications since a carburetor can atomize the fuel more efficiently it will make more peak HP. Injection can give you a broader power-band, and better average horsepower.

A 20% increase in Power going from a Carburetor to Fuel Injection is unrealistic, and would be an indication that the proper tuning was not done, and the testing was not equalized.

There are many variables to keep in mind. The first would be the use of the engine. On a Race engine that has a very narrow power-band, a properly tuned and setup carbureted engine will generally perform best. On an engine where starting in cold weather conditions, and fuel economy are priorities a Fuel Injected engine can shine. Another factor to keep in mind is the availability of, and price of quality components for the intended application. It is very simple to find components to make 500 or 600 HP to use either a carburetor, or injection. As you go up in HP it can be harder to find “Bolt-on” components to work with Injection. As you try to get to the higher HP levels carbureted systems actually become more cost effective when you’re trying to make 1500+ HP.

Lastly, and most importantly for the Street Rod, or Hot Rodder is user friendliness. If you’re dealing with a custom programmed FI system that your mechanic or engine builder setup, and you have problems 1000 miles from home you can be in real trouble. This is the key reason that some of the top builders in the country prefer to build carbureted engines for their customers.
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