Fuel Injection Vs Carburetor: What Makes More Power?

General engine tech -- Drag Racing to Circle Track

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Fatpig
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Fuel Injection Vs Carburetor: What Makes More Power?

Postby Fatpig » Mon Sep 15, 2014 1:18 am

Hi,

I would like to know what would make more power; Fuel Injection or Mechanical Carburetor and why?
I have an understanding of thermodynamics so don't hold back with your answers/theories/arguments please.

FP :D

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby RednGold86Z » Mon Sep 15, 2014 2:47 am

Fatpig wrote:Hi,

I would like to know what would make more power; Fuel Injection or Mechanical Carburetor and why?
I have an understanding of thermodynamics so don't hold back with your answers/theories/arguments please.

FP :D


You should be banned for asking this :lol:

A properly designed EFI system is most likely to be able to be set up to make more power. That doesn't mean just any old EFI system. It might mean 2 sets of injectors per cylinder. The spray position and type of spray makes a difference. It does mean closed loop lambda control, and properly tuned trims for each cylinder. It might mean individual runners - it doesn't mean "apples to apples" manifold comparison.

There's also the question of "more power" - peak or average on an engine dyno, or faster down a track.

Now, which is easier to make more power? Depends on your skills, equipment, and time.

For me, EFI is the only thing I want to touch, but that's because it's my career. I'm really not interested in guessgineering what might be dribbling out of a block of aluminum a little bit too poorly.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby Fatpig » Mon Sep 15, 2014 3:21 am

Ha, awesome. Well I'm not going to lie, I concur with you RednGold86Z.

The reason for the question is: there is an urban myth around here that carbs make more power and that's why they're still being used (regardless of class rules allowing both).
I have my own theories and conclusions as to what makes more power as well as why the myth is staunchly protected.

I've posted it to see what arguments for or against can be postulated.

FP

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby RednGold86Z » Mon Sep 15, 2014 4:12 am

You'll have a hard time making something naturally aspirated that will beat a fully developed dominator setup, so i hear. But, I bet all of the pro-stock teams wish they could use EFI.

If you allow better ignition control with the EFI compared to, say, a locked out MSD, and other electronic tricks, "Engine Management Systems" are the way to go.

Also, there's more to performance engines than drag racing.
Jeremy Schmidt
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Founder FiTech EFI
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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby Billzilla » Mon Sep 15, 2014 6:37 am

A real-world example is of the old Formula Atlantic 1.6 litre Toyota engines.
In the last year they had Webers, an engine builder I know got 238 hp from his best. The next year they went to injection, he got 242 hp. That's pretty much dyno error but he got 20 hp more at about 6,000 rpm.
Carbies won't lack any top-end power due to the (usually) better heat absorption from the fuel droplets travelling (usually) further along the inlet tract compared to an injection set-up, but they will make more power over a wider rev-range due to the great precision with which the mixture can be controlled. And there's the ability to control the mixture with respect to air density, fuel type, fuel temperature, etc.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby Brian P » Mon Sep 15, 2014 7:08 am

There have been *enormous* threads on this before.

The carb advocates always want to use the same intake manifold ... but carb intake manifolds have to be designed to resist puddling, etc., and multipoint EFI manifolds are free of that constraint.

I deal with motorcycle engines that use individual downdraft runners from an airbox, no matter whether carb or EFI, but the carb runners have constraints because of the venturi.

EFI has more tuning flexibility. If there's a rich spot at 8500 rpm I can fix it without affecting anything else. If I change the main jet on a carb, no can do. More tuning flexibility on its own might not mean more *peak* power but it'll surely run better above or below the peak.

Try telling a Formula 1 engine builder that they would have to use a carb. Try telling a MotoGP or World Superbike engine builder that they would have to use carbs.

Other reasons that the carb advocates promote - more time for evaporation, which I don't dispute - can be had with EFI by using a close-coupled injector and a shower injector at the inlet of the runner. Many production high performance motorcycles use that system.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby twl » Mon Sep 15, 2014 8:19 am

In a perfect world, the EFI could be very slightly better, if the tuner achieved metphysical perfection with his EFI system.
ANY slight lack of skill on the EFI tuner, and the carb will be just as good, or better. With real world tuners on real world engines(especially street), where the guys are not F1 or Moto GP engineers, the theoretical EFI advantage rarely shows up.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby hoffman900 » Mon Sep 15, 2014 8:45 am

Define "power". Do you mean more peak power? A stronger overall powerband? etc.

I think the answer is going to be there are very few people on this forum with high end experience in both, thus they'll pick whatever they're most comfortable with.

A carburetor will make more power depending on the manifold (most want to compare injectors placed on a manifold designed for a carburetor vs. a carburetor on the same manifold), but given an open book and designed from scratch, EFI will beat it overall.

For those who do test these things, look where things are going with the EMC entries...

As others have said above, this topic has been beat to death on this site.
-Bob

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby Warp Speed » Mon Sep 15, 2014 8:53 am

8)

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby hoffman900 » Mon Sep 15, 2014 9:10 am

Warp Speed wrote:8)


Warp,

If you guys had an open rule book with EFI (basically any inlet manifold you wanted, injector placement free, number of injectors, etc.) how do you guys think you would do? I know you have said previously you guys are down on power with the current EFI rules package.

Cheers,
Bob

Ps: to expand on my above post. It's like the merge collector thread. Putting a nice merge collector (fuel injection) on a header (think manifold) not designed for it, might not show the intended results and maybe hurt power. Design it with a clean sheet of paper, and it'll be a different ball game.
-Bob

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby 140Air » Mon Sep 15, 2014 11:07 am

Fatpig wrote:Hi,
I would like to know what would make more power; Fuel Injection or Mechanical Carburetor and why?
I have an understanding of thermodynamics so don't hold back with your answers/theories/arguments please.
FP :D


It depends.
For road racing the carb you need has to work over a broad range of rpms and airflow and must be sized to be responsive at the low end. Therefore it will be restrictive to some extent at the top end. Some carbs are better at this than others, but FI is virtually non-restrictive throughout the range. Therefore the historical experience was that FI gave at least 10% more power than the best carb setup.
However, for drag racing there is no requirement for low-end response and the carbs can be virtually as free flowing as FI to the exent that they are preferred by many racers.

The second consideration is injector placement. This involves the fuel's evaporative cooling properties and its ability to increase the density of the fuel/air mix against its volumetric displacement of air. For gasoline and Methanol the best power is produced when the fuel is injected in a plenum* above the intake tract as witnessed by the use of the "shower" injector placement in Indy racing since 1983-4 and the universal use of shower injectors in F1 until the rule converting to direct injection.
Because low mounted injectors do not produce a charge density increase, a carb setup which fogs the tract and is very low restriction, like a Predator, may equal or better the power of low-mount FI.

Direct injection is a different tradeoff.

*Classic road racing with NA engines had the intake bells out in the wind. Low mounting the injectors were mandatory to prevent a plume of fuel in the air. Indy turbo motors all had plenums by default. The style of intake in F1 evolved into the use of plenums and the Indy example (from ILMOR) showed the benefits of the shower injector placement.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby KnightEngines » Mon Sep 15, 2014 5:55 pm

I've worked with both high end injection systems & well sorted carb systems.

Carbs are easier to make more power with, but a very well set up EFI IR system with injectors firing directly down the trumpets & a second set of injectors down near the ports for low speed running can make more than any carb setup throughout the entire rpm range.

Having said that the difference is not much & the EFI setup required is $$$$, but EFI has the edge in outright competition engines.
I'm not talking 'normal' EFI tho, any regular EFI setup will be beaten by a well set up carb.

Bang for buck you can't beat a carb.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby Calypso » Tue Sep 16, 2014 2:12 am

Fatpig wrote: there is an urban myth around here that carbs make more power and that's why they're still being used (regardless of class rules allowing both).

FP


I'm getting old and lazy, but having tried both at the racetrack, I just love the simplicity and robustness of single carb with mechanical fuel pump. Put in a magneto, and it'll never stop running, if you have fuel in it.
Leaves more time to focus on tires, chassis setup and driving skills, which can have a contribution to race results as well. To my annoyance, I've lost races to slower cars than what I have. :cry:

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby jet1 » Tue Sep 16, 2014 8:58 am

Ok I'll be the devil advocate. So IN A PERFECT WORLD ONLY where ultimate hp is the only goal a carb will always make more power. Before I get jumped on let me explain. Ltent heat of vaporisation is the key. I also believe that it is next to impossible to achieve a perfect setup with a carb but with EFI one can get alot closer. So in a perfect world a carb wins. in the real world the EFI wins.

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Re: Fuel Injection Vs Carburetor: What Makes More Power?

Postby hoffman900 » Tue Sep 16, 2014 10:15 am

jet1 wrote:Ok I'll be the devil advocate. So IN A PERFECT WORLD ONLY where ultimate hp is the only goal a carb will always make more power. Before I get jumped on let me explain. Ltent heat of vaporisation is the key. I also believe that it is next to impossible to achieve a perfect setup with a carb but with EFI one can get alot closer. So in a perfect world a carb wins. in the real world the EFI wins.


Shower injectors take care of that, however and can produce a finer mist than any carb booster.
-Bob


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