Carbs make more power than FI?

[Truckedup]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

[hoffman900]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

This is only the case where the rules have imposed restriction on the EFI. Think NASCAR or NHRA Pro Stock.

In NASCAR, they are using a carbureted manifold, with a spec throttle body and locations that are spec'ed and not ideal to the application. NHRA Pro Stock spec'ed a throttle body size and that the injectors have to be in the runner - considering the tune length - this pretty much garuntees they're going to be too close to the valves. Both spec the type of injector as well.

Most of the street performance stuff V8 stuff is more of the same. A throttle body on a carburetor manifold and injectors in the runners.

All of this discounts what EFI can do for you.

With fuel injection, you can...
* straighten the runners out. No more comprising lengths and flow for a carburetor.
* run the taper that will maximize the intake ramming process as well as flow.
* you can do more with the exhaust system as far as choke sizes go and pairing. No more worrying about bad waves messing with carburetor signal. This will serve to bolster the mid range while maintaining the top.
* straighten the AFR curve out through the whole range
* not as sensitive to gforces < few dynos can test that.
* better handles forced injection. Pretty much the only way to deal with it
* Work in tandem with the ignition to run more compression and ignition advance than you could get away with prior.

In some applications, especially high revving, high output engines with a large powerband, you may need two sets of injectors. One closer to the valve for lower rpm / part throttle response, and injectors located higher up for high rpm / full throttle running.

If you look at something like a modern sportbike engine, you'll see the two injectors in effect. I used this example on another site, but let's look at Ducati's new Panigale V4.

1103cc, V4, 14:1 compression on pump gas, variable length throttle bodies, two sets of injectors per cylinder. It makes 214bhp off the showroom floor and 88lb-ft of torque.

So this engine is making 3.2hp/ci on pump gas, with a full warranty, meets emissions, has a 7500 mile service interval (oil change), and can putt around the grocery store parking lot all day if it has to. This isn't to mention how tractable the power is and the ability of the throttle bodies to work with the computer for traction, shift cuts, etc. You could not do this with a carburetor.

Here is the dyno curve (note: torque is in Nm, so it makes for a weird looking crossover point. You have English system units on the left and Metric on the right). Note the shape of the curve:


and here is onboard:
https://www.youtube.com/watch?v=SDRujrYGJ2Q&t=5s note how responsive it is (also can see the yellow flashing from the tc and hear it kick in at one point) and all lean angles. See it lugging down to 6500rpm but it makes peak power at 13,000rpm. That's a 6500rpm spread - that's larger than most street engines run at from idle to redline.

Looking at your bike for example would find big gains with EFI done right. It's an inline twin, but the intake and exhaust tracts are set up like a single. Singles are very sensitive to exhaust length (one pulse every 720*) and typically results in a hole in the power curve somewhere due to reversion blowing through the carburetor and messing up the fuel curve. Talking to a top singles tuner, on a single, the AFR could swing 3 whole points over a wide power curve. Fuel injection can take care of that.

In short, yes, carburetors can make more power than EFI, but only if the application imposes enough restrictions on the EFI that you can't take advantage of it. Putting EFI on a carburetor manifold isn't what I call apples to oranges. If you look at the applications that aren't restricted by rules or costs (street performance V8 stuff); sportbikes, Moto GP, Formula 1, and FIA/IMSA, you don't see carburetors.

[Newold1]

Over on Yellowbullet-Uratchko N/A technical discussion there is a good thread "Truly amazed by EFI" that is getting some good discussion and inputs from some knowledgeable people on this very subject. It's a good read.

[Walter R. Malik]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

This is only the case where the rules have imposed restriction on the EFI. Think NASCAR or NHRA Pro Stock.

In NASCAR, they are using a carbureted manifold, with a spec throttle body and locations that are spec'ed and not ideal to the application. NHRA Pro Stock spec'ed a throttle body size and that the injectors have to be in the runner - considering the tune length - this pretty much garuntees they're going to be too close to the valves. Both spec the type of injector as well.

Most of the street performance stuff V8 stuff is more of the same. A throttle body on a carburetor manifold and injectors in the runners.

All of this discounts what EFI can do for you.

With fuel injection, you can...
* straighten the runners out. No more comprising lengths and flow for a carburetor.
* run the taper that will maximize the intake ramming process as well as flow.
* you can do more with the exhaust system as far as choke sizes go and pairing. No more worrying about bad waves messing with carburetor signal. This will serve to bolster the mid range while maintaining the top.
* straighten the AFR curve out through the whole range
* not as sensitive to gforces < few dynos can test that.
* better handles forced injection. Pretty much the only way to deal with it
* Work in tandem with the ignition to run more compression and ignition advance than you could get away with prior.

In some applications, especially high revving, high output engines with a large powerband, you may need two sets of injectors. One closer to the valve for lower rpm / part throttle response, and injectors located higher up for high rpm / full throttle running.

If you look at something like a modern sportbike engine, you'll see the two injectors in effect. I used this example on another site, but let's look at Ducati's new Panigale V4.

1103cc, V4, 14:1 compression on pump gas, variable length throttle bodies, two sets of injectors per cylinder. It makes 214bhp off the showroom floor and 88lb-ft of torque.

So this engine is making 3.2hp/ci on pump gas, with a full warranty, meets emissions, has a 7500 mile service interval (oil change), and can putt around the grocery store parking lot all day if it has to. This isn't to mention how tractable the power is and the ability of the throttle bodies to work with the computer for traction, shift cuts, etc. You could not do this with a carburetor.

Here is the dyno curve (note: torque is in Nm, so it makes for a weird looking crossover point. You have English system units on the left and Metric on the right). Note the shape of the curve:


and here is onboard:
https://www.youtube.com/watch?v=SDRujrYGJ2Q&t=5s note how responsive it is (also can see the yellow flashing from the tc and hear it kick in at one point) and all lean angles. See it lugging down to 6500rpm but it makes peak power at 13,000rpm. That's a 6500rpm spread - that's larger than most street engines run at from idle to redline.

Looking at your bike for example would find big gains with EFI done right. It's an inline twin, but the intake and exhaust tracts are set up like a single. Singles are very sensitive to exhaust length (one pulse every 720*) and typically results in a hole in the power curve somewhere due to reversion blowing through the carburetor and messing up the fuel curve. Talking to a top singles tuner, on a single, the AFR could swing 3 whole points over a wide power curve. Fuel injection can take care of that.

In short, yes, carburetors can make more power than EFI, but only if the application imposes enough restrictions on the EFI that you can't take advantage of it. Putting EFI on a carburetor manifold isn't what I call apples to oranges. If you look at the applications that aren't restricted by rules or costs (street performance V8 stuff); sportbikes, Moto GP, Formula 1, and FIA/IMSA, you don't see carburetors.

You are totally wrong here. It has been tested several times in several venues.

F.I. may best a well tuned carburetor in every situation and parameter EXCEPT horsepower at Wide Open Throttle;
maybe EQUAL it, sometimes.

[hoffman900]

Here are the mechanical injectors on the USAC Midget engines.

TRD:



Chevrolet:


Chevrolet RO7:


Chevrolet SB2:


TRD NASCAR engine:


You can see what injection (mechanical or electronic) allows you to do with the intakes...

[hoffman900]

You are totally wrong here. It has been tested several times in several venues.

F.I. may best a well tuned carburetor in every situation EXCEPT horsepower at Wide Open Throttle;
maybe EQUAL it, sometimes.

Okay Walter, please share what venues other than EMC and where the rules aren't at play. I would like specific examples.

EMC has too much variation - development levels vary, there have been issues with exhaust systems interacting with the dyno set up which has hurt some teams, the correction factors have been an issue, there have been problems with the operator's consistency, the rules favor certain displacement combinations, etc. All these issues have been aired out on this site, by the competitors themselves, as well as the ones I've talked to privately.

NASCAR lost power going to EFI. They also run a manifold designed for a carburetor and injector location is spec'ed.

NHRA Pro Stock lost power, but they also have to run a spec throttle body and the injectors have to be on the outside of the manifold and they must enter the runner. They also lost RPM due to rules.

[Walter R. Malik]

Here are the mechanical injectors on the USAC Midget engines.

TRD:



Chevrolet:


Chevrolet RO7:


Chevrolet SB2:


TRD NASCAR engine:


You can see what injection (mechanical or electronic) allows you to do with the intakes...

I don't see a tunnel ram with two 4 barrel or 4 two barrel carbs in any of those photos or 8 single barrel carbs with straight runner intakes.

They do exist ... honest.

F.I. has the advantage in every situation other than WIDE OPEN THROTTLE horsepower and THAT is why it is the preferred fuel mixer.

[hoffman900]

How many of those tunnel ram applications have had a real, blank sheet fuel injection set up to compete with?

Every high output, blank slate racing engine, where rules aren't an issue, is using fuel injection.

From YB (http://www.yellowbullet.com/forum/showt ... ?t=2448586):

As long as we are discussing air flow through a carb or throttle body, I think we should also add the intake manifold into the mix. I would be interested in hearing what other racers have seen or done in this area.

Everything being equal, a typical cast aluminum intake manifold with a 4-brl. carb will flow about 10% more air with the installation of a 4-brl. throttle body (as part of an EFI system), even if the CFM rating for both the carb and the throttle body are the same. The reason (or theory) for this is that the carb has already mixed in the gasoline before it gets to the intake manifold. The throttle body is only delivering air to the intake manifold, the gasoline is injected directly into the runners close to the intake port of the cylinder head.

Because of the ratio of air to gasoline (typically 11 parts of air to 1 part of gasoline), there is now more room (about 10% more) in the intake manifold and runners for the air.

Here is another interesting situation regarding intake manifolds.



A typical set-up on a nitrous P/M or Mountain Motor P/S running with four 2-brl. (split Dominator style) carbs. The carbs are off-set a little front to rear on the manifold so that the fuel (air and liquid) has straighter path to the intake ports.


Here is a similar set up using four 2-brl. throttle bodies.

There is a single reason as to why the throttle bodies are off set front to rear just like the carbs, and the reason is that the intake top was originally designed for carbs, and the racer was reluctant to purchase a new top plate (expensive). There is no actual correlation with throttle body placement on the manifold as there is with carbs.


You could mount your four throttle bodies like this and it would make no difference (other than simplifying the throttle linkage). They do NOT need to be directly over the runners. According to Tim Hogan who has done a lot of work and study in this area, the air does NOT go into the runners, it goes into the plenum. The fuel (liquid) is typically never in the plenum, it is injected directly into bottom of the runners (or actually into the cylinder head, the injector bungs have not been welded in yet on this manifold).

According to Tim, when an intake valve opens, the engine will draw the air out of the plenum, and not out of the throttle bodies, so in theory, each cylinder is drawing the air out of all four throttle bodies, which is stored in the plenum. As long as there is enough air going through the throttle bodies (ie; the CFN flow is enough air) to keep the plenum full, the air is going back and forth and all around inside the plenum.

The older guys on here will remember the individual Hilborn style of mechanical fuel injection, with 8 individual stacks sticking out of the hood (remember the old match race days in the late '60's?). In that system, the only air that the cylinder could get was the air that flowed down that individual stack. With the plenum style intake manifold, each cylinder is not dependent on any single throttle body, it can get air from all of them as needed.

Accufab has tried that.


Here is the DUAL275 in the standard configuration.


Here it is with the optional fuel injector set-up (bungs, fuel rail brackets, and fuel rail). Todd Horner over at Sonny Leonard's used these on his big inch P/S car a couple years back, and says they are an advantage (using 8 injectors in the runners and 8 more injectors in the throttle bodies). He says it cools the charge inside the plenum. On the other hand, Pat Musi says it makes no difference.

You pays your money and you make your choices.

For those that don't know, George owns Accufab. It should also be noted, and George confirmed, Pat Musi's engine is nitrous fed which provides A LOT of charge cooling.

[GARY C]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

That was true in the early days of FI, you may still see it with some of lower budget systems but I don't think that's a case with one thats designed for the application.

Power per dollar would be the question now days.

[statsystems]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

That was true in the early days of FI, you may still see it with some of lower budget systems but I don't think that's a case with one thats designed for the application.

Power per dollar would be the question now days.

It certainly did show up in Pro Stock. Even with the RPM limit imposed the numbers don't show much improvement if any. Plus if we believe Warren Johnson, getting rid of the hood scoop would mitigate the RPM limit.

All it did was screw Pro Stock and make the cars look stupid.

They should have let carbs and EFI run together, with or without hood scoops. That's what Pro Stock SHOULD be.

[hoffman900]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

That was true in the early days of FI, you may still see it with some of lower budget systems but I don't think that's a case with one thats designed for the application.

Power per dollar would be the question now days.

It certainly did show up in Pro Stock. Even with the RPM limit imposed the numbers don't show much improvement if any. Plus if we believe Warren Johnson, getting rid of the hood scoop would mitigate the RPM limit.

All it did was screw Pro Stock and make the cars look stupid.

They should have let carbs and EFI run together, with or without hood scoops. That's what Pro Stock SHOULD be.

Agree. Pro Stock should have had open induction rules. Run whatever, as long as the throttle body(ies) can't be controlled by the ECU (thinking traction control here). I believe they would all be fuel injected if that was the case and it would look nothing like what the rules specified.

[statsystems]

That was true in the early days of FI, you may still see it with some of lower budget systems but I don't think that's a case with one thats designed for the application.

Power per dollar would be the question now days.

It certainly did show up in Pro Stock. Even with the RPM limit imposed the numbers don't show much improvement if any. Plus if we believe Warren Johnson, getting rid of the hood scoop would mitigate the RPM limit.

All it did was screw Pro Stock and make the cars look stupid.

They should have let carbs and EFI run together, with or without hood scoops. That's what Pro Stock SHOULD be.

Agree. Pro Stock should have had open induction rules. Run whatever, as long as the throttle body can't be controlled by the ECU (thinking traction control here). I believe they would all be fuel injected if that was the case and it would look nothing like what the rules specified.

Yup. Then it would be a true test of one verses the other. And I agree with not letting the TB be controlled by the ECU. I can't remember which MSD ignition it was that was banned in Pro Stock and Comp, but it was essentially traction control. I can't think of what MSD even called it now.

[andyf]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

If you put EFI on an intake designed for a carb then EFI will probably be the same or slightly less power at WOT. I've done some of that back to back testing and EFI sometimes makes more power and sometimes loses power. It depends on the type of gas and how good the carb guy was. EFI is much easier to tune and much more flexible plus it has data logging built in so for the average guy EFI is the better choice.

I think that eventually EFI will start making more power than carb just due to the fact that over time people wills start to tool up EFI specific intake manifolds. Looks at some of the manifolds that the OEM's are using and you can see that there is no way in heck that those intakes would work with a carb. If you took an LS based pickup truck engine and told GM that they had to use a carb they would whine to high heaven. That engine would lose a bunch of torque and drivability if you took away the high tech intake manifold and made them use an old cast iron dual plane like they did back in the 70's.

[MadBill]

I've heard it mentioned on here several times that a carburetor engine can make more power than fuel injection..I assume this might be for drag racing? Are there any specific examples to prove it? Thanks

<EDIT> Written before seeing above post.
The preceding posts highlight the complexities of such an apparently simple question. It's clear EFI has the potential to be better but for many people, your question translates to: "If I swap out my carb for a simple EFI system, will I gain power? and the answer then is: "Not necessarily." In this Engine Masters episode: https://www.youtube.com/watch?v=2sQJPZYSoUI the short answer was that the simple EFI system lost big time, because it couldn't cope with the flow characteristics of the dual plane manifold. However with a single plane, the EFI had a small but solid advantage.

Many A-B comparisons can be found showing slight superiority for a carb set up, but almost inevitably the advantage can be traced to other components (like the dual plane above) being optimized for carburation.

[af2]

OH boy!!! I see another torque vs HP thread.... I'll stop at page 1.....