Carbs make more power than FI?

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hoffman900
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Re: Carbs make more power than FI?

Post by hoffman900 »

I’m still not buying that a carburetor atomizes fuel better. You need a wet plenum and the turbulent mixing that happens in there because the droplets are so large in order to complete the atomization process. That tells me the carburetors are in fact not that efficient in atomization. How about all the black voodoo magic of plenum bottoms in Pro Stock and the conversations around burr finishes here with carbureted applications to make the carbs work better?

Furthermore, a wet plenum type of system is very package limiting and sensitive to Gforces. You also have less control of cylinder to cylinder mixture composition. I can tell you a DCOE Weber does not make as much power as FI for a couple reasons just not having to do with fueling, but that’s a big part of it. A DCOE does Ann arguably better job of atomizing fuel than a Holley as well.

Take away the wet plenum, and I would like to see how a carburetor fairs then on a high output engine. I think the atomization improvement arguments go out the window.

Pressure traces would show what atomizes better as far as combustion scatter goes. Likely, only a couple of people on here have seen data like that. Jay certainly would.

Here is Jon Kaase’s video of a clear wet plenum:
https://m.youtube.com/watch?v=7Iq1B-2paCs

How do you control where that fuel goes? It’s chaos, and some cylinders will get more fuel than others. Also, lots of liquid gas floating around...

Looking at the Formula 1 example I posted, each injector has 24 holes of .00354” in diameter. They were injecting at ~1450psi ten years ago (rules limited). As pointed out, DI injection systems run higher than that. What is the emulsion tube hole size and jet size on something like a high end Braswell carburetor?

Furthermore, Formula 1 engineers were able to time the injector as such to maximize velocity and also look at its effects on intake pulse phase delay. You do not have that luxury with a carburetor.

As for carburetor’s cost, a high end system isn’t cheap. 2 x top of the like Braswell or a BLP carburetor is what, $4000? Plus you need a separate data acquisition system because the carburetor can’t tell you anything, so throw out another couple of thousands of dollars. I will give you that a high end fuel injection system will be more expensive, but it’s also more capable. Technology and progress costs money, how much do you want to spend?

I’ve still not seen example where a carburetor has made more power than FI, outside of rules imposed limitations or limitations imposed on it by the builder (fuel injection on a manifold designed for a carburetor, limits of the person’s ability to properly set up fuel injection).
Last edited by hoffman900 on Thu Mar 22, 2018 4:51 am, edited 9 times in total.
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Re: Carbs make more power than FI?

Post by digger »

you should make more WOT hp with fuel injection even just considering the fueling aspect.

ideally this would involve:
- larger injectors and/or higher fuel pressures than most use so they can be run at low pulse widths (25-35%) and phased with inlet charge velocity.
- shower injection point well upstream of the valve.
- dedicated manifold design which would have less conflicting requirements than with a carb(s).
- individually tuned cylinders.

its definitely more expensive, and if you drive on the street then some of these most will likely need to be compromised to get the best driveability gains that are possible with injected. half assed system are never optimal
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Re: Carbs make more power than FI?

Post by LSP »

There are some NHRA Comp Elim classes that can run either. I've seen F.I. on a few also rans, and carbs are winning races.

These guys must be missing the boat?
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Re: Carbs make more power than FI?

Post by hoffman900 »

LSP wrote: Thu Mar 22, 2018 6:26 am There are some NHRA Comp Elim classes that can run either. I've seen F.I. on a few also rans, and carbs are winning races.

These guys must be missing the boat?
1) They’re index classes. Doesn’t necessarily mean there is the drive for innovation like a heads up class or other series.
2) Still lots of cookie cutter applications. Call xxx builder and order engine
3) About 50 years of drag race development with the carburetor. People fall back to what they know - that goes for builders and owners. The sport is greying...
4) The testing and building of the system we’re talking about is higher than a carburetor system.
5) Variability in development. How many of those FI systems are on combinations that take advantage of the indexes? How developed are they? If I call Reher Morrison, I’m going to get a higher developed carbureted engine than I would if I tried with my own program and using FI.
6) There are also rans with carburetors and winners with fuel injection.

For the most part, you’re seeing systems in drag racing where 90psi is considered high tech. The professional world in other series have moved on to 1500psi systems over a decade ago, and would surely be higher if it weren’t for rules.

Keep in mind this is the site where there was some blowback on DI when it was first coming out mainstream. There were statements like cars are going to explode with that kind of fuel pressure in a crash. :lol:

This:
https://m.youtube.com/watch?v=7Iq1B-2paCs
Or this:
https://m.youtube.com/watch?t=93s&v=6y-wQl1S9P4
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Re: Carbs make more power than FI?

Post by statsystems »

digger wrote: Thu Mar 22, 2018 4:23 am you should make more WOT hp with fuel injection even just considering the fueling aspect.

ideally this would involve:
- larger injectors and/or higher fuel pressures than most use so they can be run at low pulse widths (25-35%) and phased with inlet charge velocity.
- shower injection point well upstream of the valve.
- dedicated manifold design which would have less conflicting requirements than with a carb(s).
- individually tuned cylinders.

its definitely more expensive, and if you drive on the street then some of these most will likely need to be compromised to get the best driveability gains that are possible with injected. half assed system are never optimal

If you are not using direct injection, fuel stratification is always an issue.

I always made more power with MFI moving the nozzle up the runner. So unless you are running extremely high pressures, atomization is an issue.
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Re: Carbs make more power than FI?

Post by MadBill »

How about alcohol 410" Sprint Car down nozzles? :-k
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Re: Carbs make more power than FI?

Post by andyf »

I think it just depends what you are trying to accomplish. Personally I'm switching all of my stuff over to EFI. If I lose a few hp at WOT I don't care. What I pick up far outweighs losing a few hp. Built in data logging, full digital tuning capability, full ignition control, a sealed system (no constant evaporation of gas from the carb vents), etc.

In short, there are a ton of benefits from even the fairly crude EFI systems available today so I'm switching all of my classic cars over. I do not see any reason for a guy like me to use a carb anymore on any hot rod project. I imagine that there were die hards who didn't want to give up the hand crank system and I'm sure there were guys who stuck with the 6V system and the generator rather than the new fangled alternator. I know there are guys who still say that points work just fine so there is no reason for electronics in their distributor. Might even be some guys who swear that rope seals are better than O-rings. I don't care, I'm switching over.
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Re: Carbs make more power than FI?

Post by NORSK »

hoffman900 wrote: Wed Mar 21, 2018 3:00 pm
Truckedup wrote: Wed Mar 21, 2018 2:14 pm 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:
Image

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. ;)
I could not agree more,there are so many benefits with todays standalone efi it is in my mind just silly to use carbs unless the rulebook says so.
You can pick up a brand new standalone systen today for roughly 1500usd,that supports basically everything needed and fuelling/timing and logging becomes 100 times more precise than any carb can do,and like you say you are not restricted by intake manifold angles,lengths or anything to keep that clumsy carb sitting where it needs to
And no,a carb does not make any more peak power,and certainly not better midrange
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Re: Carbs make more power than FI?

Post by Ken_Parkman »

No argument on injection being better almost everywhere.

But there is also no question a low pressure atomizing injector is crap for providing a burnable mixture. it is so much better mixing air with the fuel in the injector, and really that is what a carb does with the emulsification circuit. The vaporizing fuel cools the induction charge, which increases the density and improves effective VE, not displacing it.

That's why the carb is so good at making max power.

That's also why moving the injector further up makes more power, gets closer to a carb. And (much) higher pressures - like cost is no object Formula 1.

BTW Comp eliminator is very much a max effort performance class.
Last edited by Ken_Parkman on Thu Mar 22, 2018 1:30 pm, edited 1 time in total.
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Re: Carbs make more power than FI?

Post by andyf »

Here is an article I did for Car Craft using my own 514 inch Mopar big block as a test bed. I switched from a 1250 Dominator to a Holley 2000 cfm throttle body and picked up a little bit of power at WOT. Everything else was the same including the intake manifold.

http://www.hotrod.com/articles/holley-hp-efi-install/

The 1250 Dominator was a custom built unit from BLP that cost me around $2000 so it wasn't some swap meet hunk of junk. It was as good of a carb that I could find for my engine. The Holley EFI system made more power within a few dyno pulls. I suspect it was because my carb wasn't "perfect" but that carb had been gone over by some of the best carb guys in the country. What that tells me is that the average bracket racer would probably pick up power by going to EFI since most guys can't afford "perfect" carbs. I'd expect the Pro Stock and NASCAR boys to all have "perfect" carbs but at the local bracket racing level there are just a bunch of out of the box Holley 850 double pumpers sitting on engines.

A lot of threads on Speed Talk turn into a discussion about how the perfect is better than the good enough. Sure, that is obvious. But how many people have "perfect"? Most people operate in the good enough zone and EFI is going to better than a good enough carb.
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Re: Carbs make more power than FI?

Post by NORSK »

Ken_Parkman wrote: Thu Mar 22, 2018 1:22 pm No argument on injection being better almost everywhere.

But there is also no question a low pressure atomizing injector is crap for providing a burnable mixture. it is so much better mixing air with the fuel in the injector, and really that is what a carb does with the emulsification circuit. The vaporizing fuel cools the induction charge, which increases the density and improves VE, not displacing it.

That's why the carb is so good at making max power.

That's also why moving the injector further up makes more power, gets closer to a carb. And (much) higher pressures - like cost is no object Formula 1.

BTW Comp eliminator is very much a max effort performance class.
Most modern injectors today can run upto 8bar and they comes with 16-20 tiny holes at the tip,i would assume that make much finer fuel mist than a carb,and that does not cost anything more to upgrade from a 3 or 4bar system,except another fpr and in some cases a fuel pump
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Carbs make more power than FI?

Post by Mike Laws »

It's a great topic and some good info. Pros & cons for both sides. My experience is mostly with carbs and while I cannot argue with the advantages of EFI - I have yet to see EFI outperform carbs on most NA drag cars.

I've also enjoyed working with this system for a while now on dyno's and in cars. It combines both technologies, makes big power and is easy to work with: https://www.knfilters.com/eci
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Re: Carbs make more power than FI?

Post by maxracesoftware »

Mike Laws wrote: Thu Mar 22, 2018 2:46 pm It's a great topic and some good info. Pros & cons for both sides. My experience is mostly with carbs and while I cannot argue with the advantages of EFI - I have yet to see EFI outperform carbs on most NA drag cars.

I've also enjoyed working with this system for a while now on dyno's and in cars. It combines both technologies, makes big power and is easy to work with: https://www.knfilters.com/eci
same here Mike , so far in my Dyno testing , Carbs make higher HP than EFI,
as long as you are comparing the very same Total Induction Length .
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Re: Carbs make more power than FI?

Post by treyrags »

hoffman900 wrote: Thu Mar 22, 2018 7:00 am
LSP wrote: Thu Mar 22, 2018 6:26 am There are some NHRA Comp Elim classes that can run either. I've seen F.I. on a few also rans, and carbs are winning races.

These guys must be missing the boat?
1) They’re index classes. Doesn’t necessarily mean there is the drive for innovation like a heads up class or other series.
2) Still lots of cookie cutter applications. Call xxx builder and order engine
3) About 50 years of drag race development with the carburetor. People fall back to what they know - that goes for builders and owners. The sport is greying...
4) The testing and building of the system we’re talking about is higher than a carburetor system.
5) Variability in development. How many of those FI systems are on combinations that take advantage of the indexes? How developed are they? If I call Reher Morrison, I’m going to get a higher developed carbureted engine than I would if I tried with my own program and using FI.
6) There are also rans with carburetors and winners with fuel injection.

For the most part, you’re seeing systems in drag racing where 90psi is considered high tech. The professional world in other series have moved on to 1500psi systems over a decade ago, and would surely be higher if it weren’t for rules.

Keep in mind this is the site where there was some blowback on DI when it was first coming out mainstream. There were statements like cars are going to explode with that kind of fuel pressure in a crash. :lol:

This:
https://m.youtube.com/watch?v=7Iq1B-2paCs
Or this:
https://m.youtube.com/watch?t=93s&v=6y-wQl1S9P4
They may be index classes but the indexes are set by their performance. They are not limited by them. They cannot break out. I can assure you these guys will go as fast as they can or need to to win. They are pushing the envelope just like pro stockers. Many of them are part of Pro Stock teams. Plenty of sharp guys there and with the necessary funds to go as fast as they can.
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Re: Carbs make more power than FI?

Post by Ron E »

Andy, even a 1250 on a 514" at Wot could be getting close to being restricted? Just wondering. Did you monitor manifold vac? Beauitful intake BTW..Wilson?
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