Carbs make more power than FI?

General engine tech -- Drag Racing to Circle Track

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statsystems
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Re: Carbs make more power than FI?

Post by statsystems »

MadBill wrote: Thu Mar 22, 2018 12:24 pm How about alcohol 410" Sprint Car down nozzles? :-k
I can't say for sure, but Earl Gaerte and I talked on the phone a couple of times around 1995 or so. It had to be around there because that's when I stated moving the nozzles up.

He would never come out and tell me for sure, but what I culled from his wide range of knowledge was that they give up some power to control fuel. Their corner loads and the forces generated coming out of the corner were enough to make the fuel on the inside cylinders move back out of the port.

If that's true (like I said...conversations were a long time ago and were intiated by me making some dyno pulls that were throwing us for a loop) under load there were cylinders that would go lean and then all the fuel would catch up (for lack of a better term) and then stack up on the back of the valve. When the intake valve came off the seat there was enough fuel there that what didn't go right out the exhaust would stratify.


That was a long time ago, so I don't trust my memory too well any more. But that is pretty much what I remember what we discussed. And fuel pressure, nozzle placement, checking by pass opening pressures and closing pressures. Stuff like that.
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Re: Carbs make more power than FI?

Post by Circlotron »

If you ran a high enough injection pressure and the injector is aimed just right, might the kinetic energy of the spray actually help to sweep in some of the air, so aiding VE?
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Re: Carbs make more power than FI?

Post by Newold1 »

You can't make blanket statements about EFI versus carb unless you compare apples to apples comparisons on the same spec engine in a vehicle racing.

Dyno only comparisons don't take into account the tuning while running capability of an EFI system versus a pre-tuned and adjusted carb.

Implementing EFI in classes of racing with rules that make users modify existing intake manifold carb intake systems you are not going to have optimim results.

EFI will replace carbs in almost all forms of racing except as George Klass said, "I am not going to put it on my lawn mower!" :lol:
The Older I Get, The Dumber I Get :wink:
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Re: Carbs make more power than FI?

Post by roc »

Newold1 wrote: Thu Mar 22, 2018 8:04 pm You can't make blanket statements about EFI versus carb unless you compare apples to apples comparisons on the same spec engine in a vehicle racing.

Dyno only comparisons don't take into account the tuning while running capability of an EFI system versus a pre-tuned and adjusted carb.

Implementing EFI in classes of racing with rules that make users modify existing intake manifold carb intake systems you are not going to have optimim results.

EFI will replace carbs in almost all forms of racing except as George Klass said, "I am not going to put it on my lawn mower!" :lol:
Cub Cadet and Troy-Bilt are some of the EFI mowers available now. Kawasaki engines too.
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Re: Carbs make more power than FI?

Post by andyf »

Ron E wrote: Thu Mar 22, 2018 3:42 pm 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?
Yes we had a vacuum gauge on the engine and we did see a small amount of vacuum at WOT but I think it was less than an inch. I'd have to pull out the dyno sheets to be sure but I don't think the engine was using more than about 1000 cfm at WOT since we only turn the engine a little past 7000 rpm. This point just highlights one of the major issues with using a carb to make high hp. The bigger the carb is then the less pressure drop at WOT, but a super big carb has problems at lower engine speed. EFI allows you to get around that issue.

Here is a link to a dyno pull with the 1250 carb on the engine. Manifold vacuum bounces around a little bit but it is usually one inch or less. Looks like airflow hits 1000 cfm right at the end of the pull.

https://www.youtube.com/watch?v=2zTAGAy ... 834NLVTC9w
Last edited by andyf on Thu Mar 22, 2018 9:18 pm, edited 1 time in total.
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Re: Carbs make more power than FI?

Post by peejay »

Circlotron wrote: Thu Mar 22, 2018 4:41 pm If you ran a high enough injection pressure and the injector is aimed just right, might the kinetic energy of the spray actually help to sweep in some of the air, so aiding VE?
Mistimed injection can hurt VE because of what I think of as the "air door" effect, so I don't see why it couldn't be timed to prevent reversion.

You would need very large (read: low duty cycle) injectors to see any benefit though.
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Re: Carbs make more power than FI?

Post by LSP »

Ken_Parkman wrote: Thu Mar 22, 2018 1:22 pm BTW Comp eliminator is very much a max effort performance class.
Yup......
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Re: Carbs make more power than FI?

Post by LSP »

[/quote]

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.
[/quote]

Aaaaaaaand yup....
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Re: Carbs make more power than FI?

Post by hoffman900 »

The entire argument that carburetors are better is hinged not so much on the carburetor itself, but the package.

For the carburetor to be most effective, it needs a wet plenum. Here it takes large (relatively speaking) droplets of fuel and disperses them into a chaotic environment - think of it as paint shaker for gas/air - to delay and atomize the fuel further. There was a lot of "trade secrets" in Pro Stock and other series with how to deal with plenum shape to improve this atomization process. As we know, large wet plenums that may make the most power, may not be the fastest in the vehicle due to this delay. Wet plenums also serve to dampen harmonic waves - see point #3 below. I will give this point to carburetors, as shower injectors effectively provide a similar phenomenon as a wet plenum in regards of time to atomize the fuel. The only thing is injectors can be timed so they give similar peak and a much wider and powerful powerband. A well developed carburetor package may not see much or any advantage on a 5spd drag car, but you're optimum tuning window is a lot narrower. However, the wet plenum is effected by gforces. Since the engines are typically installed in a vehicle with the point to race, this can present some issues - the magnitude of which depending on how well the package is designed.

To get the full effect of what fuel injection can do vs a carburetor, you need to compare to a single carb throat / port setup vs fuel injection. A good example would be a DCOE Weber vs a fuel injection. Here are the issues:

1) You are restricted on the port taper. The carburetor throttle blades / choke / booster size will be optimum for a given combination. You also need to move it far enough from the valve to get proper atomiztion for a given RPM. The more rpm, the further it needs to be. The further it needs to be, the more restricted you are with port taper and the worst the jet signal. The taper issue has an effect on flow and harmonic waves and restricts potential.
2) The booster / choke assembly presents an area change. The harmonic waves in the intake recognize this area change. You will loose some of the power potential by weakening the waves due to multiple area changes within the intake tract before it reaches atmosphere. This is something I suspected and is something that the 1D simulators pick up on. A wet plenum insulates the engine from seeing the carburetor in this manner.
3) The single throat carb throat / port is also sensitive to pressure dynamics and 'double fueling'. This will traditionally show up as a hole in the power curve where the system is out of tune - it sees it both from the intake and the exhaust. You can work around this with fuel injection. Calvin Elston has given us examples of header systems that work on wet plenum engines, and all else being equal, will not work on the same engine with an individual carb / port set-up. They just simply won't take throttle without spitting fuel out everywhere.

Going back to the beginning of my post, carburetors are most effective on a packaged system designed for them (ie: a wet plenum). For the same reason, fuel injection will be most effective on a system designed for it. Putting fuel injection on a manifold designed for a carburetor is not realizing its potential. Heck, even putting a carburetor on a system without a wet plenum is also not realizing its potential.

Side bar on Comp Eliminator. How are they not hinged on the indexes when you're penalized for going faster than the index at certain increments? I'm well aware of a few of the top guys being part of Pro Stock teams, which serves to reinforce my point. They've got the carburetors extremely developed but their fuel injection experience is that with an inadequate system.
Last edited by hoffman900 on Thu Mar 22, 2018 9:54 pm, edited 7 times in total.
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Re: Carbs make more power than FI?

Post by LSP »

If anyone has a bestoke EFI system & manifold that will be quicker than carb(s) down the track, the NHRA Comp guys will be all ears, with wallet open.
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Re: Carbs make more power than FI?

Post by hoffman900 »

. A well developed carburetor package may not see much or any advantage on a 5spd drag car, but you're optimum tuning window is a lot narrower
Missed my edit window. A well developed carburetor package may not lose anything to EFI on a narrow power and 5spd car, but your optimum window is narrower because the wet plenum volume is fixed.
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Re: Carbs make more power than FI?

Post by CGT »

Ive been playing with EFI for 6 or so years now via E38 GM pcm. Amazing what the capabilities are. Late model, flex fuel, forced induction EFI is untouchable. But complicated to me. Im sure the aftermarket EFI's are more simplified for users.

But Ive always loved carbs, still do, gotta love the simplicity and real time metering of a carburetor. If I put as many hours upon hours into driveability with a carb as with my late model efi, it would be very very good........as long as the weather didnt change too drastically. :D
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Re: Carbs make more power than FI?

Post by GARY C »

CGT wrote: Thu Mar 22, 2018 10:10 pm Ive been playing with EFI for 6 or so years now via E38 GM pcm. Amazing what the capabilities are. Late model, flex fuel, forced induction EFI is untouchable. But complicated to me. Im sure the aftermarket EFI's are more simplified for users.

But Ive always loved carbs, still do, gotta love the simplicity and real time metering of a carburetor. If I put as many hours upon hours into driveability with a carb as with my late model efi, it would be very very good........as long as the weather didnt change too drastically. :D
As I understand, the turbo and boosted world can thank EFI for realizing the untapped potential.

I have always been a carb guy but I don't think they stand a chance when compared to a boosted EFI combo.
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Re: Carbs make more power than FI?

Post by CGT »

Without having control over ignition, knock, throttle, ethanol content etc. Id have been through 5 broken engines trying to get the same results with carbs :lol: .

Im not saying it cant be done with carbs, just not as nice, safe or easy. WOT NA application I still like the carbs.
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Re: Carbs make more power than FI?

Post by user-23911 »

Talk about drivability and flat spots.

Not with normal setups but if you were to say add a turbo to a stock N/A (suck through carb) setup and expect it to run well, it won't.


All out power never comes into the argument, flat spots, stalling on a cold morning.......makes them a turd to drive.
For something that you want to jump into and drive to work?
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