Loss of torque with EFI?

[CGT]

50 lbs of torque? Assuming AFR was in the ballpark on both, that would lead me towards testing method, ignorance, equipment, or motive. When I hear things like that I automatically disregard the validity of the tests.....

A lot of weird things can possibly happen on a dyno. Some of them can have preconceived intent, others can be completely unintentional. Owning a dyno doesn't automatically give you magic insight into IC engines, of course it can certainly help.

Some people just accept results like that, and accept it like its the bible. Its up to you ( to chop through that and see where your or others equipment or methods could possibly be failing to work correctly)

There are ton of ways you can unknowingly get bad data. Especially at the bottom of the torque curve when pulling one from that low of rpm. The dyno driver, pulling procedure, and consistency in method can even have a very pronounced effect here, different dyno types also can me more or less sensitive to this kind of junk data when pulling from a low start rpm as well.

I can see their being some slight variations in torque one way or the other down below peak torque like that, but 50 lbs?...nah.

[427dart]

For a weekend hot rod once you get your carb or carbs right....no problems. Mine cranks right up and runs fine and still have no need for EFI.
You have to take the time to sort the carb out on the road with your A/F meter.

[Mike Laws]

In a recent article on the Hot Rod website a big BB Chevy is tuned with both a Dominator and a Holley Sniper system. It took them several days to dial in the fuel curve on the Dominator but the Holley Sniper learned its curve in just a few dyno pulls. The peak numbers were basically the same but the Sniper was down about 50 ft-lbs at the bottom of the RPM range. The article didn't mention this torque gap but I've seen the same thing happen when testing EFI vs. carbs. My guess is that it has to do with fuel mixing but I don't know if that is true or not. We don't know all of the other variables so it is just a guess what happened with that engine. For example, I assume the timing curve was the same but it might not have been. Same with the weather conditions, type of fuel, etc.

Has anyone else seen a drop in torque with EFI even though the peak numbers stayed the same? The Sniper is a throttle body type of setup so in theory the fuel mixing should be the same but maybe the injectors don't do quite as good a job as the annular boosters in the Dominator?

https://www.hotrod.com/articles/fuel-sc ... ow-to-fix/

Andy: Articles like this one always leave more questions than answers. I've seen dyno sheets that show power differences between efi and carbs throughout the rpm range on the same engine. Some favored fuel injection, some favored carbs. A well organized efi vs carb dyno shootout would be interesting.

I think the torque difference in the article is more due to cfm than anything else. The carb tuner used his knowledge to alter the fuel curve for this engine and it worked out fine. I would have gone about it differently and if you asked other carb tuners, you'd probably get other answers as well.

[Orr89rocz]

If anyone read the article and looked at the table, you can see the air fuel ratios weren’t exactly the same and the carb was much more stable across the rpm range. The efi started lean dipped rich then leaned again then richened. Its all over the place. Probably making more corrections than needed.

No word on timing used.

At peaks the efi was better so it seems the average power could just be a result of the air fuel and unknown timing

Injector duty cycle and injector timing may also have some impact on power numbers

[CGT]

If anyone read the article and looked at the table, you can see the air fuel ratios weren’t exactly the same and the carb was much more stable across the rpm range. The efi started lean dipped rich then leaned again then richened. Its all over the place. Probably making more corrections than needed.

No word on timing used.

At peaks the efi was better so it seems the average power could just be a result of the air fuel and unknown timing

Injector duty cycle and injector timing may also have some impact on power numbers

50 lbs of torque.

[andyf]

In a recent article on the Hot Rod website a big BB Chevy is tuned with both a Dominator and a Holley Sniper system. It took them several days to dial in the fuel curve on the Dominator but the Holley Sniper learned its curve in just a few dyno pulls. The peak numbers were basically the same but the Sniper was down about 50 ft-lbs at the bottom of the RPM range. The article didn't mention this torque gap but I've seen the same thing happen when testing EFI vs. carbs. My guess is that it has to do with fuel mixing but I don't know if that is true or not. We don't know all of the other variables so it is just a guess what happened with that engine. For example, I assume the timing curve was the same but it might not have been. Same with the weather conditions, type of fuel, etc.

Has anyone else seen a drop in torque with EFI even though the peak numbers stayed the same? The Sniper is a throttle body type of setup so in theory the fuel mixing should be the same but maybe the injectors don't do quite as good a job as the annular boosters in the Dominator?

https://www.hotrod.com/articles/fuel-sc ... ow-to-fix/

Andy: Articles like this one always leave more questions than answers. I've seen dyno sheets that show power differences between efi and carbs throughout the rpm range on the same engine. Some favored fuel injection, some favored carbs. A well organized efi vs carb dyno shootout would be interesting.

I think the torque difference in the article is more due to cfm than anything else. The carb tuner used his knowledge to alter the fuel curve for this engine and it worked out fine. I would have gone about it differently and if you asked other carb tuners, you'd probably get other answers as well.

Hi Mike, haven't talked to you in a couple of years. The cfm difference is a possibility. One reason why I was interested in the results is because I saw almost the same results on one of my test engines. In my case I was running a 514 inch Mopar with a 1250 BLP carb and then I switched to Holley EFI. In my case I switched to a port injection setup with a 2000 cfm throttle body. The Holley EFI system had slightly better peak numbers but the torque at the bottom of the range dropped off by 30 or 40 ft-lbs. So very similar results. I never spent much time poking at it since we were looking for other things but I've wondered about it a few times. I assumed it was due to injector placement but I suppose it could be an effect of the much larger throttle body or perhaps I had the injector pulse timed wrong.

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

[andyf]

I'll see if I can attach a PDF of the carb vs. EFI test I ran on my 514. At the start of the pull the EFI was down by 50 ft-lbs but then it pulled ahead at the end and made a little more power at peak. I never came up with an explanation for the missing torque at 5000 rpm. We made a dozen or so pulls and the loss was always there so I was fairly certain that it is real.

EFI v Carb.pdf

[gmrocket]

In a recent article on the Hot Rod website a big BB Chevy is tuned with both a Dominator and a Holley Sniper system. It took them several days to dial in the fuel curve on the Dominator but the Holley Sniper learned its curve in just a few dyno pulls. The peak numbers were basically the same but the Sniper was down about 50 ft-lbs at the bottom of the RPM range. The article didn't mention this torque gap but I've seen the same thing happen when testing EFI vs. carbs. My guess is that it has to do with fuel mixing but I don't know if that is true or not. We don't know all of the other variables so it is just a guess what happened with that engine. For example, I assume the timing curve was the same but it might not have been. Same with the weather conditions, type of fuel, etc.

Has anyone else seen a drop in torque with EFI even though the peak numbers stayed the same? The Sniper is a throttle body type of setup so in theory the fuel mixing should be the same but maybe the injectors don't do quite as good a job as the annular boosters in the Dominator?

https://www.hotrod.com/articles/fuel-sc ... ow-to-fix/

Andy: Articles like this one always leave more questions than answers. I've seen dyno sheets that show power differences between efi and carbs throughout the rpm range on the same engine. Some favored fuel injection, some favored carbs. A well organized efi vs carb dyno shootout would be interesting.

I think the torque difference in the article is more due to cfm than anything else. The carb tuner used his knowledge to alter the fuel curve for this engine and it worked out fine. I would have gone about it differently and if you asked other carb tuners, you'd probably get other answers as well.

Hi Mike, haven't talked to you in a couple of years. The cfm difference is a possibility. One reason why I was interested in the results is because I saw almost the same results on one of my test engines. In my case I was running a 514 inch Mopar with a 1250 BLP carb and then I switched to Holley EFI. In my case I switched to a port injection setup with a 2000 cfm throttle body. The Holley EFI system had slightly better peak numbers but the torque at the bottom of the range dropped off by 30 or 40 ft-lbs. So very similar results. I never spent much time poking at it since we were looking for other things but I've wondered about it a few times. I assumed it was due to injector placement but I suppose it could be an effect of the much larger throttle body or perhaps I had the injector pulse timed wrong.

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

the engine masters over the years have shown the carb beats out EFI for wot. youll see guys show up with an intake manifold all set up for port EFI...yet run a carb.

they usually say they tested both before hand and the carb came out on top...usually making more bottom end TQ...thats crucial for points

[Roundybout]

I just quickly glanced at the article. 50 lb/ft is a ton of difference. What ignition system was used? I could see timing being pulled back if knock was detected in that RPM range be a cause for this over a carb with no electronic controls but don’t think that’s the case here.

[Tuner]

Any indication of the A/F ratios for the two systems?

EFI might not have figured out the lower RPM yet.

There is an AFR chart in the article. The carb appears to have a slightly smoother curve but I doubt the difference is really significant. For most of the pull the AFR is in the mid 12's for both systems. The Sniper goes a little rich in a couple of spots but it doesn't seem to be enought to know 50 ft-lbs off the chart.

The EFI meters by PWM. The 1450 cfm Sniper is described as having 8 100 lb. per hr. injectors. With injectors that large, at low RPM the percentage of on-time pulse width is so short, the off-time is much longer than the on-time. Although there is pulsation in an engine's air flow, the air flow is relatively more continuous than the injector fuel flow.

An unavoidable consequence of large injectors is in low RPM and low power conditions there is relatively short pulse width and during the time the injectors are not spraying a large amount of dry air is entering the manifold. The possibility exists they can be sequentially activated (2 - 4 - 8 ?) as power demand requires, does anybody know if the Holley system does this?

Even though a carburetor may have uneven fuel flow, such as in the too-common situation of too large/too many emulsion bleeds we see the johnny-come-lately carb mavens use in Holleys, a carburetor delivers and mixes fuel with the air stream in a more or less continuous flow, so the air entering the engine is more uniformly wet with fuel. Probably the more important thing is the puddle of liquid fuel in the manifold and ports is more uniform.

[gmrocket]

Any indication of the A/F ratios for the two systems?

EFI might not have figured out the lower RPM yet.

There is an AFR chart in the article. The carb appears to have a slightly smoother curve but I doubt the difference is really significant. For most of the pull the AFR is in the mid 12's for both systems. The Sniper goes a little rich in a couple of spots but it doesn't seem to be enought to know 50 ft-lbs off the chart.

The EFI meters by PWM. The 1450 cfm Sniper is described as having 8 100 lb. per hr. injectors. With injectors that large, at low RPM the percentage of on-time pulse width is so short, the off-time is much longer than the on-time. Although there is pulsation in an engine's air flow, the air flow is relatively more continuous than the injector fuel flow.

An unavoidable consequence of large injectors is in low RPM and low power conditions there is relatively short pulse width and during the time the injectors are not spraying a large amount of dry air is entering the manifold. The possibility exists they can be sequentially activated (2 - 4 - 8 ?) as power demand requires, does anybody know if the Holley system does this?

Even though a carburetor may have uneven fuel flow, such as in the too-common situation of too large/too many emulsion bleeds we see the johnny-come-lately carb mavens use in Holleys, a carburetor delivers and mixes fuel with the air stream in a more or less continuous flow, so the air entering the engine is more uniformly wet with fuel. Probably the more important thing is the puddle of liquid fuel in the manifold and ports is more uniform.

the sniper isnt very adjustable...maybe the terminator you could sequentially fire the injectors?

[Orr89rocz]

If anyone read the article and looked at the table, you can see the air fuel ratios weren’t exactly the same and the carb was much more stable across the rpm range. The efi started lean dipped rich then leaned again then richened. Its all over the place. Probably making more corrections than needed.

No word on timing used.

At peaks the efi was better so it seems the average power could just be a result of the air fuel and unknown timing

Injector duty cycle and injector timing may also have some impact on power numbers

50 lbs of torque.

The power curve just looks way odd to me. Efi starts at 39 tq down at 2500, falls to 56 behind at 3000, but the air fuel was half point leaner than carb to start then started richening up tremendously diving from 12.7 to 11.4. Efi pulls within 8 lbft by 3500 then falls again down 38 by 3800 then by 4200 efi is even and starts to pull ahead.

I wouldnt put any faith in the wavey curve of that efi system, atleast more info is needed on the system timing and fueling. More tuning may have closed some of the differences. Also who knows what engine temps and oil temps were

[Tuner]

50 ft. lbs. of torque gone missing with EFI vs. a carburetor is a fine example of "you don't know what you've got 'til it's gone."

Andy, can you look at your data logs and see what the duty cycle percentage is in the RPM range where the power is down?

[CGT]

The power curve just looks way odd to me. Efi starts at 39 tq down at 2500, falls to 56 behind at 3000, but the air fuel was half point leaner than carb to start then started richening up tremendously diving from 12.7 to 11.4. Efi pulls within 8 lbft by 3500 then falls again down 38 by 3800 then by 4200 efi is even and starts to pull ahead.

Yeah, the fuel curve isn't perfect, but I don't think it can explain anything near what the power curve is showing. I can't imagine what could cause that kind of deficit, then catching up and exceeding all in that short amount of time, other than fake newz . I would like to of been able to actually hear those pulls being made. Those kind of sketchy things are usually very audible.

Dyno's can do weird things on engines pulled down that low. The torque that engine is making could possibly make those kind of pulls even harder to get real consistent. And their isn't a whole lot of engines out there that are happy floorboarded, locked up solid, dragged below 2500 rpm, then let go of. Add in a dyno operator that isn't good at or used to pulling stuff like that.... Errors and inconsistencies can happen real easy in that scenario. Once again I'd of like to of heard those pulls being made.


Interesting that their are 2 different dyno stories here and the common denominator is weird anomalies at and around the start rpm, 2 different start rpm's.

[Tuner]

You don't have to be a rocket surgeon to see a short duty cycle percentage means erratic A/F homogeneity resulting in a higher percentage of dry air entering the cylinders.