Loss of torque with EFI?

[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/

[427dart]

Could it be that at a lower RPM the reduced injector cycle plus fuel droplets to small as compared to a carb booster with a larger droplet size?
Just thinking here.

[BillK]

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.

I wonder if they had taken several days and actually tuned the EFI system maybe the torque would be the same ?? I dont think the way you put it is a fair comparison.

[emsvitil]

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

EFI might not have figured out the lower RPM yet.

[cjperformance]

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.

I wonder if they had taken several days and actually tuned the EFI system maybe the torque would be the same ?? I dont think the way you put it is a fair comparison.

I have only used 3 sniper efi setups and all on mild streeters, and yes they self learn well with only 20 / 30 mins run time but do get noticeably better after several hundred miles, based on this i think the self learn is great but seems to get close really quickly and continue 'trimming up' for a while.
I have at least 2 more sniper setups to do over the coming months, both blow thru turbo, both will be checked out on a chassis dyno so hopefully i can get these back for another dyno run after 500 or so miles and get a look at any changes from the initial runs and document what i have observed with seat of the pants.

[ClassAct]

I read through most of the carb part of the article. I'm not impressed. How does it take "days" to change throttle linkage, add a power valve to the secondary side, and change the emulsion? And then, how did the come up with a 5.5 power valve opening? That makes no sense.

As per normal, I'm not putting a lot of faith in that article. Had they spent a few more dollars and bought a carb that was already calibrated for the oddball combo, the tuning time would have been even less than the few hours it should have taken. Not days.

[GARY C]

I have read a few mag articles from the early 90's to now and I have never seen enough carb vs EFI article that tell me I don't want to spend thousands of dollars to replace my $200 dollar carb.

Most likely any power difference would be do to inappropriate size or lack of tuning ability, either the system or the system operator. If both are done correctly the power difference should be minimum if any. Most of the guys I know making serious power on EFI would not consider a self learning system because the main benefit to the extra cost of EFI is being able to tune to a specific application. A self learning system can only go as far as what has been programed by someone else.

Here are about half of them.

[andyf]

Could it be that at a lower RPM the reduced injector cycle plus fuel droplets to small as compared to a carb booster with a larger droplet size?
Just thinking here.

Could be I suppose. I don't know enough about injector physics to know if the duty cycle has an effect on the drop size or not.

[andyf]

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.

[GARY C]

I read through most of the carb part of the article. I'm not impressed. How does it take "days" to change throttle linkage, add a power valve to the secondary side, and change the emulsion? And then, how did the come up with a 5.5 power valve opening? That makes no sense.

As per normal, I'm not putting a lot of faith in that article. Had they spent a few more dollars and bought a carb that was already calibrated for the oddball combo, the tuning time would have been even less than the few hours it should have taken. Not days.

Because it's an advertisement for the FI system so they have to make carb seems difficult.

Same reason they only highlight the peak numbers in the article but never point out the massive difference in the average numbers.

[paulzig]

Most of the guys I know making serious power on EFI would not consider a self learning system because the main benefit to the extra cost of EFI is being able to tune to a specific application. A self learning system can only go as far as what has been programed by someone else.

These EZ self learn setups arent real multi point EFi systems, basically you bought yourself an electronic carburetor...

[modok]

The peak numbers were basically the same but the Sniper was down about 50 ft-lbs at the bottom of the RPM range.

Probbly the EFI does not have vac secondaries. It's that simple

[ClassAct]

The peak numbers were basically the same but the Sniper was down about 50 ft-lbs at the bottom of the RPM range.

Probbly the EFI does not have vac secondaries. It's that simple

LOLOLOLOLOLOLOLOL

[makin chips]

I read through most of the carb part of the article. I'm not impressed. How does it take "days" to change throttle linkage, add a power valve to the secondary side, and change the emulsion? And then, how did the come up with a 5.5 power valve opening? That makes no sense.

As per normal, I'm not putting a lot of faith in that article. Had they spent a few more dollars and bought a carb that was already calibrated for the oddball combo, the tuning time would have been even less than the few hours it should have taken. Not days.

Yea but how often does that happen in a Hot Rod Mag article? Almost never. They never go buy a specific custom carb. They buy a stock, get it anywhere carb every time.

[BigBlocksOnTop2]

Annular booster carburetor?