Weber Look A Like Fuel Injection!

[fkemmerer]

Some additional thoughts on the EFI vs carb question. In many cases, an EFI setup (when properly tuned) can be bolted onto an engine build for a carb and performance and drivability will improve. This is due to the EFI motor's ability to deliver an broader and more ideal range of fuel and timing in any give range of engine load and RPM (as well as responding better to transient conditions like mashing the throttle at low loads/RPMs). EFI is also very helpful in solving difficult tuning problems like big cams with short individual carbs or throttle bodies.

Something to consider is what happens when a motor is built with EFI in mind in the first place. Carbs need a strong vacumn signal to work. This is especially true at low RPMs and idle (this is why cam selection is critical with webers for example). This forces an engine builder to pick a cam that can provide some level of idle vacumn. EFI systems do not need this and therefore cam selection, intakes, etc. can be tuned for maximum power and torque without these compremise. This coupled with that fact that all restrictions required to create lower pressures to atomise fuel in a carb are eliminated give the EFI system a decided advantage in high performance applications.

- Fred

[Cobra #3170]

We dynoed my engine back to back with a 1050 Dominator and a 1650 cfm Wilson throttle body (with spacer). The manifold was a highly modified Victor Jr. The Dominator made 819@7600 and the EFI made 806 @7600. The theory was that the additional cooling provided by the fuel vaporizing upstream with the carburetor may have been responsible for the improvement. Formula 1 engines (several years ago, I am not sure what they do now) had the injection nozzles above the intake trumpets in the plenum probably for the same reason. The location of the EFI nozzles in the intake track on my manifold were not optimum due to packaging which may also account for the difference. The EFI did have a fatter more consistent torque curve and does not crap out under high G stops and cornering. That is the main reason I went with EFI. It also starts much better because it doesn't flood the engine when you move the throttle like those twin 50cc accelerator pumps do.

Originally Posted by fkemmerer

Some additional thoughts on the EFI vs carb question. In many cases, an EFI setup (when properly tuned) can be bolted onto an engine build for a carb and performance and drivability will improve. This is due to the EFI motor's ability to deliver an broader and more ideal range of fuel and timing in any give range of engine load and RPM (as well as responding better to transient conditions like mashing the throttle at low loads/RPMs). EFI is also very helpful in solving difficult tuning problems like big cams with short individual carbs or throttle bodies.

Something to consider is what happens when a motor is built with EFI in mind in the first place. Carbs need a strong vacumn signal to work. This is especially true at low RPMs and idle (this is why cam selection is critical with webers for example). This forces an engine builder to pick a cam that can provide some level of idle vacumn. EFI systems do not need this and therefore cam selection, intakes, etc. can be tuned for maximum power and torque without these compremise. This coupled with that fact that all restrictions required to create lower pressures to atomise fuel in a carb are eliminated give the EFI system a decided advantage in high performance applications.

- Fred

[fkemmerer]

Originally Posted by Cobra #3170

We dynoed my engine back to back with a 1050 Dominator and a 1650 cfm Wilson throttle body (with spacer). The manifold was a highly modified Victor Jr. The Dominator made 819@7600 and the EFI made 806 @7600. The theory was that the additional cooling provided by the fuel vaporizing upstream with the carburetor may have been responsible for the improvement. Formula 1 engines (several years ago, I am not sure what they do now) had the injection nozzles above the intake trumpets in the plenum probably for the same reason. The location of the EFI nozzles in the intake track on my manifold were not optimum due to packaging which may also account for the difference. The EFI did have a fatter more consistent torque curve and does not crap out under high G stops and cornering. That is the main reason I went with EFI. It also starts much better because it doesn't flood the engine when you move the throttle like those twin 50cc accelerator pumps do.

Any thoughts on the idea of power gains that a difference cam that was optimized for fuel injection might have allowed?

[Cobra #3170]

Originally Posted by fkemmerer

Any thoughts on the idea of power gains that a difference cam that was optimized for fuel injection might have allowed?

The cam was optimized for EFI because that was what I was going to run. We just put a carb. on it to see how the two compared. We tried varying the injection timing in relation to cam timing with different sized injectors too. I think if the nozzles were further up stream in the intake runners it might have helped but packaging would have been an issue. One thing we found was that retarding the ignition above 7000 helped with the EFI. We did not try this with the carb. because the main effort was to get the EFI right. We made so many dyno runs the engine had to be freshened with new rings when we got done.
I was really surprised at the results because several years ago we tried the same experiment on a milder engine and it was 20 hp better with EFI. That engine was in the low 700's @ 6700.

[fkemmerer]

Originally Posted by Cobra #3170

The cam was optimized for EFI because that was what I was going to run. We just put a carb. on it to see how the two compared. We tried varying the injection timing in relation to cam timing with different sized injectors too. I think if the nozzles were further up stream in the intake runners it might have helped but packaging would have been an issue. One thing we found was that retarding the ignition above 7000 helped with the EFI. We did not try this with the carb. because the main effort was to get the EFI right. We made so many dyno runs the engine had to be freshened with new rings when we got done.
I was really surprised at the results because several years ago we tried the same experiment on a milder engine and it was 20 hp better with EFI. That engine was in the low 700's @ 6700.

Interesting, what are your thoughts as to why retarding the ignition above 7000 RPM helped the power output with EFI? How much retard did you use?

[Cobra #3170]

Originally Posted by fkemmerer

Interesting, what are your thoughts as to why retarding the ignition above 7000 RPM helped the power output with EFI? How much retard did you use?

I am not really sure, I think it might be related to cylinder pressure going up with rpm because the intake duration is pretty high (292@.050). Total advance was reduced from 32 to 29.5 degrees, the cylinder heads are very good and compression, 14.7 is pretty high. The earlier engine had Edelbrock heads that were highly modified but that engine peaked at 35 degrees advance because the chambers were still basically an FE. It seems that the more advance you need, the poorer the heads are and the less power you make. NASCAR engines are all in the 20's and as you know, very efficient.
As to EFI, I am not sure that it would not have worked with the carb. too, we were out of time and just thrashing the EFI at that point so we did not check it.

[TButtrick]

Originally Posted by Cobra #3170

It also starts much better because it doesn't flood the engine when you move the throttle like those twin 50cc accelerator pumps do.

Doesn't your EFI ECM lengthen the injector pulse width to give the motor the same fuel shot on startup? A carbed car that doesn't start just as quick or "easily" as EFI has the carb setup incorrectly.

[Cobra #3170]

The carb starts fine when it is cold however when the engine is hot it will not start if you look at the throttle, any movement of throttle linkage dumps enough raw fuel to make for a very slow and rich start, it is a single plane manifold so the fuel runs right down the ports.
The EFI has a temperature curve that you can adjust for starting. You can adjust starting injector pulse width down as temperature goes up and can even adjust the rpm that determines when the engine is running and adjust the pulse width at that point too. I have an MSD with Blaster coil so the ignition is up to it if the plugs aren't soaked. This is not a street carb and has no choke plate so it is not a direct comparison to a street carb.

Originally Posted by TButtrick

Doesn't your EFI ECM lengthen the injector pulse width to give the motor the same fuel shot on startup? A carbed car that doesn't start just as quick or "easily" as EFI has the carb setup incorrectly.

[TButtrick]

Originally Posted by Cobra #3170

The carb starts fine when it is cold however when the engine is hot it will not start if you look at the throttle, any movement of throttle linkage dumps enough raw fuel to make for a very slow and rich start, it is a single plane manifold so the fuel runs right down the ports.

My experience is the opposite. On a cold first start of the day, I give a half squeeze of the throttle and no choke. Starts first crank. Subsequent warm starts throughout the day, I don't touch the throttle and starts first crank.

[fkemmerer]

Originally Posted by TButtrick

My experience is the opposite. On a cold first start of the day, I give a half squeeze of the throttle and no choke. Starts first crank. Subsequent warm starts throughout the day, I don't touch the throttle and starts first crank.

Sounds like you are acting as the "computer brain" to make the carb "smart" .
Seriously, this is one of the fundamental advantages of EFI - the computer does a much more precise job of fuel and timing delivery in a broader range of conditions that our engines operate in. This is especially important on the street where a motor must operate over a much broader range of temperatures, loads, transient conditions, etc. than a race car would encounter.

- Fred