Weber Look A Like Fuel Injection!

[D-CEL]

Steve,

The new BOSS head is sooo sexy! I like them, just not it a Cobra. They need to be out where they can be seen!
I was thinking about using the block that's in my car now building a 604 (just sounds scarier than a 598) bolt a big 14-71 and an EFI buzzard catcher on the dam thing. A chopped, steel bodied, fenderless, hoodless, 33-34 five window coupe would be the perfect home!

Ok im in! wheres your check book!!

Jason

[D-CEL]

Anthony,

Kind if true?
To say that the EFI system made less hp because the fuel was “occupying space” that should have been occupied by air… confuses me.
The mixture of air and fuel (a/f ratio) to achieve peak performance is fairly straightforward. Chemically correct is 14.7:1, slightly lower in practice. If the volume of fuel was so great that it displaced air, the a/f would be hugely rich (read to much fuel). Combustion performance would suffer or not work at all.

Are you saying that a carbs make more power because they rely on vacuum and therefore the fuel takes up less space in the combustion chamber?

I think the article was comparing the dual plane manifold and a Holley Carb vs. the early Mercury Cast aluminum EFI manifold with a single throttle body and a small square flame arrestor. It successfully showed that the EFI system made less peak hp than the carb, because the intake tract was long and more restrictive.


Jason

[Anthony]

Originally Posted by D-CEL

To say that the EFI system made less hp because the fuel was “occupying space” that should have been occupied by air… confuses me.
The mixture of air and fuel (a/f ratio) to achieve peak performance is fairly straightforward. Chemically correct is 14.7:1, slightly lower in practice. If the volume of fuel was so great that it displaced air, the a/f would be hugely rich (read to much fuel). Combustion performance would suffer or not work at all.

Yes it is straightforward. The mixture ratio is 14.7:1 by weight/mass, where as the O2 is gaseous, and the gasoline is in a liquid/vapor state. The more the gasoline is in a vapor state, the more volume it takes up, displacing the volume that could have been taken up by additional air (O2). The better you can keep the gasoline in a liquid state, the more "compact" its volume, the more air (O2) you can get into the engine. There is an optimal fuel droplet size for maximizing HP, and different factors affect this, whether the carb has down leg or annular boosters, style of intake, fuel injection, high or low pressure. Everything can be optimized. Were not talking huge values, but values that can be detected.

Originally Posted by D-CEL

Are you saying that a carbs make more power because they rely on vacuum and therefore the fuel takes up less space in the combustion chamber?

I think the article was comparing the dual plane manifold and a Holley Carb the early Mercury Cast aluminum EFI manifold with a single throttle body and a small square flame arrestor. It successfully showed that the EFI system made less peak hp than the carb, because the intake tract was long and more restrictive.

I'm saying that with carbs, you can likely better optimize fuel droplet size, optimize the degree of gasoline vapor to maximize HP, where as with EFI, you spray the fuel under high pressure, resulting in more gasoline vapor which I'm sure optimizes combustion, efficiency of combustion, emissions, but may give away a little performance.

The article compared two identical 454 long blocks, except for the intake, induction system. One was I think called a 454 HO, and the other a 454 Magnum. Anyways, one had a carb on a dual plane intake, and the other was a multiport cross-ram like EFI, (like a newer LT1) , with a single throttle body at the front of the intake, and then 8 injectors, one at each port. Interesting article.

[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.

[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.