Weber Look A Like Fuel Injection!

[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