Fuel Injection System - New-Age 455

A Technical Review

It is important that the readers of HPP don't misinterpret these test results. Both the Demon carburetor and the Mass-Flo EFI system performed impeccably.

The Mass-Flo EFI design is a wonderful piece of engineering. As the author, I have many years of EFI-tuning experience and did the dealer training for 15 years for ACCEL/DFI, so don't take what I am about to state lightly. In my opinion, there is no other fuel-injection system currently on the market that could be bolted onto a Pontiac engine, requires no user calibration, and provides turnkey performance without driveability issues. Until the Mass-Flo system was introduced, this was an unheard-of concept.

To the credit of Barry Grant, the fact that an enthusiast can order a carburetor properly, bolt it on and be at peak power is something new to the industry. But the operative word in the statement is properly. All too often the enthusiast is sold the wrong carburetor calibration by the dealer/speed shop because that is what was on the shelf. Demon Carburetion has hundreds of different calibrations, so it's beneficial to speak with the company's technical line to get the proper part number for your use. Armed with that information, you can purchase the carburetor from whomever you want.

If EFI is so great, why did the carburetor do better than the EFI system? Since the manifold was a constant and only the fuel-delivery method differed, some accurate conclusions can be made.

Latent Heat of Vaporization: Since EFI systems are dry-flow, the phase change of the fuel occurs as the charge enters the intake port of the cylinder head. This allows for the air in the runner to become heated as it travels from the throttle body to the point that the fuel is injected. A good rule is that for every 10 degrees the air temperature is increased, power drops by 1 percent. The phase change of the gasoline, demanded by the laws of nature, removes heat as it occurs. Power was down by only 3.5 percent with the EFI in comparison to the carburetor. That would represent an approximate 35-degree rise in inlet air temperature. This is a conservative increase and would probably be higher with the engine in the restricted underhood area of a '74 Trans Am.

In addition, it may appear that where the MAF sensor connects to the throttle body, it shrouds some of the airflow path. That would be easy to determine on a flow bench [Editor's note: According to Mass-Flo, the MAF flows 1,000 CFM], but my educated opinion is the charge air heating is where the power is lost, not in the MAF. This is not a design flaw of the Mass-Flo system, but rather the nature of fuel injection.

One reason newer Pontiacs have plastic intake manifolds is due to the heat-transfer problem. The decrease in volumetric efficiency from the less-dense charge may also explain why the engine wanted 4 degrees more advance with the EFI. Most likely it is a combination of the hotter air along with the placement of the fuel injectors.

Injector Placement: Almost all, if not every, company that markets a Pontiac EFI conversion uses a single-plane carburetor intake manifold as a foundation. Due to the nature of this design and the fact that it's being retrofitted, the injectors are placed at nearly a right angle to the manifold runner. This is in direct contrast to an OE application where the injector is laid on its side so it sprays into the port and not against the floor of the runner. With the aftermarket placement of the injector, it wets the bottom of the runner. Also, the distance from the injector pintle to the floor is not sufficient for the atomization to be as effective. At higher engine speeds, port flow increases, and this becomes less of a problem since the air stream carries some of the fuel away. The higher required idle speed, reduced idle quality, and higher rate of fuel consumption over the carburetor can all be blamed on the injector pointing at the floor of the manifold runner.

None of this is meant to be a blow to the Mass-Flo EFI system. The company has done a great job of offering an excellent EFI system to the Pontiac community. These guys did their homework and it shows, but the inherent obstacles of fuel injecting what is basically a 52-year-old engine design cannot be eliminated with advanced electronics.

Based on this test, if you want the visual appeal and bragging rights of owning an EFI-equipped traditional Pontiac engine that doesn't require user calibration, you can do no better than the Mass-Flo system, in the author's opinion. You will drive off with a carefree EFI system if you do the installation properly. If your desire is for the most power at the least cost and complexity along with minimized fuel consumption, stick with a modern carburetor such as the Speed Demon by Barry Grant. But don't decide yet because there is more to come in a future issue. We'll see if the chassis-dyno test provides more revelations that could tip the scales further in favor the EFI or the carburetor.