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305 Small-Block Build - Questions and Answers - What's Your Problem?

Have questions or concerns? Jeff Smith has answers.

Injector School
Steve Telkes; Saddle Brook, NJ: What is the difference between a pintle- and disc-style fuel injector and which is better for performance use in a programmable aftermarket EFI system?

Jeff Smith: We decided to go to school for an hour or so with our friend Joe Alameddine, who is one of the design engineers with Accel. There are actually three different designs that include the pintle, the disc, and the newest ball and seat style. Within the world of older injectors, we'll limit this discussion to the two you asked about. The quick answer to your question is that injector response time is a critical function that is directly related to good driveability, especially for a performance engine. Based on that, Alameddine says the disc-style injector offers many advantages. These older EV1 design injectors are larger, heavier, and more expensive to make than later, smaller, EV6-style injectors used on late-model LS engines, for example. But within the earlier-style injectors, the disc is far lighter than the pintle, which means the disc's response time will be much quicker. Moreover, pintles are also far more sensitive to foreign material in the injector because of their clearances. He even told us that these extremely tight tolerances are affected by any type of torsional movement that could put tension on the injector. Alameddine says he's seen actual examples in which a slight mismatch of the injector rail to the manifold was enough to place a slight bind on the injector housing that caused the injector to fail to open.

Beyond response time, the shape of the cone of fuel exiting the injector is also important. Alameddine says the pintle style offers a fixed cone shape usually between 20 and 40 degrees. ACCEL uses a cap over the disc that creates a tricone design that dramatically increases the surface area, which also helps driveability and throttle response. Alameddine also said that the late-model, factory ball and cone-style injectors are becoming much more fine-tuned to specific applications by directing the spray cone toward a particular spot in the intake port. That means attempting to use these later injectors in a nonstock application may be rewarded with poor part-throttle response.

Alameddine says the key to a well-executed aftermarket EFI-controlled engine can be reduced to three important considerations. First is the choice of a high-quality, fast response time injector that we've now seen would be a disc-style injector. Second is what Alameddine calls injector targeting, or the orientation of the fuel injector in the intake manifold and its position in relation to the intake valve. The third criterion is the electronic control package that allows the tuner sufficient freedom to fine-tune the way the injector is opened at different engine speeds and loads to extract that last bit of performance and throttle response. If you can balance those three variables, Alameddine says you'll have a happy engine.

More Info

Mr. Gasket (Accel); Cleveland, OH; 216/688-8300; ACCEL-dfi.com

The Dreaded Floating Decimal Point
If you're going to wade into the shark-filled waters of technical writing, you have to be willing to get bitten every once in a while. Even though this column includes numbers just about every month, numbers (unlike mere words) tend to be unforgiving when it comes to minor mistakes. Such is the case with our "Simple Battery Test" piece I penned for the Nov. '10 issue. The magazine must have been in our readers' mailboxes about 15 seconds when the emails began to appear letting me know that our milliamp definition was flawed. The correct definition of a milliamp is 0.001 amp. Where I crashed and burned was when I wrote "a typical stereo unswitched connection may pull 100 milliamps" followed by the number 0.001. Both statements were correct, but not when you put them together in the same sentence. Obviously, 100 milliamps would then be 0.100 amp. There is a rumored sighting of a lynch-angry posse of electrical engineers forming as this is written. I plan on lying low for a while. Thanks to all our sharp-eyed and electrically savvy readers who took the time to correct my current miscue.

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