One thing to bear in mind when building a model is what kind of engine it has and what kind of racing it would actually do. If you go beyond building for a 'look' and not caring about how things work, just remember that injector stacks are tuned to a particular rev range on a particular engine, and show up in the real world in any length imaginable.
Short stacks will usually be on an engine that winds tight and makes its peak power at high RPM, like the small-displacement Cosworth Ford V8. Longer stacks help low-end torque, so you'll tend to see them more on drag-racing engines that need grunt off the line. BUT...that's not always true. Just do a google image search for "hilborn injection".
You might also notice that some racing engines use staggered stacks, to broaden the torque curve.
Edited by Ace-Garageguy, 21 December 2013 - 05:40 AM.