Injected Big-BlockI recently purchased a 1978 K5 with a 454, an NP435, and an NP205. The truck was restored in the mid-1990s and is still superclean. It is basically all original except for the big-block, which I love. It even has air and cruise control. Recently the carb has started loading up occasionally. My first thought was a rebuild to keep it as close to factory as possible. Then it occurred to me that it isn't factory anyway because the big-block was never available in the K5, as far as I can find. I drive the Blazer a lot and would probably drive it more if the mileage was better, so why not inject it? My question to you, since I know you guys have done several, is which kit is the best bang for the buck? It's not a high-horsepower build. Basically it’s a stock big-block with a mild cam and good factory heads, an Edelbrock intake, and headers. The truck will be stored most of the winter (once the salt starts flying here in Illinois), so I will have plenty of time for the swap.
You are correct: Chevy never made a big-block Blazer. We are really lucky to live in an age when so many good fuel injection options are available. Once upon a time aftermarket fuel injection was sketchy at best, but these days several excellent systems are out there to choose from.
If you want to stay as factory as possible, and your truck’s big-block is mostly stock, it would be hard to go wrong with a factory TBI system. Used from 1987-1995, the Chevy TBI system is simple and reliable as a hammer and is among the most affordable of your options. Howell (howellefi.com) offers a complete system that includes absolutely everything you need to install a factory TBI system on your truck using all-new factory components. If you are on a budget and fairly mechanically savvy, you can also obtain everything you need from a junkyard, including the throttle body, sensors, harness, and computer. The bad part is that the newest TBI trucks are over 20 years old, so it can be tough to find a donor that has everything you need in good condition. You will also need either an adapter plate for the throttle body or an intake manifold from a TBI big-block truck. If you go the junkyard route, make sure the computer and the injectors come from a big-block truck.
We have always been a big fan of factory EFI systems because parts are as close as the local auto parts store. However, there isn’t much adjustability in a factory TBI system and they can’t support much more power beyond a mildly built engine like yours. If you plan on doing some future power upgrades or you want the ability to make a lot of adjustments, then an aftermarket system might be better for your needs. Most aftermarket systems will also bolt directly to your existing intake manifold, which we assume already has a four-barrel carburetor on it. Though often more expensive than bolt-on TBI systems, aftermarket EFI kits can support a lot more horsepower and usually have an unlimited amount of tuning capability. If you are like us, though, that simply means there is a lot more ways to really screw it up. Fortunately all of the modern systems also have very reliable self-learning modes as well. We have had really good luck with Edelbrock’s E-street EFI system (edelbrock.com), the FAST EZ-EFI systems (fuelairspark.com), the newer systems from Holley (holley.com), and MSD’s Atomic EFI (msdperformance.com). All four companies have systems that will bolt right into the place of your truck’s carburetor, or if you want to get even fancier, all of them also offer multiport systems for even more performance and tuning capability. The multiport systems require replacing the intake manifold (not a big deal) and tend to be more expensive. Each one of these systems offers several unique features and benefits, so it’s really up to your individual preferences as to which one will work best for you. Though it’s a bit more complicated than rebuilding a carburetor, fuel-injection is worth the effort in terms of improved mileage and drivability.
Oh, one more thing. If your truck’s four-speed is factory, then it’s most likely an SM465 transmission since the Chevy version of the NP435 is about as rare as hen’s teeth.