I have a Gen VI 454 in my Suburban that needs some work. I'm thinking about turning it into a 496 stroker. Once I find a list of mechanical components (crank, cam, pistons, heads... everything) that I'm happy with (and that are verified to work properly), I'll need to deal with the fuel system. I'm sure I'll have to get uprated fuel injectors to work with the added displacement of the new motor, but will the ECU need to get reprogrammed, too? Who does that? How do they test that it actually works? This truck will be a tow vehicle almost exclusively, and the fuel system has to be calibrated properly so that it doesn't go lean and burn up the pistons. Also, is a carburetor a viable option in a vehicle that still gets emissions tested?
The quick answer is - Yes, you will need a tune after installing larger injectors in your stroked 454.
I was considering a big block swap into my RV so I've done a bit of research about tuning solutions. I was primarily focused on swapping in the L21, so I can't speak 100% to the differences between the Mark IV and Gen VI motors.
This is what I do know... the L29 is kind of an orphan in regards to ECU tuning products, but they're out there and there are businesses on the web offering mail-in/custom tunes and the like for that platform.
Upside - L29 is a true MPI setup so you can upgrade injectors easily. I think you can swap in the injectors from the L18 (Vortec 8100) which just happens to be 496 CI so I think that should work quite well assuming the injectors fit and impedance matches.
Downside - EFILive is the only product I'm aware of that may work for tuning without any other tweaking (swapping to other PCM or whatever), and it's not an inexpensive product.
Oh and lastly - don't waste your time (not to mention violating Federal law) circumventing engine management by downgrading your truck to a carburetor. I guarantee doing that will create 10x the issues you would be solving by removing the fuel injection.
Sounds like a sweet project though, would love to discuss Chebby motor stuff more on here!
One option you may want to consider is switching to a MegaSquirt fuel injection computer. It would be the pain of a fuel injection computer replacement, but they seem to be rather adjustable and configurable, if you are willing to go through the effort.
We have had a couple of presentations at a local computer club from a guy who converted his 60s era Camaro from carbs to fuel injection using this system, and it seemed to work out really well for him.
I'm sure there are a plethora of custom programmers for the Suburban platform. However, if you're making such extensive modifications, you can probably look at some standalone solutions, like an Accel DFI or Haltech setup.
Tuners typically dial in a baseline map and strap your vehicle to a dyno where they adjust fuel/timing curves according to wideband O2 readings sampled from your tailpipe or further up the exhaust. The goal is to get steady consistent power output without triggering the knock sensor or getting unwanted detonation/timing retard, etc.
The Megasquirt 3 is the way to go giving you total control of your new setup. The EFI Analytics software, Tuner Studio and Mega Log Viewer make tuning easy but has a feature set that is up to par with pro tuning setups. The VE Analyzer Live will also help dial in various areas of your tune as will the Mega Log Viewer Scatter Plots.
I would bet your new install will also run better than the day you got it, that's how good this product has come over the last few years. DIY AutoTune is where you want to start.