How big of a cam can a factory EFI 1999 5.9 magnum be set up to handle? It will be 410 cubes and around 11 to one compression. I can get different injectors...

You're gonna want a standalone/laptop programmable efi like Megasquirt or something with a build like that. Then you can do whatever you want. Stock obd2 ecu is pretty stupid in comparison.

I know it will run with a mild cam and I will get a tuner of some sort but what is the limit within those parameters? I will get different injectors and such but with factory MAP TPS IAT... I just don't want to re-work the entire electrical system.

There are a couple of talented SCT tuners that can get the factory PCM to perform pretty good with all kinds of changes while still using the factory Magnum sensor package. Flying Ryan is a gentleman who's highly recommended for that. You will obviously need to swap fuel systems to get to EFI pressures. You will also need some sort of wideband sensor and data logger to send info to the tuner. It will cost some money to have somebody tune it for you, but they can make most anything work if you have the patience to let them work with it.

I originally purchased the SCT racer package that let me tweak all the fuel and timing tables. I would NOT consider my efforts a success. I kept trying to do it on my own and I never got the tune where I wanted it to be. After I got frustrated with SCT and my limited tuning abilities - I went to the MS3X system for mine. I couldn't see sending out for my tunes because I couldn't see myself leaving mine alone long enough to just drive it in a single configuration. Since you're having to wire all the sensors up anyway - and you aren't going to be trying to run a factory PCM controlled dash anyway - just go with MS and be your own tuner. It basically tunes itself anyway.

I'm absolutely satisfied with the MegaSquirt 3X (sequential) package mine is running on. I can change what I want - when I want, or I can let it tun itself after I give it AFR targets to hit. Just the increased throttle response was worth the price of admission and hours spent wiring it all.

Why do you think I want to get rid of all the factory gauges and such?

I want the truck (99 R/T I am trying to buy) to work like a factory truck, jump in bump the key, put it in gear and hit the gas with no waiting for it to warm up and come off the choke, all my factory gauges work just like the factory intended... but a whole lot faster. I don't have the time to build a whole new electrical system nor the skills to make it all work as reliably as the OEM, I am good at building engines so I want to push right up to the limit of what can be made to work fairly easily within those parameters.

I'm sorry. I jumped to the wrong conclusion and somehow thought you were swinging a Magnum setup in your Barracuda. If you are starting with an R/T - then you won't have to do any of that stuff I was talking about other than the tuner.

You will still want an aftermarket 255lph fuel pump to supply the larger injectors - but you won't need to go crazy there either. My 236°@.050" and .540 lift, 114°lsa cam worked just fine in mine without setting any misfire codes at all. I have no idea how much bigger you can go or if narrowing up the lsa will hurt you there.

You should contact Flying Ryan for WAY more information about what the factory PCM can be made to handle. He's tuned and tamed very many Dakota R/T combos - and created a huge happy customer base.

I have a couple of early Valiants but my driver is a 99 neon acr. I know that in them you can up the fuel with bigger injectors and pressure and pull fuel with a SAFC. The big problem with cams are the reduced vacuum at idle makes the computer think you are under load and need fuel. This makes it idle ridiculously rich without some kind of piggy back computer or Rhoades lifters.