How big of a cam can I go with speed density efi?

Also. Who or how can I tune said speed density system

85 5.0 truck

Going to be pretty hard to get some one to tune a 85 SD computer. you need to open the drivers door and look at the sticker on the door jam. should be a small one all by itself. like 2" long and 1/2 wide. with a 4# code. like 3PC3. or like A9L,A9P. something along them lines. thats you computer tune code. From that you can call someone that tunes OBD 1 ford with that code and see if he can tune it. Not all code are sopported by the aftermarked world.

If you wanted to tune it your self there some out there that you by the chip and the burner and use your lap top with there softwere and your on your own.
One o know of is www.moates.net. And a thing called 'QuarterHorse'.

As for the cam what do you wean by Big?? Big as in Lift? Duration? Or centerline?

to keep the computer happy its about how much vacuum the engine will hold at idle. For these truck its 17 to 18" of vacuum at idle.
So whats that mean in a cam??
Well its about the centerlive in the cam or know as over lap. the lower the # the more the overlap and the less Vacuum the engine will make. So for these truck the centerline should be about 114 to 117 overlap should keep these truck and computer happy. But really if you want some power i would put heads on it like come trickflow trackhead heads. you will get way more power from these truck then a cam will ever do.

Oh and with a cam with more then a 114 centerline you will not need to tune the computer.