7.4LX MPI to Carb, what cam to use
 

Now that the MPI is gone and the carb is going on, what cam can or should I use without changing the valvetrain? Remember its a GenVI block with a roller cam set up. I have also aquired another intake and carb (weber) from a 454Mag, the intake is the same as the first one I got off of a Marine Power Preimum 454, but it came with a Qjet. Which carb should I go with? The weber or Qjet? Also found some 049 oval heads, but not sure they will fit on my block, local machine shop said the would, but they are not sure it any performance would be gained. Any thoughts....?

go with the weber carb, easier to tune and adj. than the Q-jet.
just make sure it is the 1410 model for big blocks.

If you got the intake from a 454mag , its probably a rect port intake , not gonna match up well to small oval port heads (your original) , or the large oval heads (049 gm heads) that you have
unless your motor has rect port heads , in that case the 049 heads will actually flow less then your heads
as for the cam , i'm sure someone will chime in on that

The intake and carb actually came off or 7.4 PT (performance tuned) engine, I check and the part numbers are the same for a 454 Mag of same year. The 7.4PT engine also has the same heads as my engine, peanut port.

how could the part numbers match for a magnum engine , but peanut port intake?
all magnum engines i have seen have rectangular port heads / intakes , i'm not sure about the performance tuned engines , but if there peanut port i dont see how the part #'s could match with a true Magnum engine
unless , and i might be wrong , but i think that in 87-88 , they called the 454 330hp engine a magnum , even tho it was just the base model 454 , 330 horsepower

Sorry, the part numbers match for the intake and carb on the 7.4PT engine and the 454Mag, not the heads. Sorry for the confusion. According to Mercury they put the Mag intake, carb and a different cam in the 7.4PT to make 365hp as opposed to the normal 330hp. The 7.4PT was used for Bravo 3 applications. It needed some more torque to spin the B3.

Q-Jets are great but they are high maintenance. Go weber.

Just got the rebuild kit for the weber.

i'm still a little confused , are your heads small oval intake ports? , and is the intake you got rectangle? or small oval? or large oval?
just trying to save you a lot of work for negative results if the intake ports dont match up to the heads on your motor

My engine was orginally a 7.4LX MPI, with a rect. port intake and peanut port (small oval) heads. I am replacing the MPI set up (its messed up) with a intake from a 454Mag (also rect. port) going back on my peanut port heads. I know the ports dont match up, but thats the way that Merc built it, so I know it works. The parts off of the 7.4PT are also rect. port intake on peanut port heads, again, thats the way Merc built it, so I know it works.