how can you tell the diffrence?
 

Between a regular 454 and a 454 mag, i have the black cap that goes over the carb, but it dosnt have any thing on its just plain black, the previous owner really didnt know just knew it was a 454

there any like special serial numbers or ways to tell with out having it dynoed

thanks for the info

Pull the valve covers and check the head casting numbers.

Look at the intake runners , mag will be squared off and you cant see much of the head where the intake bolts up , non-mag has peanut port heads and you can see alot of the intake face side of the head , just for grins , look for the red sticker on the starboard (driver side) valve cover , if it says its 330hp its non-mag , 365/385 and its a magnum

Thats not true, I have a 330 and it was a 4 bolt main.



Just above the starter there should be a plate with the serial number on it.
Post that # and im sure someone can look it up for you.

Agreed, I have a '96 7.4L and based on the block casting number, 10237297, it's a 4 bolt main. The biggest difference between the 7.4L (454) and the Mag is forged crank (and rods, I think), large port heads (rectangular GM vs. small port oval GM, both are cast iron) and tall intake.

Don't forget cast vs forged pistons...which are the weakest link in the 7.4.

thanks for the replys guys ill have to check it all out, i dont store the boat at my house anymore so ill have to check it next time i see it.

I'm pretty sure the Merc 330hp/454cid originally was designed with a 2-bolt main block with all cast parts. It was in the late 1980's or so that the 330 came with a 4-bolt block vs a 2-bolt, but still had cast parts.