powerguy

Is there any reason not to change out a cam with the motor still in the boat if there is space in front of the motor to remove and replace it? Seems to be a lot less work involved if it can be done this way because most of the accessories can stay on the motor and the motor and drive do not need to be re-aligned. Thinking of changing stock 454 mag cams to hp425/hp450 specs, porting heads, new intake anc holley carb, new rocker arm studs with roller rockers and aftermarket exhaust.

KAAMA

iTrader: (1)

How many hours currently on the engines as they are now?

powerguy

280 hours - 1993 454 Mag's Gen V

KAAMA

iTrader: (1)

What horsepower were those rated at?---365?

powerguy

365's

KAAMA

iTrader: (1)

Sounds like the hours aren't too many without having to totally rebuild the engines just yet, but to answer your question, "yes" we have done mods like this several times. Just make sure you have enough room to get the cams out of your blocks, etc. I have seen some guys cut a hole out of the firewall with a hole saw to do this. Just be careful when doing all this stuff.

Also, when porting those GM heads just do some minor bowl/pocket work----especially on the short side radius's. This is especially true of the exhaust ports of GM heads as they are very crude. I would also especially install a dualplane intake manifold with the rectangle port heads as they are too large for a 454cid engine. I know that may not be what you want to hear, but it will give you better torque, single to the carb, and throttle repsonse. A good 750cfm Holley carb would be adaquate. Aftermarket exhausts will help enhance all the power mods that you are adding.

Are you replacing the cam with a hydraulic roller or flat tappet? What aftermarket exhaust system are going with?

powerguy

KAAMA - Not sure yet if going flat or roller cam...depends on price vs. benefit....going with gil exhaust with ss risers.... thinking edelbrock rpm airgap intake....Merc used holley 800's on the 425 and 450. Why would you suggest a holley 750?

I will put 50+/- hours per year on the boat so these upgrades should last me 4+ years before I will need to look at the bottom end of the motors.

KAAMA

iTrader: (1)

An 800 Holley will be fine---I just wouldn't go any more than an 800cfm for sure. I think the Air-Gap intake is a wise, and excellent choice for your application. The GIL's will help your engines breath much better, just make sure you do NOT over cam the engines and make sure you check piston to valve clearences. You can do it either way, but I also agree with Formulaz583 that pulling the engines would be much easier to inspect all the stuff on your engines and can get at stuff much better. Leaving the engines in your boat while adding mods is probably the last route I would take and only if really have no other recourse. I think pulling your engines to do the mods would be a good experience as well.

GLH

PG,
Just get a Cig...

squick

Powerguy,
I'm having something similar done right now. 454 EFI motor that's getting a bit of a face lift. Same vortec heads with a fair amount of machine work. New inconel valves, springs, blah blah blah. Comp roller cam, Edelbrock Air Gap, and a Barry Grant Sea Demon 750 on top. Went with the Revolution Marine manifolds as the budget was running thin towards the end of the project. She should be back in the water in a couple of weeks for a trial run and to figure out what to do with the prop. If you drop me an email, I'll let you know what kind of results I get out of it, since it seems like you're doing something very similar. [email protected]