handfulz28

Mark IV 454 MAGs, bone stock. As bad as I want an MPI setup, I keep looking at the CP Performance package.
I know cam and headwork would maximize the setup, but would I be wasting my money if all I did was bolt on the package and maybe a set of Rev/Dana/Gil/EMI exhausts?

I know I should just leave well enough alone until they pop, but I just can't
Thanks,
Michael

BY U BOY

50hp At Best

KAAMA

iTrader: (1)

I take it the 454 Mags are the Merc 365hp engines from the late 80's era??? If so, and you DON'T want to upgrade the heads or cams then, I don't know if the HP500 intake/carb set-up alone is going to help you much---even with the aftermarket exhaust systems such as you have listed in the bottom of your post.

I really think you'd be better off by just adding an aftermarket exhaust system to your stock 454/365hp Mags until you at least decide to bowl/pocket port the heads and add a better cam for the application. My opinion, but I think you'd also be better off retaining the stock GM dual plane intake manifolds you have on your engines now. The HP500 intake manifold is a single plane intake and it may act a little too sluggish and soggy in the midrange for a 454 with big GM rectangle port heads like those 454 Mags have. It's all in the combination and it all depends on how heavy the boat is and where you do most of your cruising RPM's at---all these things should be factored in on how you set the engine combination up.

If you at least add an aftermarket exhaust system you may feel a little more KICK in the mid range and maybe some RPM increase. Once these are in place, THEN anything you do to the engine such as a head/cam mods/upgrades will respond much better because of the better breathing exhaust compared to the stock Merc exhaust. Also, if you ever tear the engines down then you can also do a bore notch job on the blocks which is good for about 20-30hp on a 454. Anyway, you can try the HP500 intake/carb set-up on your engines....I just don't think you'll be happy as you may think you might be.

There are probably some guys or builders on here with 454 Mags who can chime in...those who have tried doing what you are wanting to do and can share their experience on what happened. Have fun with your project.

BUIZILLA

Kaama stated it perfectly...

JH

handfulz28

Thanks KAAMA, I needed to hear that from you guys with LOTS more experience than myself. I really had no idea what to expect from just the intake/carb; that's why I ask you guys
They'll definitely be rebuilt/replaced (1105hrs so far), but I was looking for something to blow my cash on in addition to the exhaust. I guess I'll just stick with the exhaust and maybe roller rockers that could be re-used in whatever I repower with.
Thanks,
Michael

RaggedEdge

Did the HP 500 intakes with Barry Grant 750 Holleys, and CMI E'tops on a twin 454/365 set up in a 32 Velocity some years ago. The gain was only 2-3 mph. The intakes are a little big for the 454's and worked best with a 1" four hole spacer under the carb.

PatriYacht

Use the cam kit from the 454-420hp in addition to the carb, intake, exhaust and you will have a strong running 454 for only a little more money. It's a hydraulic flat tappet with longer duration and more lift than the Magnum cam. You can get it cheap from Crane. It would be a good idea to get roller rockers in addition however. This setup will make around 450 hp.

KAAMA

iTrader: (1)

Yes, along with the exhaust, some roller rocker arms would be a very good/wise upgrade to your engines.

BY U BOY

SO YOU GAINED ABOUT 30HP PER SIDE? HOW MUCH ARE THE E'TOPS GOOD FOR?

Griff

If they've got 1105hrs Just do the exhaust and leave everything else alone till you do full rebuilds.