Intolerant1

I'm also knocking around the cost of upgrading my 454 VS. buying a 502 crate motor and selling my stock motor. The 502 is looking better all the time.

blown1500

Jayl13,
Which heads did you try? Merlin oval ports have worked for me on less than 500cid. Did not agree with your cam choice, though. Need more INFO
Intolerant1, the easy way out is to buy a 502 crate. Be warned
you need to blueprint the motor. GM does not do a very good job like Mercruiser does. The cam needs to be changed, too.

blue thunder

Well here is what I am doing to my 2 454s. I'll call them 330s, but really they are remanned engines with a garanteed min of 330. Original engines were 365hp mags, so all bolt on are too.

Using the Qjets off the 365s
Rpm performer 6055 edelbrock heads (rect)
Cast pistons
Cast crank
Comp cam 224/234@ .050 and 547/564 lift
Bore notched per Kaama
Dual Plane intakes off 502s (merc)
Stock center rise exhaust (4")
Stock Tbolt IV ignition
Thru hull exhaust

That's it. Hoping for the best. Ran these engines last year fairly hard, so I feel good about the rotating assemblies. Only spun to 4700 though. Was planning to prop to 5100rpm, but may chicken out and go to 48-4900, depending on performance.

BT

Dennis Moore

Stay with the stock carb and ignition system, unless your really going to crank up the rpm the stock carb is the best. Those heads aren't bad but an intake manifold, camshaft and exhaust are neccesary.
Dennis Moore

convincor

which is better, oval port or rectangular????

KAAMA

convincor,

The Merlin Oval port heads with larger valves (even with out any bowl porting) would work MUCH better compared to the "peanut port" heads or even the stock GM rectangle port heads by far on a 454 or even a 502. If you do get the Merlin oval port heads I would at least do some clean-up porting on the bowl/pocket areas and this will make it run even better. Of course this all depends on how much $$$ you are willing to spend.

dyno

I'm running two sets of Merlin Oval port heads on my motors one was pocket ported and one is stock they run the same in the boat...not any differance in cruising speed at all,at wot no differance either. One thing needs to be said the guy that ported the heads is not a head guy!!!If someone good did the work (jimV) I think there would be a noticable change. my motors are pretty consevative If I ran a bigger cam or over 5200 Rpm there may be some change also. my .02

blown1500

Convincor,
The oval port heads are best if they meet your needs. You need to size your heads to the airflow requirements of your engine with just barely enough being the best, usually. The smallest port with enough air flow has always worked best for me. Port volume, oval or rectangular, does not necessarily determin the flow, it is how good that port works. I can get you a reading list if you want. You can make your own choice or I'll be glad to help
Dyno, I have runengines with more power in one than the other, doing experiments or just replacing one engine. You don't usually see the difference between the two in the boat unless the difference is big. The better engine helps the weaker and the weaker drags the better down, giving sort of an average for performance. The Merlin heads are one of my favorites. Some PROPERLY DONE minor bowl work and port match really help!!!

Poorly done head work can kill any head

Jayl13

Okay I got some cast iron cheapie large oval heads from my engine dick head,
they did NOTHING over the peanut heads
if you want to do it right, do it right, get the rectangle or square port as some people like to call them.
dont go messing around with the ovals, if your buying new, then why bother with ovals when it is an intermediate step
go for the big guns
cant hurt it by putting on heads that are TOO big , plus there is no such thing as too big
that is my O2 coming from someone that took 2 stock 330s'
Put new oval heads on, bumped up compression to 9.5:1, new pistons, new performer dual plane intake, punched .030 over and with the rochester carb on dyno made 331 HP
trust me DONT mess wiht the oval heads unless they are spec'ed out and huge from merlin or dart or edelbrock ect.
but if your going to spend the money on those heads, just spend like extra few bucks and get monster rectangles.
intake wont cost you any more or less depending on ports, so dont worry there
and trash the rochesters, not worth a ****

But I did note one thing
you said your origional engines were 365's
Note here, 365 mags had the following parts
Forged crank
Rectangle heads
forged pistons
and mags could spin upwards to 5700
Make sure you know exactally what it is you have and inventory all your parts.

My cam choice was not the best one out there I would not think but to be honest with you my retard engine builder never asked me spit about how I wnated it to run, how much power I wanted, what RPM range I was in mostly
he left me to sort of stick my dick into the wind and see what stuck to it.
A-hole
anyway, like I said before it is HARD to make power on a NA motor that in essence is small cubes. (454/330 is the runt of the litter in marine engine choices-anyone disagree?)
Talk to a reputable engine builder, tell him about how much power you want out of it and what your budget allows and see what he can do for you, sometimes they have alot of crap up their sleeve, go for it.
good luck

Jason

blue thunder

Jay13... I was the one with the 365 mags originally, not convincor. Neither of those short blocks are in the boat now. I am using monster rect alum edelbrock heads. Have had both those and the small ovals on the same engines. Boat ran significantly better with the edelbrocks Point is, I agree with you to a point. The draw back to too large a port is throttle response and low rpm torque. Boats like torque and rectangles like high rpm and hp. Thats why they say rect suck for boats. My set up is not optimal thats for sure. But I would venture to say that a properly set up 330hp with good hp making oval port heads would out run me and my rectangles to 5000rpm. Rect are my best play, so I am playing that and will see. PS.. I still think you may have wiped a lobe. Your engines should make more hp than 380 or so.

BT