cam, carb, intake
 

Would it be worth it to change cam, carb and intake on a otherwise stock 330hp merc??
Was thinking about an "air gap intake", "barry grant" sea demon carb and not sure what would be a good cam.
Will be running "stainless marine" manifolds.

The boats a 25' checkmate, bravo drive with a 23p mirage plus.
Last year it ran about 60 on speedo at 42-4300 rpm. It also had corsa silencers which have now been changed to strait thru tips.
What should I expect with these changes???
What size carb??

Sure. You'll need a longer duration camshaft but stick with lower lift figures than what you'd use with rectangle port heads.

A cam around [email protected] and .535 lift with 112-114 degree lobe center.

If you plan to take the heads off, have the valves unshrouded and some bowl work done.

Don't go nuts with anything else - it is a cast crank, cast piston, peanut port 454...

I'd guess you'll see 40-50 horsepower (you'll need to prop for 4900 rpm).

heads
 

what would you say to edelbrock performer rpm heads??
They make them for marine with 2.25 intake, 1.88 exhaust valves.
For a aluminium head, there very resonable. Would this be to much for my bottom end??

If those are the 110 cc combustion chamber, oval port heads, they would give the motor a considerable kick in the pants with the right cam. If the lower end is solid and true, it might be OK. Lots of ifs. Id at least put new bearings and ARP rod bolts in it and check everything closely.

Don't turn that motor over 5000 rpm.
Crank and rods will be much happier.

Don't run that motor into detonation - the cast pistons can't take the shock loading.

Don't expect more than 400 hp out of that motor or you'll be tempting breakage.

How much do you want to do to it? Are you planning on opening up the bottom end (bearings and rod bolts) or are you looking for bolt-ons (top end pieces)?

Heads will wake it up. Will put it around 400 hp with the cam mentioned. Your money, not mine.

I pretty much agree with mcollinstn. If you are not going to do anything with the heads, you are pretty much wasting time and money. Almost any aftermarket head is major improvement over the stocker. If aluminum is over your budget, try Merlin oval port. That might be my first choice. If you stay out of detonation and don't turn it more than 5,000, the rod bolts will not break and the postons will live. The lower the rpm, though, the better it will like it. Almost any detonation will explode the motor.

bolt ons
 

want to do bolt on parts this year. reason for thinking about heads. want to do 502 bottom end next winter. can't do it all now.
what size carb ???

aftermarket heads will benefit from higher lift cam than your peanut heads. If you plan to go 502, this will require more cam as well... SO - do you start adding your "502" cam now or do you run a cast crank 454 cam now?

Whatcha wantin to do? The 502 cam will soften your bottom end up a bit. Will still be pulling WAY past 5000 rpm (which you must not exceed)...

Let us know what you really want and then we make a "menu" and calendar.

750 cfm for the 454 described above.
How you flavor the "future" 502 will affect the carb choice for it, though (800 for a 425 hp 502, 850 for a 500 hp 502).

my advice (done this two times)
dont worry about HP numbers
Go for TORQUE increases
HP does not mean piss
Torque does
these engines were built for TORQUE not for HP
just keep that in the back of your mind while rebuilding
Also I went with stock oval heads on mine, worthless
either go rectangle or dont bother with heads
did not do ****
I went from stock 330
to the following
large oval heads
RPM performer intake, holley 800
Comp Cams 224 230 515 521 110 LSA
Hypereutectic pistons and increased compression to 9.5:1
Best dyno so far with 10 degrees of idle advance is 388 HP at 5200 but the torque numbers were in the 500's
which means you have enough torque to turn some major props
was I pleased with my rebuild?
NO
My combo worked for ****
I hope you have a better time picking a combo that works better than mine
As I figure it, I wasted about 10 grand in this rebuild of my pair
Hope you do better
Jason

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.

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.

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 :cool:

Sounds good!
 

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

heads
 

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

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.

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

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:D :D
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!!!
:D :D
Poorly done head work can kill any head:mad: :hothead: :eureka:

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

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 :cool:

Hello, Jayl13,
Blue Thunder, in my opinoin, has the right idea. Too big a port will kill power. I know i'm an idiot, but talk to the cylinder head guys at ANY well known manufacturer or head shop. On 454-496 engines, a properly done set up with the OVAL Merlins. You probably have SOME problem with your oval port set up. Flat tappet hydraulic engines set up like this with 454 inches should make 425++. Big port heads would lower the torque curve at least and not make any more top. Talk to a good engine builder and post, please!

I took my 1998 7.4 (310) hp motor apart and had the following. peanut port heads, roller cam and lifters, cast intake, stock exh. stock carb. 63 mph 22 scarab 23 prop. I swapped in, gm hi-po square port heads, crane "420" merc cam, forget the part # I needed to get new push rods due to the flat tappet cam, and valley pan. dart intake, stainless exh, new ign module without a rev limiter (be careful!!) edelbrock 750 carb and a HUGE gaffrig flame arrestor and royal purple oil. I picked up 11 mph on gps. I ran against the identicle boat with 435 dyno'd hp and were dead even. I figure the engine pulls 400ish hp and I run a 26 4 blade bravo 1. the prop is a little much, but I like the lower rpms. turn 4950 all day long. just be ready to throw away all of your old parts. or go with a roller cam, I didnt know it was a roller until after I bought all the stuff! selling the boat too 23 grand and its yours.
Billy

Loosecannon22,
If you use a different cam, but still hydraulic roller, with Merlin, GM aluminum, Edelbrock, or several others, all oval port, you would have much better bottom end and an even better top end!!!!