guys i just wanted to say that i really like your forum and there is a lot of excellent resources and information here. congrats! its not easy having a good offshore boat website.

it may be a little off topic for this forum, but i recently bought my first 1998 baja outlaw 25, with a 330hp 454, trim tabs, inverters, and corsa quick and quiets. 109 total running hours.

i have been building big blocks and drag racing for years, but i dont know what it takes to build a good boat motor.

i am after good, cost effective, reliable performance. i would prefer a naturally aspirated engine, due to expenses.

1. what is the GM engine code designation for this 330hp 454? (i.e. L36, L78, etc)

2. can the computer and efi setup be easuly removed in favor of a carburetor? also does the computer run the gauges? what would removal of this system entail?

3. oval port or rectangle port heads?

4. hydraulic roller or solid roller camshaft?

5. what rpm range should i design the motor to run?

6. do aluminum casting aftermarket headers flow as well as cmi pipes? also is there another maker that makes double wall headers that are ALMOST as good as cmis?

7. will CMI pipes work with my existing corsa exhaust? what will i have to change?

8. are there any extremely common mistakes that car engine builders make when building a marine motor?

9. truck or car deck height?

10. aluminum or iron heads? in the auto world aluminum is desired becuase of the way it comabts heat. is this necessary is the marine world?

11. where can i find information on intake runner size, cam profile, etc on this engine?

above all i want a BAAAD sounding boat. can a cam/valvetrain/header combination accomplish this, or will i kill the performance of a torque monster motor?

1. there isn't one its a merc motor

2. yes you will have to add an ignition box like an msd as the pudr controls it on the efi, uses a different wireing harness, add intake manifold, marine carb, flame arrestor, larger oil cooler (if you are going to make more power), change the thermostat to 143 (efi uses 160) . No the computer doesn't run the guages

3. Small peanut port heads is what is on the 330, most use rec port when going to aftermkt on 502's but something like the merlin ovals would work well on 454's

4. Hydraulic Roller

5. Keep it under 5000 rpm if you use the original cast crank, there are several threads to hop up 330's do a search here in the tech section

6. Aluminium cast aftemarket manifolds are pretty much as good on milder engines, the CMI's will show them up when you start making bigger hp

7. ask CMI

8. to wild a cam with to much overlap, to tight piston clearance, not using brass freeze plugs, they don't use all marine components like carbs / startermotors / alternators / distributers which are explosion proofed. They forget a marine engine will be running under full load all day long not for 12 seconds

9. the 330 is a short deck 9.8"

10. Iron if you run in salt, Al maybe if anodized and only run in fresh

11. what you have:

GM 236 iron heads 2.06/1.72 valves
120cc chambers
208 cc intake ports
CR 8:1
Cam 206/211 on 114 .48/.483



The heads are the weakest link you need new ones like merlin ovals altho some on here have also had good success porting and putting bigger valves (2.19/1.88) in the peanut port heads. Not sure you will save much $ tho.

8:1 is pretty low so going to a 110cc head like Edelbrok marine oval ports would get you up to 8.7:1 and might be the way to go, they are anodized Aluminium, iconel exhaust valves and a pretty good price but fresh water only.


If you keep the cam lift under .56 you can keep the stock roller lifters anything over .51 lift with the stock pistons and you need to check the valve/piston clearance to. If you keep the duration to the 220/230 range you will still have lotsa low end torque the merc 454 mag for eg is 224/224 on 114 .483/.483 and makes about 385hp but you can probably get 410-20 hp before you have so much cam you start ending up with less low end torque than you have now

next time i'm in lake huron im gonna buy you a drink! thank you so much. information is king!

Dennis Moore has a book out called Big Block Chevy Marine Preformance . It is written for Marine applications.

Dennis seems to be a bit conservative but he covers all the stuff you want to know except EFI in detail. I think that book is worth 10 times it's price. --- Jer

ok, did some checking, turns out i was right and wrong at the same time. if it is an MPI motor, does that make it the L29 vortec? i'd like it if someone told me if there is another way to tell what i've got by the look of the outside of the motor. i pulled a plug to check WOT mixture out on the water, wouldn't you know i didnt check to see if it was a vortec-reach plug?! i'd like to not have to screw with pulling a valve cover if someone can help me.

the intake manifold is reminiscent of an ls1 intake, only this one is metal instead of composite. the throttle body comes off the intake at the starboard side of the motor.

Car guys usually set the ring end gap too tight.
Car guys usually choose too large of a cam.

woo hoo! checked a plug tonight, .700" reach! thank god i can put a carb on this beeyatch and get some real horses and quit sooting the transom. i'm going to put a 750 sea demon on it, leave the stock distributor for now,

what oval port intake has nice clean ports that line up with the vortec heads? i can't really find any info on one to fit.

also, if i were to change to a carb and intake setup, msd marine ignition, roller rockers and a nice set of either cmi or gil exhaust manifolds, how much power can i net?

i've heard of people getting 70-75hp from swapping off the stock mpi setup.