randymbtech

Hey guys,

I am re-building my Merc 330 horse 454 this winter. The motor ran fine, but it used oil and leaked oil, so I pulled it and tore it down. I am not looking for 500 horse, just a little more than stock. The motor is going in my 24 foot Four Winns Liberator. The motor has the 904 casting oval port heads, and they recieved a full valve job and new stronger valve springs. I am also using an Edelbrock Performer intake manifold.

My question is, what cam can I use to give a bit more power than the stock 330 grind? I need to keep the low end power to get this barge on plane, so that is an issue. I just feel that I can gain a decent amount of performance with the cam and intake manifold upgrade. Thanks for any help or advice!

Randy

rexcramer1

I used to have a 251 Liberator. It is still my wife's favorite of the boats we have had.

I would get a cam with specs close to those on the 454 Magnum cam. You should be able to find them with a search on this site, I do not remember them off the top of my head. I had a 454 King Cobra (same as 454 Mag) and with a Performer intake, roller rockers and a K/N filter was able to pick up 6mph from stock to get to 58mph. I went to a bigger cam after that looking for 60 and the boat lost 4mph, so the key is not to go too big.

Get some forged pistons, 9:1 compression, roller rockers, and the Magnum cam should get you a good 30-40 hp. Later you can add a good exhaust for some more ponies. You dont need a new carb, you just may need to add a little more fuel with the additional airflow

jeffswav

If you are keeping your stock exhaust the cam options are limited. A roller setup is more expensive but well worth the money. Do not go with anything bigger than the 454/502 Mag cam, or you may get reversion. If you are adding power you will need a bigger oil cooller, the one you have is beer can size and way to small. If you want to get the most out of what you have call Bob RMbuilder and he will set you up will the correct Roller Cam for your boat.

randymbtech

Thanks guys. I will look into the 454 Mag cam!

randymbtech

Hey guys, the Magnum cam is no longer available from anywhere...Mercruiser discontinued it, and so did GM Performance. I even called Scoggin Dickey Chevy, and he said he can't locate one.

I spent a half hour on the phone with Comp Cams today, the tech recomended the XM262H grind, which is 218/224 and 505/515 lift with a 112 lsa. Any thoughts on this cam in my application? I am using stock Merc 4" risers for now, just don't have the cash for big exhaust right now.

rexcramer1

That cam would be ok I think, but the Magnum cam was 224/224 with .500 lift, probably about the same hp as the one you are looking at. Less lift is better for valvetrain life. 112 LSA is right on the lower limit for reversion, 114 would be better

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randymbtech

I thought that the 112 lsa was cuttin it close too, but the tech at Comp Cams said reversion will not be an issue with that cam. I hope he's right!

My exhaust set-up is a bit funky because the 241 Liberator has the exhaust outlets on each side of the boat just above the waterline. So I am going to have to use 90 degree turn downs right after the Merc 4" riser, then it will continue down, and then turn out to the side of the boat, to meet up to the tip. It's hard to explain, you would have to see it.

rexcramer1

Are your mufflers removed?

I knew a guy with a 211 Lib with the side exhaust, it is a PIA. My 251 had the mufflers removed and the exhaust came out at the waterline through the supports for the swim platform. It came out of the exhaust, went 90, went all the way to the gunwhale, then another 90 to the back. It was all made of fiberglass.

If you get reversion though, it will happen in the manifold so the exhaust setup is not as big of a factor as you would think. Hopefully the Comp cams guy is not some dude at a desk who has never messed with a marine engine in his life

jeffswav

Are you doing flat tappet or roller? If you want somthing off the shelf, CP Perf claims to have one that will work with silent choice stock exhaust. Like I said before Bob RMbulder is the cam expert and not much more money.

blue thunder

I personally don't think you will get much of a pop without going with better flowing heads. The 330 cam was matched pretty well to the peanut port heads. More cam won't do much until you break that bottleneck.