DD13

I have a set of ported 781 heads that I would like to install on my stock 1989 Mercruiser 454 330hp engine. I currently have the stock through hull Mercruiser exhaust that exits under my swim step but I am planning on upgrading to the Dana Marine exhaust this year. Along with adding the 781 heads I will upgrade the intake to match the larger ports. I also want to keep the stock Quadrajet carburetor but rejet it accordingly after adding the intake, heads and cam. My question is what camshaft and lifters should I run for the best reliability and overall performance to take advantage of the better flowing heads? I have no preference when it comes to flat tappet or roller cams.

GPM

The hydraulic roller should make more power and last longer, the hydraulic flat tappet would be about 1/3 of the cost. Cam, lifters, valve springs, maybe rockers and pushrods. Probably knowing the size and weight of the boat and how you're going to use it would help with some suggestions.

DD13

The boat is a 1989 open bow 21ft eliminator with a bravo 1 outdrive that has an advertised weight of 2350lbs. The specific performance change I am looking for is to increase cruising and top speed without sacrificing bottom end power. Furthermore, I was thinking about reusing the stock rockers as long as they look good unless there is a good reason to change them. I will change the pushrods and valve springs to match the camshaft, which means I would need those also.

getrdunn

iTrader: (7)

Can you post a pic of what Dana exhaust your thinking about. Your going to be limited on camshaft due to reversion. But can still make some gains. Personally I would figure out exactly what exhaust your thinking about. On anything 430 plus hp your not going to see much gain if any with exhaust swap all depending on where the water dumps. I did a bunch of testing years ago so I’m just speaking from my own experience. With a 454/365 mag engine a decent cam would be the 420 hp cam I Went from 69 to 73 mph with that change only. Stock exhaust and carb Tried a set of Gil’s and were throatier and little more mid range but nothing on top end.

Depending on what gen your 330 is you’ll likely be forced to purchase roller rockers and arp rocker studs. If I recall anyway those rockers on the 330’s weren’t adjustable.

If your going to do it right do it once and be done. An eddy air gap and the 420. There’s endless cams but that is a decent cam with I’m pretty certain on a 114 lsa. Just look it up to be sure. With that combo you can get away with the QJ with out changing the needle height.

I wouldn’t do anything to crazy as those are cast pistons.

420 specs
420 Flat Tappet Hydraulic

298*/306/ @ .005"
228*/236* @ .050"
.312"/.324" Lobe Lift
.530"/.551" Lift Valve
114* +5*

A roller cam would be ideal due the lack of zinc etc in oil now adays however if it’s not in the budget just be sure and do recommend break in and be sure and get best zinc additive you can find. Do some research on that. You don’t wanna go through the expense and work and wipe out some lobes. Also when changing cams always be sure and check PTV clearance. No need to go anymore lift as those heads are pretty much done flowing at .550 lift non ported.

phragle

iTrader: (3)

What gen motor?? that will make a difference. i.e: if its a gen 6 your ahead in the lifter game seeing as you wont be running all that much cam. Also the whether it is a mark IV or a gen 5 or 6 will make a difference on your cam selection and timing chain set. If your not sure what you have, post a pick of the timing cover.

DD13

Thank you for the response, the exhaust manifolds I was looking at were the Dana Marine Flow Torque with the short risers. I would post a link or picture but I'm not allowed to until I have 10 post.


Keep in mind I would prefer for the cam to be compatible with the stock exhaust for now. Also at the end of your post you say the heads are done flowing at .550 lift non ported, what heads are you referring to? The reason for me wanting to switch the cam is to take advantage of the ported 781 large oval port heads I have to bolt on to my stock 330hp 454. I am going to look more into the 420hp cam you discussed in your post, that sounds like what I'm looking for. If I go with the 420hp cam should I use oem Mercruiser lifters? It looks like the original lifters for my engine have the Mercruiser part number 72638.

GPM

I don't know how much you're really going to gain, I believe they are flat top pistons, not much for compression. The rockers are stamped steel crap, probably work fine, I was just listing parts that should be changed for longevity. I think you'll need a fast ramp hydraulic roller to keep your bottom end and add top end, but that's just my opinion.

DD13

Mark IV

getrdunn

iTrader: (7)

There is so many possibilities however your kinda limited due to reversion. I'm basically doing the same builds now other than I'm using semi ported 049 heads and 4.25 stoke. Both GM heads like about 10/12 split on duration btwn the int and exh. The exhaust ports suffers on GM heads but a little self porting on both int and exh ports (some chamber work) helps and will make awesom torque either way. Many will open up both to 219/225-188 valves however I'm leaving as is other than new valves and hardened seats with forged pistons. Not sure what yours are. I can get away with a less lsa due to dry to the tip exh pipes. Not that it's ideal but less lsa is ideal in the marine world but just got cams from clay smith cams that are tailored to old school GM heads. Thought through right you should easily pick up a 100 hp plus while staying under 5,500. Its all about your goal and budget. How many hours on short block.

DD13

There is no hour meter on the boat so I don't know the hours on the motor.