Chris Sunkin

Do you really want to trade valvetrain reliability for 35 HP? Solid roller cams have very aggressive ramp profiles that are very hard on pushrods, rockers & springs. If you're not diligent, you'll end up with valves through your pistons. On flat tappets- you might get the peak horsepower out of the motor but unless you run flat out all the time, your motor is probably missing out on a big, fat torque curve. You can get 800 HP out of a 454, but it won't pull your boat up on plane.

In addition, it doesn't really matter what the motor dynos at- if you're using dyno headers. Mercruiser manifolds on a 600 horse motor makes it a 450 horse motor. The only thing that's going to be the equivalent of dyno headers is CMI Tractor headers. Everything else will rob HP.

The best thing you can do is have a long conversation with someone who specializes in cam/top ends for marine engines. I'd suggest RMBUILDER (Bob Madara). He can zero you in on exactly what is going to do what for you and grind the exact cam for the application. And it won't cost anymore than ordering it from Summit.

RJBBC

Thank you for the responses. The exhaust on the boat is Stainless Marine. I hope to keep the exhaust and spend that money elsewhere on the motor if the exhaust can handle the added power without strangling the motor. I am leaning towards a larger displacement NA motor such as a 540. I worry about the drive with my power goal. Maybe a 502 with less torque and 550HP would be better for this application. I am also interested to find out what happened to the compression in the bad cylinders. That would be a large concern if a batch of bad gas can toast a motor! Spend 15K and next year have the same thing happen, bad for marriage.

Chris Sunkin

What tails on the SM's? The short one's won't work with much cam.

On your drives, it would be a good idea to redirect some of your budget to updates & freshening. The bravo likes RPM less than it does torque.

Vinny P

Hye Rob,

Wow that sucks to hear. Things seem to have been going well with the new upgrades. I agree with everyone else, 600 hp from a 454 will be a bit hard to get. Then the drive issues come in to play. Personally, I am not a fan of fuel injection on modified engines unless you can tune them yourself and be well experienced at it. A carb is alot easier. If you do decided to go with a carb engine, one thing nobody has mentioned... You will need to upgrade your entire fuel system. Expect to start at the tank, run all #10 lines, a good electric and mechanical pump, a return regulator, etc, etc. As you know, I did all this on my boat, same exact set up you will need. I can offer you my suggestions if you want.

6 and 8 cylinders low... as was said, pull the head and take a close look. It will be the only way to know for sure. What head gaskets did he use when the upgrade was done?

onesickpantera

iTrader: (1)

A 502 with 550hp would probably be a good bump over what you had and a little easier on your drive.

Smitty(articfriends) knows his stuff when it comes to both engines and drives.

Knot 4 Me

Occasional WOT run?!

Do a leakdown test. My guess is your problem is in the heads. Was the A/F ratio ever dialed in with the boat in the motor? Who knows how lean it was running until you added the high pressure fuel pump and regulator.

Sorry to hear about the motor. Saw your boat sitting in the grass last Thursday when I got my boat off the lift for a river run.

Hey, just thought of one more thing to check. Make sure your hatch ram did not finally wear a hole into the top of your intake. Last time I was on your boat that ram had a pretty good divot out of your upper plenum. Not sure if a hole there would be the cause of your problem but it won't hurt to check to make sure there isn't a hole there now.

RJBBC

Good points Beadman. After reviewing the finances I think I am probably going to modify what I have. I am hearing a good set of aluminum heads, 10 to 1 compression and a stout roller cam should get the little engine that thought he could to 550HP and 600lbs of torque on 93 octane. That should keep the Bravo 1 from exploding for a couple hundred hours, I think. I am selling the fuel injection system and going to a basic carb setup. Am I crazy or just stupid?

jayhawk261

I am finding out first hand that the Mag MPI intake on these really can't make power. We went through mine last fall using Tyler Crockett's cam and valve train, .030 over, 9.5:1, RHS Aluminum heads, and we made 501hp on the dyno. The power flattened out at 5200 rpm and that was all the intake could do. I am most likely going to switch to a single plane intake efi system like the Edelbrock Victor Jr setup that uses a 1000 cfm throttle body and port injectors. I'm also thinking about building a new 555 CI short block to go with it if I can sneak it under the wife's radar!

Short answer is the stock intake pretty much sucks. A nice single plane with a carb would be better for making power hands down.

Rookie

iTrader: (4)

Let me make this clear, I do not suggest that RJBBC build a solid roller HYPO 454, I was using my build as an example to show him a hot setup and still NOT achieve 600HP

Are you saying that a reliable marine engine can't be built with solid roller lifters? You speak as if the engine will self destruct in 10 hours. It takes a little extra preventative maintenance and to be in tune with your engine. I have seen 100 hours on a solid roller marine engine that had never had a valve cover removed to relash the valves.(eventually the lash was to great and hurt the engine, LACK of maintenance)

I also personally had my merc 425's (hydraulic flat tappet) break rocker studs every other weekend (5 exhaust 2 intake) and grenade 3 lifters on me. (no maintenance needed on on hyd. flat tappet)

Sorry I feel this was directed at me, are you saying that with my near 600HP I will have troubles getting my boat on plane?? I have a boat load (no pun intended) more torque than I ever had with my 425's but now I won't get on plane? I chose to build a little higher revving motor with less bottom end torque so I can run a little smaller prop and save a little wear and tear on my drives.

Did anyone mention Mercruiser manifolds? He stated in his first post that he had upgraded his exhaust.



That is the best info he can get, talk to experts in the field that answers these question daily. That is why I threw out JimV's name. I'm sure RJBBC only wants to build this engine once.


1. Decide on Cubic inches. If you stroke to a 496 now you could use the same crank and rods for a 540 when you get bored with the 600HP and want to get closer to 700HP. (experts correct me if I'm wrong, same GEN block just 502?)

2. Heads for the build. Call the experts, I and others have used JimV with good results and he could probably tell what heads that would work good on a 454 build and later on a 496 or a 540. (probably Dart Pro1's 310cc then later port them out for larger CI)

3. Once 1 and 2 are decided call Bob RMbuilder, he has helped countless people on this site. I have never used him, but only hear good things. (but know what your overall goals of the build are,).

4. Fuel delivery I missed the MPI thing earlier, sorry. I know absolutely nothing about MPI. go carb

5. Exhaust, I'm kinda partial to the SM also.

6. 496, Dart Pro1's ported, 10.5:1, Manley 2.30" intakes, Ferrea 1.89 Exhaust, SRP pistons, Crane 741 or custom cam, comp springs, Merlin single intake and an 850 Holley. Should get you close to 575-600hp

I can only give you info on the engines I built for my own application, and I would not suggest a build like mine for the faint of heart. These engines exist and are running in my boat.

Sorry for a long winded post.
Good luck, keep us posted on what you build!

Chris Sunkin

[QUOTE=Rookie;2650997] [Are you saying that a reliable marine engine can't be built with solid roller lifters? )

I said exactly what I meant- solid roller profiles have a more aggressive ramp profile and they're harder on valvetrain componentry. Simple physics. The faster and the farther you make something move, the more force required. Weight (mass) definitely comes into play here.



Sorry I feel this was directed at me, are you saying that with my near 600HP I will have troubles getting my boat on plane??.

Again, I said what I said. I used an example of a high RPM , high horsepower motor and how it wouldn't be particularly useful in an offshore boat. Peak horsepower at the sacrifice of a broad powerband has many unpleasant tradeoffs- nothing to do with you or your setup.



Did anyone mention Mercruiser manifolds? He stated in his first post that he had upgraded his exhaust.


Again, making a point that peak horsepower and dyno sheets mean little when bolyed into the boat. Dyno'ing a motor without the exhaust you'll be using in the boat is less than useful. As I mentioned, his exhaust is one of the better one's, but his engines won't make the same power as they do with dyno headers.

People make many mistakes on engine builds and upgrades. The biggest one is not being in close consult with someone who has done it many times with the type of boats we deal with here. I know several exceptionally accomplished racing engine builders- and not one of them has a grasp of how to make a boat go fast- because they've never done it. Boats are too different from race cars for those experiences to transfer.