HaxbySpeed

Good info. That should be added to the list. With any of the Crane series that are proven to work, or any of the lunati, or anything Comp calls a marine cam, you stand a very good chance of having a strong running reliable engine. If you get the duration in the right ballpark, you will be within 15 or 20hp of any well picked semi custom cam at max. The reason is, there's too many additional design criteria (compromises) in a marine engine to actually run the "optimum camshaft". If you pick a proven shelf cam and miss on the duration a bit, you may have the power curve a little too high, or a little to low. Talking to engine builders beforehand can be helpful. If you pick the wrong custom cam, you can have tuning issues, broken parts, severe reversion, etc. Not saying custom cams, or semi custom cams aren't sometimes the best option, you just want to be confident in your ability to select one, or find someone who has experience with what you're trying to do. Just because a lobe is in the catalog, and was properly designed, does not mean it's safe for marine use. There are lobes in every manufacturers catalog that will destroy your marine valve train in short order. Do your homework when selecting a non shelf cam. Between the production cams that have already been listed, at least one will work well for 98% of the 454 to 555 marine engines that are commonly built, regardless of heads, etc.

Jason3603

This has been an informative thread overall. The situation most of us get into as novice engine builders/customers is, that we go off the opinions of recommended professionals, friends and internet forums without fact or educating ourselves completely. Then get pissed we made a decision before we had all of the information or additional information came to light afterword. I am guilty of this myself, I've made decisions the same way and paying for it. Educating oneself to the point of being able to decipher what is fact and what is opinion is very time consuming and difficult to do, probably impossible. That is why OSO needs these types of threads, where a multitude of professionals, customers and novice engine builders can get together and throw out their different experiences from the varying degrees of lessons learned. My hope is the next time there is cam, engine, head thread we can debate the facts and experiences of all without getting into this battle royal.

The lessons I have learned, there are way to many parts in valvetrain and when there is a failure it is difficult and VERY COSTLY to identify the root cause of the failure. Unfortunately I have had multiple valve failures on separate occasions and as I dug into trying to find out what was the problem, (actually going about it as an 8d) it turned into the blame game. Setup was to blame, then the valves, then the heads, then the springs and so on. What I recommend going forward is ensure all component suppliers agree on the combination of parts. It was really frustration to learn the valve supplier did not agree with what my cam selector had chose for spring pressure.

HaxbySpeed

I have found that the restriction created by marine wet exhaust often negates the benefit of the higher flowing exhaust, and the engine will still respond with a bigger split. Not always the case, but i often see it with manifolds.

MILD THUNDER

And ive seen where you can go wrong by camming an engine off "advertised" flow numbers.

Imo, the there is no substitute for a proven combo. A shop recently did a basic pair of marine 540s with afr 290 heads, and a shelf crane 651 244/256 114 lsa .630 lift cam. I do agree that cam isnt "ideal" for that combo. Then , a 540ci, with the same basic shortblock, but with 325 afr heads with cnc chambers, 241/246 .681 lift 112 lsa custom cam was dynoed.

Two different combos, two different power numbers, and 2 different power bands. The 651 290cc combo did everything better from about 3500rpm to 6000rpm. More torque, more upper rpm power. The 325 combo, made a little more torque below 3500, and fell flat at 5400.

Sometimes us marine guys have parts to work with, and buying a different cc head, to gain which may not make a difference in boat speeds, isnt in the cards. Sometimes the textbook combo, isnt in the cards. But that doesnt mean it cant make power.

Everyone told me a 320cc head would be too big for my 468s with a blower and low boost. Nearly 750ft lbs of torque , 800hp by 6000. When others have went with the textbook 265-305cc , and textbook cam, and made 100ft lbs less and 100hp less. Why? Because there blower and induction combo sucked. Theres many ways to make power, and its not always just the "cam".

StraubTech

Agreed. The thing with marine stuff is real life a lot of these engines spend 80% of the time between 3200 and 5000 rpm. At that rpm and based on piston speed of a 4.250" stroke most aftermarket marine exhaust have enough pipe area to expel the exhaust and what water is in the system. Also lift on the exhaust is no where near as important as on the intake. The peak velocity the exhaust port sees is at low lift. With the exhaust blowing down and loosing velocity lift IMO is no where near as important as duration.

Panther

I don't know anything about these two combos other than what was posted but looking quickly at the duration numbers, it doesn't look right to me for a 540 with 325 AFR's. There's a lot of variables which I don't know anything about, other than two engines with different cam's and heads were dyno'd.

Perhaps the owner didn't want to spin the engine to 6K rpm so the duration numbers were adjusted to compensate? Was is a Bravo boat or Speedmaster? I personally would have wanted the engine to spin 6k rpm if it was a Bravo boat. With the larger heads it needed more duration to make power above 5500 which is where those 325's start to make power.

I just don't know what the owners goals were with either of these builds so I can't say that either combination was right or wrong.

For argument sake, what would be interesting for me to see is how the 651 did with the 325 heads and other cam did with the 290's. Or how either engine would do with similar duration numbers with everything else being similar.

Panther

Some other variables... Was the engine dyno'd with dyno headers or the exhaust that will be used in the boat? Which engine performed better in the boat. Another variable I'd like to have confirmed. The dyno doesn't tell us everything all the time.

MILD THUNDER

Full marine exhaust and accessories.

The 325 heads and cam combo was specd by marine kinetics. Owner asked for 700hp 6000rpm engines. He made 630hp at 5800ish, and 624hp at 5500ish.

Imo, having a little more torque below 3500, to lose 30-40hp up top, and torque numbers from 3500 up, down as well, is that the 651 cammed combo would serve an offshore boat better. Unless of course he was pulling water skiers.

bigboat28

Would you choose this cam over the lunatis listed above?

bigboat28

The 771 that is.