bck

I seem to hear the specs are meaningless to the average Joe, but your average cam company tech guy knows nothing and custom cams can be more harm than good. So where does that leave someone with cam selection?

HaxbySpeed

With any engine build there are compromises, even more so with a marine engine. Budget, octane, sustainable rpm, maintenance intervals, wet exhaust, idle rpm and quality, etc. Given these are constants for most end users, and the basic architecture of the BBC, there isn't a lot of latitude when choosing valve events. If you look at cams that have proven to work well in this environment, you'll notice a trend. The cams that I have had failures with, and not all of them had issues, have ranged in size and application. Even mild custom cams with low lift have caused lifter tie bars to break off from wacky harmonics. This is most likely not a result of the actual valve events, but the overall shape of the lobe. There is some pretty serious math involved in designing a stable lobe. Duration in cams for these marine applications is fairly consistent, and its easy to get close to your target rpm based on the cubes, and quality of the cylinder heads. The biggest gains in power in the last seven or eight years has come from cylinder head design, not cams. When you try to add a bunch of lift to take advantage of potential airflow in these killer heads, but need the smaller duration to stay in your rpm window, it can be very hard on parts, can ultimately make less power do to instability, and will be difficult to tune. The damage being caused by some of these custom cams does not always show up right away, or on the dyno unless you really know what to look for. This is a very simplified explanation obviously, as is this whole thread. Hopefully it will spin off in to more productive discussions. If you need specific examples of the Marine Kinetics cams that have caused parts failures, or testimonials from the customers to validate what I'm saying, I can probably arrange it for you.

HaxbySpeed

Ask any builder who puts their name on their engines, and offers a warranty.

bck

The problem is that finding engine builders who have the knowledge and skills is getting harder all the time. I called your shop last year and I'm paraphrasing but your machine essentially said I'm so busy I'm not going to answer the phone for about a year, and that's not uncommon response. So I find an engine builder with a good reputation but doesn't really know marine engines as well as I'd like and that leaves me where with valvetrain selection?

MILD THUNDER

iTrader: (3)

I cannot answer for anyone. But from what i hear, the cams that have had premature failures amongst several professional engine builders, are those that have higher lift, with relatively low .050 duration numbers.

Ive said it many times here, and not many seem to be able to explain why my assumption is incorrect. When looking thru master lobes, or catalog cams, for marine endurance applications, the common trend, is that i cannot find anyone recommending a 240 duration cam, with a .400 lobe (680 lift) for a hydraulic rollee marine endurance application. Why is it these companies who have spent millions on lobe design testing , arent doing that, but a few of these "custom" cam guys are ? And the "out of bounds" from the norm cams, are those that are having issues.

Crane has a hydraulic roller grind that is labeled for marine useage, that has .714 lift . At first glance, one would think thats insane. Heres the catch. That camshaft is 264/272 @.050, with 328/336 seat duration. That camshaft, could have less aggressiveness, and possibly be easier on the valvetrain, than a 240 @ .050 with .680 lift. If my theory was incorrect, as it was argued on another thread, why would they not just do a .714 lift 240 duration cam? Or why do they also offer that above cam, with lower lift as well? Problem is, a 264/272 cam, isnt going to work in a 5500rpm 502. Much better suited to a much larger engine.

I am no cam specialist. All i can do is look at what the pros do, and look at the results, and speculate. Talking to guys who are in the lobe design business, that are employed by these big companies, can be very worthwhile.

Its not just about high lift wearing springs out, or guides. Its also about the acceleration of the lifter, the jerk action, that can wreak havoc on the valvetrain.

Everyone is first to argue how marine engines are so different than car engines. Theres more to separating a car camshaft profile, to a marine endurance profile, then simply the water reversion concept.

Im sure we all recall the 900sc solid roller merc engine. It was not known for valvetrain longevity. It was common to convert them to a hydraulic roller cam, in a quest for a longer lasting valvetrain. It worked, IF, the hydraulic camshaft that replaced the solid roller, was a grind that was gentler on parts. That usually was a lower lift similar duration camshaft.

My assumption, is you need to stay within bounds on duration which is relative to engine size and rpm range. The duration numbers, dictate what bounds you must stay in when it comes to lobe size. Are the drag racer guys running more lift, with similar duration, yes. They are not holding their engines at 5500-6000 for extended periods of time, and are not looking to go several years while doing so.

Most think that a camshaft is a win if it makes a good dyno number. I think its a win, if it makes a good dyno number, and doesnt beat up the valvetrain after going the distance in the boat, and meets the realistic expectations for life span.

If after a dyno session of 15-20 pulls, your custom cam is already showing issues on the lobes, how do you think its gonna look after 150 hours of useage?

Feedback from guys actually building, and field testing these combos, is priceless. Id rather take that information , than being told what "should" work, and false stories of success claims, or rebuttling with discredits, insults, and big words, in an effort to sell a product.

Your cam guy selling you a package that makes xxx horsepower, and lives xxx hours , then ask him for a reference on that combo. Not a dyno sheet, but an actual contact info, screename, email address, etc.

If your not interested in going with your engine builders cam recommendation, not confident in your cam grinders suggestion, then i would suggest getting familiar with how cam lobes are designed, and pick your own cam out of a catalog, that is a true endurance lobe design.

bck

Now if someone were to say cams with xxx lift are too much because... or spring pressures in excess of xxx are to much because... That would at least give some information to help out the guy doing it himself.

HaxbySpeed

Try asking here. I'm sure you will get some constructive input. I am usually booked six months to a year out, but I can always answer a question. Text messages usually work best.

MILD THUNDER

iTrader: (3)

That information is out there. You typically wont find it here on oso, because for years, anyone and everyone, was afraid to discuss camshafts.

You have one of these custom cams and just suffered a morel lifter failure on the dyno. Why dont you tell us what those cam specs are ?

bck

I don't know how to quote individual sentences but in your first paragraph mt, you mention "those that have higher lift". That's what I'm getting at, what is it that could be considered higher lift?

MILD THUNDER

iTrader: (3)

Imo, generally speaking, a cam with .050 duration of around 240, and a .400 lobe, is what i consider high lift. What lunati and comp cams consider high lift for a marine endurance 240ish duration cam, is around 640ish