choosing a cam for a boat?????

[scon]

i know in vehicles what total lift ,lobe seperation lobe angle, and duration will do in vehicles and what i need more or less of.....? is when chioosing a cam for a boat is weight still a factor? rpm range should be from idle to wot?\ i would imagine...but mostly how to determine what total lift i need and how much duration??? if any of u out there build boat and or automotive engines is it like building a 4x4 engine or a nitrous motor...or what i just need some direction...ive started my build and now have a 4 bolt 350 10 to 1 flat top forged piston w/ forged internals(was going to be a dirt track motor and was already payed for) but cam? im lost........64 cc head 205 160 w/200 runners...is that too mouch head for a boat????...like i said i just need some direction boats are like women to me i dont understand them ....lol

 

[John_S]

Re: choosing a cam for a boat?????

Lets start with what type of a boat are you putting this in?, what drive?, and what you are trying to achieve (race, mild (stock like), etc)?

If you were looking for a stock like or mild performance application, the flat-tops and 64cc heads may be too much compression.

If you can find Dennis Moore's Book on Chevy Small Block Marine Performance, it will help with the basics. It is out of print, so you may see some high prices, and local library might be a good choice.

 

[Lyle29464]

Re: choosing a cam for a boat?????

This is a great article that might guide you. Plus do a search on this site (resonance reversion




http://www.michel-christen.com/ExhaustElbows.pdf

 

[scon]

Re: choosing a cam for a boat?????

Lets start with what type of a boat are you putting this in?, what drive?, and what you are trying to achieve (race, mild (stock like), etc)?

If you were looking for a stock like or mild performance application, the flat-tops and 64cc heads may be too much compression.

If you can find Dennis Moore's Book on Chevy Small Block Marine Performance, it will help with the basics. It is out of print, so you may see some high prices, and local library might be a good choice.

its going in a 20ft skiboat as of now its a 305 with a alpha one outdrive...runs good now40-45 tops) i just want to get more top end out of it..i had a earlier post n everyone said i need more hp...so i have this bottom end and misc parts here but now cam im lookin for something i can pull skiers with n play with friends in there boats(race i guess u would say) but basiclly wanting more reliable hp...and id lke to see 50-55mph

 

[Lyle29464]

Re: choosing a cam for a boat?????

You can get a long block ( 350) and put all your parts on it. That would get you where you want to be with a near stock cam and a 4 brl.( lots of threads on this)

 

[John_S]

Re: choosing a cam for a boat?????

its going in a 20ft skiboat as of now its a 305 with a alpha one outdrive...runs good now40-45 tops) i just want to get more top end out of it..i had a earlier post n everyone said i need more hp...so i have this bottom end and misc parts here but now cam im lookin for something i can pull skiers with n play with friends in there boats(race i guess u would say) but basiclly wanting more reliable hp...and id lke to see 50-55mph

I would say mild performance over a stock 350/4brl:

= Needs to idle down for alpha shift interupter
= Need to do hard starts for skiiing (need low end torque)
= Need to be close to alpha hp/torque limits (around 300hp @ prop) for reliability
= Top end of 50-55mph should be achievable in a 20' run-about with 350, Your 40-45mph seems a little low, but the 305 may be tired and only a 2brl.

A 350 vortec 4brl, with just a slight cam change over stock, should be good. For durability, you would may want new springs, rocker studs, and minor other work to heads.

The forged internals are a nice start, but if you stay with the flat-tops the high-compression might lead to other issues and require expensive high-octane gas.

 

[scon]

Re: choosing a cam for a boat?????

i always run the highest octane pump gas when i fill up...i do have barrels of 114 octane...can i run thqt in my boat? or mix it ?

 

[scon]

Re: choosing a cam for a boat?????

btw it does have a quadrajet 4 barrel...freshly rebuilt and working properly it seems

 

[John_S]

Re: choosing a cam for a boat?????

i always run the highest octane pump gas when i fill up...i do have barrels of 114 octane...can i run thqt in my boat? or mix it ?

Well, sounds like you want to head down that path. Not sure if it will be 100% successful. I was thinking you could get by with 91-93 octane. Having access to 114 will allow for any mix in between. Use the thick stock head gasket of 0.051" or maybe a little thicker, if you can get it.

You should plan on an aftermarket marine ignition that will allow you to adjust the timing curves. The thunderbolt modules are fixed.

A marine Q-jet is fine, and will probably need some tuning. It may limit your intake choices, with vortec heads. You want a mid to high-rise dual plane intake.

Use a standard oil pump, not high volume.

Given the higher than stock compression (full point higher) you might want to have discussions with custom cam grinder.

Also realize, you will be spending a good deal of time on the water doing the tuning of carb and ignition.

 

[scon]

Re: choosing a cam for a boat?????

yeah i figured it would take some serious tune time..how ever we have a local shop with dyno so i can tune pretty close if not dead on as far as timing and carb settings go......is a non marine carb not recommended ...like a holley? i know the ventures could b a prob n i believe that y they use q-jets rite?i have never liked afb`s or q-jets...and is vacuum secondaries a must have? ...im a automotive guy in a boaters world now..

thanx
steve

 

[John_S]

Re: choosing a cam for a boat?????

You need a marine carb. Holley does make some marine carbs. Most are vacuum secondaries and recommend staying with that.

 

[Aloysius]

Re: choosing a cam for a boat?????

The intake manifold will dictate what type of carb to use..square bore or spread bore.

High rpm power will be severely limited by stock marine exhaust manifolds.

Overlap/long duration cams will cause water ingestion from the exhaust.

flat tappet cams require oil that contains zinc..you can't use conventional automotive oil for older flat tappet cam use.

 

[John_S]

Re: choosing a cam for a boat?????

The intake manifold will dictate what type of carb to use..square bore or spread bore.

Mainly true if he is raw water cooled and boats in salt or brackish water where a cast-iron or lined aluminum would be required. If fresh water and vortec heads and spreadbore would limit you to a Edelbrock Peformer vs an RPM or RPM Air gap. Otherwise, lots of choices.

High rpm power will be severely limited by stock marine exhaust manifolds.

The stock manifolds are good for a 350 @ 5000 rpms.

Overlap/long duration cams will cause water ingestion from the exhaust.

Yes, and have to be avoided.

flat tappet cams require oil that contains zinc..you can't use conventional automotive oil for older flat tappet cam use.

Has Merc removed it from their marine oil? Not available in an additive? I haven't heard of everyone dropping lobes on all the flat based hyd cams found in most boats before mid/late 90's. I am not sure what the poster is planning, but there are allot more cam choices in flat based that meet the marine overlap requirement.

 

[wire2]

Re: choosing a cam for a boat?????

I swapped the OEM cam out for a mild performance cam several years ago, was a bit more performance but not as much as I expected. (As it turned out, an OEM marine cam is pretty hot next to one in a car, due to higher torque requirements.)

Anyways, to bump it up to the next level, I changed the 1.5:1 steel rockers out to 1.6:1 aluminum roller rockers. Now it still idles ok down to ~500 rpm for shifting but it has a bit of burble to it. It sounds impressive if I idle away from the dock with the thru hulls open.

I already had a Holley alum hi rise under the Quadra jet, and home made double wall headers. Had to change the stock 21 ss prop to a 23" to get the revs down a bit from 5500.

I expect the 260 hp figure is well over 300 now, never bothered with a dyno.

 

[Aloysius]

Re: choosing a cam for a boat?????

I guess what I meant is never use an adapter plate under a carburetor..spacers are great, but not adapters.

The oil issue has only occurred since the development of "energy saving" oils with the starburst symbol on the bottle. These oils have the zinc and phosphorus additives removed to prevent damage to catalytic converters. since all modern pushrod engines are roller followers, there was no need for additives to prevent cam wear.

The cam lobe/lifter interface is the highest shear load in an engine. The cam is cast iron, and surface hardened. Many boaters are unaware of the change in oils, and the potential for damage to their camshafts.

As for "Mercury" oil, if it is mainly marketed for 4 stroke outboards, I'd be surprised if it had significant levels of anti-wear additives, since they aren't required for newer engines.

 

[John_S]

Re: choosing a cam for a boat?????

Mercury/Mercruiser have a number of different oils, and would not agree they are all marketed based on 4-stroke outboards. Given that only the very latest stearn drives have cats, and the issue of the zinc being well known, that they would abandon the install base of all flat-lifter cams. But, maybe they have or there is another compeling reason for them to have done so. My question is how do you know if it has been removed or not? Some API cert, etc?

What do all the car collector guys do for their old motors? Is there an addditive?

Have you had a failure that was diagnoised to not having zinc?

The zinc thing seems to be allot of smoke with only a little fire.

 

[guyaverage]

Re: choosing a cam for a boat?????

Not to drag this thread further off topic, but zinc has not been removed from starburst oils. Many (if not most) current API spec (SM) "energy conserving" oils contain 600-800 ppm of zinc/phos, The current API SM spec limits levels to 800 ppm, but even this only applies to weights up to 10w30. Higher weights, straight weights, and non-energy conserving oils have even higher levels and arent limited by the spec for how much zinc/phos they can have even if they are SM rated. Go to the 'bob is the oil guy' oil analysis forum and look at some of the used and virgin oil analysis results. There is still plenty of zinc in current oils.

While I havent actually seen the upcoming SN spec details, my understanding is that even this newer spec doesnt lower the limits beyond the current SM spec. Levels are lower than they used to be a decade or two back, but plenty for a stock flat tappet cam running stock springs. This whole zinc thing has been blown so far out of proportion its not funny. There are other antiwear agents in oil, zinc is just one of them.

 

[bigdan1]

Re: choosing a cam for a boat?????

I too want to modify my engine ....but I have only a 3.0L ...
but principles are the same ...

keep in mid that you must keep a low idle ....

your flat top pistons+ 64cc heads give around 10 toi 1 cr : ok with 91 octane

but dont go over 210 dur@.050 lift or your idle will be too high .....

high idle will destoy your outdrive when putting in gear

go for torque not for revs .....aniway a red line of 6000 rpms is dangerous :
imagine if going on loose at 6600 rpm,scary !!!!

 

[wire2]

Re: choosing a cam for a boat?????

....

but dont go over 210 dur@.050 lift or your idle will be too high .....

....

Mine idles at 500~550, shifts easily;

Crane Cams #271-113941
PowerMax Hydraulic Flat Tappet Camshaft Only
Lift: .459''/.486''
Duration: 268?/280?
RPM Range: 2000-5000

But I get more lift than above with 1.6:1 roller rockers. And NO reversion issues in 15 seasons.