Specs for an 81 5.0 Cam.. Anyone?

[Friscoboater]

Does anyone know what the cam specs for an 81 5.0 Chevy mercruiser is? I do not want to go too hot with my new engine.

Also do all engines have the drain petcocks on them?

 

[dr_bowtie]

Re: Specs for an 81 5.0 Cam.. Anyone?

do you have the part number of the cam you are wanting to know about....?

 

[ramster]

Re: Specs for an 81 5.0 Cam.. Anyone?

Stick with a marine spec cam, or something like a towing/RV type. You want peak horsepower under 5000 RPM, so not too much duration. You don't want to use a street rod type cam with a radical idle. As for the engine drains, they all have some sort on the side of the block, Chevy's have one on each side, if it is a factory marine engine it should be a brass plug or petcock. The exhaust manifolds each have a drain plug.

 

[Don S]

Re: Specs for an 81 5.0 Cam.. Anyone?

Mercruiser does not publish the full specs of their cams. Neither does Volvo.
Propriatary information is what they call it.
What are you looking for? The OEM service manual will give you lobe lift, but not much more. Manuals are in the Adults only sticky at the top of this forum.

 

[wca_tim]

Re: Specs for an 81 5.0 Cam.. Anyone?

hmmm.... not positive, but what I have says stock flat tappet cam merc pn 431-5943 0.05 duration (intale/exhaust) 200/212, lift .400/.410, centerline 108/112, lsa 110. knowing nothing else about what you're building but guessing near stock 305, something like the ones below will be a bit more than stock but not create problems... the first grind is recommended for giving a mild increase in power in a stock 305...since aftermarket cam descriptions are nearly all based on the 350, when looking at a cam for a 305, you can use the rule of thumb that a given cam in a 305 will act like one with about 10 degrees more duration would in a 350. what's relatively mild and no worries in a stock 350 could be too much for a stock 305...

edit: http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=83&sb=1

http://www.summitracing.com/parts/CCA-CL12-249-4/

ps. didn't mean to contradict above posts - took a few minutes to look things up here and tucked daughter in before hitting send - others posted in the meantime.

oh, and based on what I learned from Bond-o a while back and now personal experience, go with the brass fitting and screw out plugs so you can dig around up there with a piece of wire when you drain it. nix on the petcocks.

 

[Friscoboater]

Re: Specs for an 81 5.0 Cam.. Anyone?

I just do not want to go too small. I know that torque is the name of the game with boats.

I have a 79 Z28 with a breathed on 350 and it has a 268H from comp cams and I love the way it makes that 350 sound. Not too lumpy but you can tell you got something.

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=86&sb=2

What do you think about that?

Do all engines have the holes for the petcocks? I have never paid any attention.

 

[ramster]

Re: Specs for an 81 5.0 Cam.. Anyone?

If you haven't started the build yet, do a 350, it weighs the same, makes more power, and all the accessories will bolt right on.

 

[wca_tim]

Re: Specs for an 81 5.0 Cam.. Anyone?

I just do not want to go too small. I know that torque is the name of the game with boats.

I have a 79 Z28 with a breathed on 350 and it has a 268H from comp cams and I love the way it makes that 350 sound. Not too lumpy but you can tell you got something.

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=86&sb=2

What do you think about that? .

way too big for a 305... we're talking marine engines here. if you go with enough duration to get the really lumpy idle, you have problems with reversion (water gets sucked back into the motor ruining it - the lumpy idle comes from the same overlap that causes reversion...) and your drive can't handle being shifted into gear at mich over 500 or 600 rpms... not for very long anyhow. the cam you pointed to is really not even suitable for a 350 in a boat with stock exhaust and drive...

 

[wca_tim]

Re: Specs for an 81 5.0 Cam.. Anyone?

if you use the rule of thumb I was talking about and go with a comp cams xm cam (ground for marine applicagtions) you might get away with a 256... but tha's more than usually recommended for a stock 350, you could probably get away with it.

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=98&sb=1

assume though that the description for the one below, will be more applicable to the one above when it is installed in a 305...

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=99&sb=1

if you're looking for big power increases, do more cubes, ie 350.

 

[Friscoboater]

Re: Specs for an 81 5.0 Cam.. Anyone?

You are right. I think I was getting ahead of myself. In the back of my head i was thinking 350 for some reason.

Thanks for the info.

 

[Friscoboater]

Re: Specs for an 81 5.0 Cam.. Anyone?

What is I went to a 350? Would that 268h work? All i want to do it touch that 300 HP mark. I plan on using some Aluminum heads and aluminum intake also.

 

[Bondo]

Re: Specs for an 81 5.0 Cam.. Anyone?

Ayuh,....

An RV cam in a 350 with aluminum Vortec Heads, quenched to .042/ .045 will give you that 300hp...
Edlebrock sells a nice little package....

 

[wca_tim]

Re: Specs for an 81 5.0 Cam.. Anyone?

Take a step back and think about what you want to accomplish, then think about what you want to build. every mph on top end is going to cost you 10-15 horsepower... and that get's expensive in a hurry.

people let me know in a hurry that building a maring engine is not like building a stop light racer / street rod. imagine your camaro engine with the pedal to the floor, turning 6000 rpms, hauling a sled of logs up the side of a mountain in 2nd gear... that's what a boat engine has to do pretty much every time you run it very hard.

It's also got to stay within reasonable operating limits of your outdrive.

factor in that if you use it to pull skiers, etc... it's a pita if you don't have good manners at idle.

You can build a really radical motor if you do it right, but then it becomes much less flexible. everything's a trade off. I'll get off the soap box...

 

[wca_tim]

Re: Specs for an 81 5.0 Cam.. Anyone?

Ayuh,....

An RV cam in a 350 with aluminum Vortec Heads, quenched to .042/ .045 will give you that 300hp...
Edlebrock sells a nice little package....

very good advice... you can get in the same range with a 256 marine cam, iron vortecs (cheaper) and an edelbrock performer rpm topped with a 600 cfm marine carb. there's also some great info around on using a 350 roller block and the gm hot cam with vortec heads... with an exhaust upgrade that gets you closer to 400 than 300 horsepower from what i've read / heard. look up posts by mkos... he's done a lot of research on it and his boat apparently runs really well with a set up like that.

 

[dr_bowtie]

Re: Specs for an 81 5.0 Cam.. Anyone?

that cam you listed is nothing special....

A little more duration that a factory car cam and it is also 2deg advanced...

Advancing a cam brings the power in sooner...500rpm for every 4 deg...

thr max cam I would go would be a 218deg duration cam...after that it gets iffy...

even the 222/222 duration 447/447 lift 350HP corvette cam runs okay but you can notice a lag off idle if you install it straight up...

I wouldnt hesitate to use that cam but i also know you need to advance it 8deg minimum...13deg advanced is ideal....then it would top out at 5,000rpm and when you advance that cam 13deg it is a stump puller pure and simple...


if you want off the line torque you need to keep the duration short...adding duration without advancing thecam raises power but also the power curve...

 

[Friscoboater]

Re: Specs for an 81 5.0 Cam.. Anyone?

thanks for all the help guys.

 

[Friscoboater]

Re: Specs for an 81 5.0 Cam.. Anyone?

Take a look at this link.

http://www.youtube.com/watch?v=WSY42e7oNpw&feature=channel_page

Too radical?

 

[dr_bowtie]

Re: Specs for an 81 5.0 Cam.. Anyone?

I would say for stock exhaust yes....

here is why...one of the above posters mentioned reversion....this will be the biggest issue...

when you look at the cooling system of the boat the raw water impeller pulls water from the lake/river/ocean (whatever) and circulates it in the exhaust manifolds and it some point the water and exhaust mix right before it is expelled back into the fresh water...at that point the reversion in the exhaust will pull some of the expelling water into the exhaust and most likely back into the engine....

you have to understand that thos cams that sound like that have an overlap period to help cylinder filling...and bleed off cylinder pressure at low RPM...

the over lap period is where both the Intake and Exhaust valve are both open for a set amount of time...each cam has a different overlap period...

those lumpy cams sound great but are not for boats with stock exhaust and stock cooling systems....

plus as mentioned the stock drive system wont handle it very well...

when you put a high duration cam such as those in a boat where you need offline torque....torque is built best with short duration cams..such as stock...

dont get me wrong a higher duration cam will build more torque than a stock cam but at a higher RPM...what good would that cam even be if the boat wont accelerate to the RPM band needed to get it moving...

your best bet is to use a stock cam and like mentioned if you need more torque find a 350 block...you can add cubes adding a 383 kit (Eagle makes a whole rotating recip for 500.00) or find a 400 block...

raising the cam duration is not the way to go...there is a reason HEAVY vehicles and boats use a short duration stick....more offline torque...they build torque right from idle and not from 2500RPM or higher...

 

[Friscoboater]

Re: Specs for an 81 5.0 Cam.. Anyone?

Oh I hear you guys. that was my attempt at sarcasm.

 

[dr_bowtie]

Re: Specs for an 81 5.0 Cam.. Anyone?

This is the last boat we repowered....

too much...?