Marine cam vs auto cam

[curves]

Ok i got 305 in my checkmate,and about to build this 350.the block has the dish pistons(low compression)so i just picked up a set of 461 heads with 64cc combustion chambers,with 1.94 vavles.I'm figuring that would maybe bring engine up to 9.5.1.The motor had the 76cc chambers heads,with only 170hp stock.I'm curiuos difference on cam.I dont really want a stock marine cam,maybe a custom grind,for somewhere above the 350mag.So whats difference in marine cam?Is it duration.Maybe i could just get cam for the 350mag,and through it in there.I'm thinking about going 2.02 with heads,since ill have to have stainless vavles.Really i've been tring to figure out different for long time marine vs auto.I want something with high lift,but not too high.I'm going to buy me couple more outdrives to hold on too just incase it breaks,because i've heard omc800 can only handle 300hp,i'm tring for around 375hp,but dont think i could acheive with the dished pistons.

 

[Gimme Fuel]

An Automotive cam has a much different overlaps and lobe center profiles. Most marine cams are also designed to give much stronger low end torque that an automotive cam. This is not something you want to throw a auto cam in and go. Auto cam's have completely too much valve overlap and when running a wet exhaust manifolds (especially your stock ones) the engine will have a tendency to suck water back into the cylinders and ruin your engine in a hurry.

Also, if you are planning on running the factory exhaust manifolds, you won't see much of the power you think your engine should make. They are extremely restrictive when going over stock power levels.

Heads are where you make your power. Frankly most sbc factory iron heads won't make the power you are looking for without a ton of expensive work in which you could have bought a nice aftermarket set cheaper. If they are fast burn style chambers (vortecs) they are very prone to detonation and use much less timing than open chambers.

Be careful with that much compression on cast iron heads. 9.5:1 is about the max for iron marine motors safely. You will want to run premium pump gas also. On marine engines you usually want to run one whole less compression point than a performance auto engine due to the fact that the engine never cruises. A boat engine is essentially the same loading as if you strapped it to a dyno and held a solid load on it for hours on end at full RPM. 100% loading situation.

 

[curves]

I dont think it would be 9.5.1 anyways.I checked my heads they have hardened seats.1.94-1.5 vavles.I've been reading bigger combustion chamber makes low end power.I'm thinking the dished pistons,and 64cc should even it out about right were it should be.300hp be ok.Just too much for a begenner like me to go above that.I'm keeping bottom end original like it is hoping it will hold up.I had ? does captain calls exhalst help any at all,or is it just for sound?I know the y pipe is like back pressure same as car right?so two straight back pipes will let more air out.I believe these press in studs be ok,because not doing high lift.Whats really best for boat.soilid,solid roller,hyd?

 

[Gimme Fuel]

Captains Call makes reversion worse with big cams. The y-pipe is not for back pressure. It is actually a switchable (loud or quiet) exhaust system. Diverters in the main pipes actuate to either send the exhaust through the transom tips (loud) or divert it down the y-pipe through the outdrive and prop under water (quiet). None of it is similar to a car really. Backpressure=power loss. You will lose noticeable power when you run the exhaust through the prop. Very restrictive.

What cam is your block set up for? It is probably a hyd. flat lifter. Hyd. Roller would be best with less maintenance. You don't want to mess with solid lifters for a mild build. A hydraulic flat lifter is fine also, all depends what you want to do.

The stock non adjustable valvetrain is really not ideal for performance builds or high rpm and you need to watch for geometry issues when increasing cam size. Most of the punishment a marine motor takes is in the valvetrain. It needs to be very stable, stout, quality parts. Obviously a full roller setup is best but once again depends on your budget and goals.

 

[curves]

Yeah i want to run my 305 till it blows then have 350 put in.On the alpha's i;ve seen lot people just leave the bellow off,wasn't forsure if that was because they didn't want to replace it or if it helped and heat not going through outdrive.

 

[Instigator]

An Automotive cam has a much different overlaps and lobe center profiles. Most marine cams are also designed to give much stronger low end torque that an automotive cam. This is not something you want to throw a auto cam in and go. Auto cam's have completely too much valve overlap and when running a wet exhaust manifolds (especially your stock ones) the engine will have a tendency to suck water back into the cylinders and ruin your engine in a hurry.

Perfectly written.

I always got a kick out of the tech letters sent to the old boat mags.
"I just ran my boat after building a street/strip motor (w/the help of my neighbor that works at the Chevy dealer) for it and putting in a full race cam now the boats a turd."
Please help"

 

[curves]

would this cam work good for marine?

http://www.ebay.com/itm/COMP-Cams-X...Parts_Accessories&hash=item2c90353241&vxp=mtr

 

[Gimme Fuel]

No, not at all. That is an automotive cam. Has a lobe separation of 110 degrees. That will suck water back into the engine very bad. Comp has "marine" grind profiles. The Extreme marine series has 112 degrees of lobe separation.

Unfortunately Comp's website kind of stink and they don't specify what type of exhaust can be used with each cam. The more aggressive cams more than likely require long riser or even dry to tip exhaust. Stock merc cast iron manifolds really limit cam selection and also make it hard to see many power gains.

Here are the pages of Comp Marine cams:

Xtreme Marine:
http://www.compperformancegroupstor...Screen=CTGY&Store_Code=CC&Category_Code=HFTXM

High Energy Marine:
http://www.compperformancegroupstor...creen=CTGY&Store_Code=CC&Category_Code=HFTHEM

Crower Marine Camshafts:
http://www.crower.com/camshafts/chevy/small-block-sbc/hydraulic-flat-tappet/marine.html?mode=grid

Isky Marine Cams:
http://www.iskycams.com/pdfcatalog/2004-05/page164.pdf

 

[curves]

ok,i just keep seeing these bbc solid marine cams,but none for sbc.I was going to turn manifolds backwards,and run pipes to the back.I guess omc probaly same as
mercruiser when it comes to that.I was thinking of mounting some different manifolds that come up higher and straight baCK.hOW HARD IS THE HEADER ONES TO MOUNT TO OMC STRINGER?BECAUSE MY ENGINE COVER NEEDS WORK ANYWAYS,KINDA WOBBLY,MAYBE I CAN DO CUSTOM COVER WITH THE HEADERS.i ONLY SEE THEM ON THE JET BOATS,BUT MIGHT WORK.ok i just looked them headers up.there out my price range,600-800 most i would spend.sure would look,and sound nice,but 2,000 too much.

 

[curves]

No, not at all. That is an automotive cam. Has a lobe separation of 110 degrees. That will suck water back into the engine very bad. Comp has "marine" grind profiles. The Extreme marine series has 112 degrees of lobe separation.

Unfortunately Comp's website kind of stink and they don't specify what type of exhaust can be used with each cam. The more aggressive cams more than likely require long riser or even dry to tip exhaust. Stock merc cast iron manifolds really limit cam selection and also make it hard to see many power gains.

Here are the pages of Comp Marine cams:

Xtreme Marine:
http://www.compperformancegroupstor...Screen=CTGY&Store_Code=CC&Category_Code=HFTXM

High Energy Marine:
http://www.compperformancegroupstor...creen=CTGY&Store_Code=CC&Category_Code=HFTHEM

Crower Marine Camshafts:
http://www.crower.com/camshafts/chevy/small-block-sbc/hydraulic-flat-tappet/marine.html?mode=grid

Isky Marine Cams:
http://www.iskycams.com/pdfcatalog/2004-05/page164.pdf

THANKS FOR LOCATING THESE,I LOOKED FOR HOURS.

 

[MissBehavin]

No, not at all. That is an automotive cam. Has a lobe separation of 110 degrees. That will suck water back into the engine very bad. Comp has "marine" grind profiles. The Extreme marine series has 112 degrees of lobe separation.

An Automotive cam has a much different overlaps and lobe center profiles. Most marine cams are also designed to give much stronger low end torque that an automotive cam. This is not something you want to throw a auto cam in and go. Auto cam's have completely too much valve overlap and when running a wet exhaust manifolds (especially your stock ones) the engine will have a tendency to suck water back into the cylinders and ruin your engine in a hurry.

Remember though, Lobe Separation Angle and Duration go hand-in-hand when calculating valve overlap. A tighter LSA with less duration could have less overlap than a larger LSA with more duration.

Comparing the cam cards on Comp's website, the Comp "ebay" cam 110 LSA actually has less overlap than the mid-range Comp Xtreme Marine 112 LSA. (39 Degrees vs. 49 Degrees....Exhaust Closing plus Intake Opening).

Not that the "ebay" cam would be a great choice anyways, considering its a solid flat tappet cam. I plan on running a marine profile cam when I build my motor...why go against all the testing and research the cam companies do to tailor these profiles for our boat motors.

 

[curves]

I was wanting solid cam.i would take a stock marine one.