Building a 350 Vortec motor

[Maddoxsdaddy]

Like the title says, i'm building one for my 210 CCR Crownline. Motor bore is stock, intake will be an edelbrock performer, and most everything else will be stock as well. I'm having trouble choosing a camshaft. It is a roller motor so the cam must be hydrualic roller.

I will be using a corsa quick and quiet exhaust (thru hull+thru prop) non switchable.

I've heard a couple of different things about cams.
1) Lobe separation needs to be around 114-115 in order to avoid water being sucked back up through the exhaust into the motor.
2) Marine cams are no different than automotive cams.

Which is it? Why do i find every cam i see for marine application has 112 degrees of lobe separation if it needs to be 114-115?

Also, i'm trying to find the specs for a stock cam that came in a 2000 350 MAG... i have one being offered to me for almost nothing that came out of a new motor. I figure that one is at least made specifically for a boat motor... right?

I realize i posted on this previously but i'd still like to find the specs... now with the added confusion. Thanks!

 

[joewithaboat]

Re: Building a 350 Vortec motor

Factory 350 mag from 2000 should be 300 hp i think. Pretty sure Crane actually grinds the cams for merc. They wont sell you one but I'm sure they can recommend one of their "marine grinds" that is close. Its a pretty tame cam. It wont require much, if any, head mods.

If you don't mind modifying the heads... springs,retainers,studs etc. Call Comp or Crane

Crane has a 262 roller that is recommended for thru the prop exhaust and a 272 for transom exhaust. Their catalog is huge... use "control f " type in "marine" to locate the cams

http://www.cranecams.com/uploads/catalog/2011-master-catalog-v2.pdf



These are pretty popular from comp... see their recommendations http://www.compperformancegroupstor...=CTGY&Store_Code=CC&Category_Code=RLERCAMXMAR


Edit... looks like crane cams are HR 260 or Hr 276
http://www.cranecams.com/product/cart.php?m=product_list&c=11062

 

[John_S]

Re: Building a 350 Vortec motor

Have the seller mic the cam lift. It will either be the standard 350 roller cam or slightly larger. It will probably be the best deal for what you are looking for (near stock).

The standard roller lift should be the following, check your current cam:

I: 0.287" (0.430" at valve w/1.5 rockers)
E: 0.300" (0.450" at valve w/1.5 rockers)


The lobe lift for the 350 Mag, I suspect the following:

I: 0.301" (0.452" at valve w/1.5 rockers)
E: 0.310" (0.465" at valve w/1.5 rockers)

Any cam with higher lift than that, requires vortec head mods. I'd still check spring part numbers between the two models, to make sure Merc didn't change them.

 

[Scott Danforth]

Re: Building a 350 Vortec motor

the cam for an '88 270 hp

Merc P/N 431-5943
GM P/N 340284
Flat lifter (non-roller)

Duration at .050 - 200 intake
212 exhaust

Lift at valve - .400 intake
.410 exhaust

Lobe centerline - intake 108 deg ATDC
exhaust 112 deg BTDC

Lobe seperation angle - 110 deg

this is what I found on the 350 mag. int .433" ex .450" Dur @ .050 is in 197 ex 206 Intake centerline 105 lobe seperation 109.5

Crane does the grinding for Mercruiser

since your building a 2000, you have a roller cam as compared to my vortec headed '88 flat tappet motor.

my recommendations would be determine the exhaust you want to run, and how you operate the boat, then pick the cam from there. factory LSA is 110, not 114. you are only going to find custom grinds at 114.

if you like speed and run open exhaust, then go big. if you spent most of the time just cruising, then stick with the 262. either way, it will allow you to spin the next size larger prop and be just a bit more efficient in addition to going faster.

the stock cams were fairly tame to allow you to run 87 octane fuel from any where. I am sticking with ethanol free premium, so I will be running 91-93 octane. so I went to the Comp Xtreme Marine 262. my heads were machined for a .525" lift cam. I did gasket match the exhaust ports.

 

[Bondo]

Re: Building a 350 Vortec motor

Which is it? Why do i find every cam i see for marine application has 112 degrees of lobe separation if it needs to be 114-115?

Ayuh,.... Accordin' to Dennis Moore, 'n everything else I've read,...

It should be between 109? 'n 112? LSA...

 

[Scott Danforth]

Re: Building a 350 Vortec motor

assuming your running an open cooling system and your running the performer intake, make sure you epoxy coat the water passages with enecon. Or, find a volvo-penta or PCM dual alloy intake which is really close to the performer, however designed for salt-water use. I found mine on ebay.

if you have a closed cooling system, you can run a bare aluminum intake.

if you change cams and increase lift, you need to change valve springs - because they take a set. my local builder recommends iskendarian springs over comp cams for springs. also, take the sheet metal spring dampers out of every spring and throw them away. they will break, eat up your valve stem seals and cause a bad day.

I also recommend roller rockers over just the roller tip. the geometry is stable with a fixed fulcrum vs a sliding/moving fulcrum.

while you have the engine out, I also recommend a melling hi-volume oil pump, pickup and the metal sleeved melling intermediate shaft. this will give you 25% more oil flow

not sure if your carb or EFI. I will also be running a 2" carb spacer on my motor which is good for a small amount of torque.

 

[John_S]

Re: Building a 350 Vortec motor

Scott, good catch on the intake. Maybe I'm wrong, but thought the poster was going for a stock or near stock build, or are you just being encouraging?

 

[Maddoxsdaddy]

Re: Building a 350 Vortec motor

Im going for a slightly better than stock build. The heads are at the machine shop getting cleaned up and having .202 valves installed. My cooling system is raw water but its rare for me to go to salt. Fresh water boater here... Carb will be the stock weber 4bbl 600cfm. I'd like to get around 320-330hp but if i don't, no big deal. I'm coming from a non-vortec 235 hp 5.7 so this will be a big kick in the pants regardless. I already have the pistons, rings, bearings, rod, crank, oil pump installed and the cam was next on my to do list...

Thanks for all the information guys!

 

[John_S]

Re: Building a 350 Vortec motor

Since you went with larger valves, you probably want to match it with an RPM intake, vs a Performer. Normally, the larger valves are only needed for hp up at the 5500rpm range. If you sellect a bigger cam, than the heads will need work for the extra lift and have matching springs installed. Running in that range, would recommend roller rockers and screw in studs. You will find allot of good info in Greg's 383 thread.

 

[Scott Danforth]

Re: Building a 350 Vortec motor

Im going for a slightly better than stock build. The heads are at the machine shop getting cleaned up and having .202 valves installed. My cooling system is raw water but its rare for me to go to salt. Fresh water boater here... Carb will be the stock weber 4bbl 600cfm. I'd like to get around 320-330hp but if i don't, no big deal. I'm coming from a non-vortec 235 hp 5.7 so this will be a big kick in the pants regardless. I already have the pistons, rings, bearings, rod, crank, oil pump installed and the cam was next on my to do list...

Thanks for all the information guys!

dont waste your time or money with 2.02 valves on a vortec head. you cant spin the motor fast enough to need them. the stock valves and ports will support 400hp at 5500 RPM currently.

 

[John_S]

Re: Building a 350 Vortec motor

dont waste your time or money with 2.02 valves on a vortec head. you cant spin the motor fast enough to need them. the stock valves and ports will support 400hp at 5500 RPM currently.

I assumed it was already done and better to match components. But, if they haven't done it yet, totally agree, no need for those larger valves on the vortec head and for your application.

 

[joewithaboat]

Re: Building a 350 Vortec motor

Putting 2.02 intake valves in a new set of vortecs would be a wasted effort without professional porting. All your doing is shrouding the valve at the chambers edge. As folks always point out in these threads the vortec casting is GM's most perfected port and chamber design for the original small block. Making it better is not easy and best left to people who have flow bench access.

However if rehabbing an old set that has worn out seats, using a 2.02 can be better than sinking the valves. It is sometimes is the best way to re establish correct installed height.

 

[Maddoxsdaddy]

Re: Building a 350 Vortec motor

I'll give the machine shop a call and see if they've done the valves yet. If not, i'll tell them to cancel that. I've decided on getting a better cam than stock and going with springs set up for that cam. I'll let ya'll know what i end up with.
Thanks for all your input!

 

[Scott Danforth]

Re: Building a 350 Vortec motor

you can do some mild exhaust gasket matching, however the intake ports and valves are as close to perfect as you can get from a stock set of heads.

if you tell your machine shop what you want from the engine, not any specs, however I want X ft-lb of torque and Y RPM limit - they will have suggestions.

 

[Maddoxsdaddy]

Re: Building a 350 Vortec motor

Ordered my cam and intake... Comp cams Marine extreme 270 and matching springs ro put in the heads. Starting to get antsy.

I've never built a motor before so i'm going to need advice putting in the cam, getting everything lined up with the heads, #1piston tdc, etc....
I will have a motor builder assisting when he has time but i'd like to get some of this done myself.

 

[joewithaboat]

Re: Building a 350 Vortec motor

Ordered my cam and intake... Comp cams Marine extreme 270 and matching springs ro put in the heads. Starting to get antsy.

I've never built a motor before so i'm going to need advice putting in the cam, getting everything lined up with the heads, #1piston tdc, etc....
I will have a motor builder assisting when he has time but i'd like to get some of this done myself.

You should read Greg's entire thread before going any further then come back with your questions. Other than his being a 383 you will go through some of the same things. Pay attention to the head modifications needed. Most people who spend the money on the mods will tell you if they had it to do again they would buy aftermarket heads.
http://forums.iboats.com/showthread.php?t=524489

I'm excited for you and jealous... its on my list of things to do to my boat.. Lol

 

[John_S]

Re: Building a 350 Vortec motor

The vortec heads will need mod for the lift for that cam, unless you are getting beehive or other springs that don't have a retainer/seal clearance problem. You probably want screw in studs put in the heads, as well. Full roller rockers won't hurt, either. Even if you were able to stop the 202 valves, a RPM intake is a better match for your cam, then a performer. The Merc 350 mag (standard head version) used an intake equivelent to the rpm.

 

[Bondo]

Re: Building a 350 Vortec motor

Ayuh,.... 'course the real Choke point in a Marine SBC is the Exhaust,...

Better bump up the budget to include a Real set of Headers.......

Pumpin' all that air in, can't work if it can't get Out.....

 

[Scott Danforth]

Re: Building a 350 Vortec motor

the exhaust will cost as much as the engine. CMI's are $2300 for a set

 

[joewithaboat]

Re: Building a 350 Vortec motor

Come on guys dont be such a downer....

A 350 to 400 hp small block will be happy to be breathing through a set of GLM manifolds. A kit cost half of what you are talking about.
I agree that the more $$$ one are much nicer but if you cant afford them you can still have some fun.