Sbc cam choice

[Earthad58]

So I recently bought a 20' 95 reinell with a wake tower for $2500, well a hose popped off after a weekend of used and overheated the motor to the point it blew both head gaskets and hydro locked, after pulling the motor I found out it was a 70 sbc 400 and needed a full rebuild. This engine never really felt that powerful in the boat, in fact it struggled to pull up a wakeboarder. Instead of rebuilding I just bought a fresh rebuilt 350 off craigslist for $500, flat top Pistons, bronze guides new springs, timing chain, edelbrock intake etc, 76cc heads. Well I pulled the came and found it was a crane energizer 100052 which specks out at 216 duration and .454 lift with 110 love separation, and I had a set of 1.6 roller rockers at home so tossing those on so that will bump the lift up to about .484". I'm new to the marine world and wondering what everyone things of this setup and cam, I really don't want to have to buy a cam so I'm hoping this will work and no reversion problems, thanks

 

[NHGuy]

I think you need more lobe separation or you will get reversion. But maybe it's going to work.

To address the reversion you need high dollar exhaust. It's cheaper to get a different, ie. marine, cam.

You can test it on a run stand with the 1.6 rockers and some 1.5's. After each run (at idle, with exhaust tubes on the risers) you first drain, then pull, the riser, to check for water sitting in the exhaust manifold. No water good, water no go.

If water gets sucked back at idle (reversion) you can lock up the engine or worse.

I'd study the different sbc cams in Comps web page to get a feel for what works. Anything that does not say "needs good exhaust" in the notes, that's the profile that's safe.

And don't use the roller cam stats unless you are comparing to a roller cam for your engine, they use different ramps.

I just built a 383 with a cam that I found a very experienced guy had used in a 355 but it took $1800 of exhaust to get there.

If the 350 heads are vortec you will need to lower the valve guides for big lifts. There's a tool you can use to do it at home for $50. Only thing is you have to remove the valves to do it. Just another job to keep your boat on the shore.

If you got an early 350 with 2 piece rear main seal I think the coupler off the 400 will work. But the weighted 400 flywheel does not work with the (pre 86 ?) neutral balance 2 piece seal 350 rotating assembly .

If you got a later 1 piece 350 it uses a weighted flywheel that does not bolt up to an early coupler as far as I know,

Bondo knows the couplers, I ams sure he will be along in a while. I can help with the dampers and flywheels, I just went through all that getting my stroker going.

 

[Scott Danforth]

you may want to check that cam again. its advertized as 272 duration (you need to look at total duration, not just at 0.050" lift). https://www.summitracing.com/parts/crn-100052

272 is at the limit of duration for reversion with proper lobe separation. however at the 110 degree lobe separation, pretty sure you will have issues. you could change the factory risers to a set of Gil's

regarding the 1.6:1 rockers - depending on the year of the heads, you may not be able to run the 1.6:1 without coil bind.

I would myself get a proper marine/rv cam and run 1.52:1 rockers.

 

[Earthad58]

Wow I'm surprised, that seemed like a pretty small cam to me, is it the lobe separation that's the issue? Also the heads are old 882's, I think I should be fine on the springs, and yes it's a early 70's 2 piece main

 

[Fishermark]

Dennis Moore has a good book on building marine engines. Here's what he says about marine cams and lobe seperation:

Racing engines used in race cars and race boats will have lobe separation angle of between 104 and 108 degrees. A lobe separation angle this tight will creat a very rough idle, necessitating high idle speeds. Tight lobe separation angles (because the intake and exhaust valve will be open at the same time longer) will also allow water to be sucked back up through the exhaust system in the combustion chamber on most marine engines.

Standard car and boat engines have lobe separation angles of between 113 and 116 degrees. A lobe separation angle this wide will create a very smooth idle and is less prone to suck water back up into the combustion chambers.

He adds this

If the lobe separation angle is kept to between 109 to 112 degrees, an acceptable idle, but one with a slight lope, will be maintained and only a slight, if any, amount of water will be sucked back into the combustion chamber at idle.

 

[Earthad58]

Well I think I'm going to modify my risers and weld stainless extensions onto the inner exhaust tube and run with it and see what happens, I really don't wanna replace the cam and deal with trying to break in a new cam in a boat

 

[Scott Danforth]

Wow I'm surprised, that seemed like a pretty small cam to me, is it the lobe separation that's the issue? Also the heads are old 882's, I think I should be fine on the springs, and yes it's a early 70's 2 piece main

marine motors are a different breed than car motors. Think of a dump truck motor pulling a load up hill in sand in top gear while breathing out thru a snorkel.

Here is the stock cam for a GM marine motor at 260hp

202? duration intake
214? duration exhaust
395" lift intake
404" lift exhaust
112? lobe separation.

I went with the comp cams XM268 when I refreshed the SBC years ago which is a marine cam which also has 112 degree of lobe separation.

the flat top pistons (assuming the generic with the 4 valve reliefs) and the 76 cc smog heads are not the best starting point for a marine motor. installing vortec heads will push your compression ratio a bit high, and its difficult to get any performance with the 882's

 

[Earthad58]

What is the issue with the 882's? They are 1.94 heads, just because they are 76cc's? Also that stock cam is 214 duration and this cam is 216.... So not a huge difference, yeah a lot more lift but lift doesn't effect bottom end performance. I'd love to build a high performance screamer motor but the reality is I bought a cheap boat for $2500 that I could thrash and take friends out on and am trying to do my best and keep it just that, a cheap old boat, I am a gear head so I find myself wanting to build a killer motor but I have to remember, it had a old wore out 400 in it and it worked, so if a fresh rebuilt 350 that may not have the most ideal parts will push the boat along like the old wore out 400 than that works for me! I'm thinking I'll try the exhaust manifold modification and if that keeps me from having any reversion problems than sweet! If not than a cam swap in the boat isn't very tough. I appreciate all the advice, I just don't want to get too deep into this, I just wanted to buy a motor and slap it in and go have some fun till it blows up, then sell the boat lol

 

[Bondo]

I'm thinking I'll try the exhaust manifold modification and if that keeps me from having any reversion problems than sweet!

Ayuh,.... Just What modification is that,..??

Ya need a cam that builds power from Idle, to 4800 rpms,.....

A Big cam kills a boat motor,..... Ya gotta get up on-plane, before ya can make use of any Horsepower,....

Big cams don't make power down low,....

 

[Earthad58]

It's not a big cam by any means, basically a bigger rv torque cam, 216 duration and .454" lift is pretty much a smooth idle 1000-5500 rpm cam. The manifolds you can weld stainless exhaust pipe extensions to the inside exhaust on the riser so the water mixed with the exhaust further down stream and had less of a chance of sucking back into the motor

 

[Earthad58]

I havnt personally tried this but read up on it a bit and seems like it would make sense, I'm willing to try it, I've got a full fab shop

 

[Earthad58]

If I did do a cam swap any suggestions? I was hoping for more power than the factory motor, was aiming for 250-300, my current setup yeilds 9.6:1 compression so that's why I was hoping to run a larger tq cam to get the power up but still make good tq

 

[Bondo]

you can weld stainless exhaust pipe extensions to the inside exhaust on the riser so the water mixed with the exhaust further down stream and had less of a chance of sucking back into the motor

Ayuh,.... Weld pipes onto the stock cast iron risers,..??..?? Ain't gonna happen,.... a fools journey,....

Replacement aftermarket SSteel risers,.... Ya, that's a possibility,....

 

[Bondo]

was aiming for 250-300

Ayuh,.... Dead stock, with a 4bbl. carb is 260 hp,....

Vortec heads will get ya to 280 hp or so,....

Throw in d-dish pistons, 0" deck, 'n 'bout 9.5:1 compression ratio will easily get ya past 300 hp,...

All with an RV cam,...

 

[NHGuy]

I think you will have 300 horse with the flat tops the 9.6:1 compression and your high lift cam. Give the reversion test a try. Worst thing that can happen is it gets wet. Since you understand what is happening you can blow out the water before shutdown with a couple of revs.
Bondo is right though there's no way to add extensions to your risers. You'd need something that bolts to Mercruiser manifolds. They are not cheap. Since you can fab take a look at the ones being produced. Maybe you can make something up.
If I could weld I'd have bought the pipe from McMaster Carr and made up some water jacketed risers.
My cam is a 109 LSA with 218/224 @.050. But I have huge long risers that don't add the water til 6" from the transom.

 

[Earthad58]

Thank nhguy! I understand what everyone is saying, I was just Hopi g to drop this motor in and go lol I guess if I have to do a cam swap then it is what it is, just breaking in a flat tappet cam in a boat doesn't sound like any fun at all lol but oh well, and you would be suprised at what you can weld, stainless and cast actually work pretty well together, look it up, I have to do some welding on my olds 455 heads with stainless mig and it actually worked out great! It's all about pre and post heat and temperature control. I did find another cam at a friends that's new, it's a 204 214 duration and .420 .444 lift 112 separation, I could pick it up for prob $50