350 cam questions

[gr8shot]

Just about ready to start assembling a new 350 vortec motor for my 99 sea ray 190 signature. Short version of the story is the 305 that was in it wasn't winterized and the block cracked so I got the boat for very cheap. My plan from the beginning was to use the 431-811658 camshaft from the 305 in the new 350. It's slightly better than the GM vortec truck cam. Has a little higher lift and a little more duration.

I'm curious how much power I'm leaving on the table by not getting a better cam though. I know it would be a decent upgrade, but curious on a few other people's thoughts.

Mercruiser 431-811658 specs:
196/206 duration @ 0.050"
.431/.451 lift. 109LSA

The cam I have in mind, I've seen advertised on ebay as working well with 100% stock vortec heads is comp cams X4270HR
220/224 duration @ 0.050"
.474/.474 lift 111LSA

Comp cams also has one with slightly less duration, same lift and a slightly lower powerband.

I'm sure that's really pushing it on valve lift for stock vortec heads. But curious on some people's thoughts here on one vs the other.

 

[tpenfield]

Usually the Mercruiser cam will have little/no valve overlap. The performance cam you mentioned seems to have a fair amount of overlap, which would lead to exhaust reversion and hydrolocking of the engine.

The marine engines have mild cams, not because they want to leave power on the table, but because they have to balance the engine performance with the physics of a wet exhaust when the engine is running at idle speeds.

 

[Bondo]

220/224 duration @ 0.050"

Ayuh,..... I believe that's to much duration,.....

Ya need an "RV" cam, duration more like 214/ 218,.....

 

[gr8shot]

Comp has the 4260HR which has the same lift but 210/214 @ 0.050" duration. Think that would be more appropriate?

My heads are still at the machine shop, so I do plant to see if he can check the clearance to see if that'll be too much lift or not.

If so, then the other suitable option would be the 4258HR which is 206/210 @0.050" and .458/458 lift. I'm just not sure if thats a big enough difference from the stock cam to be worth the money. I know it'll be better, but noticeably better, I don't have that kind of experience to say.

 

[Scott Danforth]

the XM270 HR will need the stock vortec heads modified for high lift. PERIOD. technically its anything over .42" and you need to clearance check, however in most cases you can get away with up to about .45" of lift at the valve without a problem

at .474" of lift, you will mash the keeper into the seals

FYI - the XM270 HR that is also the largest roller cam in a SBC you can run with wet exhaust and not hydro-lock.

I ran the XM264 H in my flat tappet vortec head with 1.52:1 rockers and needed the heads modified.

the modification is recommended over the beehive springs. and while at it, convert the pressed in rocker studs to thread-in

 

[QBhoy]

Hi
one of the extra bits fitted by the factory on my boat was a fancy cam. The downside of this is that it tends to run very lumpy at tick over and low speed. It even tends to throw fuel out the exhausts on occasion low down the rpm. It’s all I’ve ever known in this engine obviously but I get the feeling it isn’t too well suited at anything other than near and at full throttle...given that the fuelling likely isn’t adjusted to suit it most of the time. Perhaps with you likely having a carb...you can compensate.
All that aside...you’ll likely know that you’ll maybe now need a wee prop change to suit too.
Good luck !

 

[gr8shot]

I need to get the details on what all was done to my heads at the machine shop I think, before I decide on anything. Bill at the machine shop was way more than I anticipated for the heads. So if he didn't do screw in rocker studs, and didn't clearance the heads for more valve lift, I'm probably just going to stick with the stock mercruiser cam to save money. I don't need to spend another couple hundred bucks on either machine work, or the parts to do the machine work myself, then springs, retainers etc, just so I can spend another $300+ on a cam. That turns into $500 to maybe gain 30-40hp. The more I think about it, the more I think that with the stock mercruiser cam, vortec heads, the edelbrock performer EPS intake, and edelbrock 1409 carb, which is the setup I've already got ready for the motor, I should have more than enough power to move a 19' boat with ease.

It's just really easy to hop online and read about guys making 350+hp with relative ease and want to do the same, even though I really don't need that much power for this relatively small/light boat. (19' and 3000lbs)

My block should be done at the machine shop next week, and he's holding on to the heads for me while he does the block. So i might have him measure and see just how much lift I can get away with, and go from there.

 

[Scott Danforth]

you can make over 500hp with a 350 block in a boat...... if you plan it from the beginning.

prior to ever doing any machine work, or buying parts, you need to plan what you want to do.

the stock mercruiser 5.0 in my 19 foot boat would hit 49.8mph a stock 350 would probably push it harder

 

[76SeaRay]

I am building a 1996 5.7L Vortec and went with the recommendations from others on here. I am using the Comp Cams 08-416-8 (XM264HR grind) cam with Comp Cams 850-16 roller lifters. I will be using 1.5 ratio roller tip non self-aligning rockers (don't have a part number for these yet) and Comp Cams 4808-8 guide plates. My machine shop knew exactly what to do with replacing the press in rocker studs with screw in studs (note slightly longer studs to accommodate the guide plate thickness) and milling down bosses for the valve springs for the extra lift (don't know the part number for the springs). I went with Speed Pro H423DCP-20 Hypereutectic pistons. Block was line bored and honed, cylinders bored 0.020, and rods reconditioned. I also had it balanced. Machine shop said that it should come out with a compression ratio around 8.5 or so and I should be able to run 87 octane pump gas. Shop also said piston clearance will not be a problem and it should hit around 300 to 310HP. I do need to go back and ask what thickness of head gasket to get. All in I will be around $3,500 which is a bit higher than some internet long blocks but I know exactly the quality of work and what has gone into the engine. Also a bit higher than I wanted to spend but I should have a solid runner without going overboard on horsepower (I have an Alpha 1.5 to 1 drive). I am doing most of the assembly of the engine myself. I will also be rebuilding the outdrive myself. Hope this helps you with your build.

 

[achris]

Another thing to consider....

All well and good getting an engine to produce high power at the top end, thus requiring a 'large' propeller to hold the engine down to the max RPM. But just make sure you have enough power in the low and mid range to get the boat going fast enough to allow the revs to increase into the top end. No good having a 500hp engine, with a 27" prop if the engine can't make enough power (in the 2K to 4K band) to get 'over the hump'... :facepalm:

Chris........

 

[Scott06]

IThe more I think about it, the more I think that with the stock mercruiser cam, vortec heads, the edelbrock performer EPS intake, and edelbrock 1409 carb, which is the setup I've already got ready for the motor, I should have more than enough power to move a 19' boat with ease.

.

Yes I don’t think you will be disappointed with a 5.7 with Edelbrock intake and carb. I have a sea ray 200 with 5.0 and 4 bbl edelbrock. Does great pulls up skiers with ease even with 6-7 people in the boat.

assuming you keep the drive that was in there you’ll have to step up in prop pitch for sure

 

[gr8shot]

Another thing to consider....

All well and good getting an engine to produce high power at the top end, thus requiring a 'large' propeller to hold the engine down to the max RPM. But just make sure you have enough power in the low and mid range to get the boat going fast enough to allow the revs to increase into the top end. No good having a 500hp engine, with a 27" prop if the engine can't make enough power (in the 2K to 4K band) to get 'over the hump'... :facepalm:

Chris........

The cams I was looking at, and have mentioned are all truck cams. Made for lower rpm power, and peak around 5000-5500rpm. I get it that you want more overall power under the curve, rather than a high peak number and less power at lower rpm. Totally on board there. The want for a bigger cam is strong. But as much as I want it, I'm in pretty deep already, and still have to buy all the bearings, rings, maybe pistons if they had to bore the block. Unless for some reason the cam in the 305 mercruiser is trashed when I pull it, I'll probably stick with it. Would be easy enough to upgrade later on if I change my mind. The motor is pretty easily accessible in the boat.

 

[Scott Danforth]

The cams I was looking at, and have mentioned are all truck cams. Made for lower rpm power, and peak around 5000-5500rpm. I get it that you want more overall power under the curve, rather than a high peak number and less power at lower rpm. Totally on board there. The want for a bigger cam is strong. But as much as I want it, I'm in pretty deep already, and still have to buy all the bearings, rings, maybe pistons if they had to bore the block. Unless for some reason the cam in the 305 mercruiser is trashed when I pull it, I'll probably stick with it. Would be easy enough to upgrade later on if I change my mind. The motor is pretty easily accessible in the boat.

stick with a Marine Cam unless its a stock truck cam. Any performance truck cam can run with overlap and dont suck up water up the exhaust in a truck like it would in a boat.

which is why the LSA and valve timing are different in a marine cam.

the cam in a 305 is not the same as the cam in the 350, however its close enough to work.

if your looking at marine roller cams, the CM264HR would be my recommendation, however you will need to have the heads modified.

any machine shop will have bored your block. any motor that has been run for any length of time will have cylinder wear requiring a bore and hone. cylinders egg shape and taper even if there isnt a ridge

you are better off buying a complete rotating assembly and K-kit vs shopping the components one at a time.

 

[Scott06]

It looks like both the 5.0 carb and 5.7carb (both 2 bbl and 4 bbl remans) from mercruiser all use the same cam P/N 431-811658 .

 

[achris]

It looks like both the 5.0 carb and 5.7carb (both 2 bbl and 4 bbl remans) from mercruiser all use the same cam P/N 431-811658 .

That's correct, and has been since Merc started using the SBC . I was about to point that out.

Chris......

 

[Scott06]

That's correct, and has been since Merc started using the SBC . I was about to point that out.

Chris......

yeah only 5.7 I saw that did use a different cam is the 357 bravo and 350 mag which call for 431-866022T. I assume this is why the bravo version of the 357 is 325 hp and alpha is 275 hp.

 

[QBhoy]

Hate to be a kill joy but I’d maybe keep it sensible with it all. I think one of you’re biggest limiting factors will be the hull you have.
I can tell you from experience with my own 18ft hull and v8 mpi (with a fair bit of power)...every mph is hard work. The hull I have is a heavy heavy hull. Wide too at about 8ft. Not your typical ingredients for fast. She does have an apex stepped hull with a flat running pad to sit on at high speed though. If I know the hull you have, it doesn’t. It will be even harder to get her fast. I think I have around the 300hp mark or just over on a good day. She has ran at 67 gps once or twice with one prop but generally she will be a 60 or just over boat on most occasions and on the limiter if pushed.
the biggest single difference made with my boat was getting the prop dialled in. I think even for my boat to pass the 70 mark...it would take at least another 50-100 hp.
I’m pretty sure your hull will be harder pushed again to get anything like that. Even at that, god knows how she will behave without a pad on the hull.
Love to hear how it turns out though. Lots to think about with props and even out drives and ratios. Good luck.

 

[Scott06]

Hate to be a kill joy but I’d maybe keep it sensible with it all. I think one of you’re biggest limiting factors will be the hull you have.
I can tell you from experience with my own 18ft hull and v8 ....
Love to hear how it turns out though. Lots to think about with props and even out drives and ratios. Good luck.

I think good advice keep it simple.

In that boat a 290 - 300 hp relatively stock 5.7 (4 bbl carb) will pull very well. My 21 ft with a 5.0 does very well, 5.7 in smaller lighter would only be better. While I enjoy a nice long WOT, the opportunity due to needing calm water or having a boat for of people makes this few and far between

 

[gr8shot]

I decided to stick with the marine cam from the 305. I've got a clean vortec truck cam in great shape too. But the marine cam has a little more lift and a little more duration. So why not run it? It looks like brand new, no signs of wear at all.

Hate to be a kill joy but I’d maybe keep it sensible with it all. I think one of you’re biggest limiting factors will be the hull you have.
I can tell you from experience with my own 18ft hull and v8 mpi (with a fair bit of power)...every mph is hard work. The hull I have is a heavy heavy hull. Wide too at about 8ft. Not your typical ingredients for fast. She does have an apex stepped hull with a flat running pad to sit on at high speed though. If I know the hull you have, it doesn’t. It will be even harder to get her fast. I think I have around the 300hp mark or just over on a good day. She has ran at 67 gps once or twice with one prop but generally she will be a 60 or just over boat on most occasions and on the limiter if pushed.
the biggest single difference made with my boat was getting the prop dialled in. I think even for my boat to pass the 70 mark...it would take at least another 50-100 hp.
I’m pretty sure your hull will be harder pushed again to get anything like that. Even at that, god knows how she will behave without a pad on the hull.
Love to hear how it turns out though. Lots to think about with props and even out drives and ratios. Good luck.

I really don't see myself ever going that fast! At least not at the lake we usually go to, it's very small by most standards. Usually pretty calm though, but with my wife and kids on the boat, they aren't really interested in top speed. Just get on plane and cruise to our swimming spot, yank the kids around on a tube, or head to where we like to fish. It'll be nice knowing I can even do 50mph, let alone maybe 60. My 17' with the 3.0 thats in need of a new prop strugges to hit 30mph.

 

[NHGuy]

It will have plenty of power for a 19 footer. My previous boat was an 87 19.5 footer with a 5.7 carbed Mercruiser. It didn't need wide open throttle for a holeshot.
Only thing that engine had was whatever Comp Cams said was do-able without reversion and a carburetor rebuild.
If you aren't going to be going full speed a lot you will be fine. Although it is nice to be able to go out on a near flat day and trim it up to see how much speed you get!
The good thing about a 350 is that it won't be working too hard, and when you want to change speed it will happen quickly.
I think the best thing about camming my 87 was the midrange punch that it got, though it was probably helped by the carb work. Fuel economy improved too.