350 camshaft

[stugots1992]

Does anyone know the numbers for a 1992 350 magnum camshaft.. I have a manual for mercruiser 350 specs but it doesnt specify if its the magnum series or not.. just says 5.7 chevy.. I know the magnums are rated about 20 hp more from standard 5.7 260. is that the cam ?? or is it just an increase from the vortech heads and roller components? camshaft could be the same but i want the numbers because over the winter i am going to put a little bit bigger one in and port/polish the heads/intake and play around with the carb... To clarify another thing i heard about the magnum; I was told it has forged internals.. true or false...
Thanks,
Bobby

 

[TALLCHERRY]

i have a 92 chevy 350 magnum in my check that i rebuilt from the crank up with a new block this past winter, because the last owner did not know how to winterize it and the block cracked, i can tell you that its a 2 bolt block, with cast pistons and crank, my cam was replaced before i got it so dont know about stock cam. i know the mags that 4 barrels on them opposed to 2 on 5.7s. i have new edelbrock alum heads intake and carb.

 

[stugots1992]

intersting, I have been told all marine engines from factory are 4 bolt mains... maybe the one you yanked out wasnt a factory engine or something or maybe i was misinformed.. I wish you had some cam numbers, I looked at summits website and they have a few for the engine, I want to go with the cam they got for the powerband to be 1200-5200 rpm's.. they said it has a chopier idle and mid and top range power is a huge increase... I have not ripped into yet but tell me this; the cam/lifters are hyd roller right? I was aslo told this engine has vortech heads and its all roller with forged internals, this difference seprates it from its the standard 260 hp 5.7. mine has what looks to be a very similar intake to a edelbrock performer (dual plane/ a little rise to it) the carb is a 4barrel carter/edelbrock, looks to be a 600 or 650.. I guess I wont know anything until i ripp the actual engine down and see for myself.. because most of the stuff "I heard" I actually read from mercruiser manuals, other sites and marine engine forums..

 

[stugots1992]

Basicly my understanding of a marine's lower end is like a big truck or RV, you probaly will never find a 2 bolt main big truck or RV engine.. They require the lower to stand up to the loads of torque and from heavy towing demands etc.. Boats need that beefyness aswell becasue of the torque demand.. Maybe I am wrong though, I still want to build this thing up to a beast, if its rated around 270-280 hp I know I can easily get in the 300's with the changes I mentioned in the other reply's.. I will also change ignition over to MSD and get more fuel to go with it flowing better.. Then hopefully find a prop that likes the set-up..

 

[wca_tim]

most marine small blocks are 2 bolt mains... no forged inernals - all cast, at least from the factory. standard marine roller cam, have specs around here somewhere if you want to know.

with well balanced engine with good comonents you're fine up to 500 horse with a 2 bolt main... and I know lot of people running factory bottom end pushing 400...

do your homework on cams, if you make a mistake you can suck water back into the engine from the wet exhaust and lunch engine in no time.

comp xtreme marine cams... are pretty decent and a fairly safe bet. go fairly conservative if you're running stock exhaust because of above, also need to keep idle down to keep from chipping teeth in the drive when you shift into gear and so it's not a pita to maneuver, etc...

something like this perhaps?


http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=201&sb=1

the edelbrock is a 600 cfm marine carb, 1409, decent easy to set up carb

if you've got vortec heads, don't mess with them, a good top end set up for reasonable / usable power on a marine 350 is something like a comp xm264hr, edelbrock air gap or performer rpm, the edelbrock carb is fine and you're good to go... whatever cam you go with make sure has relatively wide lobe separation angle - more important as you increase duration. also, you want a split duration... to compensate for exhaust flow limitation with heads and exhaust.

the merc thunderbolt ignition you presumably have is a very good ignition. You won't notice a difference with an msd or crane unless you need the multiple spark for idle quality. not an issue unless you go a lot further than you're thinking about.

Just some random thoughts off the top. enjoy playing with it!

ps. magnum is just a word that sounds cool...

 

[wca_tim]

If you want a good book to read cover to cover about building marine small blocks, get a copy of dennis moor's book on small block marine engine performance. some of the information is a bit dated, but there's a ton of good stuff in there. It's out of print.. so interlibrary loan...

 

[stugots1992]

Thats cool thanks.. I have seen 2 bolts hold up to some sh*t as well, I have had a ton of mustangs that I have done up.. I have read things and been on other sites and everybody kind of contridicts eachother about these things.. Its really my first decent boat, I want to do a few things to it becasue thats just how I roll.. Its a persuader 202br, runs low 60's now (gps dont worry) but this engine is strong and I think I can squeeze some more out of it...lol I have read/heard these v8 boats where typically
4 bolters, it would make sense, if its not then it really doesnt matter to me, I will make it go faster either way.. I like the cam in that link I will check into it.. thanks

 

[PA-Checkmate]

I had a 89 350 magnum in my Scarab rated at 270hp. From memory the cam was very mild with lift around .390-.400 and duration in the low 200's. It's basically a truck cam.

 

[wca_tim]

stock mercruiser hydraulic roller cam: pn 431-811658; intake / exhaust; duration @ 0.05 197/207, lift .430/.450 lobe centers 106atdc/112btdc lsa 109.