How much cam?

[disco_charger]

Hey kids, I got a question. If I continue to run my BBC Large Oval/Open chamber circa late 1970's heads on my boat, how much cam can I run before I get into major surgery on the heads? I'm thinking hydraulic roller...I'd like to go pretty big...
Disco

[Dennis Moore]

Disco,
It all depends on your valvesprings, if you have the GM dual valve springs (the ones used on the rectangle port heads) maximum lift is about .540 inches. The single valve spring with damper will only work with about .500 lift.
You need a camshaft with approximately 218 to 224 degrees intake duration and 226 to 234 degrees exhaust duration @.050 check with 110 to 112 degrees lobe separation angle. Call Comp Cams for a recomendation. You can also buy the book BIG BLOCK CHEVY MARINE PERFORMANCE by calling 626-675-3548.
Sincerely
Dennis Moore

[HM]

Hey Disco,
check out this thread regarding hydraulic roller lifters.
Roller cam

[disco_charger]

Thanks guys, Yeah I was reading that Holy Moly. I'm not sure what I'm going to do yet, but I'm exploring some options. I figure the easiest way to make power is through the heads and cam, but I haven't made up my mind yet. Might not do anything to the motor. I'm still exploring my options.
Disco

[HM]

Hey Disco,
I have heard from several sources that if you want a pretty big cam and long life, then solid lifters is the best option. Solid lifters require more maintenance like adjusting lash and winter storage(not that big a deal for us SoCal guys).
I am sure there are guys out there with big hydraulic roller set ups that have gotten nice life out of their motor. But what is long life? All relevent.
You probably read about my personal failure with the hydraulic roller lifters, but, I got a good season and a half with some pretty hard running. The bad part was that the rest of the motor was in great shape before the lifter let go (and several other lifters were cracked). I had compression checked the motor a month before and it was like new. When we pulled the motor apart, even though it had gone nuclear, you could tell the motor was in great shape, all the bearings were not showing much wear, all the pistons looked great--I mean everything looked great. The engine builder I took it to for the rebuild thought that I may have blown it up on the first or second run in it - I had almost 300 hours on it.
So is my story only antedotal or is it representative of a general problem? I think with the mfg'ers stopping production and several other sources having problems and Crane giving me almost $1000 worth of parts for free including shipping from FL to CA, I would think that there is serious merit to the problem. Perhaps in another year, when the last mfg'er is caught up on production and all the cam companies have the good hydraulic rollers on their shelves, it might no longer be a serious problem.
I am making a couple of changes to my motor this year, and may make a cam and lifter change. I am getting rid of the cam gear drive because I can not get the cam end play tight enough with a cam driven waterpump to stop the variance in timing.

[BOFH]

Easiest, perhaps, but not the best. Think "chain" and "weakest link" for a moment. Most factory designs are very balanced. This is done because it is the cheapest and most reliable way to get a given HP. When you replace one or tow parts, you loose that balance. This can mean you get less out of your new parts than you could (best case) or you put unusual stress on other parts causeing premature (and sometimes spatacular) failure.
My personal limit for bolt on parts is $500. If I am spending more than that (labor is me, so that is not included) I will go ahead and do a full design and rebuild.
That said, a notch or two up in cam is not too bad. I do not like roller lifters. They break more often than flat lifters, and I have bad luck. If you are under 5000 rpm, hydrolic lifters are the way to go. Easy and simple. Over 5000 rpm, get solid. Anti pump up lifters are little different (and in some cases, only the packaging is different) from standard, and setting them loose is dangerious. (Try and find that part of a broken ring!)
If you are pulling, or replacing the heads, raising compression is a big plus as well. Higher compression works on ANY engine, with the requirment of better fuel, and carefull monitoring.

[Dave F]

Camshafts are not something you can suggest without knowing some details.
In my opinion, hydraulic rollers do make the best power size vs. size, but also in my opinion should not be run more than 6000 rpm. I have the same opinion for oval port heads.
So, with that range in mind, here are my suggestions with matching compression ratios.
Major detail include:
RPM range, compression ratio and cubic inches play the biggest role in cam selection.
The second biggest role is played by your exhaust system in a boat.
As Dennis said, staying with stock compression and stock valve springs stay under a .550 lift and no more than a 226/234 112.
Those numbers will be ok to about 5500 rpm or so.
GM has a cam right from you local dealer in this range; part #12366543 224/234 110 .527/.544
If you want to run larger than what Dennis has suggested I would suggest an absolute minimum of 9.5:1 compression, prefer 10:1 or higer depending on fuel capabilities.
With those numbers for a 454-502 no more than a 234/242 112.
The catch to that cam is that it's a Crane cam. Crane generally likes to have a higher lift than stock GM and Comp cams. Therefore, needing springs.
This cam can take you to the 6000 rpm range which combined with your head selection is the limit in my opinion.
DAVE

[disco_charger]

OK, I probably should have specified. New heads may be coming, but I'm exploring the option of just going rebuild on the heads. Maybe springs and valves, roller rockers, valve job, port and polish. However, not sure could be anything at this point. Looking to make some power and stay pretty reliable. I figure I can get a more radical cam profile out of a roller, but at what point do I have to start cutting valves and the like. I will run a smaller head gasket and bump my comp up to about 9.5 to 1. I know I'm going to some kind of thru the transom header and probably either a tunnel ram/ dual carb, or a dominator and Super Vic, Dart, Merlin, whatever intake. Not sure on that yet. Still jacking around about that. It may have a lot to do with what I find at the Long Beach/Pomona Swap Meet. I'll probably cut my impellor down to a B and look at turning less than 6000. Hell, maybe I'll just buy another boat. Not real sure. I may just be the proud owner of a 16' Witchcraft with a 90 HP Merc! I hear Gig almost never uses his and it's faster than 77 Charger's boat
Disco

[Dave F]

The only thing I have to say at this point concerning your head gasket is becareful of quench space.
I've read that .035" is the absolute minimum staying under 6000. However, I prefer a little extra cushion of .038-.040" at 6k.
In any case with any hydraulic lifter it's my opinion you need to stay 6k or under.
good luck
DAVE

[HM]

Hey Disco,
you are not going to hack up that award winning vintage machine are you? J/K LOL, as you noticed, the guy who tied with you for vintage boat, who I can't remember at this time , had a very hacked up vintage boat!
This wouldn't have to do with your family's racing roots and the dropped jaw reaction to your fairly stock river boat?