uhpguy

Ok, I have searched and searched not here but the whole internet. I have a 21ft Chris Craft Scorpion I bought a couple years ago. It orginally came with what I was told was a gen V 330hp 454(it did have a forged crank and forged pistons, along with large oval port heads and a marine 4 barrel high rise intake). Short story, I blew that engine up due to oil problems. Replaced it with a gen IV shortblock I put together. I used the gen v flat tappet cam from the previous engine. I have since broken the factory cast crank(broke at a crank throw and did no damage) in the gen IV motor and am in the process of replacing the crank with a forged version. I was contemplating a cam change while I have it down but can not for the life of me find any info on the cam thats in it. The only markings I can find are on the distrubutor end of the crank. It has "MP" stamped on one half and "Z010" on the other half. Any ideas on what this is?

picklenjim

Probably be best to just get a new cam and lifters. A hydraulic roller would be sweet if it's with in your budget. If you plan on using the old one hopefully you kept the lifters in order so you can replace them on the same lobe their worn to.

uhpguy

Its not that I plan on reusing it, its more a matter of what it is, so that I know if I am actually upgrading or not. Make sense? I am considering this Comp cam: 249-11-240-4

picklenjim

Ya it would be nice to know but not absolutely necessary. It may be the one on the bottom of this list.
http://www.partsgeek.com/assets/perf...42-1229915.pdf
That comp cam may have a little high of a power band for a stock 330-454 which will probably only see 4800 rpm max. Little too much duration. May want to concider one step lower to this.
http://www.summitracing.com/parts/CCA-11-236-4/
It's like 400 rpm lower on each end of the power band. It would make better power in the rpm range you are going to be operating in.

uhpguy

Jim, I actually came across that same chart and wondered about that. I dont know how much it matters, but it does have the large oval port heads, a dual plane high rise aluminum intake, domed pistons with 10.2 compression, and a decent exhaust system(cant find a name anywhere on it). I plan on a little more prop, as the engine would pull to 6000 no problem before the crank broke. The cast crank broke from just being stupid. I was towing another boat and kept trying to get them on plane.

picklenjim

Oh, for some reason I was thinking that it was a 330. In that case that 249-11-240-4 cam would be the best choice in my opinion of the Comp cams. Those are some good parts you got there. With 10.2 compression and iron heads be sure you run 93 octane and be conservative on the timing to avoid detonation. Should have at least a 750 CFM carb and a good fuel pump and at least 3/8" lines. With out a good fuel pump you could lean it out on the top end at those rpm's. Also good insurance is a set of Inconel exhaust valves. Their expensive but necessary for the high exhaust temps you'll be making.
21 foot boat with that engine probably would work best with a 25p prop.

uhpguy

Jim, the heads were on the previous "330" engine but are marine heads with inconel valves and it does have 3/8 line all the way from the tank along with a good fuel pump and a 750 edelbrock carb. I say "330" only because thats was I was told and dont know enough to say what the actual hp is. I have figured out along the way that I believe it was probably the 385hp judging by the heads and intake, plus the forged crank and pistons. I have always been into outboards(non racing, factory type stuff) and small block fords. The whole chevy bb thing is new to me as is proper cam selection. This go round, I am just looking for a little for umph from an off the shelf cam. If I dont go out of the states to work permantly, then it will be getting an aftermarket big cube engine in time as I love the hull. Is there another brand off the shelf cam you would suggest over the one I picked?

uhpguy

Picklenjim, you stated my boat with my engine should have about a 25 pitch prop. The boat is an 83 chris craft scorpion 210 bowrider. I just looked and I currently have a mirage plus 17 pitch prop, part number 48-18278. Last time out with the z010 cam and the 10.2 compression it would turn 6200 or so and hit 55-57mps gps. With just the cam change wont the 25 pitch be too much? I was thinking more along the lines of a 19, possibly a 21 in the same mirage plus, unless you or someone else has a better suggestion

picklenjim

Your turning way too many RPM's. It's because of that 17P prop. That's way to small for that boat and motor. Should be maxing out at more like 54-5500 rpm's. Those piston's aren't stock. Stock 385 hp would only have like 8.5 or 8.75:1 compression. You have improved exhaust and will have a better cam, good intake and carb. I would think you will be making like 425 hp. if not a little more. Remember with 10.2:1 compression you are at your max compression for iron heads. Always be sure you run at least 93 octane.

Boats in the 21-24 foot range with stock power will be running 21-23P props. With your extra power in your 21 foot boat a 25 should be just right. Should be running more like 70+ at 5500rpm's. If you were turning 6200rpm's and only running 57 thats not good. That big block shouldn't be run over 5500. I'm surprised you didn't blow it up. Must have had one hell of a hole shot. Are you sure your tach is correct ? By the way what drive do you have and do you know the ratio of it ?

uhpguy

It did jump up on plane quite quickly. And yes I know it was turning too many rpms. I wouldnt run it that way, just hit it a couple times to see where the rpms would go and got right back out of it. It is a bravo one diesel drive. I will have to look at it later today for the ratio, but it seems like it was 2something:1 on the upper