Small Block Chevy Cam Selection ?

[baddassbaron]

Looking for help in Cam selection for small block chevy. What do you think with setup below?
In talking with Jegs and Comp Cam they suggest, 12-240
Gross Valve Lift - .480 /.489
Duration at .006 tappet lift - 270 / 286
Lobe Seperation 112
Here is my Boat and motor setup setup running in Fresh Water (Great Lakes)
19ft Hull (similar to a Donzi, but better)
350 chevy. Apha Drive
350 bored over .040 flat top pistons
Edelbrock Performer aluminum heads 64 cc chambers
Performer Intake
750 Holley Double Pumper
MSD Ignition
4 Inch thru hull exhaust
Suggestions for a better cam or is this pretty decent with current setup?

[Havasu Hangin']

Compression?

[cstraub]

Getting close to the end of the month, must have alot of that cam on the shelf. Which edelbrock head? Your a little over carbed for an I/O engine.
Chris

[baddassbaron]

Thanks for the replys !
Guessing at compression - 8 to 1 ?? (should be better after all installations). Based on setup what do you think compression is ? The Edelbrock heads I have are the Aluminum Performer series, straight plug 64 CC (brand new, not yet installed). Can I make the 750 Double Pumper carb work? (also brand new not yet installed). The Comp Cam 12-240-4 power range is supposed to be 1800 to 5600. Comp said it should rock.

[1BIGJIM]

To get an estimate on compression ratio you need to supply more information on the pistions and head gasket. I built a small block years ago with about the same combo you are trying to assemble. Now I am guessing compression ratio you have would be around 9:1 just guess. You can run 10:1 with no problem with those heads. There so many factors in determining correct compression ratio. You need to CC the heads, need deck height, pistion height and so on. I ran a Comp Cam on a 110 center line in a small block, and it really moved. Had a little trouble with idle and loading up.
Hope this helps

[rmbuilder]

Dan,
There are some elements to consider with your current configuration. With the Edelbrock Performer heads/64cc combustion chamber, your compression ratio will present some potential problems. Given flat top pistons, that usually have –5cc for valve relief, it will be impossible to maintain optimum quench and a pump gas usable compression ratio. Given your parameters of 4.040” bore and 3.48” stroke the numbers are:
Using .000” deck and .039” gasket, you will have optimum quench, however your CR will be 10.44. Even the ability of Aluminum heads to withstand ½ point over iron will yield excessive compression to be reliable with marine gas.
The stock deck of .025” and a shim gasket of .026” (total of .051”) yield a CR of 10.15.
A stock deck of .025” and a .039” gasket (total .064”) nets an excessive quench that will cost power and detonation resistance, yields a CR of 9.84.
The 12-240-4 cam mentioned is the CompCam XM-270H-12. The cams late IVC numbers may help bleed of some excess cylinder pressure, but unless you plan on running more than 5200-5400 RPM @ WOT the engine will not be within its optimum power band, and the 54* overlap with stock manifolds makes for potential reversion problems. Also the I/E ratio of your head does not require as large a duration split as the 12-240-4 cam offers. My suggestion would be to address the build issues first, then design the cam that works best in that configuration.
Bob
MarineKinetics

[baddassbaron]

RMbuilder
Thank You, thats what I needed to know
Ever in Michigan. Great advice
Dan