bg383

I've come down to a cam that i believe is suitable for my Set Up, however, its a "boat cam" (comp camXM278H). It's going in a 383 with 10.6 compression, 3:73 gears, 3000 stall, AFR/Broadix 195 heads, airgap intake,750 carb,1.52 rockers, 87 monte carlo, Will see street most of the time (some strip) so I wanted a cam where low-end torque is Present.... A cam with a nice racey (rough) idle. Looking for 500/500 HP/TQ....Does anyone oppose this set up; Are there dyno numbers on this cam(can someone run a dyno sim); And any other cam sugestions?

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that cam grind comes up as a ford big block cam, not the best choice for a sbc of any size

bg383

actually the cam is from the X marine line up...from comp cam website. Hyrdro Flat Tappet.

NatesZ/28

Boat cams are interesting...well cams in general are (I know I need to get out more). Im no genius, so I'd ask COMPs opinion BUT boats need lots of off idle power to get the thing moving onto plane and a smooth even powerband because the prop can come into play as far as pitch and what happens if the prop leaves the water. You dont want a peaky cam in a boat...it'd be impossible to drive.

That being said, there was an article with COMPs guru Godbold saying the best intake and exhaust lobes hes ever designed are XFI designs...and that theyre using them on custom cams for carbs. The cam itself doesnt know what its going into, the designations are there to help classify things for our benefits, not the motors

1989IROC-Z5.7L

Dont marine engines run backwards to car engines?

jccaclimber

I don't know about all engines but, the sbc a friend of mine has in his boat runs something backwards. Rather than a timing chain or 3 gear set (where the cam and crank rotate the same direction) he has 2 helical gears, such that the cam and crank rotate opposite directions.

Camarslow

^What he said, powerband for a boat is crucial to how it operates. To reach 500hp/500tq a cam that provides the amount of off idle torque and powercurve that a boat cam provides, may not get you the results you are looking for. It's possible that cam may work just fine for your purposes, but you really should contact comp and see what they say.

NatesZ/28

It depends on the application. In 2 engined boats, the engines rotate opposite of each other. One turns clockwise the other counter clockwise to cancel each other out; in single engine apps I think they use a conventional rotation, but dont quote me on that

Call comp, iskenderian, schneider, cam dynamics ETC and ask them what they think

I might think about asking COMP about an XFI lobe'd cam for your motor

Wild Weasel

Not quite true.... twin engined boats can have either opposite turning engines or they can reverse the gear box and turn the prop the opposite way.

rv34

I have no input to this, but my 85 Chris Craft hads a 305, that spins the same way of a regular car engine.

basiccamaro

As far as rotation goes in a boat-

For a single engine boat, the industry standard is for the prop to turn to the right. Many marine conversion companies do this by running a regular car engine turned around backwards in the boat, running the gear box right off the front (if it was in a car) crank snout with no harmonic balancer. Evidently the harmonics and vibrations can run right down through the gearbox and prop shaft and dissapate out into the water through the prop. It's been done for years with no problems and seems to work quite well.
While you can get left hand props, there is a much larger, easier and cheaper selection of both props and cams using this method. Prop torque affects boat handling at low speeds during docking maneuvers, especially in reverse. Most mariners are used to dealing with the affects of running a right hand prop vs. a left hand prop. Sometimes there are rudder offsets or fins to deal with the torque forces at higher speeds and during accelleration and decelleration.
And it also increases engine to hull clearance in the boat by having the flywheel in the front. Usually straight inboard boat engines are slanted downward in the back (of the boat).

Sometimes they will run the engine in the normal front to rear placement, such as in a car, it all depends on engineering, boat size and weight, shaft length, strut angle, prop diameter and a few other things. But in a single engine boat this will require the engine to run backwards if you want to run a right hand prop.

If you have a twin engine boat, one engine has to run backwards in order to have counter rotating props to balance the torque side forces.

I am most familiar with older Chris Craft marine conversions of small block Chevy engines.
Chris Craft started using flywheel forward 283's in both single and twin engine boats in the very late 1950's. Later they made "F" and "FL" (left hand prop rotation) models that were flywheel aft, and then later, another flywheel forward version called the "Q" and "QL" that were designed from the get go to have closed cooling systems.
In all of these models there were standard and reverse rotation engines available for the needs of each application.

An interesting note, in the Chris Craft conversions the cams and distributors turned the same way whether or not the engine was a reverse rotation engine or not. The firing order was adjusted accordingly, but the cams both turned the same way.
The reverse rotation models used two meshing cam gears instead of two seperated gears with the normal connecting chain.

basiccamaro

Oh, I forgot, in many cases more modern marine car engine conversions are just using standard car rotation engines and doing the counter rotation through the use of special gear boxes in order to make the props turn whichever way they need them to go.