flywheel vs. flexplate on small block alpha
 

Im running 400 hp 355 small blocks with alpha drives using the coupler that attaches directly to the crank. These engines will only run 5500 rpm max. What id like to do is get rid of the heavy 153 tooth merc flywheels and go with 168 tooth SFI approved flexplates. The only disadvantage i can see in losing the heavy flywheel is losing the rotating inertia for shifting purposes at low rpm and possibly stalling instead of stumbling on the shift. I plan to idle between 700-800rpm in neutral. Let me know what you guys think. Im very curious as to what critical purpose the heavy wheel has in respect to my setup

flexplates are meant to have a torque convertor to take the shock of power on power off,,
the shock of the prop engaging or throttling thru waves I imagine would not be good for a flexplate..
They do make aluminum flywheels that would accomplish your goal

How would the shock affect the flexplate if the coupler is not attached to it?

good point...dunno then.. someone smarter than me will have to answer! :)

I have a 375 horse 350. Put a 16 pound flywheel on it, figured the lighter flywheel would reduce rotational inertia for quicker reving, but not bring it as low as a flexplate and cause stalling during shifting. I have no issues. Also since my rpms are in the 5200-5600 range, and I am not slamming a clutch into it at 8000 rpm I was not as concerned with getting a high dollar race approved one. Also my legs aren't wrapped around the bell housing either.

a lot of V-drive and jet boats run a flexplate, usually a JW Wheel or similar, to let the engine rev faster. these are light boats so the inertia of the flywheel is not as critical. I would think part would depend on the size and weight of the boat and the conditions you boat in. a heavy boat will pull the engine down faster or if you boat in rougher water that requires throttling alot the light flywheel may make the engine drop too much in rpm when you get off the throttle.

What are you trying to accomplish with lighter flywheels?

in a heavier boat don't bother without a lot of H/P...

Tried the flex plates and lost the ability to idle in gear. I have a two new flex plates available....cheap. Not a big deal to try as long as R&R the engine twice isn't a concern.

in your application a flexplate could be used bit imo it would be a waste of money as nothing would be gained.the only reason you need a flywheel or a flexplate is as a means to spin the engine for starting.

Ayuh,.... An idle of 800 rpms is Too high for an Alpha drive,...

'n with a flexplate, insteada a flywheel, it'll stall every time ya shift into gear,...

Really Bad idea, with No pay-back,...

The only advantage you'll gain is the total weight loss of the Flywheels . It wont Idle in Gear worth a dam , and losing the rotational inertia for faster accel , is negated by the Sterndrive anyway. The frictional losses of 2 , 90 degree gear sets way offsets your MOI reduction of lighter flywheels.

Hull design, weight, and water itself (ie:load) vs engine power is our largest obstacle against acceleration rates of our boat. Not the engines ability to accelerate.

A small tunnel boat with big cid BBC may be a different story......but very small story.....lol.

okay guys sounds good I think I'll stick with the fly wheels.thank you everyone for your time

i run a 434 hp 355,,like ,emtioned your not going to really notice the differance..tryed it in a stock cat with a small ram thripple disc set up..kept going through starters bendix's and sheering off the teeth on the flywheel..went back to the big flywheel..

Call me crazy but, I'm going to use an SFI rated flywheel on my bbc. Maybe it's overkill but for 225 bucks (made in USA, billet steel RAM) I'll take the peace of mind.

Even though there will be no "hit" like a manual gearbox drag car would see, the thought of a flywheel coming apart and tearing through my hull makes it cheap insurance.

i would be more concerned about a stock balancer,i have seen what can happen when one comes apart in a boat and it gets ugly.

exactly...never seen a flywheel issue except on a drag boat..

I have an SFI damper as well.

Like I said, maybe overkill but at 225 bucks I'll take it. Also, I need a zero balance flywheel.

Several years back here in Cleveland, (when we use to have racing here) a team had a flywheel come apart and saw right trough the hull. They barely got the boat out of the water before it sunk.

One advantage of a lighter flywheel is the rotational inertia would be less when the drive is coming in/out of the water therefore less stress on the drive.

Nothing wrong with stepping up to SFI rated stuff......unless it's Procomp crap.

Not a real advantage leaving the water, it will change rpm easier with less inertia if the throttle isn't pulled back. It should be a big advantage on reentry for any mismatch of rpm to boat speed.

I doubt you'll get the boat out of gear at 700-880 RPM idle and at the at speed going into neutral, your going to eventually break something. The Alpha shift scenario is totally different than a Bravo or TRS. The lower the idle speed the easier it is on the outdrive.