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flywheel vs. flexplate on small block alpha

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flywheel vs. flexplate on small block alpha

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Old 04-18-2014, 11:53 AM
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Originally Posted by infiniti383
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
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,...
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Old 04-18-2014, 06:50 PM
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Originally Posted by infiniti383
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
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.
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Old 04-18-2014, 07:08 PM
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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.
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Old 04-18-2014, 09:01 PM
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okay guys sounds good I think I'll stick with the fly wheels.thank you everyone for your time
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Old 04-18-2014, 11:17 PM
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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..
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Old 04-19-2014, 09:44 AM
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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.
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Old 04-19-2014, 09:59 AM
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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.
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Old 04-19-2014, 10:33 AM
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Originally Posted by mike tkach
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..
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Old 04-19-2014, 11:49 AM
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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.
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Old 04-19-2014, 02:53 PM
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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.
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