CcanDo

Flywheels are available in several weights. Some are made from aluminum and others are made from steel. Both materials are offered to create a specific weight flywheel.

It is an assumed fact, the lite weight flywheel accelerates and decelerates more rapidly than a heavy flywheel.Therefore,one may select the lite flywheel because of throttle response.Conversely,when the prop leaves the water the engine may instantly hit the rev limiter or over rev.The lite flywheel will also have a limited amount of stored energy.Therefore,starting,idle quality and dock manners will be effected. Also of concern is that a lite flywheel may collect more heat and cause an imbalance,not only in the flywheel but in the drive plate.

Comparatively,the heavy flywheel will start and idle better and have better dock manners.However,throttle response will be less than with the lite flywheel.The heavier flywheel may also be more user friendly at cruise because, there is less throttle response.

In my opinion, the heavier flywheel offers most advantages.However,a throttle jockey that jams the sticks forward may increase the risk of detonation. Jamming the throttles forward would ask the engine to over come imbalances plus spool up the heavier flywheel.

Would anyone care to share their opinion?

Edward R. Cozzi

I seems you have answered your own question. For most marine applications the heavy flywheel gets the job done with less risk to the rotating assembly. Way back in the early 80's the late, great Keith Hazell and I tried aluminum flywheels in a 38' Bertram Competition race boat. The revs came way too quickly and we were constantly zinging the limiters in load-unload-load situations. Dean Gellner and Tommy Hoffstetter could expand on this better than I can. I'm old and way past my prime. WTF do I know anyway? Who am I? Why am I here? Where's my Depends? Somebody answer that damn phone! I've fallen and I can't get up.

Chris Sunkin

Ed,

You're sounding very vice-presidential tonight. Perot been calling again?



On the flywheels, the only real application where aluminum works well is in shorter-stroke drag race engines where you're making horsepower up high but sacrificing some of that mid-range toprque. The need to be able to build revs quickly is the primary factor there. Losing flywheel mass in any application where there's engagement/disengagement of the driveline to the driven surface hurts you both ways. Larger mass prevents RPM flares on the disengagement when your timing isn't millisecond-perfect and upon re-engagement where you might not be right on the throttles, one way or another. Lastly, aluminum lacks the long-term durability of steel. It's not going to like those back and forth shock loadings. We had it pretty much down to a science of how many runs an aluminum flywheel would make before it popped. I've hairline-cracked some steel flywheels but have never grenaded one, regardless of how old it was.

turbo2256b

iTrader: (1)

Aluminum works good on road race cars for quicker revs and shifting

articfriends

iTrader: (1)

I always thought aluminum flywheels were for drag racing but it seems every p-class racer looking for a edge is running them these days too,Smitty

CcanDo

The V12 Allison uses something like a 100# flywheel.First,so that it will idle and second,to help with RPM spikes.

We are not even remotely considering a 100# flywheel.However,we feel it needs to be heavier than the shelf item 27#,10-18 machined steel.The starter ring on the 27# flywheel is welded at three located points.It is my understanding,welds are required to prevent the starter ring from dislodging. Balance of the welded starter ring flywheel may or may not be a problem as temperature of the flywheel is increased.Therefore, the 27# option is eliminated.

The next shelf item weight is 35# w/pressed on starter ring.However,it is said, only 10% of the marine flywheels are sold at this weight.We have used the 35# unit and it seems acceptable.However,it doesn't seem very scientific not being sure 35# is ideal.

The next shelf item BBC weights are 40# and 50#.I'm not aware of other weights.However,custom weights are available.

I'm of the opinion, 10-18 may require Cryogenic treatment.Cryogenic treated Billet Steel may also be worth considering.The opinion is based on concern for balance.

Little is said about flywheel weight, it is an abstract, complicated component.Factors ahead of the flywheel include displacement,cam,crank to rod ratio,timing,timing ramp,induction system and etc. Behind the flywheel is the driveline, gear ratio,prop pitch,hull weight and etc. Application is also a major part of the equation. Not all boats are race boats. Durability becomes more of the requirement in the hi performance pleasure boat.

It is interesting,there doesn't appear to be a distinction between engines for V hull and catamaran.However,the catamaran seems to break loose when it is packing air under the tunnel. Therefore,there must be a change in the Torque/HP to weight rato at that point. Step bottom V hulls probably experience some of that change as well.

Engines are basicly offered in one size fits all. While that theory might be deemed "good enough", I'm not sure it is totaly professional.

In my opinion, a large part of the total design includes focus on the flywheel weight. It would then be said, this combination is recommened for the specific hull,hull weight and intended application.

What is your opinion?

Panther

I think p class racing these days is more about acceleration than top speed and not running in rough water since a majority of the courses are somewhat short or on inland waters.

Hy-Velocity

Smitty please send me an [email protected]- I want to talk to you about your outdrive additive. Thanks

BenPerfected

I am not sure I buy the free reving theory in a marine application. When the prop breaks loose you still have a direct connection to the drives . As the drives use 25-50 HP, wouldn't this act like a "big" flywheel (add resistance) to free reving? I can see a small benefit to a heavy flywheel around the docks, but not sure it is significant. Who has measured the impact at idle? I suspect the Mercury wheel weight is based around a stock GM flywheel because it is inexpensive and comes with many of the engine packages.
Aluminum flywheels may have acceleration benefits over steel, but they cost more and offer less corrosion resistance. The flywheel cost, corosion resistance and weight are the only easy things you can measure in a marine application.

CcanDo

Perhaps we will have some formulas in the near future. There might be some fun in applying calculations to a specific boat or two.