Why do some jet guys run Flywheel instead of Flexplate ??

[DUECE'SDAD]

Both of the last two engines (one 454 one 455) had clutch "flywheel" on them, as opposed to the thin flexplate. What is the benefit of using the heavy slingin weight. What would be beter in the cruiser with the stockish 454 ? ? I have one of each (flyhweel,flexplate)

[Fire Water]

Flex plates are designed to be bolted to a torque converter which gives them added strength. They are sometimes used by themselves but often will be bent or distorted by the starter. Usually what happens is the plate will "flex under the load of the starter to the point that it runs off the start gear teeth. If the engine is low compression or has a timing control they my be used to save weight.

[98 Vector 21]

Very Good responce from fire water, Lets not forget about the Ballancing effects..of a flywheel and/or the harmonic balancer...

[Nucking futs]

do a search on here, this has been brought up many times and everyones opinion differs. I use a flex plate but I run a low HP engine.. Only 600 H.P.

[Wicked Performance Boats]

If you change over from one to the other. Make sure you regap your driveline end clearance. Becausethe flywheel is thicker. I'd make a spacer to take up the difference. I prefer flexplates but you must use the SFI approved ones. They are thicker and wobble less. Budlight

[Wicked Performance Boats]

oh, they're lighter and cheaper too. Budlight

[holorinhal]

If You had You'r rotating assymbly balanced with a flex plate,would using a flywheel change anything?Just currious...Hal

[BLOWN JOB]

flex plate rives quicker fly wheel is heavier smother reaction when youre boat comes out of the water its not so violent you have more time to react most big motor boats use a lightend fly wheel or a flex plete for a quicker response

[MarKist]

If You had You'r rotating assymbly balanced with a flex plate,would using a flywheel change anything?Just currious...Hal
What?? :rolleyes: your kidding rite? I thought so.......LOL :D
Markist

[DUECE'SDAD]

On my other jet (almost 10 yrs ago) I used a good flex plate, it worked great. I thought that maybe the weight of the flywheel once spinning might help with idle. You know the extra rotating weight there on the end helping turn the pump ?? ? So looks like i will be running flexplate again.

[Fire Water]

In regards to the question about balancing. Engines can be either internal or external balance. Examples are (stock GM 350 SB internal) (stock GM 400 SB external) Flexplates are nuetral in balance. If the engine is externally balanced and uses a flexplate it will require the use of an external ballance weight. A flywheel for an internally balanced engine is nuetral in balance. A flywheel for an externally balanced engine is different than a flywheel for an internally balanced engine. The externally balanced flywheel must be included in the balancing process during engine buildup. It's also a good idea to have even the internal balanced flywheel present during buildup just to make sure the engine is balanced as best as possible. Confusing isn't it.
If you really want to be sneaky you can do what I have done 350 SB's have two freeze plugs on each side of the block. Most 400 SB's have three, but there are a few that have two. My block has two freeze plugs and by using an aftermarket crank that's internally balanced my motor looks like a 350, but it's really a 406 stroker with full roller valve train.

[drysumpjet]

Although I can't confirm this, but I heard the heavy flywheel results on more shock load on the crankshaft...which is transfered to the main bearings....when the boat comes off of a wave, drops, and lands hard. Perhaps especially true with engines that are "solid mounted" to the stringers. This may be due to an added "gyroscope" effect by the addition weight of a flywheel verus a flexplate. To exaggerate, the spinning crankshaft/flywheel assembly wants to thru the bottom of the boat when the boat "lands" hard, after coming off a wave. Ever play with a gyroscope as a kid? The weight of a spinning wheel is hard to move around. For that reason, I prefer a flexplate.
In setting up a flex plate, I found it helpful to check for flexplate runout while the engine is still on the engine stand. This might require additional spacers between the stand and the engine block to accomodate for the crankshaft/driveshaft adapter. While an electric drill drives the oilpump, I run the starter and observe the flexplate runout (with sparkplugs removed). Mainly due to the lack of support of the torque converter, I have noticed many flexpates (even new flexplates) have up to a 3/8" runout, which will cause our dreaded starter "kick-out". This is not very pleasant to address once the engine is installed in the boat! I bet I will get slammed for this, but to correct excessive runout, pry the flexplate with a large screwdriver to correct, in a direction to compliment full gear engagement to the starter. The flexplate bends easier than you think! I attempt to get the runout less than 1/16".
And of course, your results may vary!!!
Also while on the engine stand, this is a good time to check for the need of starter shims.
Joe

[Wicked Performance Boats]

Just buy an aftermarket SFI approved flexplate. The're .060 thicker and don't wobble nearly as much. Budlight

[Brooski]

Budlight, what is SFI, and where would I get one. I need to replace my flexplate this winter, due to my one "bad spot" on my flexplate, which I think may be from runout, since I could not find any bad teeth when I inspected it. Remember hearing my "zing" every once in awhile??? :cry:

[460 jus getn it]

Weight would be my answer.

[holorinhal]

Firewater ..Thank's for the explaination.I really appreciate the detailed response.
Markist..I did'nt know what the deal with that was,sorry for My ignorance,but now I do thanks to Fire water. I really appreciate You'r valuable input also!....Thank's...Hal
Brooski..SFI(SFI Foundation inc.) is a specification and certification program that certifies parts for racing applications.
An SFI aproved flexplate is a flexplate that has been approved for racing by the SFI foundations spec program and is approved for racing.
These parts or flexplates,in this case, are manufactured by several different companies.
You can visit the SFiwebsite(sfifoundation.com) to see what manufacturars are a member.You can purchase an SFI aproved flexplate from places like Summit or Jegs.or Your local speed shop,or do a search on the web for SFI aproved flexplates...Hope this helps....Hal

[Wicked Performance Boats]

Firewater ..Thank's for the explaination.I really appreciate the detailed response.
Markist..I did'nt know what the deal with that was,sorry for My ignorance,but now I do thanks to Fire water. I really appreciate You'r valuable input also!....Thank's...Hal
Brooski..SFI(SFI Foundation inc.) is a specification and certification program that certifies parts for racing applications.
An SFI aproved flexplate is a flexplate that has been approved for racing by the SFI foundations spec program and is approved for racing.
These parts or flexplates,in this case, are manufactured by several different companies.
You can visit the SFiwebsite(sfifoundation.com) to see what manufacturars are a member.You can purchase an SFI aproved flexplate from places like Summit or Jegs.or Your local speed shop,or do a search on the web for SFI aproved flexplates...Hope this helps....Hal
Thanks Hal, Could'nt have said it better. The thickness and quality is way better. Budlight

[sleekcrafter]

I run the flex plate for two reasons, less static weight and less rotating mass. I have run them as long as I've had boats, and have never had problems. I do however use SFI approved flexplates.

[Placecraft Dragstar]

I never have had a problem with running the flex plates being SFI certified and its less rotating mass, so its better on all your parts

[River Rat 005]

I never had a problem with a stock flex plate in my lake jet boat with 9 to 1 and 500 hp. My hydro has an sfi flex plate with 12.5 to 1, locked out timing, no timing retard and it's been working great for 4 years now.

[Brooski]

Thanks for the info BL and Holorinhal. :boxed:

[MAXIMUS]

The sfi flex plates are ok for low performance engines. On both my blown injected motors (540 & 460) I use an aluminum flywheel & they work flawlessly. With a flex plate on there I couldn't make them live. The flex plates are not as true & I set me gear tolerance very tight so I don't rip teeth off when they get shitty during start up. I went through some painful times changing flex plates & starter gears until I learned... :rolleyes:

[DUECE'SDAD]

So basically the people put what ever they had laying around !!!!

[Rondo]

I have to agree with Drysumpjet. Last summer I replaced my flexplate and I bought two new SFI plates and a brand new GM stock flexplate. They ALL had run out of 1/16 to .250"!!!!! The plate I replaced was the original that came on the boat. [1978 454] I found out that it doesn't take much to bend these plates! Especially the stock ones! I will never use a stock one again. Like they said, these are designed to be bolted to a torque converter and that is what makes them stiff.
However, I was considering a flywheel to replace the flexplate. I have a friend who uses one and he said he cut it down to drop the weight. I'm not sure how much he shaved off but he says it works great.
I chose one of the new SFI approved plate and I still have starter kick out once in a while.
This is off the subject, but I also noticed some problems with my mini starter too. It seems to not fit as nice as it should. It has a slight twist at the mounting bolts and I am suspecting the start gear is not "true" to the ring gear.
That's my 2 cents. It sure sucks when that starter goes ......"ZZZZIINNNNGGGGG" :cry: