Lightened flywheels for street motors?

[slowlearner]

Collecting bits for my new mouse motor... ie. upgrading from a judsoned 40hp 1200 to a blown/intercooled/efi 1300. Got a good 1600 crank and flywheel for it. Was planning to have it lightened some, but a mate said, "apparently that's not a good idea". Love to hear people's thoughts. Who's got a daily/cruiser with a lightened flywheel? Also, wonder whether I should have it 8 dowelled or not. Projected figures aren't super high, maybe 100-120 hp max at the flywheel...

[Zach Gomulka]

Who doesn't have a lightened, 8 doweled flywheel would be a much shorter list.

I'd love to hear why he thinks it isn't a good idea (as long as the crank is counterweighted), I can't think two more proven modifications than those.

[Donny B.]

Zach is right.  Definitely 8 dowels and a lightened flywheel.  Engine response is much better with a lightened flywheel.  All high performance engines should have 8 dowels unless you use a flanged crank.

[richie]

If you are going to use the stock 1600 crank you mention without added counterweights then for a daily keeping some weight in the flywheel may make it easier to drive, what pulley are you planning on using? and get the crank 8 dowelled for sure, its cheap insurance

cheers Richie

[nicolas]

exactly what Richie said. weigh the counterweight crank and a stock one. the weight that is added to the crank can be removed from the flywheel IMHO. but to that extent that the  flywheel doesn't warp because it doesn't have much material left to disperse the heat.
i used a very light flywheel on my 1641 cc engine in a square back. never had any issues.
i will reuse this flywheel on a 78 stroke counterweighted  crank and it is still heavier compared to a stock crank and stock flywheel.

However! i went to the BMW museum and they used small but very heavy (18kg - 22kg) flywheels in there race engine in the late 70's early 80's. i still haven't fully figured out why. the only reason may be to 'keep on turning' with a higher CR- engine (continuation of the rotating object, i can't express myself better, but you know what i mean).

[slowlearner]

If you are going to use the stock 1600 crank you mention without added counterweights then for a daily keeping some weight in the flywheel may make it easier to drive, what pulley are you planning on using? and get the crank 8 dowelled for sure, its cheap insurance

cheers Richie

I'm planning on having the stock crank/rod/pistons/flywheel balanced with counterweights. I'm using an alloy multirib pulley for a serpentile style belt system.

[AJ]

Like Richie said, keep the weight in the flywheel, its always good for the bearing life on a street motor. Some say never go under 6kg on a flywheel because of the lack of rotating mass at the flywheel will make the crank flex and pound the bearing. And thats includes even cv cranks.

/Andreas

[modnrod]

However! i went to the BMW museum and they used small but very heavy (18kg - 22kg) flywheels in there race engine in the late 70's early 80's. i still haven't fully figured out why. the only reason may be to 'keep on turning' with a higher CR- engine (continuation of the rotating object, i can't express myself better, but you know what i mean).

"Flywheel Effect".
Good for helping small low torque motors maintain speed up and down rolling hills with less throttle needed, good for cruise economy, good for easy driving (especially slow creeping in first through the city).
Also good with high revs off the line to help prevent the motor bogging down.  

PS; I forgot, heavy flyheels are also CRAP at "blipping" between gears or on/off throttle stuff. 

[Bruce]

maintain speed up and down rolling hills with less throttle needed,

That's a myth.  It takes hp to climb a hill.  If all it took was a heavy flywheel we'd all have 100kg flywheels.

The flywheel I use is less than 4kg.

.... good for the bearing life on a street motor. Some say never go under 6kg on a flywheel because of the lack of rotating mass at the flywheel will make the crank flex and pound the bearing.

Not IME.  My engine has 89,000 miles on it so far.  How much more bearing life is necessary?

[cedric]

I think you need torq for up hill in low rev.....