The (very long) thread titled "Lightened Flywheel Questions" brought out some good discussion on some of the negative effects of LIGHTER flywheels on your engine and driveline. But I noticed there was some confusion regarding Lightened flywheels. First, let me define these:

Lighter: A flywheel that was designed and manufactured to specifications that call for it to have less mass, and thus less rotational inertia. The pros and cons were thoroughly discussed in the other thread. Read it if you haven't.

Lightened: A flywheel that has been MODIFIED to have less mass and thus less rotational inertia.

Obviously, both have the same end goal: to improve throttle response and free up some of the torque to accelerate the vehicle. However, in my (somewhat qualified, but that's always subject to debate ) opinion, one should never lighten a flywheel.

Let me give you an example of why I would never lighten a flywheel: This is a true story. An engineer here was doing in-vehicle tests that involved high RPMs and thermal shocks to the flywheel/clutch. As he was revving the engine up preparing to engage the clutch, there was a loud *BANG* and before he knew what happened, he saw the ring gear of the flywheel jutting up through the floorpan of the vehicle. It had sheared apart at 7000 RPM and basically buzzsawed through the bellhousing and into the cabin. He was unhurt, but shaken. Basically, the repeated thermal stresses and high speeds led to the catastrophic failure of the F/W.

When the flywheel manufacturer designs the part (as my company does), they do extensive research into the burst strength of the flywheel. Every hole, thread, contour, and corner is analyzed to ensure that it can handle the stresses of high speed and temperature. And they are designed pretty close to the limits of these stresses, for cost and weight reasons.

When you take a flywheel and machine/drill/whatever, you are doing 3 things:
1) You are reducing its thermal mass, making it more susceptible to cracking,
2) You are reducing its overall burst strength,
3) By virtue of the machining process, you are introducing stress raisers into the part.

One can successfully lighten a flywheel if you are careful. You need to analyze the stresses at the areas being reduced. Also, the better the surface finish, the lower the stress raisers. NEVER DRILL HOLES -- they cause balance problems in addition to being stress raisers. But the analysis and care required to do this successfully to ENSURE the integrity of the part, to me, is not worth it.

Buy a REPUTABLE lighter flywheel if you must.

 

ahh stupid ?
are there lighten flywheels for auto's? i mean dont ppl who have automatics have a different style of flywheel.. i think so.. cause when we did my boys swap he got the long block and i think he had to find an auto flywheel to put on it... not sure.. but i bet this would help out

thanks

 

"ahh stupid ?"

-- huh?

Automatic transmissions do not use flywheels. There is a component called a flexplate that connects the crankshaft to the torque converter cover, but this plate simply serves as a flexible adapter that allows the TC to "balloon" under high pressure.

 

"When you take a flywheel and machine/drill/whatever, you are doing 3 things:
1) You are reducing its thermal mass, making it more susceptible to cracking,
2) You are reducing its overall burst strength,
3) By virtue of the machining process, you are introducing stress raisers into the part."

Like allenp said, lightening a factory flywheel beyond its engineered design is not the best plan of action. Yes, I am awhere that many run lightened flywheels and they swear by them. It mainly comes down to "how much risk are you willing to take"?

Me......I try to keep it to a minimum.

Good info as always Allenp

 

Was the vehicle rear wheel drive with a longitudinal tranny? Scary.

 

shattershields... are used for protection from driveline bits entering the cabin or going anywhere outside the shield for that matter. automatics do have flywheels...lightening your iron flywheel does not make sense when affordable, effective alternatives are available, like titanium and aluminum...

 

so they do?? ahhh haaa
hmm..so then you could with the aftermarket ... manual or auto? huh

 

Hmm.. I don't care if I have a scattershield, I don't want my flywheel coming apart.

Show me an automatic transmission that has a flywheel.

 

Yes, I believe it was an early prototype C5.

 

Can you post the link to the "long" thread please?

 

Link as requested>>>>
https://honda-tech.com/zerothread?id=170541

 

Scattershields are better than nothing but I've still seen plenty of shrapnel fly around when a flywheel lets-go, even with a scattershield. I would rather not have a flywheel "kiss life goodbye" period. And since when was Titanium an affordable, effective alternative?

Automatics do not have flywheels like manual trnasmissions. A few remote examples use a flywheel, in addition to a flexplate, to interact with driveline vibrations/fluctuations. It does not however serve as the mating friction surface for the clutch disk. Flexplates are still used to mount the T convertor and serve as the flex coupling.

 

True, never say never, I am sure there are some auto that use a f/w. But it's rare nowadays. The torque converter usually represents enough inertia that they're not necessary.

 

so if someone said "I have a lighter flywheel" in their auto EX, their lying?

 

They are full of "it"

You would not lighten a flexplate.


[Modified by SLPR, 8:46 AM 6/14/2002]

 

why would you lighten a flex plate.. they are light enough already

 

oops your rite titanium is not affordable, i meant CHROMOLY...i was on a conference call when i wrote that, my apologies..

 

I have never seen a cross-section of a Honda automatic transmission. But I know that 95% of automatic transmissions do not use a flywheel like those found in a manual transmission. If there are other ways to lighten the inertia of the torque converter assembly, I do not know of them. But I am no expert on auto trannies.