Flywheel mass

[d00df00d]

For cars with single mass flywheels, is there a reason -- OTHER than drivability and cost -- why they're not as light as possible from the factory?

I'd imagine a lighter flywheel might have less heat capacity and vibration damping; theoretically, that might shorten the lives of the clutch and certain parts in the engine and transmission. Can't find much discussion of either possibility, though.

Anyone know, or have any thoughts?

 

[4wheeldog]

Flywheel mass makes idle much smoother. But I guess that is a "Drivability" issues, as well. Getting a manual transmission vehicle moving with an extra light flywheel requires a lot of clutch slippage.

 

[dareo]

ultra light flywheels are fun for toy cars but you will want flywheel mass on regular drivers.

 

[Kuato]

Stuff above is true, but the main reason: torque. With a low mass flywheel there is no momentum and any load put on the engine will lower the rpm with little movement of the vehicle - but acceleration once things are fully engaged and moving is much faster

Higher weight flywheel will initially transfer more motion to the vehicle. Think about one of those old tractors with the huge flywheel on the side - it's how a low hp engine could move all the mass.

Street vehicles are a compromise between the two, although I'm sure that a sport car's flywheel is proportionately lighter than a truck's, since the intent is different.

 

[Rand]

Originally Posted By: d00df00d
For cars with single mass flywheels, is there a reason -- OTHER than drivability and cost -


Might as well say do brakes do anything important besides stop you.

The weight is all about drive-ability and intent no other reason in a normal car or truck.

 

[mjoekingz28]

They (light flywheels) probably allow cars like yours to spin up the revolutions alot more brisk. Also, I would expect engine braking to pull you forward.


Probably an asset for high revving racecars.

 

[dailydriver]

Originally Posted By: 4wheeldog
Flywheel mass makes idle much smoother. But I guess that is a "Drivability" issues, as well. Getting a manual transmission vehicle moving with an extra light flywheel requires a lot of clutch slippage.


^^^THIS, especially for cars with small, no torque output engines trying to move a 3200+ lb. ride from a standstill.

A very light flywheel IS less noticeable on high torque, powerful rides with that same mass.

The next time I change this clutch it will get a 2 or 3 disc, small diameter, very lightweight clutch, with an aluminum alloy flywheel.

 

[d00df00d]

Originally Posted By: Rand
Originally Posted By: d00df00d
For cars with single mass flywheels, is there a reason -- OTHER than drivability and cost -


Might as well say do brakes do anything important besides stop you.

Well, I could ask what the point of a Brembo BBK is besides added stopping power. In that case, the answer would be comprehensively better heat management, easier pad changes, better pad selection, and (at least in my case) big reductions in unsprung and rotating mass.

I could also ask why -- other than cost -- the car didn't come with brakes like that. In that case, the answer would be that while cost is the main consideration, there's also the fact that fixed-piston calipers introduce more failure points.

As I mentioned in the first post, I've seen a post here and there that alleges that a lightweight flywheel has other effects. Mainly they focus on less torsional vibration damping, which would make it harder for the engine to maintain low RPMs and theoretically could increase wear on certain engine parts. Was wondering if anyone here could comment.

 

[mjoekingz28]

Maybe it is like a crankshaft.

Engines probably couldn't run without a heavy crankshaft. Especially single cylinder engines.

 

[OVERKILL]

Originally Posted By: mjoekingz28
Maybe it is like a crankshaft.

Engines probably couldn't run without a heavy crankshaft. Especially single cylinder engines.


This is apparently a Subaru flat six crank:

Note the absence of heavy counterweights

An engine will run without a heavy flywheel. But they can be very sensitive to RPM drag down which makes taking off with a grabby clutch really fun.

 

[SHOZ]

My Gen Coupe 2L turbo came with a dual mass flywheel. They were prone to the springs breaking. I went to a lightweight single mas and it is harder to get going. The clutch disc doesn't help a it will barely slip, more so either on or off.

But I will next be putting in an OEM +13 Gen Coupe dual mass and disc as they were much improved.

 

[mjoekingz28]

OVERKILL,
Dont argue with me. We all know counterweights are for keeping it smooth. A heavy crankshaft is for inertia and keeping it spinning between firings.

 

[OVERKILL]

Originally Posted By: mjoekingz28
OVERKILL,
Dont argue with me. We all know counterweights are for keeping it smooth. A heavy crankshaft is for inertia and keeping it spinning between firings.



What?

You specifically stated:

Originally Posted By: mjoekingz28
Engines probably couldn't run without a heavy crankshaft.


Note YOUR use of the word PROBABLY, meaning you were NOT SURE. I posted an example of an engine with a very light-weight crankshaft. And please don't tell me what to do or not do, that's not going to result in this heading in a good direction.

The job of the FLYWHEEL is to keep it spinning smoothly between firings BTW, not the crankshaft.

 

[OVERKILL]

Another interesting crankshaft, the Windberg Lightweight, this one for the 4G63:

Note the absolutely tiny counterweights!

Just over 25lbs.

 

[OVERKILL]

And a "back in the day" crank out of a Model T Ford, note the complete absence of counter-weights:

 

[javacontour]

Drivability. It probably makes the car smoother at idle and less likely to stall if a stick shift.

As lighter mass flywheel is easier to stall when pulling away from a stop in a stick shift car.

Originally Posted By: d00df00d
For cars with single mass flywheels, is there a reason -- OTHER than drivability and cost -- why they're not as light as possible from the factory?

I'd imagine a lighter flywheel might have less heat capacity and vibration damping; theoretically, that might shorten the lives of the clutch and certain parts in the engine and transmission. Can't find much discussion of either possibility, though.

Anyone know, or have any thoughts?

 

[mjoekingz28]

Counterweights are to make it smooth, not heavy.

I tell ya what, why dont you and all Canadiens stay out of the US. I worry more about our northern border than I do the one with Mexico. Ya'll already killed the Camaro from 1967 when GM let yall build the fourth gen. Stay out of detroit and quit running the Canadian National railline where KC Southern should be. Yall are bullies and I do not like you. So just stay up there and I will probably call D.C. To see if we can tighten border security to keep Canadians out of America. Go build a Can-Am or something.



A counter balancer is to counter balance- not to make the crankshaft heavy.

 

[OVERKILL]

Originally Posted By: mjoekingz28
Counterweights are to make it smooth, not heavy.

I tell ya what, why dont you and all Canadiens stay out of the US. I worry more about our northern border than I do the one with Mexico. Ya'll already killed the Camaro from 1967 when GM let yall build the fourth gen. Stay out of detroit and quit running the Canadian National railline where KC Southern should be. Yall are bullies and I do not like you. So just stay up there and I will probably call D.C. To see if we can tighten border security to keep Canadians out of America. Go build a Can-Am or something.



A counter balancer is to counter balance- not to make the crankshaft heavy.


??????

Where did I say counterweights were to make the crankshaft heavy???????

This is what you said:

Originally Posted By: mjoekingz28
Maybe it is like a crankshaft.

Engines probably couldn't run without a heavy crankshaft. Especially single cylinder engines.


In case you forget your own words from a few posts ago. YOU were the one who ascribed significance to the weight of the crankshaft, I simply pointed out an example of a lightweight crankshaft and you lost your mind

Good luck calling DC BTW, I was there last week. Most Americans I meet are great folks, you appear to be the exception.

 

[asand1]

A Subaru boxer is a terrible example, horizontally opposed engines don't need counter balances because they have identical rods and pistons literally countering each other already. Counter balancing is needed for I and V configurations, and while it does add overall weight, that is not the intended purpose.

And simply put, heavy flywheels keep you from stalling while pulling away from a stop. Manufacturers would love to cut fuel consumption with lighter flywheels but its just no feasible.

Quit bickering, you sound like my two daughters.

 

[OVERKILL]

Originally Posted By: asand1
Counter balancing is needed for I and V configurations, and while it does add overall weight, that is not the intended purpose.


I believe the Model T Ford example shows that they aren't needed on an inline, but are certainly part of any modern inline or vee engine. And indeed their purpose is not to add overall weight

I've seen plenty of antique engines without counterweights, all similar vintage to the Model T. And yes, I cede that the Subaru example was a poor one given the nature of the boxer engine when discussing counterweights, however crankshaft weight was the topic at that point and I was simply trying to illustrate the prevalence of lightweight crankshafts in the market (which a boxer has) and that post wasn't about the significance of the counterweights, but rather the weight of the crank. Hope that clarifies that a bit