Do lightweight flywheels make much difference?

[jdgFirefly]

Originally Posted by autoteach

well, that mass*velocity is linear inertia. Distance from the center for a rotational object has to be considered. You could produce a flywheel that weighs 20lbs that has the same inertia as ones weigh 18, 15, or 5 lbs.

Excellent point! I totally forgot about that!


Also what exactly is a DMF and where can I get one

[autoteach]

dual mass flywheel = DMF if you were wondering. They have fairly good reasons for using them, but blah blah blah.

Anyway, assuming you were joking about DMF (which I think is only internet speak), IAGTGNCIALFRAVMR. (I am going to go now cause I am leaving for Road America Vintage Motorcycle Racing)

[dcb]

thx for the heads up Dre, will watch closely and compare what little baseline I have 53.6mpg lots of engine on coasting. I figure I currently have a shot dmf because of the clutch drag and because when I rock the car back and forth in gear, it sounds like this video (sans George Harrison background music) from the bellhousing. But the car has never appreciated being bump started, so that will be interesting.

but to the OP, it won't make much difference if you are cruising at a constant 70mph. You would have to be pulsing and gliding to really take advantage of the reduced weight. I do that a fair bit. And p&g has higher returns at slower speeds (though aero mods help the high speeds), fits in especially well with around town driving once you get the hang of it (will beat the pants off your hiway mpg)

http://www.youtube.com/watch?v=bFnLM...layer_embedded

Originally Posted by dremd

Oh, and a few notes from a guy who just (450 miles ago) went from a Single mass flywheel (19 lbs with clutch bolted on) to a dual mass flywheel(52 lbs with clutch bolted on).

1) I can run 100-150 rpms less with same load.
2) Starting is much smoother.
3) bump starting is now effortless vs cumbersome (could never do it with picky passengers)
4) idle is much more quiet
5) other drivers are much more apt to drive it at lower rpm's than they were before (small sample size of 2).
6) shut down is now smooth and silent.

Best sum it up is smooth, smooth, smooth.

EDIT: as an FYI: I thought I had a DMF to begin with . . . . previous owner swapped it (apparently)

[steffen707]

Originally Posted by autoteach

Heavy flywheel, better mpg. I dont have the patience to explain it right now, but believe me (7 lbs is really light, tough to drive)

Originally Posted by autoteach

well, that mass*velocity is linear inertia. Distance from the center for a rotational object has to be considered. You could produce a flywheel that weighs 20lbs that has the same inertia as ones weigh 18, 15, or 5 lbs.

A contradiction that you yourself have pointed out, its not just mass of the flywheel but where that mass is in relation to the center of said object.

So a blanket statement of "heavier is better" isn't true.

Oh, also I have never heard gears chattering and the clutch chattering in my crx with 7lb fidanza flywheel. I also have a stock clutch in there instead of an aftermarket one that most people with 7lb flywheels would have. Maybe Hondas are just made with anti-gear and anti-clutch chatter lol. I'm sure this does happen to people, but not to my 1.6l honda crx.

I'm starting to pull the vx swap today, hopefully in a month or two it'll be rip roaring in the new car.

[dcb]

the chattering was at idle, which you shouldn't be doing anyway

[wdb]

Here's what flywheels do. I particularly like the fact that the engine is only firing every now and then.

http://www.youtube.com/watch?v=FccOq...layer_embedded

[steffen707]

Originally Posted by wdb

Here's what flywheels do. I particularly like the fact that the engine is only firing every now and then.

I saw something like this before, very good video.

So the link to our ongoing debate/discussion would be that a heavier flywheel like those big ones in the video store more power or store the power longer? Than say a lighter flywheel, completely disregarding what autoteach had explained earlier about the distance of mass to center of rotation??

I would bet that with the engine in the video, it would have to fire more often with a light flywheel, because it would slow down faster, right? Again this is a point against light flywheels giving more mpg in a car; however, the car isn't going to skip a few strokes here and there like the engine in the video.

The car engine if locked by cruise control at 70mph and is at say 1500rpm, is going to keep firing and keep injecting fuel for every cycle. So is it safe to say that the flywheel is a "load" on the crank and engine? The heavier one will store more intertia, but will be a higher load on the engine. So if my assumption (insert ass outa you and me joke) is right, and the engine has to keep firing on every cycle, but the engine "sees" a lighter load, then it will "see" more vacuum from the MAP sensor, and thus inject less fuel because the more vacuum you have the less fuel the fuel table will have the injectors inject. ???

[steffen707]

or maybe this means that if the lighter flywheel doesn't store enough energy then it will want to slow down the motor faster, thus making amount of fuel greater to keep things reving at a constant 1500rpm??? i bet there is a formula for this relationship..........

[cujet]

I put a lightweight flywheel on my Turbo Miata. It was about half the weight of the OEM flywheel.

The car did accelerate noticeably better. Especially in 3rd gear, when traction was not as much of a problem.

However, I lost all of the kinetic energy stored when upshifting. The high RPM's of the engine more quickly dropped off upon the shift. So, there was less of a surge in acceleration immediately after the shift.

I always got 27MPG, no more no less. The flywheel made no difference in MPG.

[dcb]

yah, single cylinder vehicles pretty much need a flywheel to keep running, which makes the aluminum blade lawnmower test a bit of a red herring. The lower the rpm you want to run at the bigger flywheel you need. Multi-cylindered vehicles, are less needing of a flywheel, since there are more power pulses and more roatating mass to carry the cylinder compressing through to ignition.

FYI, here is a nice DMF animation, for NVH fans everywhere

http://www.youtube.com/watch?v=YnaXB8q3uzQ