VX flywheel and clutch.
 

So I have to replace input shaft bearing on my vx trans...

So while it's apart I'm going to do Clutch, input shaft bearing gear/syncro inspection and re seal. I know the VX has a lighter flywheel then most (CX is NEXT lightest I think) but someone on HT weighed a flywheel at 15.9 lbs.

Now that im replacing it... I have a brand new Stock replacement level Exedy clutch and flywheel. Flywheel is lightened (have yet to weigh)..

Would it be better to use stock or lighter...

Lighter has the effect of losing torque
lightweight flywheel doesn't decrease torque, but it does decrease inertia, meaning more torque will be needed to to accelerate a vehicle off the line ( daily driving).


So I'm hypothesizing a tiny drop in City mile per gallon with a tiny increasing highway so it kind of depends on the driving... thank you.

I've been giving this some thought lately. Keep in mind that these are my thoughts/theories, and are not based on any testing. A heavier flywheel makes engaging the clutch easier and probably stores a bit of energy to get the car moving that would otherwise come from extra fuel. But once the clutch is engaged, I think the flywheel is just making the engine work harder and use more fuel while accelerating. If you "pulse and glide," you'll never recover the energy used to accelerate the flywheel. I can't imagine flywheel weight having much effect on the highway. Unless I was doing a lot of stop-and-go driving in hilly areas, or a lot of towing, I'd try to get rid of as much flywheel weight as possible. Which is what I plan to do with the CRXFi.

I don't really want to do all the ecomodder but driving. I do let off gas for red lights early and accelerate correctly. "Everytime you use the brakes you waste the fuel you used to get that speed"

I'm thinking lighter is better also.

A lighter flywheel will give you economy on stop and go. It is basically the same principle as lighter tires.

One disadvantage is that your engine will be easier to stall, and to not make it stall you would have to give it more gas and your fuel consumption will increase a bit untill you get the hang of it (and maybe even after that as you still have to rev a bit higher).

Once evertyhing is up to speed it will not make a difference.

I think (i am not sure about this) but you do need some kind of rotating mass (for energy storage) so that the engine has enough inertia to compress the cylinders. The mass of the crankshaft or the pistons may or may not be sufficient for this.

Disclaimer: i have never built/rebuilt an engine, this is just based on what i have read on the internet. But i am an engineer.

I think you have this is backwards. The reduced weight should me less inertia and less torque required to spin up to a given speed. The down side will be that it will spin less once power is removed, as in a shift to neutral. The car might drive slightly more jerky. I have thought of this too, but I still have the OEM flywheel and clutch after 248,000 miles, so... not fixing what ain't broken.