Thread: Lightweight vs stock flywheel; momentum

a heavier flywheel would be better, the heavier flywheel would have more momentum, where as the lighter flywheel would have less. the lighter flywheel has less mass to move therefore less inertia. where as the heavier flywheel have more mass more interia. its basicly the same principal as what flywheel would cause the car to roll farther. the heavier ones for more inertia to dissipate.

but also you have ot take into consideratin beyond the flywheel weight and into the fact that the flywheel isnt going to make the engine run more efficently or take that into consideration to give the car more mpg. only tuning the ecu and other componenets of the car are going to greatly effect the differences in mpg.

i havent ever really seen any study done about the flywheels weight vs mpg given the fact that most people can probably zero out the difference by tuning. say you take a car with a heavier flywheel that may cause the car to get say 3% better gas mileage over a car with a lighter flywheel, well then you could just go in and retune the fuel map for a 3% gain in mpg and then you would basicly zero out the factor of the heavier flywheel gettng better gas mileage so you would have a lighter flywheel and better gas mileage, however this is mainly in theory as you will still see principals inertia and the dissipation of a larger mass verses a smaller mass, or smaller rotation mass.

in reality the differences in mpg from heavy to light flywheels is probably really slim, and flywheels are probably not the best place to go looking for more efficent miles per gallon, also not the cheapest, where as improving air fuel ratios and eeping up with oil changes and clean air filters, things like that, that are really going to have a larger effect on the mpg.

While i didnt do any math on this, I'm fairly convinced that the gains of a lightened flywheel, specifically the ability of the engine to rev up and maintain RPMs with less power, will outweigh the 'advantages' of the heavier flywheel's momentum, as said momentum must also be fought against deterioration in speed. The lighter flywheel is easier for the engine to maintain power-wise and as such you can be lighter on the throttle. So if you ask me, you're better all around with a lightened flywheel both on acceleration and cruising. Only place the heavier one would do better is coasting in gear, in which case you can just go to neutral.

Newton's Law #1

"an object in motion will stay in motion and an object at rest will stay at rest unless acted on by an unbalanced force"

Please close the thread.

Thing is though, with the light flywheel, not as much inertia is kept, thus on a highway you have to hold the throttle open further to constantly provide power to the lightweight flywheel. Heavier flywheels eat more gas to get up to speed, but once you are cruising the inertia will help.

I for that reason am not installing the light flywheel into my new car, plus mountain driving sucked with it .

I'm pretty confident saying that at cruising RPMs, the difference is going to be pretty much 0 when you take all the complex physics into account.

Thank you guys, you've told me pretty much what I wanted to hear, that you all agree with me that the heavier flywheel makes the car coast further .

I understand, but I've been trying to find an answer to this one for a while. I personally didn't gain any MPG's going to a light flywheel, did I loose some? Well that's hard to tell too when you install more then one big part at a time.

Now you have to weigh in the information and how accurate the information is from both sides. The lightweight flywheel = better gas mileage side says it's lighter to spin, thus uses less energy (aka fuel), to spin it up, no comment on continuing to spin it.

The other side, lightweight flywheel = worse highway gas mileage, says since it has less inertia you have to compensate by pressing on the gas more.

Here are some quotes that I've found on the web (take with a grain of salt ).

Source



Source




Thus I believe if our highways where all 100% flat, then lighter flywheel would be the same as heavier. But since our highways consist of constant Up and down (at least where I live or travel), the gas mileage gets lost. Up hill because of less inertia thus having to press on the gas more, down hill because lighter flywheel engine brakes faster thus you slow down more and need to press on the gas more to make it back up.

The other side, lightweight flywheel = worse highway gas mileage, says since it has less inertia you have to compensate by pressing on the gas more.

i wonder by having the lighter flywheel if weather or not it not only requires more accelleration percentages to sustain the same ammount of intertia as a stock flywheel would have, if in return you would have to incorperate more throttle percentages opening up the throttle wider, using more gas. thus causing you to incorperate more thorttle percentages and more accelleration percentages over a stock setup to maintain speed.

IMO i say @#$% it and love the gains you see from a lightweight flywheel verses any negative you might be able to conjour up lol.

i believe most people would say that too, i love lightweight flywheels for the fast accelleration and the fast decellerations, on the highway with boost lightweight flywheel is just crazy.

In a perfectly flat, frictionless world located in a vacuum, it wouldn't matter whether or not you have a LW or a heavy flywheel when doing highway speeds.

However, we're not on that world, and that means we have stuff like drag, air-friction, wheel friction and all those things to fight against, which all slow down the car.

And since MPG is best when cruising at a constant speed, the less energy you need to put into the rotating part of the car, the better MPG. Which means that the heavier flywheel will have a higher amount of inertia, and requires less energy to keep that momentum.

Sir Isaac Newton ended this thread a few hundred years ago.