aluminum flywheel weight savings?

peterome · Jan 24, 2011

Dark04GT said:
The flywheel is just a spinning piece of metal. There is absolutely no computer calibration needed. Any loss in fuel mileage is the result of you over reving the car / not maintaining your revs while you shift.

Once you learn how to use your aluminum flywheel (takes a day or two) everyday driving is pretty much the exact same as before.

+1 on the don't get an overly aggressive clutch.

No... really I know how to drive my car with this AFW. I have had it for 3 1/2 years and it feels like it could go another 3 1/2 years. I also drive even slower because of the gas mileage drop. When I am shifting between gears and I step on the clutch pedal my RPMs rise above from where it was at right before I depressed on the clutch pedal. In order for my RPMs to rise fuel has to cause this. With my Factory FW when I was shifting between gears and I depressed on the clutch pedal the RPMs did not rise because fuel was not being dumped. This constantly happening through out the day while I am driving will cause my gas mileage to drop. Unless you can honestly give me a better explanation because I was able to get at least 17 miles to the gallon locally and now I get like 13 and this honestly started right after I put this set-up. Don't get me wrong it feels stronger with the AFW that's why I have had it the past 3 1/2 years.

Shiroelex · Jan 24, 2011

peterome said:
Unless you can honestly give me a better explanation because I was able to get at least 17 miles to the gallon locally and now I get like 13 and this honestly started right after I put this set-up. Don't get me wrong it feels stronger with the AFW that's why I have had it the past 3 1/2 years.

That's about the drop I saw in mpg right off the bat. I threw in an IAC restrictor to bring the RPM down between shifts, and that seemed to help some.

Dark04GT · Jan 24, 2011

peterome said:
No... really I know how to drive my car with this AFW. I have had it for 3 1/2 years and it feels like it could go another 3 1/2 years. I also drive even slower because of the gas mileage drop. When I am shifting between gears and I step on the clutch pedal my RPMs rise above from where it was at right before I depressed on the clutch pedal. In order for my RPMs to rise fuel has to cause this. With my Factory FW when I was shifting between gears and I depressed on the clutch pedal the RPMs did not rise because fuel was not being dumped. This constantly happening through out the day while I am driving will cause my gas mileage to drop. Unless you can honestly give me a better explanation because I was able to get at least 17 miles to the gallon locally and now I get like 13 and this honestly started right after I put this set-up. Don't get me wrong it feels stronger with the AFW that's why I have had it the past 3 1/2 years.

your revs should not be rising while you are shifting in normal daily driving. There are two reasons for this- either
1) your throttle body is staying open / sticking
2) you are still on the gas while you are pressing in the clutch

And if you are off the gas between shifts and your rpms are rising/staying about the same than it doesn't even make that much of a difference. Being off the gas means your tb is closed and your engine is using very little fuel.

crazystang25 · Jan 25, 2011

with the aluminum fw you dont have the inertia of the heavier stock fw to help keep the crankshaft spinning when you are cruising so you have to give the give the engine more gas pedal to keep it at the same rpm when you switch to an afw therefore you use more gas because of that.

Maxpowers · Jan 26, 2011

crazystang25 said:
with the aluminum fw you dont have the inertia of the heavier stock fw to help keep the crankshaft spinning when you are cruising so you have to give the give the engine more gas pedal to keep it at the same rpm when you switch to an afw therefore you use more gas because of that.

That doesn't make sense to me. Putting lighter wheels on doesn't make you push the pedal down harder.

Dark04GT · Jan 26, 2011

crazystang25 said:
with the aluminum fw you dont have the inertia of the heavier stock fw to help keep the crankshaft spinning when you are cruising so you have to give the give the engine more gas pedal to keep it at the same rpm when you switch to an afw therefore you use more gas because of that.

That doesn't make any sense at all.

Reasons:
1) engine spins the crankshaft, not the tranny
2) Hypothetical- flat surface, hwy speeds- keeping a car at the same speed (or same rpm) relies on an equilibrium between a) the force pushing the car forward, b) all drag and rolling friction losses. What material is in the driveline does not factor anywhere into this equilibrium unless it changes the rolling friction- which in this case it does not.
3) Inertia is the resistance of an object to change it's velocity. If you are at a constant rpm (constant velocity), inertia does not even come into play. Now if you are changing velocity- it requires less force to turn the aluminum flywheel- resulting in better acceleration and marginal (unmeasureably small) fuel mileage improvement.

crazystang25 · Jan 27, 2011

The heavier flywheel has more inertia than the afw therefore it will keep the engine keep the engine internals spinning with less effort. And no one said anything about the tranny.

patman0911 · Jan 27, 2011

In a steady state cruise condition, the flywheel is not doing anything other than smooth out combustion pulses - the greater mass of the iron flywheel helps resists RPM climbing more when a cylinder fires and falling in between pulses - the flywheel is not adding any net energy to the system.

Yes, when you let off the gas, RPMs will fall slower with the heavier flywheel but that's cancelled out by the fact that it takes more energy to spin it back up again and more energy to spin it up in the first place. A little of that energy is returned when you let out the clutch taking off from a stop or on an upshift and makes driving smoother without requiring as much gas and as delicate a throttle/clutch balance.

Dark04GT · Jan 27, 2011

patman0911 said:
n a steady state cruise condition, the flywheel is not doing anything other than smooth out combustion pulses - the greater mass of the iron flywheel helps resists RPM climbing more when a cylinder fires and falling in between pulses - the flywheel is not adding any net energy to the system.

Well written. The flywheel is not adding any energy into the system unless you are accelerating or decelerating crazystang. Once the flywheel is at a constant speed / constant rpm- inertia is out of the equation.

007 · Jan 27, 2011

Dark and the other are of course correct.
I think its interesting to note that a lighter drivetrain offers more of an advantage to cars with more aggressive diff gears.

Anyway. I'm in the market for a flywheel. What are my options? Any recommendations?

Dark04GT · Jan 28, 2011

I like my fidanza flywheel. My fidanza makes a little more noise with my clutch down low (just above idle ~800-1200rpm) than the stock stuff did but that is probably more the clutch rather than the flywheel. I saw your other thread and I think if you are already in the area- you might as well go aluminum.

I would say the improvement it made over the stock flywheel is slightly more than going from a steel to an aluminum driveshaft. (but of course you are going from an auto to a manual so it will be completely different.)

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