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View Full Version : Lightweight flywheel from a mpg standpoint

Lazarey
11-09-2010, 09:05 AM
Considering putting a lightweight flywheel on my strictly DD S14 when I put in a new clutch. I know it's odd but I actually enjoy tracking the gas mileage on it. Over 34 fill ups, I have averaged 28.7 mpg. I was wondering how a lightweight flywheel would affect that. On one hand, it would take less effort for the engine to spin up, but the rpms would fall faster which in my mind could make the engine have to use more gas to catch it before it stalls.

I know there are much smarter people than myself on here, so I thought I'd ask your opinions.
Sileighty_85
11-09-2010, 09:40 AM
It should help since your lighting the rotational mass that the engine has to turn.
Frees up power and engergy the engine has to use to rotate it.

I put a Lightweight flywheel on my RB25 and man i can notice a difference as far as revs go especially when it falls back to idle.

Not to sure on the gas mileage yet seeing that i just got the engine running last friday

The way i kinda see it:
Think about throwing a 10lb weight and and a 20lb weight in the air, which is gonna require less energy and force to throw and catch?
Lazarey
11-09-2010, 10:10 AM
I agree with you on all of that, just wondering if the engine has to use more fuel to catch the engine as it rapidly spins down and if so, how much more...
Hywarp161
11-09-2010, 10:27 AM
when i installed a lightweight flywheel in my wife's tiburon she averaged an extra 100 miles to a tank of gas. But if i drive it goes the other way lol. The motor is doing less work to generate the same amount of horsepower.
Sileighty_85
11-09-2010, 10:42 AM
I agree with you on all of that, just wondering if the engine has to use more fuel to catch the engine as it rapidly spins down and if so, how much more...

Nah should you less, even though the engine will decel faster it shouldnt have to use as much engery to catch it since it lighter
S14DB
11-09-2010, 11:06 AM
It should get better hwy mileage cause there is less rotational mass. You may loose some city millage if you do a lot of stop and go. You loose some stored tq(potential energy) in the flywheel for launch. So, it takes a little more gas to get going.

A "street" lightweight will be heavy enough to not take to much gas on the launch. But, still get benefits on cruise. The gains will outweigh the losses.

A "race" weight will be undesirable on launch.