I just had the flywheel changed on my 74 2.0L 914. Mechanic said the old flywheel was a "lightened" one and my new one is stock. I'm curious about you all's opinions on the difference; pros and cons of each. Apparently the PO decided to go for more high end acceleration than low end? I've never seen anything about this on the forum.

I hear a lot about this with race engines over on the 911 forum. Keep the one he removed its worth $ to someone.

It's all over here about advantages / disadvantages of a lightened flywheel.

Basically it comes down to the engine will spin up faster, but stall easier with a lightened flywheel.

Sorry, no free horsepower though.

I had a lightened flywheel on a 74 2.0L back in the 80's and it would spool up way quicker but was a bit touchy when releasing the clutch without enough rpms! You could stall it out easier when starting!

Over all I loved the feel!!

Edit: Slits beat me!!

there are a bunch of threads about this around here.

it might spin up faster
definitely race cars use these
but yours not be worth a mint, depending on how light is it and wear tolerances...

a lot of people like moderately lightened flywheels on the street
weigh yours and see how light it is.

Thanks, interesting. I'm anxiuos to feel the difference.

From my Corvair days... I used aluminum flywheels..

Heavy flywheel tends to smooth out idle and make starting from a dead stop easier. More rotating mass.... let off the gas and the revs drop slower and smoother.

Depending on how much less the lightened flywheel weighs...
Engine will accelerate faster.. BUT, at the same time... Letting off the gas is like stepping on the brakes. They do take some getting used to.
You can go too far and make the car unpleasant to drive in regular traffic.

Personally, i really liked the way the car felt with one.

I think some early 911 2 liter flywheels had holes drilled in them to make them lighter

We are using this flywheel currently with an F first gear and a tilton
(similar to an on/off switch)

this makes getting started from a dead stop difficult.

....What he said's rght......have 1 in my 75'..when something's wrong! will
stall easier.

Good info here on the pros/cons of each.

Fuel economy - A heavier flywheel will increase MPG on the hwy since it's easier on the engine at cruise (flywheels literally store power/torque)

A lightened flywheel simply frees-up HP to go to the rear wheels that would otherwise go to spinning the extra weight of the flywheel. Thus the motor feels more powerful on acceleration.

aircooledtechguy is right on. I've lightened flywheels for dirt track racers in the past. They say it helps acceleration because it doesn't take as much to spin a light flywheel as it would a heavy one. Flywheels store energy so once up to a steady cruising speed it takes more to slow down a heavy flywheel than a light one. That generally will give you better MPG because the engine doesn't have to work as hard because the momentum of the flywheel keeps the engine turning. One has to be carefull about weakening the flywheel if you take too much off of it. There is a fair amount of pressure on the flywheel.