dmoffitt

my car revs SO much faster w/ a crank that's been lightened. sorry i wish knew the physics behind it, but i can at least provide you w/ a real-world answer. i chose to stick w/ a stock flywheel for now, but will be putting in a light one the next time i do a clutch (probably no time soon w/ the sachs sport/race disc and KEP p-plate). my only reasoning for the heavier flywheel was to prevent a car that already loves to stall / idles poorly from doing so even more... i already have to keep blipping it gently upon coasting down to a stop or it'll die...

Danno

"my car revs SO much faster w/ a crank that's been lightened. "

Is that in neutral or in gear pushing the car down the road? In neutral, if you've removed 25% of the weight from the only moving parts, like the crank, flywheel, rods & pistons, yes it will rev-up a lot quicker in neutral.

Hook up that lightened engine to a driveshaft, spinning the gears and pushing a 3000lb car down the road, a 20lb weight savings won't make as much of a difference. However, since the crank is the highest revving component, its inertia will be quite high and saving 20lbs from the crank & flywheel @ 6000rpm will have a more beneficial effect on acceleration than say... 20lbs off the wheels & tires, which will only be spinning at 1700rpm (1st gear).

BoostGuy951

I would think that while idleing with no load, the lighter flywheel and crank would make it easier to maintain idle. It would seem that it would only try to stall while engaging the clutch with light throttle.

BoostGuy951

Anyone got and weight figures for the stock crank/stock fly, and Lightened crank/fly?

I spoke with Scott Gomes of Under Pressure Performance through email, and he said that they would lighten and balance the factory flywheel to the same weight as the aluminum one for $275. That is a similar price to some of the aftermarket aluminum flywheels I have seen. Which is a better bet?

Assuming money and weight are the same, which is the better decision?

Mike S

$275 for lightening....yikes. My local machine shop took my stock flywheel down to about 14lbs....i think that's 5 or so lbs lighter for $120 including balancing. That's quite a premium he's charging there.

BoostGuy951

Well... I think the Aluminum ones are weighing in at around 7 lbs. He said he could get it to the same weight as an aluminum one. Maybe that is the reason for the increased price. I am just guessing though.

NZ951

Yup, ally ones weigh 5-7lbs from what I have seen... how hard are they to install? Do they affect triggering at all?

emilysgranny

Dannos point is well taken on the engine unloaded and engine loaded. Pure engineering dynamics , plain and simple. Acceleration theory applied to torque because of mass. Instead of worring about any performance gain ,which would be minimal due to the total reciprocating drive train mass,consider the increased bearing life due to the weight reduction. As to harmonics , there are formulas for that too , and they are quite complicated.Anyone who has design theory will attest to that. Just look up your valve spring design.

B951S

Can we hear from more people with lightened flywheels as to drivability / stalling and benefits. I think this is the mod most people will do 'while they are in there' when doing clutches.

David Floyd

No problems with stalling or drivability with lightened stock flywheel, for me

OZ951

Aluminium flywheel, Aluminium pressure plate, lightened crank, zero issues.

Rob

Same for me as well.

Danno

You have to consider that the 951 has the heaviest crank and flywheel of any 4-banger out there. So by lightening these up, we're just falling in-line with the others out there. From what I've seen:

flywheel: 19 lbs --> 6lbs (-13)
crank: 59 lbs --> 43-49lbs (-10 to 16lbs)

There have been a couple cases of lightened cranks flying apart at the track, but there's so many variables that you can't say the lightening in itself was the problem. The balancing is very critical to longevity as well and if you can maintain dynamic balance on a per-journal basis with the crank, rods & pistons, you're most of the way there. So taking off 25-lbs from the flywheel & crank should be quite a significant weight savings off some very high inertia parts. Then another 2-lbs off the con-rods would be a major improvement since they are a major contributor to the shake that requires balance-shafts to even out. Longer rods would help make the engine smoother as well.

TurboTommy

I have these lightened parts. Human nature somewhat dictates that I want to justify the expense by exagerating the benefits. But I'm not doing that. It's basically what I said in my previous post in this thread. There is a more pleasant feel in low load conditions like matching revs on a downshift for example; that's about it. In racing conditions, every bit of an advantage counts, so it's more of a big deal in that situation.

NZ951

Plus you have knocked 26lbs off the weight of your car! Thats a decent saving from a pure "general" weight saving plan. I am a pyscho about weight now! Never used to be, but am now. I take out everything that is not estential to my driving experience.