I can rev mine to 7k and it will hit back to idle before stock hits redline. I think you missed the point anyway. I guess you wouldn't think heavy connecting rods make a difference either....so the Z06 uses titanium for no good reason. Rotating mass is bad.

And you mod your car the way you want, I will get everything available and don't worry about my money.

 

Is the flywheel the only mod to your car? If not them you can't pick one component out of the group of mods and qualify your response. Reving to redline means nothing..... you missed the point that its under load (the total mass of motor, clutch flywheel, transmission, differential, brakes and wheels/tires) that determines acceleration. A few pounds less on the flywheel compared to the total rotating mass is insignificant....unless you enjoy redline revving contests at a stoplight. seriously... I would guess that a set of lightweight wheels/tires would make a bigger increase in performance.

 

Richard, I have to disagree. Here's an informative, well written article by Bill Watson that gets to the point and provides the necessary physics and math to resolve this.

Effects of Wheel and Driveline Mass on Acceleration

by Bill Watson

Background on this article:

A Turbobricks member had commented that they thought wheel
and tire rotating inertia was substantial enough to be a major power requirement of an
accelerating automobile. They quoted a magazine article that ran two different wheel sizes and
ran the quarter mile as a comparison in acceleration. The difference in elapsed times was
quoted as proof of the inertial differences. The reply below was written to recognize that:
1) The effective gear ratio of the tire diameter change was largely responsible for the change in ET,
not the reduction in rotating inertia.
2) Rotating inertia IS an important thing to consider in our automobiles, but not the items that rotate at 'wheel speed'. Items that rotate at 'crankshaft speed' are the real culprits, having significantly larger power requirements to accelerate.


I have studied the subject extensively and have published the equations
of effective inertial mass in the g-curve User's Guide.

ROTATING INTERTIA

Rotating inertia is quite interesting, and is proportional to gear ratio
squared. Engine inertia thus becomes dominant very quickly, since it is affected
by differential ratio and tranny ratio. Wheel inertia does not pay off nearly as
well. Of course, the reduction in unsprung mass is good and I'm not covering
handling or braking issues here today. Naturally in that frame of reference, a light
wheel has additional advantages.

To appreciate the extra power requirements of items with rotating inertia, I have found it easiest to
convert these inertias into an "equivalent mass" that the car now has to carry around. If one
flywheel had "100 pounds" more equivalent mass than another, it's the same as putting a
100 lb bag of sand in the car, year-round.

BOTTOM LINE: One additional pound (0.45Kg)in a wheel not only adds a pound to the
'scale weight' of a vehicle, it adds an additional 0.5 pounds (0.23Kg) of effective
mass. If we consider all 4 wheels, this one pound increase per wheel adds 4 pounds (1.8Kg) to
scale weight, and 2 pounds (0.9Kg) of effective mass. (The magazines that did the
tests, alas, used ET instead of trap speed to quantify their results - clearly a
gear ratio and launch issue! See The $15 Dyno for details).

WHEEL SPEED INERTIA

Here's the math. For wheels it becomes easy since the wheel diameter
cancels out. From page 42 of the g-curve User's Guide:

Effective Mass (wheel) =
(1544/Dia^2) * Wheel Inertia (where dia = inches, inertia = in-lb-s^2)

If we assume that a wheel/tire combo has it's mass evenly distributed
about the cross-section, Inertia of a wheel is (W*Dia^2)/3088. (W= weight of
wheel/tire in pounds). If you substitute this in, the equation becomes:

********* Effective Mass = W/2. *************

In fact, if we use the same tire and use a lighter rim, note that the item
that changed mass has an even lower radius of gyration!! You'd get even
less than the half pound. My point - do it for the handling or looks, not
for improvement in quarter mile performance.

CRANK SPEED INERTIA

On the other hand, you'd be surprised how effective it is to lighten
engine components that rotate at crank speed.

Again, from page 42 of the g-curve user's guide:

Effective Mass (crank) = (1544/Dia^2) * Gdiff^2 * Gtrans^2 * Crank Inertia
('Gdiff' is differential ratio, 'Gtrans' is trans ratio)
I say 'crank inertia' but mean anything that rotates at crank speed.

On a 5.0L mMustang with a T-5 transmission, 3.08 gears, a 3.35 first gear,
and a 24.9" tire, (Total 'crank' inertia is around 4.8 in-lb-s^2).
THIS IS THE EQUIVALENT OF 1272 POUNDS (577Kg) OF ADDITIONAL
MASS IN LOW GEAR!
In second (1.93 gear ratio), it's the equivalent of 422 pounds (191Kg) of additional mass.
This is significant and measurable.

Our Volvo 4-cylinder engines with the AW-71 automatic tranny
have approximately 2.5 in-lb-s^2 of equivalent crank inertia. With a 3.73
differential and 2.45 low gear, that is the same as having 609 pounds (276Kg) of additional
mass in the car in low gear!

You can see that reducing flywheel mass has big payoffs, particularly in
low gear. It is not hard to cut an 'equivalent' of 100 pounds (45Kg) out of the car
in low.

HIGH STALL TORQUE CONVERTERS

This is also a good time to discuss high-stall torque converters used with
automatic transmissions. For the short period of time leaving the
starting line while the engine 'hangs' at stall speed, the vehicle is accelerating
***but the engine is not.*** This means that the effective weight is
reduced by the crank term, which is over 600 pounds (272Kg) in our example! Think
of the ramifications of this - most people think that the reason that high
stall speed torque converters improve acceleration is that they allow your
engine to start the quarter mile with a higher HP level at the flywheel.
THIS IS TRUE, but the reduced inertial mass is also a big player.. 15%
better acceleration over that small interval. If you record g's with time
it's really obvious.. even slipping a clutch on a stick shift at constant
rpm shows this effect.


- Bill Watson

 

Thanks Charlie..... good info. I didn't consider the high speed rotational inertia of the motor.... only the total rotating mass of the driveline.

 

Charlie, good base equations but short of the stored energy trade off. True if one accelerates from zero rpm’s that is a factor especially in 1st gear where it is most significant. But that is eliminated with a high rpm launch by using the stored energy to overcome vehicle inertia. e = 1/2mc^2 where the rotating flywheel speed is significant because it is the squared factor.

 

SpinMonster , Mitchalsup & Whitediamond are all for the lighter Fidanza Flywheel. The winner is Fidanza Flywheel. Let me know the best place to get a Fidanza Flywheel & clutch for my C6. SpinMonster, what clutch did you use with the Fidanza Flywheel in your C6? From all the information that I have gathered on the subject from this Forum and others, there is a performance gain with the lighter Fidanza Flywheel

 

Actually it is the car I had. I bought it new in 1971 and foolishly sold it 4 years later for a lot less than I had in it. I can't afford one now either.

I did get a call from the dentist in Florida who owns it now. It had passed through several hands before he got it, campaigned hard in A Gas then laid up behind a barn for some years. He's doing a full factory restoration on it. I sent him some photos from when it was new. I hope to get a chance to drive it again when he finishes.

 

To place my choice, I much prefer a light flywheel too. The factory setup in my C5 ZO6 seems quite heavy. A heavy flywheel is good for launching a heavy car and will make for brutal tire smoking upshifts in the quarter, but as has been said, this is stored energy. Once used during the upshift, it must be replaced before the next shift. A lighter flywheel may not bang the gears as hard, but it allows the engine rpms to increase faster - therefore accelerating faster, even in gear.

It is not just with blipping the throttle for downshifts that I prefer a lighter flywheel. I like to shift at the pace that creates very little work for the synchros. To do so with my stock setup means waiting a very long time for the revs to drop from lets say 2nd when I shift into 3rd. I would have sworn that there was enough time to bake a cake in between shifts with my ZO6 up shifts. But since absolute accuracy is demanded, I will refrain. Whether this is really times faster is probably an exaggeration, but I can sure understand the statement having once had the factory lightweight flywheel installed in previous Vettes You can speed things up by ramming the shifter home, but this is abusive to parts. A light flywheel drops the revs just as quickly as they are allowed to rise. You can definitely feel the difference when accelerating out of a corner.

I appreciate the comments of others that have made the change. I will certainly do so once the original clutch has bit the dust. I’ve got 70K miles now. Wonder how much farther before it goes. What a pain to change compared to C3’s.

Chuck

 

To place my choice, I much prefer a light flywheel too. The factory setup in my C5 ZO6 seems quite heavy. A heavy flywheel is good for launching a heavy car and will make for brutal tire smoking upshifts in the quarter, but as has been said, this is stored energy. Once used during the upshift, it must be replaced before the next shift. A lighter flywheel may not bang the gears as hard, but it allows the engine rpms to increase faster - therefore accelerating faster, even in gear.

It is not just with blipping the throttle for downshifts that I prefer a lighter flywheel. I like to shift at the pace that creates very little work for the synchros. To do so with my stock setup means waiting a very long time for the revs to drop from lets say 2nd when I shift into 3rd. I would have sworn that there was enough time to bake a cake in between shifts with my ZO6 up shifts. But since absolute accuracy is demanded, I will refrain. Whether this is really 3 times faster is probably an exaggeration, but I can sure appreciate the feels expressed. You can speed things up by ramming the shifter home, but this is abusive to parts. A light flywheel drops the revs just as quickly as they are allowed to rise. You can definitely feel the difference when accelerating out of a corner.

I appreciate the comments of others that have made the change. I will certainly do so once the original clutch has bit the dust. I’ve got 70K miles now. Wonder how much farther before it goes. What a pain to change compared to C3’s.

Chuck

 

Check my sig

I agree, I did that too.

 

I agree, I did that too.

 

Check my sig

I agree, I did that too.

Jim, 6k is 6k: the speed the same when you drop the clutch with either flywheel. I don't see a luanch as being powered by stored energy. If there was no rotational mass the car would still launch. The power that the motor is making drives it and that seems to be far more a factor than inertial momentum. The car spends far more time IMO climbing in rpm in gear than it does engaging a clutch. One has to consider which is more important, the bog you experienced or the reduced time climbing in rpm....rev speed.

I was always under the belief that a stroker lost any benefit of added TQ due to the slower revs it made. I don't recall any 383 all motor set-ups doing much if any better than the short stroke 346's (that rev faster) in the 1/4 for the same reason. The heavy rotating assenbly and piston speed make 383 a poor candidate to rev out to 8k like a solid roller set-up can. All motor 346's tend to do just as well.

 

6K is not really a 6K comparison, it's kind of like the Bee stopping the train theory. I agree that the rotating mass with a large rpm spread has an advantage with the light flywheel. But drag racing other than the Corvette with street tires where you come off the line near idle needs the stored energy. It can also be looked at if the clutch engages between power strokes one needs to over come that along with the resultant elasticity of the total drive train. When you do a launch with total hook up your relying on a lot of activity within the engine to absorb that shock. When we launched at 8K with the light wheel the bog was a killer and the shift points also suffered. With the heavy wheel that all went away and it was awesome. We turned much faster laps in Circle track racing do to corner speed being low along with the low rpm’s and no time for a shift. Even in road racing situations one has to use the entire rpm range at times depending on track and again the lighter wheel was fine. So I’m not disagreeing with you just a variance in our applications.

 

OK, I bet you're a good chess player too.

 

I went to Aluminum flywheel and as stated by others no apparent loss of power, no launch problems, no chatter, no driving problem etc etc. and yes car does rev faster.

 

SM... Wow what a great forum. I'm 58 yo and am just now "getting back into cars" after 30 years into bikes. On a bike, one of the things you can do to radically increase the accelleration is to go to lightweight wheels. Each wheel on a bike (think about it; the size of the wheels compared to the vehicle size itself) is a flywheel. To "go faster" you have to wind it up, and torsional forces are one of the hardest to overcome (i.e. it's not just flywheel weight but the diameter too). Bikes wheels have moderate weight, massive diameter. NOBODY who ever went to superlight rims (today = composite) has ever said anything other than Wow!

Light flywheels on bikes help a lot too, but generally you can't buy one (have a machine shop take 2-lbs off of stock flywheel as a rule of thumb; 4-lbs on BMW's).

SM: Keep carrying the load. Always "naysayers" abound. Plenty of theorists vs. real-world people.

Not yet a Vette owner, I'll be buying a late-'06 or early-'07 because where I live simply doesn't support a Vette because I am "buried in the city" (but I'll retire and be gone in a year).

My forecast mods: Intake, mild cam, hi-flow cats, computer tune, 160F thermo, LIGHT FLYWHEEL and depending on what I hear about the A6, maybe an uprated converter. That's it (massive low/mid-range, better-topend power, low noise). Oh yeah extra soundproofing, massive audio wattage.

Story: I told a kid this story today "from the old days"...

When a kid (1960-'64), I couldn't afford a car, so hung around with the school wrench-heads (street-racers, for money) and learned a lot.

When street-racing, listen to the other guy gun his engine. If it takes a long time to come back to idle zzzZZZOOOOOOMMMmmmmmm-idle, race the guy. If it goes zzZOOM-idle (superfast accel-decel) then bite your tongue and slink away (the guy has super-hi compression and a light flywheel so "race car").

From 1960's street-racing I saw a lot of lightweight flywheels, if you were serious (and liked making money) you had one.

Again, to all... GREAT FORUM

P.S. I too have a technical Masters, so I "understand the math" (lightweight flywheels *work*).

PPS>> So why-then do cars have heavy flywheels?
Answer: To make it easy to get going from a stop while pointed UP A HILL. The stored-energy in the heavy flywheel allows this. And yes *generally* less wear on the clutch because less slippage is required to get going under any condition.

 

what kind of flywheel will the Z06 have? AL, nodular iron, cast iron?

 

Digging for info..... found old.. gold? Good reads.. still searching...