quote Originally posted by Archie: Don't be like that. Some people just have to hammer on those that have a valid opinion based on what they do all the time. They try to beat up on the people who really do have some technical knowledge. They beat on you hard enough & long enough that you give up on trying to help people who ask technical questions. Then they go on other forums & beat up on PFF & say that there are no good techs posting on here. Archie

What is your input on using heavy 30# flywheels V/S lightweight aluminuim on V-8 swaps. You have 20 plus years using 30# weights attached to V-8s and now that you have went to lighter flywheels. What differance have you saw first hand with the change?

quote Originally posted by MstangsBware: What is your input on using heavy 30# flywheels V/S lightweight aluminuim on V-8 swaps. You have 20 plus years using 30# weights attached to V-8s and now that you have went to lighter flywheels. What differance have you saw first hand with the change?

Glad you asked that.

My Steel F/W's are 29#, the Aluminum F/W's are 13#.

The engine revs faster however streetability with the Aluminum F/W kinda sucks. However, unless you're powershifting every shift, the RPM drops too fast between gears, you almost have to blip the throttle between gears to keep the RPM up.

The Aluminum flywheels on the SBC's would be great for road racing or mountain racing where you want the engine RPM to drop fast as soon as you let up on the gas, for engine braking. But it's a pain in the butt for normal driving.

The lighter F/W also effects idle quality. On injected SBC's, the actualy idle is always 100 to 150 RPM below the desired idle you have set on the ECM.

When you describe my flywheels as heavy, you really don't know what you're talking about. A stock ZO6 LS7 Flywheel & clutch assembly weighs over 65# & they're doing just fine. Sure, you can put an Aluminum F/W on an LS7 but you'll may have to live with other driveability issues.

Now I know that you and others are going to start bashing me for my opinion. That's the reason I never volunteered my opinion to this thread previously. Because it just gets old after a while.

Archie

Based on archies post, if you have a obd2 v6, the speed at which the rpms drop can be adjusted in the ecu.

quote Originally posted by Archie: Glad you asked that. My Steel F/W's are 29#, the Aluminum F/W's are 13#. The engine revs faster however streetability with the Aluminum F/W kinda sucks. However, unless you're powershifting every shift, the RPM drops too fast between gears, you almost have to blip the throttle between gears to keep the RPM up. The Aluminum flywheels on the SBC's would be great for road racing or mountain racing where you want the engine RPM to drop fast as soon as you let up on the gas, for engine braking. But it's a pain in the butt for normal driving. The lighter F/W also effects idle quality. On injected SBC's, the actualy idle is always 100 to 150 RPM below the desired idle you have set on the ECM. When you describe my flywheels as heavy, you really don't know what you're talking about. A stock ZO6 LS7 Flywheel & clutch assembly weighs over 65# & they're doing just fine. Sure, you can put an Aluminum F/W on an LS7 but you'll may have to live with other driveability issues. Now I know that you and others are going to start bashing me for my opinion. That's the reason I never volunteered my opinion to this thread previously. Because it just gets old after a while. Archie

Good information.

quote Originally posted by Archie: Now I know that you and others are going to start bashing me for my opinion. That's the reason I never volunteered my opinion to this thread previously. Because it just gets old after a while. Archie

Well, Its my thread and from this I have learned quite a bit more than I did before. I have ran a lightened flywheel in a '70 Bug and it was a blast but you (Archie) did remind me about needing to "bump" the gas pedal between shifts to keep the RPMs up.

Like everything else, you gain at one point by taking away from another. Just have to find a happy medium that fits the driver and what the car is used for.

Its seems to me that BMW has the right idea using a "medium weight" flywheel to get a bit of both ends of the spectrum.

Keep it coming and thanks,

Steve

yup. there is still the clutch assembly or the torque convertor.....so - lighten away - there will always be ballast.....

any removal of weight in the rotating assembly is a good thing. everytime. no exceptions. (well - exception - unbalanced removal - lol)

yes, I can imagine a heavier flywheel will create a smoother idle - but, has anyone mentioned why that is? it is because it resists change in RPM.


edit: and for the shifting - this is for the same reason it spins up faster - it also spins down faster. it hinders NOTHING, especially when you know your shift points & rpm ranges. but, if it really bothers you - dampen the return spring on your throttle body.

[This message has been edited by Pyrthian (edited 12-16-2008).]

Out of curiocity, what's the flywheel weight on a stock '86 2.8?

And how does a "#29" or "#63" translate to lbs? Or does it even translate directly?

(w/ all due respect, i think Will was being exceptionally rude)

-Michael

------------------
"A guy know's he's in love when he loses interest in his car for a few days." -Tim Allen

He who dies with the most toys... still dies.


Check out my restoration!

quote Originally posted by Archie: The engine revs faster however streetability with the Aluminum F/W kinda sucks. However, unless you're powershifting every shift, the RPM drops too fast between gears, you almost have to blip the throttle between gears to keep the RPM up. The Aluminum flywheels on the SBC's would be great for road racing or mountain racing where you want the engine RPM to drop fast as soon as you let up on the gas, for engine braking. But it's a pain in the butt for normal driving. Archie

That's exactly what I was refering to in my first post on the subject using a modified V6 flywheel on the V8, letting off the gas rapidly in first or second gear caused the car to take a dive abruptly and you could hear how far the engine had to climb back up to speed for the given gear in between normal shifts. The light weight may be good for total performance but as bmwguru and you have pointed out driveability will be affected and to some that aspect is more important than the gain in acceleration. To me it's just as annoying as the positive shift kit installed in my old automatic Z28 became after the newness wore off. I actually began to dread the kick in the seat of the pants at the shift points. Driveability is an important factor to consider in exchange for the benefit the lighter flywheel affords and you may have to adjust your shifting possibly toward being more aggressive to consistently reap the benefits from it, certainly worth giving a lot of thought to.

Theres only a few reasons for a flywheel. One is to supply a place for the starter to crank it over, another is to provide a mount for clutch/torque converter, and finally its there to smooth out the inheirent imbalance of a bunch of cylinders firing. We had race cars with little tiny flywheels & V8s (Supermodifieds) which you had to push at 50mph to start, and wouldnt idle at less than 1500-2000 rpm without shaking themselves to pieces.

quote Originally posted by rogergarrison: We had race cars with little tiny flywheels & V8s (Supermodifieds) which you had to push at 50mph to start, and wouldnt idle at less than 1500-2000 rpm without shaking themselves to pieces.

The gains in this situation would be valuable but your not in the car very long so you can live with its negative points.

I've learned so much in this thread

In my experiance there is only one drawback to a lightweight flywheel. This is for street driven vehicles in particular.

Losing too much weight from the flywheel does make the engine rev quicker. The drawback is that is also significantly lowers the momentum held in the rotating assembly. This can lead to choppy shifts as the RPM's drop too quickly for the long throw shifters fieros come equipped with. Sometimes this can be adjusted in the ECM but not always. Sometimes adding a short throw shifter can also help, again not always. You can only shift so fast with the stock fiero transmissions. If the flywheel is too light you can pass that point and you have to start matching RPM's to get the smooth shifts. No fun on the street. The correct weight for the flywheel should be chosen based on each particular setup.

Flame suit on.

quote Originally posted by bmwguru: If you are planning a turbo setup, I'd stay away from a superlight flywheel. That would actually hurt the boost because there would be less mass loading the engine.

quote Originally posted by bmwguru: The numbers on a dyno will probably show better with a lighter flywheel, but as for actually driving a turbo BMW or VW on the street, a mid sized flywheel feels better. I should have never even stated my opinion for the cars "I WORK ON". I am not going to continue this debate. Just don't expect much help from me in the tech section in the future. I am not a GM tech. The cars I work on don't use pushrods, and I still don't understand why GM uses them. Dave

Ahh... the real answer comes out.

Customer satisfaction is a perfectly valid reason (probably the MOST valid reason for a business owner) to go with a heavier flywheel. I'm not knocking that. If you'd said "Lighter flywheels make more power, but I use heavier ones for my customers because they give better driveability", I wouldn't have questioned that at all.

However, when you say that a light flywheel will hurt boost, you've got most laws of physics telling you otherwise. You're going to get called on that...

quote Originally posted by Fierology: Out of curiocity, what's the flywheel weight on a stock '86 2.8? And how does a "#29" or "#63" translate to lbs? Or does it even translate directly? (w/ all due respect, i think Will was being exceptionally rude) -Michael

If digging into unreasonable claims to find the truth makes me rude, then I'm just going to continue to be rude. Only a pretty bent social order values seemliness or pedagogy over truth. You only learn new things by having your ideas challenged... but that always comes in the form of disagreement. Disagreement is essential to learning. Any social order that poo-poo's disagreement is not going to foster any learning.

Those numbers are pounds.
The stock 2.8 flywheel is 13ish. The combined weight of the stock flywheel and clutch ends up being close to 30#. Even with an 8# aftermarket flywheel, the whole assembly is still close to 25#, so the flywheel by itself isn't going to make a huge difference in MOI.

I have a modded 2.8 flywheel on my Northstar. The engine is "only" 280 cid, but has high compression and high VE (strong vacuum on overrun) and makes for stout engine braking. I love it. On the highway I just lift off the gas and slow down faster than most people on their brakes. I can't wait to try a Tilton clutch on it for a serious reduction in MOI.

[This message has been edited by Will (edited 12-17-2008).]

From my experience, when you rev an engine at idle, it will create little to no boost. You can barely hear the turbo spool. It needs a load to make the turbo really spool up. Yes, there are ways to get around this, but that isn't where this discussion is going, so that point is moot. A lighter flywheel theoretically should not make as much load on the engine, thus not making the turbo spool as easily.
Now there are ways around this, but for a daily driver that wants a fun ride, I'd just suggest that they go with a mid range flywheel and save the expense. Like I said, I am going by what I have done for years and have made my customers happy.
Dave

quote Originally posted by Will: LOL... That's absurd.

I believe that's the remark Fierology was referring to as being rude Will, regarding that response to bmwgurus comment on lighter flywheels possibly hurting boost performance due to reduced load. What I understand is meant by his comment is that since a load on the engine is what causes the turbo to spool up in the first place, reducing that load will ultimately reduce boost levels or onset at the same points between shifts with a lighter flywheel in the same way that it is near impossible to reach full boost levels in first gear due to how easy it is for the engine to move the car before a sizeable load is reached as compared to any of the succeeding gears.

The car is always a much larger load than the flywheel (or at least it sure should be).

Did you read that David Vizard article I linked above? He discusses the tradeoffs between having energy off the line in the form of a heavy flywheel and being unencumbered by the flywheel further down the strip. The same can apply to the low boost in 1st gear argument... do you want to hit boost in 1st gear or do you want to accelerate faster in 2nd gear?

And that's only really a consideration in a platform like the Fiero with a heinously short 1st gear. I'd bet turbo Vette owners aren't worried about boost in 1st gear...

[This message has been edited by Will (edited 12-17-2008).]

quote Originally posted by Will:\ ...... If digging into unreasonable claims to find the truth makes me rude, then I'm just going to continue to be rude. Only a pretty bent social order values seemliness or pedagogy over truth. You only learn new things by having your ideas challenged... but that always comes in the form of disagreement. Disagreement is essential to learning. Any social order that poo-poo's disagreement is not going to foster any learning. .....

well, most of us have found ways to speak truth & discuss topics without being an ass. but, like everything else - learned skills.

The root reason the turbo won't spool when you rev from idle is because of a lack of gas flow for a sustained period of time, not a lack of engine load.

The problem is that when you're revving in neutral the engine doesn't require enough throttle opening to pass enough gas to really spool the turbo. Even at redline, you have way less flow pushing on your vanes then when you punch it in gear.

The load of moving the car allows you to push the pedal farther down and hold it there longer which gives the turbo more flow and the time it needs to spool before you have to back out of the throttle at redline. (But the root issue is mass flow and time, not load. )

-FTF E

quote Originally posted by Will: If digging into unreasonable claims to find the truth makes me rude, then I'm just going to continue to be rude. Only a pretty bent social order values seemliness or pedagogy over truth. You only learn new things by having your ideas challenged... but that always comes in the form of disagreement. Disagreement is essential to learning. Any social order that poo-poo's disagreement is not going to foster any learning.

Pyrthian responded well:

quote Originally posted by Pyrthian: well, most of us have found ways to speak truth & discuss topics without being an ass. but, like everything else - learned skills.

Truth is the best thing out there, and as Pyrthian said, the key is in how you say it. As I said earlier, I've learned lots from this thread. But we're all here in a friendly manner, and getting people P/O'd and argumentative isn't the way to go. No one appreciates it. Arguments are great when they're positive. I've had many arguments with people where we never get angry, because we're arguing about the topic at hand instead of about how stupid their arguments are.

-Michael

If you tell someone that you think they're wrong nicely, they usually ignore you.

quote Originally posted by Will: If you tell someone that you think they're wrong nicely, they usually ignore you.

No Will, you're wrong. A few people have told you that your method was wrong and you didn't ignore it. You in fact responded to it with the quote above.

Archie

P.S. Notice how nicely I've told you that you were wrong in this very post. See how nicely it works?

A

Pots and Kettles.

How effective has anyone telling you they think you're wrong ever been?

quote Originally posted by Will: Pots and Kettles. How effective has anyone telling you they think you're wrong ever been?

Actually, customers, friends & others have been quite effective when they present their opinion in a civil manner. I consult with them all the time.

People who present themselves as jerks or hurl insults to support their case are ignored & get the same treatment in return.

You can guess which list you're on.

Archie

quote Originally posted by Archie: People who present themselves as jerks or hurl insults to support their case are ignored & get the same treatment in return.

I could post some comments from a customer of yours, but instead I'll just commend you for being so magnanimous.

quote Originally posted by Will: David Vizard published an investigation of how much lightweight flywheels actually help/hurt and found that a Mustang could dyno 85 HP higher in 4th than in 1st.

Will,

I read through Dave's article but it appears to be incomplete. The only figures I can find are Fig 3, 7, 8, and 10, but he references a bunch of others in the text.

Am I doing something wrong, or are there pieces of the article missing?

-Bruce at FTF

quote Originally posted by Will: I could post some comments from a customer of yours, but instead I'll just commend you for being so magnanimous.

There you go again. This discussion got started because some people felt that you couldn't make your point in the discussion without resorting to insults & attacks.

Here I try to have a simple discussion with you in a civil manner & you have to jump back into the insults & attacks.

So here you have "customer" & some comments, What does that have to do with the discussion we were having?

As part of my year end reports on my book keeping program last weekend, I had the system list out & count all my customers. That report dates back to 1994, prior to that all my book keeping was done by hand.

Since 1994, I've had 2402 customers. I have a list of all their names, addresses & contact information & since I've had the same 800 number for 17 years they all know how to get ahold of me too.

Somehow I'll bet that the customer you'd like to quote would also like to remain anonymous.

I guess that it'll never end with people like you. You want to argue & then when you start losing you change the topic to insults & attacks on the person that you're losing the discussion to. You've done it a few times already in this thread & I expect that you'll continue to do so.

So hurl some more insults. As I said in my 1st post in this thread, certain people can't have a civil discussion without it turning into attacks & insults.

Archie

[This message has been edited by Archie (edited 12-18-2008).]

I swear Archie, you play the victim like none other. Truly masterful work.

a light flywheel decreases stored energy, true. typical serious drag racers almost always use heavier than stock flywheels to increase the amount of energy put down when they launch. the downside is that when decelerating the heavy flywheel will push the engine against the brakes and increase stopping distance or require you to increase braking force. this in turn cooks your brakes and during a race or spirited driving hot brakes are no good.

a light flywheel does in fact transfer more energy to the wheels but theres a kick. since the flywheel is lighter the overall load on the motor is less. load is more important than hp in that its a direct relation between traction and power generation. to compensate you must use more throttle angle or start lower in the gear.
a light flywheel can be more difficult to drive on smaller motors, the prime example is using an 8lbs flywheel on a honda engine. it can be rediculous at first to get it to roll in first without stalling but you can easily learn how not to do this.

as for mass reduction there is no way of saying that you want all of the weight on the outside of the wheel and none in the center. its a simple lever action, the further out from the circle you go the static weight actually ends up 'weighing' more dynamiclly. the difference between a lightweight flywheel/crank combo may mean you drop 20lbs but it has a much more substancial improvement than if you drop 50 lbs at the rims since they are further away from the center of power(crankshaft). the only reason flywheels have holes on the inside is because there still needs to be a strong friction surface for the clutch disk to smash into regularly. Ford racing sells a performance flywheel for 5.0s that has a negligible difference in overall weight but they relocated all of the weight to the center. this way theres no drivability problem but the transfer of power is more fluid and acomplishes the same task as a lighter flywheel.

to say that a lighter flywheel hurts turbo/supercharger performance is only slightly wrong. it all goes back to load. if you have a huge turbo with tons of lag, decreasing the weight on the flywheel will increase lag since the engine wont reach the same load level at the same rpm. its also generally the case that while you must wait slightly longer, the time it takes you to get there is dramaticlly cut down(dependant on where your starting out at, a crx flywheel is close to 30lbs, ours is 16lbs). this is really the only case a problem arises, on better built systems with correctly sized turbos or supercharger pullies there are no real downsides reported(aside from minor off the line issues with stalling). 1.8t owners who really pay attention(apparently not driving) have noted that it does take a couple hundred rpm more to start boosting but the time it takes them to reach that higher point is almost cut in half.

i dont know the math but there is a way of calculating how much a static object 'weighs' dynamiclly. so if you take your whole car, subtract 8lbs by putting an aluminum flywheel in, you also get to subtract 28lbs(random guess) off of the car while acclerating due to what drivetrain parts are absorbing energy. generally the closer to the crankshaft you get the less and less weight you need to remove before noticing huge gains(titanium valve spring retainers being the prime example).

to dumb it down further, if your going for big hp drag racing with very hard launches then get the heaviest flywheel you can. otherwise, if replacing a clutch is only due to a racing injury and not because you burn them out from stop and go traffic/shitty driving skills/washington dc traffic then get an aluminum flywheel. (price is usually an issue but i found em on ebay for 150 dollars, not 400 from spec)

quote Originally posted by megafreakindeth: if your going for big hp drag racing with very hard launches then get the heaviest flywheel you can.

This is wrong.
Did you read the David Vizard article I linked (here it is again: http://www.popularhotroddin..._increase/index.html )? Of the two cars tested, both were faster in the 1/4 with lighter flywheels. The reduction in launch energy was *easily* compensated by increasing launch RPM just a little bit.

I think you need to really hit the books... case in point: what's the definition of "load"?

[This message has been edited by Will (edited 12-19-2008).]

At this point it's clear to me that practically everything contributed to the subject has some truth depending on the conditions. In the little searching I've done so far the best all around performance favors the stock flywheel; fuel economy, driveability, comfort and in some cases engine dependability. As has already been stated there is a happy medium since there is a sacrifice to be made in either direction you travel from that point. From what I've found in searching, the lightest flywheel available is probably no good for anything outside of strictly performance driving, if you have to rev the engine to near 2000 rpm to launch without stall from every street light that will certainly take its toll on the clutch and fuel economy to say the least. There is also the issue of how much performance if any you stand to gain by making the change on a daily driven car where a few thousandths of a second saved on acceleration can not be felt, there has to be a large enough difference in weight between the two flywheels to make it worth the effort.

The best decision obviously requires quite a bit of consideration above and beyond being able to accelerate a little quicker. Formulas for mathematicle proof should be deployed more often in these discussions because the facts are more important than our speculative theories and more than a few of us here have the knowledge and understanding to math it out in laymens terms for all to understand especially where exponential changes are involved.

For those interested in info supporting comments made by bmwguru regarding the effect of flywheel weight on turbo euro cars;
http://www.europeancarweb.c...flywheels/index.html

Lightening a stock flywheel alleged best all around instead of an aluminum fw;
http://www.racetep.com/flywheel.html

Here's an association with bearing failure in some porche and VW engines due to overly light flywheels:

http://www.tunacan.net/t4/tech/flywheel.htm

quote Originally posted by Will: Here's another similar article: http://www.stockcarracing.c...ucing_moi/index.html

Thanks Will. That second article had more of the missing charts and graphs. I've seen threads on lots of car forums about the benefits and drawbacks of changing flywheel weight but the problem is that most of the people talking about it really have no idea what they're talking about.

Basically it goes like this: f = ma

But the reason I like those articles is that I've never seen anyone quantify it before.

Was interesting to note though that the higher of the two rates of acceleration used in Dave's articles was 600 RPM/sec and Dave suggested that high rate of acceleration was only applicable to highly tuned track cars while the 300 RPM/sec rate was more applicable to street cars. The impact of flywheel inertia was much lower at the 300 RPM/sec acceleration rate.

-FTF E

Heh. I'm looking at total weight for clutch + flywheel to be ~10LBS for my turbo engine. Increase the idle speed and decel enrich. Flat-shift ignition cut for in between.

Lighter = faster. If I can't get it off the line that's my fault, not the flywheel's.

If it's a DD, you can still cut a LOT of weight and have an acceptable idle, and still transfer alot of "free" HP from the MOI decrease.

http://img.photobucket.com/...ndy/SD4/DSCF1054.jpg
http://img.photobucket.com/...ndy/SD4/DSCF1053.jpg

Just my $.02

------------------

My Web page | The Turbo Super Duty Build.
You know that little voice that says it can't be done? I duct-taped its mouth shut and pushed it down a flight of stairs. (Leader of the Insurgency)

quote Originally posted by Joseph Upson: For those interested in info supporting comments made by bmwguru regarding the effect of flywheel weight on turbo euro cars; http://www.europeancarweb.c...flywheels/index.html

Spouting the same story with no serious explanation. Premature synchromesh wear? How the heck is that going to happen when most lightweight clutches have disks with LESS MOI than stock? That's reducing the amount of energy that the synchros have to deal with on each shift. They also say that engine damage may result, but the very important words "if not properly balanced" are easy to miss.

quote Originally posted by Joseph Upson: Lightening a stock flywheel alleged best all around instead of an aluminum fw; http://www.racetep.com/flywheel.html

These guys are trying to sell you their product. Surging and bucking at cruising speed? Due to a light flywheel? Give me a break. That's an engine mount issue.

quote Originally posted by Joseph Upson: Here's an association with bearing failure in some porche and VW engines due to overly light flywheels: http://www.tunacan.net/t4/tech/flywheel.htm

I'm extremely doubtful about the simple act of lightening the flywheel contributing to bearing failure, HOWEVER, David Vizard did note that reducing the mass of the harmonic damper on engines he's tested has resulted in LESS power output due to crankshaft torsional harmonics (he blames it on the valvetrain, but I'm not convinced that the phenomenon isn't due to highly resonant crankshaft absorbing the energy). So just maybe there's more to the story than what's in that article (ya think?).
That is, of course, ASSUMING that the stock flywheel has a neutral balance. If the stock flywheel is NOT neutrally balanced and the lightened version IS, then the source of bearing failures is heinously obvious.

quote Originally posted by FTF Engineering: I've seen threads on lots of car forums about the benefits and drawbacks of changing flywheel weight but the problem is that most of the people talking about it really have no idea what they're talking about.

No joke.
The list of problems attributed to flywheels that are "too light" is like the list of symptoms attributed to PMS.

quote Originally posted by FastIndyFiero: If I can't get it off the line that's my fault, not the flywheel's.

No joke x2.
People complain about problems with cars that are really problems with drivers... Like Ralph Nader's idiotic book about the Corvair. Guess what? THE CAR IS DIFFERENT. You can't drive it the same way and expect the same results.

[This message has been edited by Will (edited 12-19-2008).]

Here is a quick vid of my wife's VR6 Fiero with the 5.5lb aluminum flywheel and 500g damper. I don't need to rev between shifts and with the variable intake, I have power from 1,500rpms to 7,500rpms. It does rev pretty quick. I also have an electronic throttle actuator with fly by wire, so that may help. Before I had all the programming figured out, the engine would "flare up" automatically between shifts, but that was resolved quickly by adding a clutch pedal sensor.

quote Originally posted by Will: No joke x2. People complain about problems with cars that are really problems with drivers... Like Ralph Nader's idiotic book about the Corvair. Guess what? THE CAR IS DIFFERENT. You can't drive it the same way and expect the same results.

My intent was to show some supporting evidence of what bmwguru was proposing Will, I don't believe he made any comments about synchromesh wear so that along with anything else mentioned in the article not said by b..g... will have to be taken up with the author and you missed an important part of those important words you quoted; "if the ALF is too light or ".


According to David Vizzard;

"The principle reason the factory puts heavier flywheels on is for idle quality. The flywheel's mass smoothes out the engine's compression and firing impulses."

So it stands to reason that if your flywheel is much lighter than stock you will have just the opposite, so bucking and surging just might be a problem between shifts as the light weight flywheel allows rpm to drop down into the idle range between shifts particularly on much smaller displacement engines. They did use the qualifier of "almost no weight" regarding the flywheel. Of course they're trying to sell a service but that by default does not automatically discredit what they're saying.

I didn't confirm it but it appears the light flywheel association with VW/Porche engine bearing failure is dealing with four cylinder engines and their configuration dynamics in the engine series involved so it's interesting info but not relavant to our engines.

The article by David Vizzard is interesting but since the opening post for this thread asked this question as well: "could you feel much difference in acceleration" I feel it's important to draw attention to this statement by DV:

"The most critical part of a fast quarter-mile time is the launch. Here, the extra energy of a heavy flywheel is available with no prior penalty. This makes the answer to "heavy or light" anything but obvious in the case of the lower-output factory-stock machine. The Vortech-blown 5.0 though is much nearer a clear-cut case of light is better."

That along with the apparent emphasis of his tests on drag racing and road racing, the need for more than 400 hp to get "much nearer a clear-cut case of light is better.", the fact that the factory stocker he referred to runs 12.5s quarter miles and the overall test showing about a .6 mph gain in the 1/4 mile for it, all of that compared to what you can expect from what has to be at least a 55% flywheel wt reduction keeping in tune with the article, for a 3800 V6 rated at ~200 hp and 220 lb/ft running "you guess" in the 1/4 mile in stock form,

well, you'll have to draw your on conclusion as to whether you will feel the real performance difference and not mis interpret the driving modification it will evoke due to inertia change in such a lower powered platform relative to the test mules (actually quarter horses), it will certainly be less than .642 mph difference in a 3800 and considering normal spirited driving falls way short of 1/4 mile bursts around town, from the data listed it appears that unless you hold full throttle long enough you will actually suffer a loss of performance with a much lighter flywheel if you stop short of 1/8th mile.

[This message has been edited by Joseph Upson (edited 12-30-2008).]

quote Originally posted by Joseph Upson: you missed an important part of those important words you quoted; "if the ALF is too light or ".

I didn't miss them. I thought it was pretty obvious they had bearing on the discussion.
To summarize:
"Lightened flywheel with improper balance leads to bearing failure" - perfectly believable.
"Lightened flywheel with proper balance leads to bearing failure because it's too light" - I do not believe this and will not without some heavy duty experimental evidence.

quote So it stands to reason that if your flywheel is much lighter than stock you will have just the opposite, so bucking and surging just might be a problem between shifts as the light weight flywheel allows rpm to drop down into the idle range between shifts particularly on much smaller displacement engines.

No. The page in question specifies "bucking and surging at cruise". Do you cruise at idle speed? I've been told that LT1/T56 cars surge at cruise because the plenum is undersized for the engine. This effect *might* be made worse by a lighter flywheel, BUT remains fundamentally a tuning problem with the engine, NOT a function of the lighter flywheel. The lighter flywheel would probably have almost no effect because the gear ratio in question is so extremely tall.

With a given flywheel inertia, a larger displacement engine will spool down faster than a smaller engine due to greater internal friction and pumping losses.

If you allow the RPM to drop THAT low during a shift, you're driving the car wrong.

quote "The most critical part of a fast quarter-mile time is the launch. Here, the extra energy of a heavy flywheel is available with no prior penalty. This makes the answer to "heavy or light" anything but obvious in the case of the lower-output factory-stock machine. The Vortech-blown 5.0 though is much nearer a clear-cut case of light is better." That along with the apparent emphasis of his tests on drag racing and road racing, the need for more than 400 hp to get "much nearer a clear-cut case of light is better.", the fact that the factory stocker he referred to runs 12.5s quarter miles and the overall test showing about a .6 mph gain in the 1/4 mile for it, all of that compared to what you can expect from what has to be at least a 55% flywheel wt reduction keeping in tune with the article, for a 3800 V6 rated at ~200 hp and 220 lb/ft running "you guess" in the 1/4 mile in stock form,

Both cars cut BETTER sixty foot times with the light flywheel than the heavy one. This blows away the idea that heavy flywheels are better for launching. The 1/8 mile MPH dropped, but the amount is small (<0.5 mph) and could easily be the result of inconsistent shifting. The 1/8 ET *improved*, so I would call the modification a performance increase. As DV said, performance past the 1st corner is lightweight all the way. The only question was the interaction of 60 ft times with flywheel mass. DV subsequently showed that 60' times can be IMPROVED with the right techniques and a light flywheel.

When you evaluate "bang for buck", consider the weight of the clutch also. In a Fiero, the clutch weighs as much as the flywheel, so the total assembly weight is pushing 30#. Going from a 14# flywheel to a n 8# flywheel brings the assembly weight down to 24#, which is not such a big drop from 30. The situation is even worse with the Mustang, as that large diameter clutch probably weighs 20# or more. Thus the stock assembly is ~44# and the lighter assembly ~31#.

The engine also has its own internal MOI in the crankshaft and rotating assembly. That weighs over 50#, but can not be directly compared to flywheel weights do to significant differences in geometry. LIke the internal resistance of a battery, the internal MOI of an engine is basically inescapable. Once all the different MOI's are found and addressed, the change in flywheel weight is really NOT that big a change in the engine's way of running it every night