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I just read a pretty informative article in HOT ROD-- special series on power tips. How to Choose a Flywheel I've found myself somewhat baffled over the lightwieght vs. standard flywheel opinions. And based on some of the post that I've read, I don't think I'm alone. This article helped clear things up quite a bit.

In summary, the author explains that the purpose of the flywheel is three fold:
1. it provides friction surface for the clutch
2. it's a means of turning the engine over via the starter
3. IT STORES ENERGY TO GET THE CAR MOVING!!!!

As a ballpark recommendation, a street or drag race car wants a heavy flywheel, conversely, a roadracer needs a lightwheight one.

A good illustration in the article was comparing a bicycle tire to a 150 lb semi tire. You can make them roll at the same speed, but it takes a lot more energy to get the big tire going and subsequently to get it stopped. In motion, the heavy wheel has more inertia or stored energy than the small one.

When you dump the clutch, the flywheel releases the stored energy which makes the car move ahead. The engine relies on stored energy for a couple of reasons. The engine does not make power for every degree of crankshaft rotation. Because its weight resists change in motion, the flywheel tends to smooth things out between power pulses.

However, once the car gets moving, a heavy flywheel is a burden. The article doesn't explain, but I'm assuming that the inertia of all the drivetrain (transmission, driveshafts, wheels, etc.) can effectively take over for the flywheel.

I would love to copy the article for all interested to read, but of respect for their copyrights will resist. It is full of excellent examples of how this inertia thing all plays out with different gear ratios and power sources.

Summary: Light flywheels are harder to launch but will spin much quicker once in motion.

Quote: On the street it's advisable to err on the heavy side. A heavier flywheel will always make the car easier to drive normally-- when pulling away from a stop or when shifting. Street cars with super lightweight flywheels shudder horribly from a standing start, jsut as they do under light load at low engine speeds. A light flywheel lets an engine drop too far while the clutch is in during a part throttle shift, and that can cause the enging to bog, as well.

I hope this helps.

My question: Those of you who have use the lighter flywheels, (ie 10lbs), how did it drive? and how stock or modified is/was your engine/drivetrain (approximate horsepower, etc.)?

Looking forward to more discussion
 

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Good Post -- Anyone use a light flywhl on strt?

> I just read a pretty informative article in
> HOT ROD-- special series on power
> tips. How to Choose a Flywheel
> I've found myself somewhat baffled over the
> lightwieght vs. standard flywheel opinions.
> And based on some of the post that I've
> read, I don't think I'm alone. This article
> helped clear things up quite a bit.

> In summary, the author explains that the
> purpose of the flywheel is three fold:
> 1. it provides friction surface for the
> clutch
> 2. it's a means of turning the engine over
> via the starter
> 3. IT STORES ENERGY TO GET THE CAR
> MOVING!!!!

> As a ballpark recommendation, a street or
> drag race car wants a heavy flywheel,
> conversely, a roadracer needs a lightwheight
> one.

> A good illustration in the article was
> comparing a bicycle tire to a 150 lb semi
> tire. You can make them roll at the same
> speed, but it takes a lot more energy to get
> the big tire going and subsequently to get
> it stopped. In motion, the heavy wheel has
> more inertia or stored energy than the small
> one.

> When you dump the clutch, the flywheel
> releases the stored energy which makes the
> car move ahead. The engine relies on stored
> energy for a couple of reasons. The engine
> does not make power for every degree of
> crankshaft rotation. Because its weight
> resists change in motion, the flywheel tends
> to smooth things out between power pulses.

> However, once the car gets moving, a heavy
> flywheel is a burden. The article doesn't
> explain, but I'm assuming that the inertia
> of all the drivetrain (transmission,
> driveshafts, wheels, etc.) can effectively
> take over for the flywheel.

> I would love to copy the article for all
> interested to read, but of respect for their
> copyrights will resist. It is full of
> excellent examples of how this inertia thing
> all plays out with different gear ratios and
> power sources.

> Summary: Light flywheels are harder to
> launch but will spin much quicker once in
> motion.

> Quote: On the street it's advisable to
> err on the heavy side. A heavier flywheel
> will always make the car easier to drive
> normally-- when pulling away from a stop or
> when shifting. Street cars with super
> lightweight flywheels shudder horribly from
> a standing start, jsut as they do under
> light load at low engine speeds. A light
> flywheel lets an engine drop too far while
> the clutch is in during a part throttle
> shift, and that can cause the enging to bog,
> as well.

> I hope this helps.

> My question: Those of you who have use the
> lighter flywheels, (ie 10lbs), how did it
> drive? and how stock or modified is/was your
> engine/drivetrain (approximate horsepower,
> etc.)?

> Looking forward to more discussion
Good Post!!!! I would also like to know if anyone uses a lighter than stock flywheel on the street and with what results?
 

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Not on a Datsun, but have had one

I haven't run a lightened flywheel in my Datsun, but I did have one in my old ('54)VW Bug. Totally different engines, but the physics are the same.
My Bug had a 1835cc with dual webers. Had plenty of power, and when I added the lightened flywheel, I noticed a increase in its willingness to rev and some extra hp on top. Obviously this is due to less weight and inertia as mentioned in the article.
Some drawbacks, where that when the clutch was depressed, the rpms fell off faster than they used to. This necessitated the need for faster shifting to keep the rpm from falling off too much. But, this is where a short shifter made this an easy task. Starting from a stop was another thing. I had to rev the engine slightly more than I had previously, and sort of slip the clutch to get rolling.
Overall, I would say getting a lightened flywheel depends on several factors. In a torque monster engine, a lightened flywheel probably won't hurt anything, since there is probably more than enough torque at low rpms to get moving, regardless of Flywheel weight (to a point). If you have an engine that can only benefit slightly with a few more hp, then don't do it. If you have hp to spare, or have an engine that produces most of its power in the high rpm, then adding this isn't so much of a concern. You must also be prepared for faster shifting, so either practice and/or get a short shifter. I enjoyed this on my Bug, but am hesitant to install it on my Datsun. I think I'll just stick to the original 240 Flywheel. (By the way, these are slightly less heavy than their 280 counterparts, although the same size)
 

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Not 10 but 20.

Hi guys.

Let's try to figure it out.
I had my flywheel lightened. I was aware of those issues, and decided not to go krazy with 10-13Lb flywheels but stay a bit more conservative. So, I had them shave 4Lb off original 24Lb wheel. I had it done together with a dual friction clutch installation, and WOW!!!! what a difference it made. It does spool quicker, and you DO need to rev it a bit higher. But, not too much. All over I am a happy camper with that combo.

I would not put 10Lb flywheel on street car. You gotta rev really hi to get moving, keep it up there most of the time, and shift razer quickly. Too much pain in the ass. Thou for roadracing kinda setup it would be highly desirable combination. Hope it helps.

Eugene
 

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Does anyone know the weight of a 240 flywheel (nc)

> Hi guys.

> Let's try to figure it out.
> I had my flywheel lightened. I was aware of
> those issues, and decided not to go krazy
> with 10-13Lb flywheels but stay a bit more
> conservative. So, I had them shave 4Lb off
> original 24Lb wheel. I had it done together
> with a dual friction clutch installation,
> and WOW!!!! what a difference it made. It
> does spool quicker, and you DO need to rev
> it a bit higher. But, not too much. All over
> I am a happy camper with that combo.

> I would not put 10Lb flywheel on street car.
> You gotta rev really hi to get moving, keep
> it up there most of the time, and shift
> razer quickly. Too much pain in the ass.
> Thou for roadracing kinda setup it would be
> highly desirable combination. Hope it helps.

> Eugene
 

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Re:13 lbs.

> Hi guys.
> I would not put 10Lb flywheel on street car.
> You gotta rev really hi to get moving, keep
> it up there most of the time, and shift
> razer quickly. Too much pain in the ass.
> Eugene

I have to disagre. Now, I don't know how the 10lb flywheel will work, but I have the 13lb flywheel from Centerforce,(incidently, that is the one they now provide, HKS no longer makes the 10 lb one, but Arizona Z does, and the cost is similar).
I might have to slip the clutch a little more on start, but I don't really see it. I have a lower gearing than I should,(still have the stock 3.54 w/ the ZX tranny), and that alone will require a little more slipage.
As for razor quick shifting, no. The revs do fall off quicker as it gians revs quickly, but not as much as people say. I can't granny shift, or it falls to idle, but a normal shift is fine. Part of it is the way I drive, but alot of myths are out there about the lightened flywheels. I love it and wholeheartedly endorse it.
-Bob Hanvey
73 240 3.1L
 

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Re:13 lbs.

> I have to disagre. Now, I don't know how the
> 10lb flywheel will work, but I have the 13lb
> flywheel from Centerforce,(incidently, that
> is the one they now provide, HKS no longer
> makes the 10 lb one, but Arizona Z does, and
> the cost is similar).
> I might have to slip the clutch a little
> more on start, but I don't really see it. I
> have a lower gearing than I should,(still
> have the stock 3.54 w/ the ZX tranny), and
> that alone will require a little more
> slipage.
> As for razor quick shifting, no.
> The revs do fall off quicker as it gians
> revs quickly, but not as much as people say.
> I can't granny shift, or it falls to idle,
> but a normal shift is fine. Part of it is
> the way I drive, but alot of myths are out
> there about the lightened flywheels. I love
> it and wholeheartedly endorse it.
> -Bob Hanvey
> 73 240 3.1L

Although I'm sure there is no direct correlation between horsepower and drivability of a Z with and inline 6 and a lighter than standard 23lb flywheel, I would imagine that both the amount of horsepower available and the strength of the cluth/pressure plate would influence the driveabliltiy of a Z with a lighter flywheel. In other words, if you have an improved after market clutch and pressure plate and an engine that is making more horsepower that stock, you are going to be fine with a lighter flywheel. But,,,,you wouldn't want to lighten the flywheel too much on a stock engine, with a stock high mileage clutch. Do you agree?
 

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I agree, to a point.

> I have to disagre. Now, I don't know how the
> 10lb flywheel will work, but I have the 13lb
> flywheel from Centerforce,(incidently, that
> is the one they now provide, HKS no longer
> makes the 10 lb one, but Arizona Z does, and
> the cost is similar).
> I might have to slip the clutch a little
> more on start, but I don't really see it. I
> have a lower gearing than I should,(still
> have the stock 3.54 w/ the ZX tranny), and
> that alone will require a little more
> slipage.
> As for razor quick shifting, no.
> The revs do fall off quicker as it gians
> revs quickly, but not as much as people say.
> I can't granny shift, or it falls to idle,
> but a normal shift is fine. Part of it is
> the way I drive, but alot of myths are out
> there about the lightened flywheels. I love
> it and wholeheartedly endorse it.
> -Bob Hanvey
> 73 240 3.1L

I'll agree with you, because of the 3.1L that you have. I had a lightened flywheel on my old bug(read post below) and it definetely affected the driving behavior of the car. The reason for this is because a 1.8L VW is probably putting out [email protected] has to work too hard to get the car moving. Hence the benefit of a slightly heavier flywheel to store some of this potential energy. Try the same thing with a Honda, you'll get the same result.

Since you have a 3.1L probably putting out 250ft/lb the negative affects of a lightened flywheel are hardly noticeable. 250ft/lbs in a car that weighs 2400 is more than enough, to negate any negative effects of lightening the flywheel. But an engine producing 150ft/lbs in the same car will have a harder time trying to transfer energy to the drivetrain. This is where a slightly lightened flywheel, 18-20lbs would be best. Unless of course, you always drive with the pedal to the metal, then of course lightened flywheels can only benefit performance.

240Dave
 
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