Lightweight Flywheel Information

[Bobpantax]

After reading the other two threads on this subject, I felt the need for some precise data on the subject. I called and spoke to two expert Daves about the 17.5 lb Fidenza aluminum flywheel. The first Dave was the Dave at Roe Racing that all of us who have done business with Roe know as a very knowledgeable individual. The second Dave was the technical expert at Fidenza. I asked both Daves the same questions. 1.Will use of the lighter flywheel cause a loss of torque? Answer: NO. This is a myth. The weight of the flywheel is part of what makes up the 12 - 17% driveline power loss we all use to calculate flywheel horsepower. Use of the lighter flywheel reduces the driveline power loss. It permits the engine to reach higher RPMS faster - less power needed to turn heavier mass of heavier flywheel. 2.Will use of the aluminum flywheel cause around town stop and go driveability problems? No. Dave from Fidenza added the following: If the stock clutch is used with the new flywheel there should be no problems. The problems come when people change to a racing clutch at the same time that they change to the aluminum flywheel and then try to use the car as a daily driver. It is the racing clutch that causes the problems. A racing clutch is not meant to be used in a daily driver. I felt that the foregoing resolved the issue. Anyone disagree? If so, please explain why using sound technical analysis as opposed to subjective, off the cuff comments. Thanks.

 

[Ron]

While I too did the same research you did, including speaking with the very nice and knowledgable people at Fidenza (an excellent company that stands beind their product), I found that the aluminum flywheel did nothing "perceptable" to improve the responsivness, acceleration, or deacceleration of my Viper.

Facts are great and I'm all for them, but how it feels is what matters.

My opinion only... many others swear by them.

 

[_Niz_]

I had one installed a month ago. It is made by RPS. There IS a noticeable difference in responsiveness and accelaration. It is nothing exaggerated but it is noticeable!!

 

[Bobpantax]

Before this thread gets off point,which would be unfortunate, I want to remind those who choose to post that this thread is not about whether performance is increased. It is also not about subjective feelings. The post addresses whether or not the installation of an aluminum flywheel causes a loss of torque or any impairment of driveability in a daily driver. My research led me to the conclusion that the answer in both instances was "no". Whether or not there are positive benefits is not the subject of this thread. That issue has been beaten to death in the other two threads. Thank you in advance for any relevant responses.

 

[ruckdr]

This may be off topic from the "torque" issue, but what is the weight of a stock flywheel. (17.5 for the aluminum as you stated)?

 

[gthomas]

You probably saw my posts on the subject then.
With that said, the only negative (also from my other posts), is that it may be more prone to dying at idle while cold (engine, not weather).
This does not mean that you are going to have to hold the accelerator pedal, etc. until it warms up. Just that, like when it dies at idle sometimes, it may do it a few more times.
No loss of power, allows you to get there a little quicker.





EDIT: The weights for the formula on said post is for a motorcycle.
stock:20 aluminum:9-10
For Viper: Fidenza=17.5 stock=33-35ish

EDIT EDIT: I swear by them.

 

[1TONY1]

With a more aggressive clutch....not what I would call a "racing" clutch....yes, the drivability was worse. More of what I call cam lope, bucking/jerking while at a neutral throttle position in the lower gears only. I have no experience with a stock clutch/alum combo. I am now back with the stock flywheel.

 

[Steve 00RT/10]

I believe a stock flywheel is 43 pounds. I noticed absolutely no driveability issues whatsoever using a stock clutch. While I still have the stock flywheel, the odds of me going back to it are slim and none.

Steve

 

[rcdice]

I'm sure in your research you read this thread:

http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB14&Number=492325&Forum=UBB14&Words=&Match=Entire%20Phrase&Searchpage=2&Limit=25&Old=3months&Main=492325&Search=true#Post492325

My concern w/ the aluminum flywheel was not so much the daily grocery getting driveability as much as issues with a hard launch w/ sticky tires. The above thread illustrates why many drag racers advise against them. My car has never been on a 1/4 mile track but I do occasionally launch it on the street. For a primarily road course car, I think it's the way to go. For a car where standing starts are important, I'm not so sure.

Also, I'm sure Dave x2 are both honest men. However, they do both have an interest in selling new lightweight flywheels. You stay stock, they don't sell one. Just the cynical side of me talking.

 

[ViperInBlack]

One of our most trusted vendors who sells flywheels suggested that I steer clear if the car is a grocery getter. To paraphrase him: pulling away from an intersection is more complex since there is less flywheel inertia to move away in slow traffic.

Just repeating what I was told when I attempted to order.

 

[gthomas]

A vendor advertises their aluminum flywheel, at 16.5 pounds, is 49% lighter than the stock weight.
{is/of X %/100}(cross multiply)(unknown is x)
{16.5/x X 51/100}
{51x = 1650}
{x = 32.352941}
Between 32 and 33 pounds.

 

[AG98RT10]

I don't know about the SRT, but in my RT, driveability is only marginally affected by having the Fidanza flywheel with stock clutch. It occasionally will surge a little in the lower gears at slow speeds... Not enough to cause a problem.

I think the benefits in faster rev-up outweigh any disadvantages. I also think it helps a little on the track when using engine braking entering turns - one more place where there is less rotating momentum. But what do I know? Seems to me this is one those things that you just naturally do when you have do clutch work, anyway.

 

[BigCarrot]

A vendor advertises their aluminum flywheel, at 16.5 pounds, is 49% lighter than the stock weight.
{is/of X %/100}(cross multiply)(unknown is x)
{16.5/x X 51/100}
{51x = 1650}
{x = 32.352941}
Between 32 and 33 pounds.

I could have done that in my head a lot easier.

 

[gthomas]

I know BC, but I did it for Bob.

 

[Tom F&L GoR]

I recently heard a lawyer say this, and perhaps it applies here. "We are in violent agreement!"

In one of the other posts, there was a calculation of the effect of the lighter flywheel. It translated the reduced inertia into the equivalent vehicle weight reduction. Don't quote the numbers, but the lighter rotating weight was equal to carrying about 200 pounds less static weight (i.e. a passenger.)

So to compare where you gain and where you lose:

Having a stock flywheel is like a 200 pound guy running into the back of your car just as you accelerate. His inertia helps you get going relative to the lighter flywheel.

But now he's stuck on your bumper and you have to carry the extra 200 pounds along upon every circumstance that the engine must accelerate or brake (with clutch engaged.)

The analogy gets a little fuzzy when you compare steady state speeds or cornering, since then the difference isn't the effect of 200 pounds, but the effect of the 20 pound weight difference.

Anyway, perhaps it helps to decide not if lighter flywheels are good, but if they are good for you.

 

[gthomas]

Yeah, those were mine. And the numbers were going from a 20 pound stock to a 9-10 aluminum flywheel.
Those were for a motorcycle.
The Viper would be going from 32-33 pounds to 17.5.

EQUIVALENT WEIGHT=0.5x(flywheelweight)x[(flywheel radius x gear x final drive ratio)/(tire radius)]squared

 

[rcdice]

Ok guys, please don't make me think too ******* a Saturday afternoon. With the above formula in mind, what effect would shorter gears (ie. 3.45 vs. stock 3.07) have with an aluminum flywheel?

What about larger tires? (ie. 17" vs. 18" vs. 19")

Just curious.

 

[Steve 00RT/10]

I believe a stock flywheel is 43 pounds.

This is wrong. I just dug out my old flywheel to confirm the weight. It weighs 32.5 pounds....as others have stated above with their computation.

One of our most trusted vendors who sells flywheels suggested that I steer clear if the car is a grocery getter. To paraphrase him: pulling away from an intersection is more complex since there is less flywheel inertia to move away in slow traffic.

IMO...unless the SRT10 is a different animal, there is little truth to the 'complexity' of the operation. Granted, the flywheel inertia is less, but the Viper engine is massive. Just to try it........I have started in 4th gear from a stop with the lightened flywheel and not stalled the car.(about 1500 RPM with a little slippage).

Our car has been in many long parades at very slow speeds and in bumper to bumper/stop and go city traffic(the few times we get to a city). There is no discernible difference in clutch/engine engagement. While I have driven sticks since 1964, my wife only has about 13 years under her belt with manual transmission cars. She also noticed no difference when we switched the flywheel and has yet to stall the car.


Steve

 

[ViperInBlack]

Steve:

If driven solely on the street, is there, then, any advantage for an aluminum flywheel?

 

[Steve 00RT/10]

If driven solely on the street, is there, then, any advantage for an aluminum flywheel?

Alice,

The answer to that is very subjective. I would guess that a majority of people who own Vipers drive them solely on the street. Yet many of this group will still modify their car in some way........just because.

For example; An open 3" exhaust with Belanger headers might never see a track, but it sure sounds good! When our car starts, the neighbors 2 blocks away can hear it. Everybody likes a little street tango once in a while. Lots of times that could be from a roll to 80 or so. I think the first 2 gears are where the flywheel is most noticable for spool up time.

You might, someday, try autocrossing. It is lots of fun and you can't hurt the car. You should try it. There must be places near you to do this. I believe it makes a noticeable difference there as well. From a safety standpoint, both for racing and street, I believe the car stops faster with a lighter flywheel.

Therefore, by my twisted logic, there are no disadvantages for street use which thus means it must be advantageous.

BTW--nice article in the 1/4ly

Steve