Lighter flywheel?

[varanus]

I know there have been a lot of discussions about the possible advantages of a lighter flywheel. The conscesous I got was that for the street and road racing it is good. But for drag racing the heavier stock flywheel with it's inertia was better.
My question is-is there a point where the extra inertia is not a factor. For example if my car puts down say 600/600 to the wheels, is there now such an abundance of flywheel inertia that a lighter flywheel would be fine for drag racing and still be good for orad courses?

 

[1TONY1]

I have the same thoughts and questions.

 

[FE 065]

I've drag raced motorcycles with and w/o their flywheel(s). They always revved faster without one! I'd have to think the only way a lighter flywheel could hurt dragstrip performance is if it made getting off the line smoothly a little harder. Or if you granny shift so slow the revs fall down in between shifts! Twirl a ball on the end of a string.. which spins up quicker and easier; a ball on a short string or on a long string?

 

[varanus]

Good point, but in the case of a car the energy is not transfered until the cluth is engaged. In dumping a clutch, will there be a harder launch with the heavier flywheel because of the heavier mass already at speed? Will it make up for the quicker revving of a lightened flywheel once the car in fuly in gear and in motion?

 

[FE 065]

A harder aluminum flywheel launch can be had by raising the launch RPMs. 95% of the Vipers racing probably aren't leaving the line over 3000 rpm (their slicks aren't that sticky), so there's plenty of room. If a car was running huge wrinkle wall slicks and already coming off the line at 5000 rpm or more, then it might be time to wonder whether bogging at the start might become a problem with an lighter flywheel. I'd take faster revving throughout the 1/4 and alter my starting line technique to compensate for any inertia loss. With 488ci it'd seem easy enough to do.

 

[1TONY1]

If a car was running "large" wrinkle wall slicks and already coming off the line at 5000 rpm or more

= ME

 

[FE 065]

You're the guy!

 

[Ron]

Though I know many will disagree and some quite strongly, but from the "seat of the pants" perspective, I do not see the value in the Viper having the aluminum flywheel.

I have gone from OEM to aluminum and back to OEM and driven the car in the same day each time before and after. I could, if I tried real hard, convince myself there was a differance, but honestly I could not tell which was which. Maybe the 1996 cam allows the engine to have snappier throttle response than the later cars, masking the flywheel's benefit... don't know, but I'm happy with the OEM wheel.

 

[Chuck 98 RT/10]

Blasphemy Ron! You'll be ostracized for that one!

Too date, I have only read one post of an actual ET increase. It was .1 or .2 Everything else has always been SOTP which doesn't sell it for me.

 

[Steve 00RT/10]

I know there have been a lot of discussions about the possible advantages of a lighter flywheel. The conscesous I got was that for the street and road racing it is good. But for drag racing the heavier stock flywheel with it's inertia was better.

I just had a Fidanza flywheel and new cluch put in 2 weeks ago. I drove our car 30,000 miles with the OEM flywheel. IMO there is a definite increase in low end acceleration. The engine spools up much faster. As far as noticing a difference(bogging) in starting from a dead stop--it's pretty much negligient. I am aware of the potential torque issue, but don't really care. I did for xcrossing and track stuff. You should theoretically be able to brake in a shorter distance as well. I xcrossed in a small lot last week end. There is no doubt in my mind it helped my time. Next spring, I will get it dynoed again and we'll see if it affects torque much. I'm at 438HP & 480 torque now. I am very pleased with this addition. Maybe do the rear end in the spring.

....The Fidanza people say that the lighter flywheel allows more HP to the rear wheels--right now--balancing out the torque issue. I know many may argue that point. I do know that at 3700 RPM, I now have big tire spin with warm tires when floored in first gear--which I didn't have before. I've even gotten some spin at 3700 RPM in 2nd. gear. It never did that before with warm tires.

Steve

 

[joe117]

Here's my experience,
I had experience with replacing a 24lb flywheel with an 8lb in a stock car. There are no standing starts in stock car racing so I don't know how it would have done at the drags. My car would run 5k to 8k rpm in a lap. No low speed running at all under green.

When I went to the light wheel, I thought the car accelerated faster and I did win the first race after changing over. It seemed to be an improvement. I can't say that we ever timed any clean laps for comparison.

The second chance for comparison came after about 9 races. I got caught by a surprise inspection and was disqualified for that night after finishing second, because of the aluminum flywheel. My class required a stock flywheel. Only a few people knew I had it and they probably talked too much and it got to the wrong people.

Everyone cheats a little in stock car racing.
Anyway, I had to go back to the stock wheel.

The first time I went into a turn with the old flywheel I almost hit the wall. The thing seemed to pull me along after I let off the gas. It seemed like a really big pull.

I didn't really notice the difference on braking when I first started using the aluminum but I sure did notice it when I went back to the stock.

Going from 24lb to 8lb is a big change. Is there that much of a change when you go lightweight on the V10? I don't know.

 

[varanus]

what is the weight difference from stock to the fidanza?

 

[Steve 00RT/10]

Going from 24lb to 8lb is a big change. Is there that much of a change when you go lightweight on the V10? I don't know.

From my reading---it is a bigger difference---- 43lb. to 17.5lb.

Steve

 

[joe117]

I'm thinking the % change would be the thing to compare.

 

[Steve 00RT/10]

I'm thinking the % change would be the thing to compare.

You could be right, but then wouldn't the weight of the car also come into play as a relative percentage? It's getting too deep for me. Maybe a HP,torque,flywheel guru will jump in.

Steve

 

[slaughterj]

I noticed no SOTP or dyno difference due to the aluminum flywheel.

 

[joe117]

Sure, I think that the weight of the car would make a difference.
The 43:17.5 change is about the same as the 24:8 that I had.

I'm thinking that in first gear, the Viper is traction limited and the light wheel can't hurt you. You have more power than you need.

After you get past the point of traction limit, the light wheel must help some.

Even removing the weight of the stock wheel itself from the car might be worth half a tenth, aside from not having to spin up all that extra mass.

The other thing I just thought of was that I didn't have any special, light clutch, only the wheel was special.

 

[BruceW]

It's the relative change in the mass polar moment of inertia of the entire rotating assembly (crank, rods, pistons, belt,pumps, etc.) that counts. The polar moment of inertia defines the resistance of an object to rotational acceleration. My gut feeling is that the reduction in that due to a lighter flywheel is fairly small. Anyways, weight change alone doesn't make a meaningful comparison.

 

[joe117]

I don't think I would expect it to dyno any better. After all, the dyno isn't measuring acceleration.

Perhaps I'm thinking wrong but I don't see it changing the final HP or torque numbers.

 

[joe117]

Of course, there is always the question of, why do they have any heavy flywheel at all?

It must change something or they wouldn't just add 43lb to the back of the engine.

 

[Steve 00RT/10]

I e-mailed PVO last month to get their take on lightened flywheels. According to the e-mail I got back, Herb Helbig thought it an interesting topic for the next 1/4ly. The only thing they came back with right away was fear of not enough heat dissipation. I called Fidanza and they say they have never had a heat problem with well over 400 installed in Vipers to date.

Is it not true that all stock and track cars typically have a 8lb(Or there abouts) flywheel? There must be some performance advantage or they wouldn't do it. As for SOTP--perhaps it wakes up a 'creampuff' more than the older models. There is no doubt in my mind that the car feels stronger in 1st and 2nd.


Steve

 

[Marv S]

This is from pre-Findenza-Viper days but still has some good info from a racer... http://vca2.viperclub.org/forums/showthreaded.php?Cat=&Board=UBB22&Number=222762

Another note: The Comp Coupe light weight flywheel is not AL. It's steel and much lighter than the stock SRT steel flywheel. It will fit into the SRT-10 but will not work in the Gen 1 or Gen 2 Vipers. I asked why they didn't go with an AL insert like the aftermarket flywheels were and they said there was concern about warping with AL from long exposure to high heat and race conditions


Here's some things I have observed as well as some great info from Erik Messley on flywheels:

The lightweight flywheels out there have steel inserts. The McLeod (~16 lbs.)is most common and, if ever needed like from lots of drag racing, McLeod will replace the insert for a modest fee if you send it to them. The TNT flywheel insert can be replaced at the track, by the user, if you have a spare insert with you. The TNT may use bolts that differ from stock (use new bolts) & The TNT flywheel is about 1 pound heavier than the McLeod.

Check out Sean Roe's prices.

If you replace the flywheel I recommend having it balanced, then mark it and the pressure plate and balance them as a unit. The flywheels are usually VERY well balanced, but the pressure plate may not be. E-mail me if you want more detail on how this is done.

The following is from a post made many months ago by Erik Messley that has lots of good info:

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quote:
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Originally posted long ago by Erik Messley:
We did change the flywheel to a number of lighter versions. For street use, staying around 40 lbs total weight (flywheel, pressure plate, friction disc) is very nice.....much crisper throttle response, improved engine braking, not difficult starting from a stop, no appreciable surging problems, and a marked improvement in the twisty road sections coming out of corners, etc. For a combo of track and street use, with a bit more emphasis on track usage, a 30 lb total weight will dramatically improve throttle response, etc.. Track times will be markedly improved due to the improved responsiveness and initial acceleration between corners and improved engine braking (the rear brakes are a bit wimpy for track usage and the flywheel/engine combo helps balance the car a bit better under braking). Downside is a bit harder to start from a stop, and a much smoother throttle foot is necessary to keep the car from surging at constant speeds while cruising down the freeway. For track usage, a combined weight of 20 lbs or so is wonderful. Throttle response is instantaneous, engine braking remarkable, and acceleration markedly improved. Keeping the MOI (moment of inertia) as low as possible is the key. The stock combination has a MOI of over 1950 lbs! (highest I've ever measured on a car!). A good carbon/carbon triple disk will be in the 175 lb range. You wouldn't want to try one of these on the street as stop and go driving will wear them out extremely quickly, starting from a stop is a bit touchy, plus the engine revs so quickly that without race type rubber, first and second gears are pretty useless (it just spins the tires.......kinda fun, but not very practical!). For the money, a lightened flywheel is an extremely good value for the overall performance gained. You do need to be honest with yourself as to the actual usage of the car prior to your selection though. Too light for your application or tolerance level will definitely result in disappointment. Hope this information helps you. Erik Messley

Stock clutch with McCleod flywheel makes an excellent street driver and will certainly help on the track as well. If memory serves me correctly, the total weight ends up right around 50 lbs. I haven't done the actual MOI of this combination, but since you are taking a large amount of the flywheel weight off of the outer edges (aluminum vs steel) I would conservatively guess that the MOI would fall around the 1500 lb range or roughly a 25% improvement. It's definitely noticeable but very tractible/drivable.

 

[gthomas]

EQUIVALENT WEIGHT=0.5x(flywheelweight)x[(flywheel radius x gear x final drive ratio)/(tire radius)]squared
factory steel=over 20 pound
aluminum aftermarket=9-10 pounds
Going to the aluminum flywheel will shave off over 200 pounds in first, over 70 pounds in second, etc..
A flywheel stores energy to dampen compression and power pulses from an engine.
The aluminum flywheel will allow the engine to rev up quicker, improves throttle response across the band.
However, when cold, it will be more prone to dieing at idle(until it's warmed up).
I posted this before, I've only done the flywheel upgrade as a total package(flywheel, clutch, pressure plate, throwout bearing, and shifter).
It will improve your car.
I did not want to get into an arguement with the last person who told me it only helps on road courses, and not at the drag strip. It will help all around performance.
But, if you want total strip performance, get an automatic, with a manual valve body, even I cannot shift faster than that.
But if you want to improve your all around performance in keeping with the all around use, upgrade it.
EDIT:OOHHH YYEEEAAAHHHH....mass in motion tends to stay in motion, so a lighter flywheel will be easier to engage/disengage.

 

[GTSnake]

EDIT:OOHHH YYEEEAAAHHHH....mass in motion tends to stay in motion, so a lighter flywheel will be easier to engage/disengage.

And that's exactly why I got mine. It was the first mod I did to my car after smooth tubes. I wanted it to spool up and down quicker so it didn't feel like a lumbering V10. I can't really say it made much of a SOTP difference and definitely didn't get any more HP but when I blip the throttle it definitely revs up quicker. I would imagine in road racing that would be an advantage.

 

[George Bryce]

I bought one, I tried it, it is for sale. With my sreet et tires @ 15#, I launch at 5500 rpm....with the stock iron wheel. I did not 60 foot as well with the lite wheel.
1.48 with the iron...1.55 with the alum. I know the car has more power at the shifts with the iron wheel. It sounded way cool with the lite wheel. Quicker revs with the clutch in. fyi, GB3

 

[COOLASP]

Ive been concidering a lighter flywheel for all the reasons I have just read, and I'm still concerned the motor is designed with the OEM flywheel weight behind the motor, if one would change thie weight, would this adversly afect the motors longevity?

 

[joe117]

"adversly afect the motors longevity?"

I just don't see how it could. What are you thinking it would do to cause trouble?

 

[DEVILDOG]

My experience, engine is much more responsive and revs much quicker. Shifting is a blast. No problem with launches. Concerning above, would think engine would last longer with a lighter flywheel to turn.

 

[Jack B]

One correction - you cannot compare flywheel weights directly. You have to compare the polar-moment-of-inertia. This will give you a basis for calculating the minute loss of horsepower due to the heavier wheel.

Remember, a car that sticks well (drag strip) needs that extra rotating mass to generate a 1.4 - 1.5 sixty. For every tenth you drop the sixty you will improve your ET by as least two tenths.

 

[gthomas]

It also comes with an OEM exhaust that was developed for that motor? Same thing.