flywheel lightening

Hi While the cold wind and rain falls here in the UK which means the Speedster stays in the garage. I would like to investigate the benefits/drawbacks of flywheel lightening for a stock 1600 twin port injected engine for road use. Has anyone played with this as a bolt on tune for their engine???
Many thanks Nigel

Nigel,
A lightened flywheel will give you a faster run up in RPM's / a quicker throttle response in bigger motor, but is minimal in a smaller 1600cc motor.
I would do it if, I was changing out a clutch or flywheel seal but to to pull the motor just to change out the flywheel, it's a lot of work and be sure to reset the end play to .003 - .005

Second what Alan says; I've read that for street cars it's better to stick with the stock weight flywheel; something to do with inertia.

A flywheel stores energy. The heavier the flywheel, the more energy it stores, but it also takes more energy to get the mass of a heavier flywheel turning.

Heavy vehicles or vehicles that tow benefit greatly from a heavy flywheel. The heavy flywheel makes it easier to move the big vehicle from a standstill. It also allows the engine RPM to maintain during a shift. Instead of a quick drop in RPM, the RPM stays near constant allowing a smoother shift to the next gear. A heavy flywheel feels "torquey" off the line.

A light flywheel is just the opposite. It takes very little energy to speed the light flywheel up (revs up quick) but also drops RPM quickly during a shift. Not a problem in a small light vehicle with good synchros and a well-adjusted shift linkage. It would be a disaster in a heavy vehicle or with a slow shifting transmission, the engine would feel almost as if it wanted to stall during stop light take-offs or shifting.

To get the "feel" of it without spending money, grab a couple of bicycle wheels. Hold the axle and spin the wheel. A light roadbike wheel spins up very easily. But just brushing your fingers across the spokes IMMEDIATELY slows or stops the wheel. Now go to a heavy bicycle wheel, mountain bike Huffy wheel with big tire on it. Do the same experiment. Much more energy is required to get the wheel turning and it resists stopping.

The gyroscopic effect is amplified by additional weight. For your light car a light flywheel would be beneficial. But I am unfamiliar with what "light" is for your application (so I'll let others more familiar with your specific engine give that info).

angela

Nigel -

The benefit of a lightened fly-wheel on a stock motor would be minimal. As Angela so elequently explained about inertia, when you drive with a lightened flywheel, each time you lift-off or apply the gas while driving, you & your passengers experience a more exagerated feeling of lunging back & forth (kinda like riding with a person learning to use the clutch in a manual shift vehicle).

The ol' lightened fly-wheel trick on a stock engine is a slippery slope, because then you'll want to switch to solid transmission mounts, then bigger displacement, which will need bigger carbs, then trick transmission gearing...etc,etc,etc.

As our buddy 'Hoss' would say - that's my 2 kroner (whatever that is?).

Peace - Out!

Angela,

You have addressed this very well, I am impressed !

Me too! I loved that explanation and learned a lot from it too!! Thanks!

So for competing in gymkhanas, sprints and city street racing, a lightened flywheel would be an advantage where on a long highway drive it might be a disadvantage (unless you cut in and out/across lanes of traffic like some of the idiots on I95).

I bought a 12.5# 8 dowel lightened flywheel when I rebuild my T1 engine. Cost about the same as having the old one doweled, surfaced and magnafluxed. (and it mated to the Counter weighted crank - which probably added the same weight back to engine!)

"on a long highway drive it might be a disadvantage"

I kinda like it on the motor, ESPECIALLY, on the highway. Acceleration in the upper rev ranges is much quicker than with a stocker. You can speed up or make a quick lane change without having to set your calendar waiting to get up to speed. You can also take advantage of openings in traffic that would ordinarily be lost to you.

The biggest draw back to a lightened flywheel, in most driving situations and especially in drag racing, is the aforementioned drop in revs between shifts. You quickly move in and out of the "pocket" where maximum horsepower is available. You have to speed shift in competition, and tend to buck the car a bit until you get used to it. But you really DO get used to the engine and the effects on the car and . . . I like it a lot.

Alan/Ricardo - you're welcome! I'm not an engineer, but in plain language, that's how it works.
angela

Nigel: The stock flywheel weighs between 17 and 18 lbs for a one piece forged. There are also ones with pressed on ring gears and cast ones. I

"I have never really notice the difference. "

It isn't too noticable to the ear or even as a "feeling", but watch the tach next time you're out it falls off quite a bit, considering.

You know that the sweet spot/optimun RPM range for maximum horsepower on these little engines isn't all that broad. I drop out of it every time and have to play catch up, unless I power shift to one degree or another. Of course, not for around town, but when we go racing and even on the "on" ramps sometimes if I want to get ahead of the flow quickly.

Rain'in on the parade entry here ?!!
My understanding is that this mod is to be done ONLY in conjunction with:
BALANCED CRANK
ROD and PISTON weight variations tighter than stock. CC's variations between cyls also
tighter.

wow-talk about opinions. One thing everyone is leaving out-lighter flywheel=more engine vibrations. Think of a big V8 on the front there is the harmonic balancer and to the rear is the flywheel. One main purpose is to reduce the vibrations from the engine.

Ligheter-revs quicker but more vibrations
Stock-well gee the reverse!

The balanced crank and rods can reduce the vibrations so not required but an advantage.

I had a 65 bug when I was in High School that had a 12lbs. flywheel. Reved like crazy

D

I for one would not take a VW style flywheel down below 12 pounds for a street machine. Also, all flywheels were not created equal so to speak.....when lightened a bunch they can "cup" and cause a lot of problems with slipping clutches and the like. Also, while I am not aware of a single flywheel blowing up, the thought of 10+ pounds of shrapnel moving at 8000rpm give me pause to consider that a bit...also, some fair number of flywheels (even those you buy perhaps as new /reconditioned) are +/-50 years old. A new proper forged, heat treated and relieived, and properly machined flywheel may be a better place to start....but that wasn't the question.

A friend of mine is a cycling enthusiast - well, OK, he's a cycling freak!

Anyway, he just spent about umpteen thousand dollars on a bicycle that was 5lbs lighter than his previous ride and he revels about how much quicker he can accellerate or climb hills. Knucklehead that I am, I asked..."wouldn't it have been cheaper for you to just LOSE 5lbs?"

Would this logic also apply to my fat a$$ driving in my Speedy (vs lightened flywheel)?

Just wondering...

No. There is a huge difference between static weight and rotational weight (thank heavens 'cause I gotta whole bunch of static weight).

On a bicycle, the "rule of thumb" is 1 pound of rotational weight is like 3 pounds of static weight. Being an avid cyclist, my opinion is that it is much greater than that - more like 5 to 1. But I have no numbers to back this up, just tired legs. That's why the first thing I spend money on with bicycles (and likel your friend as well) is in the wheels. My mountain bike wheelset, complete is just under $1000.... It was real hard to pony that up because my first racing bike was $540 complete! Ouch!

Any place on a bicycle, a bike rider or a car that you can loose weight is beneficial. But the greatest benefit occurs from losing weight on the things that have to move (wheels and feet). Especially on the things that must CHANGE speed quickly like wheels, flywheels and feet.

That said, I'm on a diet because there is no bicycle on the planet to overcome the "insulation" I've developed as I slide kicking and screaming through my 40's...
angela

Thanks for that clarification, Angela!

You're right about the tough realizations we encounter as we go through the aging process. My static weight vs my dynamic waist gives my doctor more reason to lecture me!

At this rate, even the TT Kremer 911 in the pic below would feel the extra effort needed to move my fat a$$. Man, I GOTTA lose some weight - my 30" waist pants are getting a LITTLE snug!!(I KNOW that the SOC folks who have seen me in person are really laughing right about NOW!)

Peace - Out!

Wow thanks for the great reponses and some excellent engineering explinations.

I was digging through a 356 performance book today searching for further info on flywheels as I was sure that the good Dr P. would have done his homework in the fatherland (as they do) and dug up some interesting facts. The original 2 piece engine fly wheel on pre A models was about 20 ibs, this droped down to approx 18 lb on the A and the for the S90 was dropped to 14lb. SCCA racers drop down to 10lb but do not recommend any lighter than 12lb for the road. So 14lb feels like a good place to start considering how much lighter a Speedster is than a standard VW.

On reading the book it also got me thinking about the other end of the engine and pulley sizes and the number of fan blades another good source of cheap horsepower views welcomed

On that I've read that it's good to keep a fairly heavy steel crank pulley to help with harmonics. When I did the upgrades to my engine I chose to buy the Gene Berg Achiever pulley in stock size (forget about power pulleys on these cars as they'll be prone to overheating; fresh airflow into the engine compartment is critical as it is). You can also install a Porsche 356 generator pulley on your generator or alternator; they're smaller than the ones for VW's and thus make the fan go 11% faster. That'll help with your cooling.