RBP

I know I've seen threads on this but don't remember what the opinion was. On the 1990 to 1998 3.6 cars with the heavy flywheel is there an operating problem when one replaces the heavy flywheel with the lighter options being offered? I think I recall some of the model years have stall issues on off throttle. Any comments on this issue would be appreciated. A friend of mine has a 1991 and I have a 1996. He is replacing his with an RS flywheel and I would like to do the same when I have to service my clutch. I figure it better to know going in than having a drivability issue after doing all the work.

earossi

There was a stalling issue with the 95 model 993 when installing a LWF. The issue did not repeat in later year cars. I've had a LWF in my 98 with no issue.

RBP

Thanks for the input. Can you tell what the difference was when you changed it? I don't track my car and have no intent in doing so. Is the LWF better for track / racing applications and no so much for normal drivability?

Bill Verburg

I have a l/w flywheel in both my '95 and '97, no stalling problem but also have custom chips

The '95 used to have a stalling issue w/ a/c on only and only sometimes. I believe that it was more related to a vacuum issue as there was an associated abnormally low idle that disappeared when the engine was t/p'ed w/ the same chip still installed.

sand_man

I have a '95 and have decided to take the plunge on the LWF and associated parts. If I am unable to dial out any stalling issues with mods to the ISV, then I will likely chip it. Another thing that has been commonly mentioned when going LWF is more noise from the transmission when idling (described as a rattling).

There are lots of threads on this to read through, if you search...

OverBoosted28

If you go the LWFW route, get the GT3 disc with the sprung hub! This should eliminate the rattling some associate with this conversion.

Mark in Baltimore

I had a LWF on my old race car. It seemed a bit more lively, but, honestly, the effect was very subtle. After a few stints in the seat, I really couldn't say that I could feel much difference.

For a race car looking to shave tenths of a second off of a lap time, though, a lighter flywheel certainly is a better mod than a heavier one and is de riguer. For a street car, the change would be highly debatable.

I had a some occasional stalling issues when I drove my 1995 on the street but never on the track. Supposedly, installing a new ISV valve will curtail any stalling issues. Lots of threads in the archives.

Here, read this and make your head spin : https://rennlist.com/forums/993-foru...m-new-isv.html

sand_man

For me, I not only like the idea of losing the weight (though mine is street driver), but also the simplicity offered by the LW flywheel. Although my factory DM flywheel has not given me issues (yet), it's one more thing I hope not to worry about, once it's out.

Bill Verburg

All l/w flywheel will use either a rubber or spring center clutch. I am unaware that anyone sells the rubber ctr for our cars

Only the 996/997 Gt3RS use the simple l/w flywheel w/ spring ctr clutch disk.

These were first used on the 964 RS, the same parts are used right up through the last 997GT3RS, some part #s were changed along the way along w/ some minor changes but it's essentially the same clutch f/w setup
here are the 2 kinds of 993 clutch and f/w that are available, there are variations w/ relatively minor spec differences
L top & bottom spring ctr clutch disk & single mass 993RS/CS f/w also used on 964Rs , 996GT3RS, 997GT3RS, smaller versions were used on all 911 thru '76

center top & bottom stock dual mass 993 clutch disk and dual mass f/w

R top, the same pressure plate is used fro both setups.


The rattling heard is the loose gears on the transmission shafts, this can heard in all 915 and g50s w/ single mass and spring ctr clutch disk to a greater or lessor extent, some are nice and quite but some sound like clothes dryers w/ lots of loose change rattling around in them.

sand_man

I have sourced the spring centered clutch disc: 996.116.015.30

Cupcar

I have a '95 and intstalled the LWF from the GT3 RS 4.0 which is a further lightened 8 pound version of the 11 pound 964/993 RS LWF. The 4.0's mass is machined from the periphery which really drops the moment of inertia.

At first stalling was a *real* issue with this flywheel, but it was fixed with increasing the coast down injection turn on point by 500 RPM, setting idle advance to 10 deg BTC and most important - readjusting the idle opening of the ISV.

I did a little research using Bosch catalogs and noted that the same Bosch ISV is used for a lot of cars, some as low as 1600 cc displacement. I figure the basic opening of the valve has to be such that it fits the lowest common denominator 1600 cc engine and that it is too much to ask for the ECU to open it quickly enough from that small opening to catch the idle in a 3.6 liter engine - or 3.8 in my case - with a LWF. So to me, opening it a bit made sense to me.

I opened it and idle return works fine now but with a bit of looping as it finds idle, looping that I think would go away with a more careful ISV adjustment, but really doesn't bother me. I still kill the engine time and again but I have a taller first gear that makes roll off a touch more difficult.

Cupcar

One thing I forgot is the 4.0 flywheel uses a different clutch plate and sprung clutch center than the normal 993 unit. I didn't weigh it but I think the clutch plate is lighter as well.

It all bolts together perfectly using the normal clutch extension tube and throwout bearing as the 993 RS.

BTW, the sprung clutch center makes no difference in the gear rattle. It is just a torsional shock absorber.

mgerber

Big topic and i will avoid the debate over whether or not it makes a noticeable difference on the street. I did mine with a regear and new LSD so the entire package was very noticeable for me personally (and others who drove the car before & after). Mine is a '95 and I did a lot of research on what to look for and how to make it work without stalling. I have only had the car stall on me a couple of times, and I have also modified how I drive to minimize the potential for stalling. Also recommend you talk to someone like Steve W that has done a lot of these.

Things to do/check to avoid a bad experience per my research and experience:
- upgrade ECU (for '95)
- smoke test intake and if you find leaks fix them
- ultra clean or new ISV
- new O2 sensor
- relatively new plugs, wires, rotors and caps
- if the above does not work you then need to do what Cupcar suggests which is start modifying the system (beyond my desire or expertise level)

You will also hear a lot of gear rattle after you do the LWF. I had no issues with it, but some do.

Cupcar

It should be noted that the light flywheel I used is an extreme case since removing 27% of mass from periphery of flywheel as with the 4.0 version LWF is no small thing.

All the other things above suggested were done when I built the engine with new: ISV, caps, rotors, distributor, spark plugs, wires, plastic manifold to head adapters and seals, fuel injection plenum seals and tubing. Fuel injectors tested, calibrated with new seals.

So, I think my idle return problems were just related to the extra light wheel and may not have happened with a normal 993 LWF.

But the throttle response is superb!

vincer77

I have just received amy Aasco mid weight flywheel for my 97. It tips the scale at about 18 pounds and I am hoping will have enough inertia to avoid some of the driveability issues, but still almost 1/2 the weight of the dual mass.

I will post my observations when she is back together.