burgass

Hello
Has anybody experience or opinion about fitting Sport Clutch and presure plate (Sachs or RS ?!?) on a early C4 89. As I understand the early C4 has a single mass flywheel and changing it to the RS LWF would not give such a gain. I plan on tracking the car most of the time so I wonder if fitting a stronger clutch is a good idea and if so which product should I get.
Regards

JasonAndreas

Dual-Mass Flywheel - 13.6kg (30lb)
1989 C4 Single Mass Flywheel - 8.6kg (19lb)
Carrera RS lightweight Flywheel - 5.5kg (12lb)

Christer

Burgass

I would wait until you actually need a new clutch, and then go for the RS item with the RS fluywheel if you feel that way inclined. FVD have 'triple plate' clutches and all that sort of stuff, but doubt if you need anything like that....

burgass

Christer
Is the RS flywheel such a big gain for an early C4? Looking at the discissions I can sens that I might get problems with the idle. I was thinking of only changing to RS clutch andf I was wondering if that ckutch is a straight forward bolt on my normal flywheel?
Regards

Christer

Hi

I don't think it is a straight bolt on, thats the problem. You are right that some people have stalling issues, so I am thinking maybe just stay with your current clutch, and use another stock item when you need a replacement. There is no reason for an upgraded clutch on the track. At the drag strip maybe, but not the track...

KirkF

I have the lightened flywheel in my '89 C4. It was installed by the previous owner.

I can't wait for the day when I can justify ripping it out and throwing it into a muddy field somewhere.

You mentioned you were planning on using the car for mostly track use so you may enjoy whatever gains a lightened flywheel get for you, but for regular driving, especially if you have air conditioning, its a royal pain in the ***. Causes the idle to fluctuate wildly, stalling, etc.

Chipping the car to compensate for this problem is only partially effective.

Kirk
(And as with all my other posts this is my opinion from MY ACTUAL EXPERIENCE. If anyone disagrees thats fine. )

Christer

There are also plenty of other people who have ACTUAL EXPERIENCE and have only minimal problems when the car is cold.

914und993

My 1990 C4 with LWF ACTUAL EXPERIENCE: when car was cold, or A/C was on, it took special attention to keep the engine from dying on declutch. A chip mod that was intended to alleviate this made little difference. While I loved the lightweight flywheel feel, it was a PITA as an in town daily driver. So it seems experiences vary. Feeling lucky?

Chip

JasonAndreas

So who made your chips? I don't think a chip will do much for the lumpy idle but it should resolve the stalling problem.

KirkF

Chip,

Your LWF symptoms are the same as mine. You get used to it after a while and its not that often I dont catch it before it stalls. However its not the way I want my Porsche to run. Mine is mostly only unstable when the extra load of the A/C is introduced.

Very embarassing when you have guests in the car.

For track use I suspect there would be few issues.

I would be interested in hearing if anyone with a LWF and A/C has a chip that has solved all of the issues. I would gladly change chips to solve the problem.

Kirk

Andy Roe

I thought that it's not the chip that causes the problem with stalling, but the actual DME (not the relay) needs to be upgraded. The standard DME cannot keep up with the sudden drops in RPM when a LWF in installed. One sure was to fix it is to source an RS DME, as they were designed to run with a LWF.

Christer

Andy, is that actually true? I can't see that the RS DME is going to be quicker module as such, although I can see it running slightly different maps to take into account the slight loss in rotating mass. I have never seen an RS that idles higher than a standard model for instance.

JZ Machtech for example say they have carried out many LWF conversions and that beyond some minor idling issues when cold the cars do not have any problems. They do say that they have heard of cases where there have been problems but speculated that this is more due to the fact that the cars are 11+ years old, so aging electronics and other bits and pieces contribute to the fact that the reaction times degrade over time. I think their approach is that if you go for an LWF then you need to check the car over in general to make sure all is well, which I do not think most people do. They just install the LWF and off they go, and maybe a slight myth has been created? I have no affiliation with JZ Machtech, they do not sell the LWF conversion of course so no gain for them to bull**it....and in any case I would speak to them (or your local specialist) directly if you have concerns. I am not quoting JZM here, just recounting what I remember.

914und993

"Aging electronics" is not the issue with the LWF. I did mine when my C4 was only 6 years old, and running perfectly. It would still die on declutch with the A/C on. The problem is that with the reduced rotating mass of the LWF, a load like the A/C (or the cold oil of a cold engine) allows the engine to decelerate so rapidly that the idle stablilizer doesn't have time to kick in and prevent a stall. When you decelerate in gear with your foot off the pedal, the fuel injectors are actually turned off - to reduce emissions. Then you declutch and the engine dies. The usual chip fix is to raise the idle speed, so that when the decelerating engine hits that higher idle speed, there is more time for the system to start supplying fuel to the engine. This in many instances is not enough.

I'm not sure how the RS handled this problem. Did it have air conditioning? Though the OBD-1 993s (1995 model year) had the same problem with the LWF as the 964, the post 1995 993 (OBD-2) seems to be immune from the problem, I don't know what it is doing differently.

Chip

JasonAndreas

The dme software can be adjusted so that the the ICV is opened quicker. One of the reasons its happening when its cold is that the table/array that says how much it should open the ICV when your foot is off the gas is based on RPM and Engine temperature. There is also a load table based on AC used for controlling idle, what do you want to bet that the aftermarket chip you have hasn't changed this? Does anyone have a spare RS dme or eprom they want to let me borrow for a day? Switching to an RS pulley with only one belt to slow the engine down should also help. The delivery guy just dropped this off; (thanks ViperBob!) so sometime next week I will have a much better idea of whats possible to fix with an eprom burner&emulator.

914und993

I don't have my C4 anymore, so its not available to experiment with! I have heard that more recent chips do a better job of controlling the stalling.

The RS pulley modification might help some incremental amount, because the alternator will be turning 20-25% slower and putting less drag on the engine, and of course because of the reduced parasitic losses when you get rid of one belt.

Chip