Lighter Flywheel
06-20-2001, 07:11 PM
#16
Hi Steve,
Thanks for the detailed response. I'm aware of the compromises you speak of. I thought I did my homework. I was aware, and can live with, pretty much everything but the surging. No one has reported surging of this nature except me. Andial claims great drivability with their heavier version. Since I am the only one reporting it I wonder if there is something going on with my car. My thoughts are directed toward the ECU and it's inputs, specifically the throttle position sensor and/or O2 sensor. As I noted above, I had this surging before the light weight flywheel, the flywheel just made it worse.
Are you saying, that due to the nature of the compromise I have made, that there is nothing I can do about the surging except put the stock flywheel back in? Is the Euro OBD an option for me (can I just pop the chip in on my '95)? Yes, I do have a modified chip. It came from Cyntex, through Fabspeed, when I bought my Fabspeed supercups. It's supposedly tuned to the exhaust, which is no longer on my car (too loud). The same salesman talked me into a bored throttle body at the same time. (At least I didn't buy a carbon fiber air filter cover...) My mechanic duplicated this chip on his programmer and made some changes for the light weight flywheel, but I don't know exactly what he did. Do you have a chip that would work for me? Would it solve the surging problem that seems to be caused by the ECU cutting fuel?
Thanks again,
Tom
Thanks for the detailed response. I'm aware of the compromises you speak of. I thought I did my homework. I was aware, and can live with, pretty much everything but the surging. No one has reported surging of this nature except me. Andial claims great drivability with their heavier version. Since I am the only one reporting it I wonder if there is something going on with my car. My thoughts are directed toward the ECU and it's inputs, specifically the throttle position sensor and/or O2 sensor. As I noted above, I had this surging before the light weight flywheel, the flywheel just made it worse.
Are you saying, that due to the nature of the compromise I have made, that there is nothing I can do about the surging except put the stock flywheel back in? Is the Euro OBD an option for me (can I just pop the chip in on my '95)? Yes, I do have a modified chip. It came from Cyntex, through Fabspeed, when I bought my Fabspeed supercups. It's supposedly tuned to the exhaust, which is no longer on my car (too loud). The same salesman talked me into a bored throttle body at the same time. (At least I didn't buy a carbon fiber air filter cover...) My mechanic duplicated this chip on his programmer and made some changes for the light weight flywheel, but I don't know exactly what he did. Do you have a chip that would work for me? Would it solve the surging problem that seems to be caused by the ECU cutting fuel?
Thanks again,
Tom
06-20-2001, 08:10 PM
#17
RL Technical Advisor
Hi Tom:
Happy to help.
There is no question that the changes you made before the RS flywheel impacted the surging & drivability issues. Chip tuning for off-idle response is quite sensitive and too many folks add too much or too little fuel and timing in there that will make the car run very jerky. The lack of mass in the RS flywheel amplifies these problems.
Larger throttle bodies upset the calibration of the throttle position sensor and its linearity. This passes more air from just off-idle to WFO and that low end transition is partly to blame. It might be just lean enough right there to make this a tough thing to resolve.
I do not know what Cyntex does in their mapping so I cannot say how well they compensate for all of these changes you have. Further, I would need to know exactly what your mechanic did to "tweak" things before I can tell whether I can improve on that.
Euro OBD would require the European version of that DME and it would probably not pass California smog, much less start your car,....... Not worthwhile, IMHO.Certainly a Euro OBD chip will not start in your DME.
I would need to see some real-time lambda numbers and timing data to see what is going on and suggest a fix or make a custom chip for you.
Don't give up!!!!
Happy to help.
There is no question that the changes you made before the RS flywheel impacted the surging & drivability issues. Chip tuning for off-idle response is quite sensitive and too many folks add too much or too little fuel and timing in there that will make the car run very jerky. The lack of mass in the RS flywheel amplifies these problems.
Larger throttle bodies upset the calibration of the throttle position sensor and its linearity. This passes more air from just off-idle to WFO and that low end transition is partly to blame. It might be just lean enough right there to make this a tough thing to resolve.
I do not know what Cyntex does in their mapping so I cannot say how well they compensate for all of these changes you have. Further, I would need to know exactly what your mechanic did to "tweak" things before I can tell whether I can improve on that.
Euro OBD would require the European version of that DME and it would probably not pass California smog, much less start your car,....... Not worthwhile, IMHO.Certainly a Euro OBD chip will not start in your DME.
I would need to see some real-time lambda numbers and timing data to see what is going on and suggest a fix or make a custom chip for you.
Don't give up!!!!
06-21-2001, 01:57 AM
#20
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David,
The TT pressure plate sounds like a logical upgrade...along with a stock clutch disc, I would think that clamping power would be increased, but that clutch "twitchiness" would not be a big problem. I think the aluminum PP is pretty light for a street car (OK for a track car), although I have dealt with Strasse fairly often in the past year, and they have yet to steer me wrong.
The TT pressure plate sounds like a logical upgrade...along with a stock clutch disc, I would think that clamping power would be increased, but that clutch "twitchiness" would not be a big problem. I think the aluminum PP is pretty light for a street car (OK for a track car), although I have dealt with Strasse fairly often in the past year, and they have yet to steer me wrong.
06-21-2001, 01:57 AM
#21
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David,
The TT pressure plate sounds like a logical upgrade...along with a stock clutch disc, I would think that clamping power would be increased, but that clutch "twitchiness" would not be a big problem. I think the aluminum PP is pretty light for a street car (OK for a track car), although I have dealt with Strasse fairly often in the past year, and they have yet to steer me wrong.
The TT pressure plate sounds like a logical upgrade...along with a stock clutch disc, I would think that clamping power would be increased, but that clutch "twitchiness" would not be a big problem. I think the aluminum PP is pretty light for a street car (OK for a track car), although I have dealt with Strasse fairly often in the past year, and they have yet to steer me wrong.
06-21-2001, 09:57 AM
#22
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I was looking at an aluminum flywheel for my race car and my mechanic was emphatic about me not going with one and using the lightweight RS version instead. He had an experience with a customers factory GT-2 that they tried an aluminum flywheel in and it is not as stable and the outer edge started to move and did some damage to the crank. Turned out to be a rather expensive test for them. Maybe Steve can give his recommendations in that regard, maybe it was their particular application that didn't suit the aluminum flywheel or a vendor specific problem. Anyway my mechanic is a firm believer that when you try to out-engineer Weisach you are going to throw a lot of money down the drain and end up with less performance.
Greg
Greg
06-21-2001, 01:40 PM
#23
RL Technical Advisor
Hi Greg:
The only aluminum flywheels that we use are the full-race setups from Aase Bros Racing. These have been quite bulletproof and use a 3-plate Tilton 5.25" clutch. We have used well over 50 of these things by now with no troubles on the DME trigger ring moving about or the the whole unit squirming on the crank. Its quite well done and if installed properly, should not give any problems.
If this is what he used on that GT-2 car, its possible that he might have gotten a bad one.
These are NOT streetable whatsoever! Race car use only and not cheap, at that.
Any street or dual purpose car ought to stick with the RS setup, IMHO. Its pretty foolproof for what its intended to do. There may be an aluminum flywheel designed for the Sachs PP and disc but I'm not aware of it.
The only aluminum flywheels that we use are the full-race setups from Aase Bros Racing. These have been quite bulletproof and use a 3-plate Tilton 5.25" clutch. We have used well over 50 of these things by now with no troubles on the DME trigger ring moving about or the the whole unit squirming on the crank. Its quite well done and if installed properly, should not give any problems.
If this is what he used on that GT-2 car, its possible that he might have gotten a bad one.
These are NOT streetable whatsoever! Race car use only and not cheap, at that.
Any street or dual purpose car ought to stick with the RS setup, IMHO. Its pretty foolproof for what its intended to do. There may be an aluminum flywheel designed for the Sachs PP and disc but I'm not aware of it.
07-01-2001, 01:12 PM
#24
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I have a 95 993 C4 and recently installed the RS LWF and clutch. I had the off throttle problem described above, but I also have The Program installed. All we did was put the car back on the dyno and reprogrammed The Program for the lighter flywheel and voila, no more off throttle problems.
Check with The Racers Group regarding The Program.
Check with The Racers Group regarding The Program.
07-03-2001, 10:56 PM
#25
I have my heart set on a 94 964 with a LWF in it. As is (K&N filter, Weltmeister chip, stock exhaust, Sachs clutch) it stalls when the A/C is turned on, and this, only erratically. I am hoping that the seller and I will soon reach an agreement so I can ask Steve to make me a chip and modify the ISV. This thread just proves to me, once more, that Steve is the person to solve this (and many more issues). Hopefully, I will soon have a report on this.
Regards to all,
Gus
Regards to all,
Gus
