Recently had my BBI slave cylinder + GT3 pedal spring install, then subsequently (my fault, don't ask long story ) my clutch upgrade done by BBI. Just want to report my experience and the part numbers because I had some trouble identifying just exactly what Sachs "2.5" clutch that I've seen in various post means. Also shout out to BBI of Huntington Beach, a first class Porsche tuner with VERY competent techs.

If anyone sees error in my explanation please alert me and I'll correct it. I'm not an expert, just sharing information.

For the BBI slave cylinder, it's a good idea to change the assist-spring for the clutch pedal from stock, to the stronger GT2/3 clutch pedal spring, otherwise it would be too stiff. The GT2/3 clutch assist spring is part number 997.423.081.06.

For the clutch, I learned the "Sachs 2.5 kit" comprises of various Sachs parts put together and named "2.5". Each part could/would change depends on whether you would like to use sprung or solid clutch disc, or stock vs lightweight flywheel. Those decisions need to be googled and discussed as these parts influences noise, engagement, damping/vibrations of the clutch.


Anyway, "my" version of Sachs 2.5 (again:
Sachs 999 764 Pressure Plate: This is crucial for tuned car - you want at least the 764 plate otherwise clutch would slip :-).
Sachs 999 856 Sport Higher Friction Clutch Disc: I decided to use sprung (versus solid) hub. This particular disc is made for use with lightweight flywheel *ONLY*.
AASCO lightweight flywheel: Premium part - google this to find out why I decided to use it. NB: LWFW makes a white noise - see description below.

 

Evaluation of the BBI slave by itself:

1. It is stiffer and I wouldn't necessarily recommend it if your car is a daily driver, or if you are older, etc. The stock feel is so soft, but with BBI it is now a little too stiff. I wish for something in between. I had a manual non Turbo 997 and the stiffness of that clutch - in between stiffness of stock Turbo and BBI-slave Turbo, was perfect.

2. I don't feel engagement point is that different, but YMMV. I still stall if the music is on too loud LOL.

3. I appreciate the BBI slave because the leak of the stock system drove me crazy, but I am not "in love" with it as far as the feel, engagement point, etc. Strictly personal preference so no flame please.

 

Evaluation of the Sachs clutch kit - note that I upgrade the clutch AFTER I install the BBI slave:

1. No change in stiffness. If there is a change in engagement point, I didn't feel it.

2. As expected no more clutch slip.

3. Subjective sensation: The engagement "feels" more solid and snaps sharply into gear. I feel like the car accelerates a little harder, but this is NOT a night and day difference and could be entirely in my head. I was told to expect this from the lightweight flywheel, but perhaps drivers who are more advanced/talented and aggressive than I am would appreciate this better.

4. Noise of lightweight flywheel: I agree with the common description of this sounding like someone putting a bunch of small metal screws in a plastic box and shaking it LOL. *Only* heard at idle, when stopped at traffic light. If you listen to music at moderate or loud level, you won't hear it. Without music you WILL hear it. It's not so much the loudness at idle that changes, more like a new white noise at idle. I actually enjoy it *sometimes* because it is a sign of the LWFY, and occasionally turn down the music to hear it :-). The Aasco wheel is incredibly pretty btw - a work of art. Google it and you will want it.

 

Congrats! You'll like the LWFW set up and I bet you'll quickly forget about the heavier pedal.

Not many people know about it but Sachs Motorsport now makes an even better heavier duty pressure plate than the 999.764. It's about $500 more expensive as the 764 but worth it if your car spends a lot of time at high rpms as it has a higher burst limit. The part number is 001.487 and it's a high clamp Sachs Motorsport version of the 7GT3 4.0 clutch plate. The 487 can only be used with the OEM LWFW and will NOT work with the OEM DMFW or the Aasco. I just replaced my 764 with the 487 and it feels amazing.

OEM LWFWs are also an option if you want even a lighter FW option than the Aasco and stay with factory parts. The OEM LWFWs are quite a bargain as you can get a brand new 11lb OEM LWFW for about $350. It's about 20% lighter than the Aasco giving you an even lower MOI allowing the engine to rev slightly faster still.

Another disc option is the proven OEM 997GT3RS 4.0 disc. It has redesigned damper springs which are very quiet in comparison to the other sprung disc options. On my car the LWFW noise is virtually inaudible.

 

Ohh, ohh. I think I just found my next clutch (if I ever need another one).

And perhaps if your car is more of a DD (which mine isn't),.. perhaps that GT3RS 4.0 disk with the Aasco flywheel?

Wish I'd known this all last year.

 

LWFWs are not rocket science. These are your choices.

1: OEM LWFW
a. (0.31) - German part 11lbs (used on 964RS, 996.1Cup, 997.1GT3RS)
b. (0.81) - German part 8.2lbs Same part as 0.31 with more material machined away from the outer perimeter of the flywheel. It has a 20% smaller friction area and I would not recommend this on high power turbo cars as it will wear the clutch disc faster. (used on 996.2Cup, 997.2GT3RS, 4.0RS, GT2RS)

2. Aasco LWFW - USA part 13 lbs

Keep in mind that the Aasco may not work with a 4.0 disc due to it's design which is different from OEM. If using the OEM 4.0 disc I would stick with the OEM LWFW. It's a proven set up using OEM parts with no surprises..

If I'm not mistaken, the 999.856 clutch disc is the old style sprung disc used by Porsche on the 996GT3RS. It has blue springs. The 4.0 disc is the successor to this disc and has the redesigned sprung hub which is quieter.

 

Thanks for your input. Yeah I realize I might be a little older and not as "robust" :-) as other Porsche driver, so therefore the stiffer feel bothers me more than most people.

Ah too bad I didn't know there is a choice better than Aasco. The 997GT3RS 4.0 is also made out of billet aluminum?

Could you explain the bold'ed part above? I assume LWFW allows the engine to rev up faster because of less moving mass? What's MOI?

 

MOI = Moment of inertia. It's measuring a combination of raw weight,.. AND how far that weight is from the center. The further out the weight is,.. the more energy it will take to spin up and slow down the wheel.

I.E.,.... a 6 lb bicycle wheel that has most of it's weight located in the outer rim could easily take more effort to spin up than a 10 lb wheel, where all the weight is in the hub.

 

You're welcome. Again, my bet is that you will get used to the pedal feel. I'm not familiar with the BBI slave but perhaps that makes it "heavier" than the factory GT2 slave set up? Couldn't really say. As such, my advice to people is to always do the Porsche designed proven factory OEM GT2 slave conversion that way you have the exact same set up as designed by the factory. My preference is always OEM.

Make sure you have the GT2 assist spring. I don't have the part number handy but can post it up later. It's in PET.

The OEM LWFWs are both made of billet steel. MOI is correctly explained by the poster above. I see no reason to leave weight on the table an as such my recommendation to people is to use the OEM 11lb flywheel in combination with the OEM RS4.0 disc. The 764 PP is very good but for those desiring the next step up the 487 is the way to go.

 

Adding data: I was informed by someone very knowledgeable that the part number for the GT2/3 clutch assist spring is 997.423.081.06. If you are going to use either BBI slave or GT2 slave conversion, it's important to switch the clutch spring from stock to GT2/3's to lessen the stiffness.

 

Has your clutch spring been replaced or are you running the stock one?

 

My clutch spring has been replaced, however looking at my invoice's part number, it seems like it is not the right spring. The invoice could be a typo so I am checking with BBI now to see what the actual order from the dealer states.

Pwdrhound gave me the correct GT2/3 spring part number (thanks) and I posted it above.

 

Question please pwdrhound, for others reading this (not for me - too late ): Does the more robust pressure plate 004.487 increase stiffness of clutch pedal? Compare to 997.764 is there anything negative about this pressure plate other than the higher cost?

"Burst limit" - is that how clutch is rated?

Thanks again for all the very interesting & helpful information. This thread with your info might just be mandatory reading :-) for those interested in upgrading clutch. BTW, confirmed with BBI that my pedal spring indeed has the same part number as what you gave me.

 

The 487 plate feels comparably "stiff" to the 764. The main difference is that the 487 is a bolted plate while the 764 is riveted (as most plates are). The rivets are a failure point of the pressure plate in case of an over rev or sustained high rpm operation. When that happens the steel straps will basically slice the bellhousing wide open. I've never seen it but my shop has on numerous occasions.

The reason the 487 is bolted is to withstand the 8800+ rpm capability of the GT3 engine (the OEM 7GT3 4.0 plate is bolted also). The bolts give it a higher rpm burst limit compared to the riveted 764. The 487 is basically a high clamp variant of the OEM 4.0 plate. I also think that Sachs had removed some mass from the outer portion of the 487 plate as the official weight is listed as slightly less than the 764 thus giving the 487 a lower MOI. The reason I say this is that the engine seems to even a little more rev happy than before but that may just be in my head. Unfortunately I did not get a chance to compare the 764 and 487 side by side to verify this.

For me the switch to the 487 made sense since my engine basically sees all track use and lives near it's 7500 redline but on Motec I've seen just over 8k on several occasions. Having a pressure plate that can withstand higher revs was a big plus. Clamp wise my source at Sachs told me that the 487 is the strongest pressure plate they offer.

Finally, because the 487 is bolted, it can not be used with a dual mass flywheel as the heads of the bolts stick up higher than the rivers and as such would interfere with the housing as the dual mass is rather thick. Same applies with the Aasco lwfw so that can not be used. Basically the 487 is engineered to be used with the factory OEM LWFWs and there is really no need to look elsewhere. If it's good for Porsches Cup cars, it's good enough for us..

Hope that helps...

 

Keep us updated.