Show full size 924Board.org
Discussion Forum of 924.org
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 Technical FAQ924 FAQ (Technical)   Technical924 Technical Section   Jump to 924.org924.org   Jump to PCA 924 Registry924 Registry

Just shed 7.5 lbs of rotating mass
Goto page 1, 2  Next
 
Post new topic   Reply to topic    924Board.org Forum Index -> Performance Upgrades
View previous topic :: View next topic  
Author Message
-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Mon Nov 20, 2006 3:16 pm    Post subject: Just shed 7.5 lbs of rotating mass Reply with quote

This worked out quite nicely. I started looking for a 911 pressure plate to get some extra clamping force on the clutch. Turns out that Sachs made cast iron plates as part of a stock clutch kit and also a "sport" kit that includes an alloy plate. The alloy plate weighs a whopping 7.5 lbs less than our stock 931 cast iron plates!

All I could dig up on clamping pressure numbers are these-

7200-7900N for stock 931 pressure plate
7800-8500N for stock 911 pressure plate

There is _definitely_ more pressure at the pedal. I might look into reinforcing the firewall to avoid any possibilities of fatiguing the metal. We'll see how tiring it gets to operate too...

The only trick is that replacing the throw out bearing is much more of a pain in the a$$. Maybe there are some tricks on the 911 board.

Anyway, you can use the pressure plate from any of the 915 transaxle cars - 911SC, 80's 911 Carrera. I think the years are '72-'86.

ps - I've got an extra good 931 pressure plate if anyone wants it (not the rusty one in the pics!).


_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet
Back to top
View user's profile Send private message Send e-mail Visit poster's website
bass gt  



Joined: 02 Dec 2004
Posts: 971
Location: Johannesburg for now!!

PostPosted: Mon Nov 20, 2006 4:15 pm    Post subject: Reply with quote

Nick,

I discovered the same thing a while ago. I bought an old 911 pressure plate off ebay, and not only did it fit right up, but it seemed a lot lighter.
What friction plate are you using??
This whole clutch issue is starting to bake my noodle, what with the different S1 & S2 clutches, blah blah. I am looking for a proper race spec clutch, and as i am in the process of having a 2.2 litre engine built, i am on the hunt for a decent clutch. The other option is to have a friction plate custom made
Or is the Ford Bronco friction plate you guy's use over there much stronger than the OE Sach unit??

Steve
Back to top
View user's profile Send private message
-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Wed Nov 22, 2006 2:16 am    Post subject: Reply with quote

I was curious what the 944/951 spring centered clutches look like? The spline is obviously the right size. Maybe they're not a 225mm disk? There are lots of disk options floating around for them.

I'm using the stock OEM clutch disk. I felt like it could use a little more "grab" before, hopefully the new pressure plate will help.

For what it's worth, there are a lot of bad stories floating around about the Spec clutch disks. A handful of newer Corvette owners have had there cars practically sawed in half when their Spec disks blew. I read a couple of the stories, and these weren't high mileage abused disks either. Spec's response was 'sorry about your luck' in all the cases. Apparently the 'vettes are made such that the disk won't saw the driver's legs off if it lets go. Something I wouldn't want to chance!

I'm not sure about the other brands out there, Centerforce, etc. Sachs seems to at least have a good reputation for holding together; as far as I know at least.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Chrenan  



Joined: 15 Jan 2003
Posts: 3899
Location: Canada

PostPosted: Wed Nov 22, 2006 4:33 am    Post subject: Reply with quote

Nick, I'm assuming this upgrade wouldn't work on a 924?
_________________
1987 951 - M193 Version for Japan
Back to top
View user's profile Send private message
bass gt  



Joined: 02 Dec 2004
Posts: 971
Location: Johannesburg for now!!

PostPosted: Mon Nov 27, 2006 10:22 pm    Post subject: Reply with quote

Nick,

Just to give you, and those that may be interested, an update. I have ordered the same pressure plate as you, the Sachs Sport 911 clutch kit, and found that AP racing, a rather well known brand, make a cerametallic, 6 paddle friction plate spcifically for our cars. Now this may be a tad strong and aggressive for steet use, as it is a specific race clutch, however Helix Autosport make a full range for the S2 and GT models, from street use to group N. Happy days. This is going into my new engine, which i am currently seccing up. I will give you a taster once the list is complete.

Regards,

Steve
Back to top
View user's profile Send private message
Raceboy  



Joined: 01 Mar 2004
Posts: 2321
Location: Estonia, Europe

PostPosted: Mon Nov 27, 2006 11:57 pm    Post subject: Reply with quote

Bit offtopic, but Steve where are you sourcing main and rod bearings? I assume you're using .25mm oversize ones?
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche
Back to top
View user's profile Send private message Visit poster's website MSN Messenger
bass gt  



Joined: 02 Dec 2004
Posts: 971
Location: Johannesburg for now!!

PostPosted: Tue Nov 28, 2006 12:18 am    Post subject: Reply with quote

Raceboy,

I beleive we are fitting VW Golf items. The rods i thiink will be Steel Golf items, with custom pistons to suit. I'm guessing here, but if golf rods are going in, golf bearings must be ok. Crank may ned a macine to size up ok, but we shall see.
BTW, going for 7 mm valve stems! Custom build. Difference in restriction is amazing.
Back to top
View user's profile Send private message
-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Tue Nov 28, 2006 1:51 pm    Post subject: Reply with quote

Chrenan - no luck on the 924na. Although, I don't remember the na plates being too heavy to begin with. The 931 plate is a monster!

Steve - your latest build sounds great! I believe that the Golf rods use a smaller diameter on the big end. Turning the crank down a mm or so definitely won't hurt that cast iron diesel beast. Did you consider looking into having the crank offset ground to gain some displacement? Or are you restricted within your class? I'm looking forward to hearing about the results.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet
Back to top
View user's profile Send private message Send e-mail Visit poster's website
JSMotors  



Joined: 30 Jun 2006
Posts: 22
Location: Howell, Mi

PostPosted: Mon Dec 11, 2006 12:48 pm    Post subject: Reply with quote

Nick-

Why wouldn't this upgrade work on a 924 NA? Any way to make it fit? Are you only using the pressure plate or a full assembly?
Back to top
View user's profile Send private message
endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Mon Dec 11, 2006 2:40 pm    Post subject: Reply with quote

The 931 flywheel is stepped. I believe (someone please correct me if I am wrong) that the pressure plate mounting surface is higher than the friction surface of the clutch.

Also, the 924 torque tube is designed for a 24 tooth x 13\16" x 8 1\2" disc and the 931 is 23 tooth x 1 1\16" x 8 13\16". I don't know of any other disc that would fit the 931 pressure plate with the 924 torgue tube. Ofcoarse this can be fixed by changing to the 931 tube and tranny if your willing to go that far.

I've been researching this subject for quite a while as my clutch is starting to show some weekness at my current boost level and I would like to turn it up a little more in the future. Too much torque

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....
Back to top
View user's profile Send private message Send e-mail
-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Tue Dec 12, 2006 4:08 am    Post subject: Reply with quote

I think the biggest difference between the 931 and n/a plates are that the 931 is a pull-type (TO bearing moves away from engine to disengage clutch) and the n/a is a push-type (TO bearings moves toward engine).

The stock 931 plate is a massive piece of iron! I don't think the n/a plate is very heavy to begin with.

The 931 flywheel also does have a small "step" in it - but it's just a raised portion around on the outside of the pressure plate. I think it's just there to help center the pressure plate. You could probably shave it off without any ill effect. The mounting surface of the pressure plate and the clutch surface are at the same level on the 931 flywheel.

Todd - good luck resolving your clutch trouble! I don't know of any easy ways to get a bigger disk in there.

Here are a couple pics, I don't think I have a shot of the surface side of the flywheel...



_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet
Back to top
View user's profile Send private message Send e-mail Visit poster's website
endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Tue Dec 12, 2006 9:51 am    Post subject: Reply with quote

Interesting. I've replaced hundreds of clutches and I have never seen one the "pulls" the throwout bearing! Nor have I seen a ring gear mounted to one. Crazy Germans!

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....
Back to top
View user's profile Send private message Send e-mail
-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Fri Jan 12, 2007 2:06 am    Post subject: Reply with quote

!Achtung!

If you look _really_ closely in the pic of the two plates, you'll notice a raised rivet just clockwise of one of the bolt holes on the alloy plate. On the stock plate, the raised rivet is just counter-clockwise of the bolt holes. In fact, there are two rivets next to each other on the stock plate, but one is sunk.

The 931 ring gear has a cut-out for the raised rivet - which is in the wrong place if you use the alloy plate! When you bolt the ring gear down it will deform and not sit flush, which you won't notice until you try and shift gears and find the clutch dragging...

I drilled new cutouts into the ring gear and now the gear sits perfectly flush against the pressure plate. I warped the gear that I first bolted on without the cutouts, luckily I had an extra one to drill.

The 911 ring gear (for the 915 trans) should bolt right up and be correct. Unfortunately, I didn't have one lying around.

Shifting should be much improved - aka, I should be able to select 1st and reverse.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet
Back to top
View user's profile Send private message Send e-mail Visit poster's website
arx  



Joined: 16 Dec 2005
Posts: 129
Location: Estonia, Tallinn

PostPosted: Fri Jan 12, 2007 4:56 pm    Post subject: Reply with quote

Quote:
I think the biggest difference between the 931 and n/a plates are that the 931 is a pull-type (TO bearing moves away from engine to disengage clutch) and the n/a is a push-type (TO bearings moves toward engine).




Thats a weirdest clutch I've ever seen
Back to top
View user's profile Send private message
Raceboy  



Joined: 01 Mar 2004
Posts: 2321
Location: Estonia, Europe

PostPosted: Fri Jan 12, 2007 6:09 pm    Post subject: Reply with quote

Argo, sellist tüüpi sidurid on nii 931'l kui 944'l kui teistel Porschedel.

_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche
Back to top
View user's profile Send private message Visit poster's website MSN Messenger
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> Performance Upgrades All times are GMT + 10 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group