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Old 12-20-2007, 12:05 AM   #1
RyanPerrella
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Default Lighter weight pressure plate, or flywheel combo DUAL DISC CONVERSION

I have the clutch and flywheel out to service the RMS and just out of curiosity thought I would see what the thing weighed. I weighed the entire flywheel, pressure plate, throw out bearing, clutch arm and clutch disc and came to 51 lbs. 38 for the pressure plate assembly and 13 for the flywheel and clutch disc. This seems excessive to me.

I had heard from engineers that when designing a clutch rotating assembly you want to have a pound for every 100 on the entire car. This being a safe estimate by a factory engineer doing the simple math I wuld think a 35-36lb unit would be a nice target. I believe some companies are selling assemblies that are sub 20lb units to street users of early 911's. I do know that if you go to light it can rev quite quickly but be a pain in the *** to drive as its more prone to stall with less mass. I dont know if anyone has a setup that can lighten the stock one, but I thought it would be nice to lighten this whole rotating assembly up and make the engine more rev happy so to speak. Which, for the GT would be a step in the right direction and fitting to its personality. I honestly haven't driven my car in 4 months or so now, so i cant really comment on how it does feel. (I don't really remember honestly.) But I think it would be nice to lighten this thing up by 12-15 lbs.

I have seen other porsche pressure plate assemblies that have an aluminum housing and are drastically lighter then the one used in the 928's. I think it was a 964 or 993 that I specifically felt, i was suprised when i lifted it up that it was as light as it was. I know everyone and their mother makes aluminum flywheels but I dont think thats worth doing for the 928 as the flywheel itself is pretty small. I dont know that making one out of aluminum with a steel friction face would be cost effective and be beneficial. So I am wondering if there is a 20-25lb pressure plate that could be used instead.

This is completely exploratory and just an idea but i thought I would post it as I am considering adding a Turbo or SC if i do end up keeping my car and would at that point give the stock clutch assembly some attention. The clutch in the car works great as is and is ust a couple years old but I thought it would be nice to liven up the engine a bit and i think taking 15lbs out of the rotating assembly could be advantageous.

Concerns are of course adaptability, cost and wether or not lightening the flywheel and clutch assembly would, or could possibly cause a vibration to occur in the engine itself.

I was looking at Carl's webpage as I know he recently started selling a new clutch setup but it looks very similiar (pressure plate anyway) to the stock one and there is no mention of it being any lighter. I dont know specifics about what would be needed to make it work in a 928. I suppose you start first with the diameter of the flywheel and go from there. I know if you used a smaller diameter clutch and PP that the weight loss would be less of an issue as the mass is then centralized to the centerline of the crank but you would still need to use the stock ring gear to sun the starter motor. Again I dont think its worth messing with the flywheel as the stock unit is pretty basic. Its not a rubber puck or spring loaded flywheel like 964 and later 911's which are by design very heavy.

Anyone had similiar ideas and care to share them?
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Last edited by RyanPerrella; 04-05-2008 at 09:57 PM.
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Old 12-20-2007, 01:18 AM   #2
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I figured

Is this just not an area that anyone else thinks should be given any attention?

I was just looking on Ebay and found a sachs sport PP for a 993 that weighs less than 10lbs, there must be something lighter then the one in the 928's
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Old 12-20-2007, 01:26 AM   #3
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Do a conversion to a double disc clutch and save about 15lbs. (45lbs vs 30lbs for the dual disc clutch assembly, not counting t/o bearing or arm)

there is no real reason to need more.

mk

Quote:
Originally Posted by RyanPerrella View Post
I have the clutch and flywheel out to service the RMS and just out of curiosity thought I would see what the thing weighed. I weighed the entire flywheel, pressure plate, throw out bearing, clutch arm and clutch disc and came to 51 lbs. 38 for the pressure plate assembly and 13 for the flywheel and clutch disc. This seems excessive to me.

I had heard from engineers that when designing a clutch rotating assembly you want to have a pound for every 100 on the entire car. This being a safe estimate by a factory engineer doing the simple math I wuld think a 35-36lb unit would be a nice target. I believe some companies are selling assemblies that are sub 20lb units to street users of early 911's. I do know that if you go to light it can rev quite quickly but be a pain in the *** to drive as its more prone to stall with less mass. I dont know if anyone has a setup that can lighten the stock one, but I thought it would be nice to lighten this whole rotating assembly up and make the engine more rev happy so to speak. Which, for the GT would be a step in the right direction and fitting to its personality. I honestly haven't driven my car in 4 months or so now, so i cant really comment on how it does feel. (I don't really remember honestly.) But I think it would be nice to lighten this thing up by 12-15 lbs.

I have seen other porsche pressure plate assemblies that have an aluminum housing and are drastically lighter then the one used in the 928's. I think it was a 964 or 993 that I specifically felt, i was suprised when i lifted it up that it was as light as it was. I know everyone and their mother makes aluminum flywheels but I dont think thats worth doing for the 928 as the flywheel itself is pretty small. I dont know that making one out of aluminum with a steel friction face would be cost effective and be beneficial. So I am wondering if there is a 20-25lb pressure plate that could be used instead.

This is completely exploratory and just an idea but i thought I would post it as I am considering adding a Turbo or SC if i do end up keeping my car and would at that point give the stock clutch assembly some attention. The clutch in the car works great as is and is ust a couple years old but I thought it would be nice to liven up the engine a bit and i think taking 15lbs out of the rotating assembly could be advantageous.

Concerns are of course adaptability, cost and wether or not lightening the flywheel and clutch assembly would, or could possibly cause a vibration to occur in the engine itself.

I was looking at Carl's webpage as I know he recently started selling a new clutch setup but it looks very similiar (pressure plate anyway) to the stock one and there is no mention of it being any lighter. I dont know specifics about what would be needed to make it work in a 928. I suppose you start first with the diameter of the flywheel and go from there. I know if you used a smaller diameter clutch and PP that the weight loss would be less of an issue as the mass is then centralized to the centerline of the crank but you would still need to use the stock ring gear to sun the starter motor. Again I dont think its worth messing with the flywheel as the stock unit is pretty basic. Its not a rubber puck or spring loaded flywheel like 964 and later 911's which are by design very heavy.

Anyone had similiar ideas and care to share them?
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Old 12-20-2007, 01:35 AM   #4
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Is the twin disc setup that much lighter?

I would think the twin disc is smoother take up. How many people have retrograded their S4 or GT, GTS to this older setup? Is the weight loss noticeable?

This is the type of thing i would prefer over creating something. The main goal would be to reduce the weight of the massive PP thats in the car
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Old 12-20-2007, 01:50 AM   #5
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Sterling---

Carl's flywheel is plenty tested......read up buddy.

near $800 for the flywheel and you can service the friction areas if need be.


--Russ
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Old 12-20-2007, 01:57 AM   #6
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the twin disc setup requires a mid plate.

Is there anyone thats weighed the pp, two discs and mid plate, and if so can you post what that figure is?

I guess you would need a different flywheel if you went with this as the PP looks to be of a smaller diameter, although i guess you could machine new holes in the existing flywheel without having to buy a $700 aluminum flywheel
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Old 12-20-2007, 02:02 AM   #7
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I shipped an early twin disc clutch, flywheel, centershaft for about 75 lbs. total, if memory serves me correctly.

don't know if you can use a 16V flywheel on later 32V engines, but someone here might know.......

--Russ
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Old 12-20-2007, 02:24 AM   #8
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Kibort just stated the complete dual disk setup is 45 lbs, that is discs and all,
I am going to the aluminum disc from carl, i was one of the first and I paid iirc around $430USD for it, so where the $800 -$700 mark is coming from I dont know. I have yet to weight the entire setup but also have a GT1 spec clutch to go in at the same time.

you can use the early flywheel on a later engine, do a search, you need an auto flywheel from an S4 to put the ring over onto it. The dual disc cars rev alot faster than the S4 + cars from my experiance.
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Old 12-20-2007, 02:33 AM   #9
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straight from Carl's website:

alloy flywheel available for either 77-82 and 83-95, both with dual disc clutch.

$429 + shipping for the early one
$529 + shipping for the late model

6 lbs weight loss from stock unit.

--Russ
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Old 12-20-2007, 02:39 AM   #10
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i get the flywheel idea, it saves 5 lbs

but the big monster is the single disc PP which with the T/O Bearing and arm weighs 38lbs. What does the twin disc PP, mid plate and its arm and T/O bearing weigh? I doubt its less than 30lbs? If not then I am still looking for a PP thats made with an aluminum housing instead of the tank like, stock steel one.
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Old 12-20-2007, 02:58 AM   #11
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that saves 5 lbs off of a dual disc flywheel which is alot smaller than an S4 so you will see more weight savings there too. and the only difference between the early and late plates he lists is that the late plates do not have a timing ring on them.
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Old 12-20-2007, 03:41 AM   #12
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15 lbs lighter. you cant reallly notice the difference. on the dyno, it is not detectable, but in quick neutral revs it does rev a bit quicker.

If you wanted to save 15lbs, this is the way to do it. the other main reason, is greater clamping force as well as the weight is on a smaller diameter as well.

this pic shows a fair comparison of everything. however, there is not a starter ring on the 84. that weighs around 2 lbs.

first pic is the 84 clutch dual disc, second pic is S4 and last pic is side by side comparison of the components, including the flywheel

so, 13lbs savings , apples to apples.



mk


Quote:
Originally Posted by RyanPerrella View Post
Is the twin disc setup that much lighter?

I would think the twin disc is smoother take up. How many people have retrograded their S4 or GT, GTS to this older setup? Is the weight loss noticeable?

This is the type of thing i would prefer over creating something. The main goal would be to reduce the weight of the massive PP thats in the car
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1987 928S4 - Holbert Race Car Replacement Project.
http://video.google.com/videoplay?do...67&q=928+video
Laguna Seca SCCA ITE race with Comp Coupe Viper '08
https://www.youtube.com/watch?v=Sih48Dby9d0
TV Highlights
http://videos.streetfire.net/video/5...bdf5891242.htm
Porsche GT3-Caddy CTSV race LAGUNA '08
http://www.youtube.com/watch?v=xYbFeIai2Ng
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Old 12-20-2007, 04:04 AM   #13
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Thanks Mark

I may look at picking up a used dual disk setup on the cheap and throw it in and see what i think.

What flywheel would i use that would accept the early dual disk setup and be read by the GT's crank sensor? Does the 84 clutch arm work on the GT? Doesn't the earlier clutch arm get attached via a smaller diameter pivot ball? Or would I just use the original GT arm?
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Old 12-20-2007, 04:07 AM   #14
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If i bought Carls aluminum flywheel, could I use that with a factory porsche supplied early dual disk clutch kit and bolt everything in and be running with that?

What else would I need? the starter ring gear? the mid plate? (I assume used wold work in both cases?
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Old 12-20-2007, 12:49 PM   #15
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Those are great questions for 928 intl.

i do know you need the lower bell housing from an early car. thats nice, as then the lower bell housing has the starter attached directly to it, loosing another 2lbs of that bracket.

Then, you need the automatic 85 flywheel and the timing gear from an S4 (?)
(928 will press this on. have someone do a quick spot weld before you install)
Then, the rest of the entire early clutch set up is bolted on. I think you just use the same clutch lever arm that comes on the car. you also use the early clutch slave cylinder.

There you have it, 15lbs less rotating mass, which is like having 20more HP in 1st gear and only 1hp in 4th gear.

mk


Quote:
Originally Posted by RyanPerrella View Post
Thanks Mark

I may look at picking up a used dual disk setup on the cheap and throw it in and see what i think.

What flywheel would i use that would accept the early dual disk setup and be read by the GT's crank sensor? Does the 84 clutch arm work on the GT? Doesn't the earlier clutch arm get attached via a smaller diameter pivot ball? Or would I just use the original GT arm?
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1987 928S4 - Holbert Race Car Replacement Project.
http://video.google.com/videoplay?do...67&q=928+video
Laguna Seca SCCA ITE race with Comp Coupe Viper '08
https://www.youtube.com/watch?v=Sih48Dby9d0
TV Highlights
http://videos.streetfire.net/video/5...bdf5891242.htm
Porsche GT3-Caddy CTSV race LAGUNA '08
http://www.youtube.com/watch?v=xYbFeIai2Ng
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Old 12-20-2007, 12:49 PM
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