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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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 Posted: Wed Mar 12, 2025 9:12 pm Post subject: |
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| morghen wrote: | Awesome find!
Curious how it will work out. |
Me too!
It should have low pedal pressure, low noise and it has a sprung hub.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Raize
Joined: 18 Sep 2013
Posts: 289
Location: Scotland
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| Posted: Fri Mar 14, 2025 8:52 pm Post subject: |
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Cool looking clutch. Was the one that held 330nm just the stock clutch? Then you upgraded to 500nm... so what's the rating on this one?
Pedal pressure is presumably just directly proportional to the friction coefficient and the spring plate spring rate, so will be interesting to find out the driving characteristics of this new one. I'm gonna guess to get a light pedal pressure it will be a bit grabby. |
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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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| Posted: Fri Mar 14, 2025 9:20 pm Post subject: |
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| Raize wrote: | Cool looking clutch. Was the one that held 330nm just the stock clutch? Then you upgraded to 500nm... so what's the rating on this one?
Pedal pressure is presumably just directly proportional to the friction coefficient and the spring plate spring rate, so will be interesting to find out the driving characteristics of this new one. I'm gonna guess to get a light pedal pressure it will be a bit grabby. |
300 Nm was Spec stage 2+, the current 500Nm is a Spec stage 3+. Both Spec are quite streetable, very light and not grabby.
If you go up to a stage 4 and above you are getting puck style clutch with unsprung hub. Not my favorite type...
The new Uniclutch is a twin disk, game changer, you can have a light pedal pressure without a supergrippy friction material and still be able to hold an enormous amount of torque. Uniclutch also have a sprung hub. The downside is that they can be noisy depressed because lose plates but it should be minimized with springs to keep the plats from rattling.
Its rated to 1320 Nm, with a continuous torque rating of 30% less than that, so a 1000Nm? I won't come close to that!!
And its not that expensive, about $1000. Considering the price of Spec or an original clutch and that you don't need to refinish the flywheel (a feature with the uniclutch) its almost a bargain.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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fblade
Joined: 07 Dec 2020
Posts: 43
Location: UK
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| Posted: Fri Mar 14, 2025 10:15 pm Post subject: |
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| Well done for trying @safe, really hoping it works |
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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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| Posted: Sun Mar 16, 2025 9:49 am Post subject: |
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Some new goodies turned up from Mittelmotor.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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| Posted: Sun Mar 16, 2025 9:52 am Post subject: |
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Weight difference between original pistons and rods to my Omega pistons and Mittelmotor rods.
A HUGE 276 grams!! (about 0.6 lbs) Per cylinder!
_________________
/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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morghen
Joined: 21 Jan 2005
Posts: 9023
Location: Romania
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| Posted: Sun Mar 16, 2025 9:29 pm Post subject: |
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Thats pretty crazy. New engine should feel a lot different i think.
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Supercharger and EFI kits
https://www.the924.com |
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Raize
Joined: 18 Sep 2013
Posts: 289
Location: Scotland
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| Posted: Wed Mar 19, 2025 8:00 am Post subject: |
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Do you have a rev limit in mind for this build?
Volumetric efficiency isn’t really a problem any more for you with the big turbo , it’s just what the internals can take… |
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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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| Posted: Wed Mar 19, 2025 8:35 am Post subject: |
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| Raize wrote: | Do you have a rev limit in mind for this build?
Volumetric efficiency isn’t really a problem any more for you with the big turbo , it’s just what the internals can take… |
7500 is my thinking.
I think Joakim said he takes his to 8000+, he has some other valves and springs too.
_________________
/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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| Posted: Thu Mar 20, 2025 2:24 am Post subject: |
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Did some calculating of forces on piston acceleration piston+rod weight.
Original rods/pistons and current limiter 6700 rpm:
1481 gram: 41350 M/S2 => 61250 N
New /rods/pistons at 7500 rpm:
1204 gram: 51815 M/S2 => 62380 N
Roughly the same forces, 1.85% more with the new configuration and the ARP rod bolts are stronger than the original stuff.
If I didn't have any brain farts I think 7500 will be perfectly fine! Assuming the valves hangs on and the head/cam still can breathe.
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/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Mike9311
Joined: 14 Dec 2004
Posts: 1792
Location: Chicago-ish
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| Posted: Wed Apr 09, 2025 12:43 am Post subject: |
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Its that lighter piston and the small end mass of that rod that will really help survive the rev forces. These parts are still built like a diesel which I think is good for general long term health of your build. Especially with that boost! I think I try too hard to make things too light on the bottom end for this type of build so this is perfect!
You are running a NA head right? The NA stock was stronger at the lower lift ranges when I tested it. Stock NA vs Stock 931 are not far apart at all and each obviously respond to mild porting
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car |
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safe
Joined: 18 Mar 2017
Posts: 661
Location: Sweden
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| Posted: Wed Apr 09, 2025 1:12 am Post subject: |
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| Mike9311 wrote: |
You are running a NA head right? The NA stock was stronger at the lower lift ranges when I tested it. Stock NA vs Stock 931 are not far apart at all and each obviously respond to mild porting |
Yes, NA head. Do you have any flow data?
I found a new unused NA head (without valves and cam), I'm thinking I'll get that head prepped.
I'm diving into a G31 gearbox right now. The 1st gear dog ring and slider looks horrible... I'm looking to replace the bearing retainer for a one piece retainer too.
For some reason the NA snail shell has that retainer stock. Otherwise the one from a 930 gearbox are the same.
Some other stuff:
Its probably well known that the Pinto engine's headstuds (ARP) fits perfectly in the 924, Ideola used to sell them.
But I think that the Pinto maincap studs (ARP) also is a fit.
If you want a really trick head gasket, Silvio Ruggiero at Turbo Crime Engineering in Italy makes one. You might have seen his crazy 931 build on youtube. He communicates perfectly in English. Resonably priced too for custom stuff at €280.
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/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Mike9311
Joined: 14 Dec 2004
Posts: 1792
Location: Chicago-ish
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| Posted: Thu Apr 10, 2025 12:55 am Post subject: |
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Good to know, thanks!
I believe you are right about main cap fasteners too
Give me a bit, and I will dig up any data I have. I am away for a long weekend so I won't have access to everything
If you have any other ideas for the G31 please share. I am always dreaming of doing something radical to that 1-2 set up it has. Not sure what just yet
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car |
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