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safe
Joined: 18 Mar 2017
Posts: 588
Location: Sweden
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 Posted: Wed May 19, 2021 11:52 pm Post subject: |
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| Juho wrote: | 
Should i remove these ridges when porting my 931 head? |
You should look what Michel Mount did on the land speed record 924.
You might find a thread on that here or on rennlist.
Special cam , solid lifters, 931 head (ported, not sure anyone would say how), stock crank tear droped oiling holes, dry sump, carbs, aftermarket rods and pistons 13:1, race gas.
I think it reved to 8000 and 200+ hp
That is probably what is possible to get out of it.
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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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Cedric
Joined: 27 Aug 2004
Posts: 2609
Location: Sweden
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| Posted: Thu May 20, 2021 1:45 am Post subject: |
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It think it was stated at 225 something on the dyno, which i think is where the last iteration of scca gt3 racers had if i remember the forum discussion from long ago. More than that is tough.
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1980 924 Turbo
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safe
Joined: 18 Mar 2017
Posts: 588
Location: Sweden
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| Posted: Thu May 20, 2021 2:06 am Post subject: |
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| C�dric wrote: | | It think it was stated at 225 something on the dyno, which i think is where the last iteration of scca gt3 racers had if i remember the forum discussion from long ago. More than that is tough. |
Yes, I've read 210 and 225.
As far as I know Michael is retired, but I also know that he sometimes takes a job like porting a head if its for a fun project. He can probably supply a good cam for that too.
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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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Juho
Joined: 03 Oct 2018
Posts: 379
Location: Finland
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| Posted: Thu May 20, 2021 3:38 am Post subject: |
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I plan on going
my 285 cam from my na car
11-12:1 on pump gas
cbrr100 itbs 44mm
Fabricate own exhaust manifold
wasted spark
forged rods
vw flat tops
931 head ofc
im happy if i achieve 150 hp with this setup |
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Cedric
Joined: 27 Aug 2004
Posts: 2609
Location: Sweden
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| Posted: Thu May 20, 2021 3:57 am Post subject: |
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If you have someone local that have a good rep with head porting it could be worth to maybe let them do some light work on head, if you aim for na power, alot of the performance will be in the head.
JoakimS engine makes 347hp on pump fuel at 1 bar of boost, which is roughly 173hp n/a, but his head has alot of work done to it. 150-160 should be possible but with some lighter head work.
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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Juho
Joined: 03 Oct 2018
Posts: 379
Location: Finland
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| Posted: Thu May 20, 2021 4:11 am Post subject: |
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| C�dric wrote: | If you have someone local that have a good rep with head porting it could be worth to maybe let them do some light work on head, if you aim for na power, alot of the performance will be in the head.
JoakimS engine makes 347hp on pump fuel at 1 bar of boost, which is roughly 173hp n/a, but his head has alot of work done to it. 150-160 should be possible but with some lighter head work. |
is he running stock valves? |
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safe
Joined: 18 Mar 2017
Posts: 588
Location: Sweden
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| Posted: Thu May 20, 2021 5:03 pm Post subject: |
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| Juho wrote: | | C�dric wrote: | If you have someone local that have a good rep with head porting it could be worth to maybe let them do some light work on head, if you aim for na power, alot of the performance will be in the head.
JoakimS engine makes 347hp on pump fuel at 1 bar of boost, which is roughly 173hp n/a, but his head has alot of work done to it. 150-160 should be possible but with some lighter head work. |
is he running stock valves? |
No.
In a turbo head the ratio between intake and exhaust valves favour the exhaust compared to an NA head.
I would fit an intake valve that is as large as possible in the 931 head if used NA (as long as it doesn't shroud itself in the head = to close to cylinder wall for flow).
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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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Juho
Joined: 03 Oct 2018
Posts: 379
Location: Finland
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| Posted: Thu May 27, 2021 3:43 am Post subject: |
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| Theres a company working on 924 head, but found some intresting stuff |
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morghen
Joined: 21 Jan 2005
Posts: 8883
Location: Romania
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| Posted: Thu May 27, 2021 4:02 pm Post subject: |
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Mittelmotor sell ready to use CNC modified and bench flowed/guaranteed/demonstrated NA and turbo heads ready to flow up to 165hp NA and who knows whats the limit for the 931 heads.
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Juho
Joined: 03 Oct 2018
Posts: 379
Location: Finland
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gegge
Joined: 27 Jul 2007
Posts: 1124
Location: Sweden
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| Posted: Tue Jun 01, 2021 2:52 am Post subject: |
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The major bottleneck is the tiny valveseat due to the 40mm inlet valve, but even worse is the absolute flat NA combustion chamber. With a larger valve you get shrouding, so an excentric valveguide is essential (or larger bore or a repositioned head). The flat combustion chamber is killing flow because of the sudden transition from the small valve curtain area to infinite baffle. That is why the 931 head is better. Short inlet radius is the next to adress, don´t make it even worse. The venturi should be prior to the valve guide and any modification upsteam the inlet duct make no sense.
12mm lift and 40mm manage some 150hp at most. Making 225hp is truely impressive out ot this engine. I spend a lot of money and all I got was 173 cfm @16mm, that is no way near 200hp.
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Carl Fredrik Torkildsen
924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs |
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Mike9311
Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish
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| Posted: Tue Jun 01, 2021 11:38 pm Post subject: |
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Gegge, I am working on your offset/eccentric guide idea right now.
Harder for me to make the guides since I have to drill them already installed for the intake
It will be 42/38 but only because that was the off the shelf choice for the exhaust in super alloy. If any diameter adjustment is needed it will be on the exhaust side. Exhaust valve seat will be in beryllium free copper seat alternative to draw the most heat out of the valve. would have preferred 42/36 but I wanted the better valve. Seats are done awaiting install.
I have everything I need except the fixture for the head which is not yet complete. I am ramping up to full speed on this now since I need the head. Bottom end is ready with cometic on the way (back up thicker cometic already in hand)
Planning 1mm to 1.5mm eccentric intake guide
_________________
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: 588
Location: Sweden
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| Posted: Tue Jun 01, 2021 11:57 pm Post subject: |
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| Mike9311 wrote: | Gegge, I am working on your offset/eccentric guide idea right now.
Harder for me to make the guides since I have to drill them already installed for the intake
It will be 42/38 but only because that was the off the shelf choice for the exhaust in super alloy. If any diameter adjustment is needed it will be on the exhaust side. Exhaust valve seat will be in beryllium free copper seat alternative to draw the most heat out of the valve. would have preferred 42/36 but I wanted the better valve. Seats are done awaiting install.
I have everything I need except the fixture for the head which is not yet complete. I am ramping up to full speed on this now since I need the head. Bottom end is ready with cometic on the way (back up thicker cometic already in hand)
Planning 1mm to 1.5mm eccentric intake guide |
Are you using a smaller valve stem?
_________________
/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: 1678
Location: Chicago-ish
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| Posted: Wed Jun 02, 2021 2:47 am Post subject: |
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Yes, the 5.94 - 6mm which is why I want to use appropriate material to draw heat quickly from them when they are on the seat. These are a standard stem size for the ford modular v8 plus the same size stem is used reliably in racing (by now rather old school racing, volvo's etc)
I haven't decided yet if I will cut (machine) or grind the groove for the keeper
Beehive springs etc. Weight savings over the entire head will be -800g or more. My first go around will be with lighter springs. Such a massive reduction in mass can easily take less spring pressure
I have a nice drill but the length-of-cut (depth-of-cut) is cutting it close depending on how long I want the guide to be. Will likely grind some clearance on it near where it is held so I can go a bit deeper. My thoughts have been pushing me to keep the guide longer for support and heat removal. The guide material is manganese bronze since I have good luck running tight clearances with a high revving Ducati 748 I built years ago. Machined my own guides for that as well... see below
Current plan: 42/38
Ducati guides I made in the past
valve comparison. old pic so this may be 40mm example
_________________
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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924 FAQ (Technical)
