924Board.org

Juho · Joined: 03 Oct 2018 Posts: 377 Location: Finland

I found a turbo engine for sale, and i want to put it in a na car at somepoint. Do i have to get a turbo torque tube and transaxle aswell or use na weakee clutch?

MikeJinCO · Posted: Sun Nov 29, 2020 11:42 pm Post subject:

No expert on the 931, but I would think the relocation of the starter from low right to high left would create several problems. I assume the starter relocation is required by the turbo. Do you graft a 931 bell housing to the NA torque tube? Then how do you actuate the clutch?
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

safe · Joined: 18 Mar 2017 Posts: 586 Location: Sweden

A 931 bell housing should work and be the easiest.
931 flywheel, 931 pressure plate and a 915 clutch disk. I think (counting on it) that the 915 clutch disk will fit the NA torque tube.
I guess you need a 931 starter, clutch slave and master cylinders and whatever else you need to fix with the clutch.

It might just be easier to build a turbo kit for the NA engine.
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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

morghen · Joined: 21 Jan 2005 Posts: 8880 Location: Romania

The NA gearbox, TT and clutch would hold the 931 power..maybe not for 200k km...but it would hold....the problem is not if they would hold, the problem is if they fit to the 931 engine. The 931 is a very different car from many points of view.
You should also get the torque tube and gearbox, as well as the clutch from the 931, also the servo clutch and the pedal assembly you need from the 931.
Depending on which 931 version you got it from, you also need engine bay wiring, ignition modules, sensors..its a different car.

Honestly if you want more from your 924, you could just sell the 931 engine and strap a modern turbo and efi to the NA engine, it will be faster than the 931 and cheaper to maintain. Or if you just want a little bit more and dont want to keep your car on jackstands for 1 year, you can buy the supercharger kit i will sell next year. Bolt on, 3-4h to install by yourself, everything included, reversible mod.
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https://www.the924.com

Juho · Joined: 03 Oct 2018 Posts: 377 Location: Finland

my plan was to find a na engine but found a turbo one for a good price so i bought it, 924 engines are impossible to find here

morghen · Joined: 21 Jan 2005 Posts: 8880 Location: Romania

Well, hmm...depends on whats the state of that engine.
If i were you, i'd put all NA gear on that 931 block, and strap a modern turbo to it and efi it. But use the NA flywheel and upgraded NA clutch.
If i wanted to keep it without turbo, i'd take that 931 engine appart, replace the pistons with custom high compression ones, reassemble that engine using NA stuff and efi, and enjoy the 170hp+ it could make if tuned properly.
In any case, i'd keep the NA gearbox and TT as well as clutch, pedal and wiring.

So i'd either put NA gear & efi on the 931 engine and run it as a high CR NA or leave it as it is internally, put the NA gear on it and strap a modern turbo and efi to it. Either way, its more or less a waste of money since for mild street applications...there seems to be no real advantage of the 931 engine vs the 924 NA engine. I mean you can get 200hp from both and keep them reliable....its just the 931 is some extra money spent.
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https://www.the924.com

safe · Joined: 18 Mar 2017 Posts: 586 Location: Sweden

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

You should consider a VW 1.8t...
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

TJC · Posted: Sat Dec 12, 2020 2:21 am Post subject:

Juho · Joined: 03 Oct 2018 Posts: 377 Location: Finland

cant decide between high compression na or turbo engine, i just want to have a engine to build and keep driving my 924. i just want the turbo head to get better flow

safe · Joined: 18 Mar 2017 Posts: 586 Location: Sweden

Juho · Joined: 03 Oct 2018 Posts: 377 Location: Finland

I mean high compression na engine with turbo head

MikeJinCO · Posted: Sun Dec 13, 2020 3:23 am Post subject:

I have been porting and flow testing a 931 head. With the NA head unless some really serious porting(a la Gegge) is done the flow tends to stall at .400 lift. On the 931 head the flow continues to climb to .500 lift so much more potential. Due to changes in my testing methods I can't accurately compare the two. By cleaning up the casting/machining marks above the valve and smoothing and enlarging the sides of the short side radius I have gotten about a 8-9% improvement in flow using the existing valves and seats. I will install 7mm stem valves and the intake has a 12 degree back cut rather than the standard 20 degree. Several sources have said that the shallow back cut significantly helps on ports that turn about 90 degrees, the smaller valve stems will help also.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

Juho · Joined: 03 Oct 2018 Posts: 377 Location: Finland

Juho · Joined: 03 Oct 2018 Posts: 377 Location: Finland