924Board.org

[Mike9311]

If you look closely at the header pic close up, you can see the holes were slotted open

Search Ebay 924 Weber. You will see the weber setup with intake or just intake by itself

I do think I saw the intake somewhat recently somewhere a lot cheaper but not sure where unfortunately
_________________
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

[MikeJinCO]

The one at Rallye Sport would be a bunch cheaper than stock, I'd buy it but I already have one on the NA and my second setup for the 931 head. He had it advertised on the RMVR forum on tapatalk.
_________________
Mike


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

[safe]

[Cedric]

[safe]

OK, the turbo head is better by a reasonable margin, but I think there is a lot that comes with a change to that head. I would use use a custom set of pistons to increase the compression to be able to reap the benefits of the head.
Its an easy choice to use it if you want to maximise the 924 engine. But if want to impove a 95hk k-jet, there is more that can be had from the NA.

My EFI conversion is running now. It is really nice to be able to push a button and the engine starts and runs really nice.
_________________
/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

[TJC]

Personally my motivation for using a Turbo head is actually economic as well as functional, meaning that they can be made to flow better than a NA head plus the ability to use off the shelf VW flat tops, plus I just happen to have a spare '81 Turbo engine laying around.
I was following this thread to educate myself on the availability of off the shelf headers and Weber friendly intake manifolds and now I see that doesn't seem to be an issue. Perhaps the bigger issue may be valve train and camshaft selection and availability and I've been following a couple of other posts regarding those items...and I may just have to contact my old cam grinder and see if he would be interested in this dinosaur project!
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

[MikeJinCO]

With headers it gets pretty crowded down there. You might have to go to a shorty or remote filter, With the hoses for a remote it does get quite tight. My remote filter setup with a feed from the Accusump makes it plumbing nightmare down there.

When the Brits did showroom stock racing back in the late '70's they found the the stock exhaust manifold was a real problem area so the ported it with good results(in one of the books). The internal passages are very crude, I tried porting one and matching it to the down pipe with some success. That cast iron is very hard and tough to work with particularly compared to the aluminum head. To me the design of the NA exhaust isn't bad, the manifold is just very poorly made.

I also would be concerned about the heat from the increased surface area of the headers affecting the alternator and starter.
_________________
Mike


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

[anthonimartini]

i have pretty much an entire donor 931 so i could use hydraulic bell housing to move the starter in a better place as well as the alternator setup to get that out of the heat and into a more accessible place. one thing i am curious about is if i could use the 931 bellhousing with the 931 style pressure plate and the NA 924 clutch disc as to retain my extremely low mileage 20mm torque tube. i was planning on swapping my lsd from the g31 into my na snailshell since it barely has 30k on it and it shifted like a new car. also the 25mm torque tube has questionable pilot bearing surfaces. this is becoming quite a dilemma. too many parts too many choices. i may just build an engine with the 931 head and 87mm vw pistons so i can get some solid specs on it. IE actual compression, deck heights etc. i have on block that needs overbored and one good low mileage std block i could build with the std euro pistons.
_________________
ive saved alot of 924's
current:
79 MochaSchwartz 931
83 944
87 924S
Instagram @anthoni.jpeg
formerly known as turbellion, lost password.

[safe]

Does anyone know how large the combustion chamber of the 931 head is?

Using the flat tops with 39.5 mm compression height (41 mm stock euro NA) should result in 10.6:1 with the NA head. That would be pretty good with premium fuel.

(I've measured the dish in the euro NA pistons to 19.8 ml, 1 mm of 86.5 mm is 5.87 ml, so loosing the dish would be equivalent of 3.37 mm of compression height)
_________________
/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

[Cedric]

[safe]

[MikeJinCO]

If you go the flat top piston and shave the block route, adjustable cam gears are available from CatCam in Netherlands and at least Piper in UK, Newman probably also. I got one form Catcam last year for about $125 last year.
_________________
Mike


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

[Mike9311]

Don't ask me yest why because one day I will tell you anyway but...

Every 1mm of combustion 'stock' shape from the gasket mating surface is worth 4.8cc. I don't mean when you shave but when you add. shaving obviously doesn't work that way

I have seen some UK work involving CarreraRSR that studied how far you can open a 931 head. 26cc seems the limit according to that study
_________________
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

[Juho]

what about using 931 pistons with na head?

[safe]