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Does anyone have specs for the camshaft?
Lift, duration, lobe centers.

Also, is it the same cam in the NA and turbo?
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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

[Rasta Monsta]

Not the same. Somewhere I have the spec sheet for the 931 can I used, I'll try and find it.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

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I tried to measure the stock NA camshaft today, it is really mild, zero overlap, not a lot of duration.

Then I tried to measure the performance camshaft from Mittelmotor that I have. That has some overlap a little more duration and a little more lift 12.2 mm instead of 11.7 mm.

My setup was not very precise so I won't present specific numbers that might be wrong, lift was easy to measure on the shaft, assuming the stock one isn't too worn and accepting that a caliper is not good for more than down to a 1/10 mm.

The Mittelmotor cam has maybe 10 degrees more duration on the intake and maybe 20 more on the exhaust.

Trying to decide which cam to use on my turbo conversion.
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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

[Cedric]

Just dumping some text i copied somewhere on this board. If i have time i will search through my data a bit more, i did some engine simulations on several hundred cam combinations. I remember it being pretty sensitive to exhaust during, due to the log manifold, it responded much bettet to intake duration.






PORSCHE 924 - NORMALLY ASPIRATED (N.A.)

Cam Profile Seat Duration, .015" .050" Duration
Cam Lift*
Stock 046 cam 255� 223� .472"
Improved Stock 260� 225� .478"
Stage 1 268� 232� .500"
Stage 2 276� 239� .520"
Stage 3 284� 248� .538"
Stage 4 290� 254� .548"




PORSCHE 924 - TURBO

Cam Profile Seat Duration, .015" .050" Duration Cam Lift*
Stock 046 cam 255�/255� 223�/223� .472"/.472"
Stage 1 268�/260� 232�/225� .500"/.478"
Stage 2 276�/268� 239�/232� .520"/.500"
Stage 3 284�/280� 248�/242� .538"/.520"
Stage 4 290�/284� 254�/247� .548"/.525"


* gross cam lift with zero valve lash.

All of the Turbo cam specs are listed as "intake/exhaust".

The normally aspirated (N.A.) Improved Stock cam is designed to be a mild warm-up over the original stock cam. It is intended to be a replacement for the stock cam when someone just wants a really nice running stock motor. A more modern cam design technique enables better valve control at higher rpms. Additionally, the slight increase in area under the curve also gives some extra performance over the stock cam. The idle quality is identical to the stock cam since there is such a small difference in seat duration.

The stage 1 N.A. and turbo cams are a hot street performance grind. There is no loss in low end torque with most of the gain in the mid-range thru top range RPMs. Since it is ground on a new billet, it bolts in just like a stock cam.

The stage 2 N.A. and turbo cams are designed for an engine that has a free flow exhaust system. There is a slight loss in low end torque but a bigger gain in mid-range and top end power.

The stage 3 N.A. and turbo cams are designed for an engine that is driven on the street and also used for club race events. The large gain in mid-range and top end power to 7200 rpm make it ideal for road racing. This cam is intended for modified engines running higher levels of boost and that are driven hard and spend most of their time in the 4500-7200 rpm range.

The stage 4 N.A. and turbo cams are designed for race only use.


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Porsche 924 Stage I Turbo Cam
Seat duration*: 268� / 260�
.050" duration**: 232� / 225�
Gross cam lift: .500" / .478"
Hot valve lash: .015" / .015"
Net valve lift: .485" / .463"
* with .015" hot valve lash
** with zero valve lash

Lobe separation angle = 112�

At .015" hot lash:
Intake opens 22.0� BTDC
Full intake lift at 112� ATDC
Intake closes 66.0� ABDC

At .015" hot lash:
Exhaust opens 62.0� BBDC
Full exhaust lift at 112� BTDC
Exhaust closes 18.0� ATDC

Max. RPM = 6500 with stock valve springs at sotck installed heights with stock lifters

Intake : Outer Spring : Inner Spring : Total
Valve open : 50.5 lbf @ 1.667" : 11.5 lbf @ 1.555" : 62.0 lbf
Valve closed: 196.1 lbf @ 1.182" : 36.8 lbf @ 1.070" : 232.9 lbf

Exhaust : Outer Spring : Inner Spring : Total
Valve open : 50.5 lbf @ 1.667" : 11.5 lbf @ 1.555" : 62.0 lbf
Valve closed: 188.2 lbf @ 1.204" : 35.4 lbf @ 1.092" : 181.6 lbf

Set the initial cold valve lash at .011" intake / .011" exhaust. After the initial break-in period is over (see below), check the hot valve lash. Allow the motoro to cool down and then adjust the cold lash by your measured cold-to-hot delta so that the valve lash will grow to .015" when the engine is hot. It is the hot valve lash that really matters.
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1980 924 Turbo
www.instagram.com/garagecedric/

[Carrera RSR]

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[Juho]

can i put aftermarket cam from my na engine to my turbo head?

[Cedric]

[Rasta Monsta]

My bad, I guess it's the aftermarket cams that are different between NA and turbo
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[anthonimartini]

hey there safe, not trying to ruin this thread but i was told you had bought a set of those ali express h beam rods. i just ordered some. how did they work out? im assuming you received them? did they fit the the 924 rod bearings correctly?
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ive saved alot of 924's
current:
79 MochaSchwartz 931
83 944
87 924S
Instagram @anthoni.jpeg
formerly known as turbellion, lost password.

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[gegge]

I measured the OEM cam too. Let me know if you want numbers to compare.

Stock cam is a very good turbocam, especially as long as you keep stock exhaust manifold (log) and a tight turbine housing. The flow balance of the turbo 40mm inlet and 36mm exhaust is not optimal, since they flow almost as good. The NA 40/33 balance is better. i would therefore not recomend using the Mittermotor cam with additional exhaust duration. If you need additional duration, go for inlet duration. Inlet time do compensate for exhaust area.

I choosed to increase lift to 13,5mm and slightly more duration in my turbo engine for more power in the 4000-6000 band. I belive 0.050" was 231 degrees. (compared to my NA 251 cam which I considered too hot for my turboapplication.)
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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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