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ted von Kampen

Several posts awhile back got me to thinking. The 2 liter NA engine is not interference. While I realize the instructions for setup call for the timing marks to align, I wonder if anyone has assessed the engine performance if the belt is set a notch or two either side of the TDC and timing mark settings?
Mostly curiosity on my part.
Would seek comments if you have any experience in this subject.
I have a 1981 Porsche 924 2.0 NA.
Ted

MikeJinCO · Posted: Sat Sep 12, 2020 3:02 am Post subject:

The fellow who does my machine work has said many times that on US V8's advancing the cam about 4 degrees will really improve low end performance. Many Crower cams come with a built in 4 degree advance. Of course that will subtract from the top end, but few street motors normally run in that range. I believe that our pulley is a 44 tooth so moving it one would be about 8+ degrees. That may be a bit much. Now if the block has been milled then you could calculate the amount that the cam has been retarded.

I believe the cam pulleys that Ideola had(and may still have) are marked for adjustment.
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Mike

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

Raize · Joined: 18 Sep 2013 Posts: 186 Location: Scotland

Less area under the curve in both directions. There's a few threads on here of people trying it.

Fifty50Plus · Posted: Sat Sep 12, 2020 8:08 am Post subject:

8 degrees is too much for anything. Rule of thumb is: advancing the cam moves the torque curve lower in the RPM range while retarding it moves the torque higher in the range. Usually only effective when you are using a non stock camshaft such as one with more lift and changed lobe centers (race cam).
On race cams we used to change the advance/retard less than 2 degrees.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

gegge · Joined: 27 Jul 2007 Posts: 1124 Location: Sweden

No gains on a stock engine. IIRC the OEM cam is advanced 2 deg already.
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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

XLR8 · Posted: Mon Sep 14, 2020 5:43 pm Post subject:

This discussion interests me. In replacing the head and gasket on my '82 NA, my mechanic and I noticed there was slightly different timing on one cam gear/camshaft, compared to another from a different head.

The difference IIRC was about 1/2 a tooth offset. We elected to install the cam gear/camshaft that had the more advanced timing. I "feel" the car has more than it did (but I rarely get above 5k rpm).

Can anyone add to the above regarding cam gears. I did try searching at the time, but couldn't find anything ...
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'81 Porsche 924 NA
'89 Eunos Roadster NA6
'06 Landcruiser HDJ100

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Fifty50Plus pretty much summed it up

You are right though about machining changing things. This is why using an adjustable cam gear and spending the time to check and adjust helps get it back to spec or the way you want it.

You can also use offset keys.

Building an engine right now and, when I get to this point, I will post up some pics of the process.
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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