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Belt timing and tuning vs performance

 
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ted von Kampen  



Joined: 14 Oct 2016
Posts: 141
Location: Scottsbluff, Nebraska

PostPosted: Sat Sep 12, 2020 1:36 am    Post subject: Belt timing and tuning vs performance Reply with quote

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
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 929
Location: Maysville, Colorado

PostPosted: Sat Sep 12, 2020 3:02 am    Post subject: Reply with quote

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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Raize  



Joined: 18 Sep 2013
Posts: 136
Location: Scotland

PostPosted: Sat Sep 12, 2020 4:12 am    Post subject: Reply with quote

Less area under the curve in both directions. There's a few threads on here of people trying it.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1102
Location: Washington DC area

PostPosted: Sat Sep 12, 2020 8:08 am    Post subject: Reply with quote

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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gegge  



Joined: 27 Jul 2007
Posts: 1084
Location: Sweden

PostPosted: Mon Sep 14, 2020 5:22 am    Post subject: Reply with quote

No gains on a stock engine. IIRC the OEM cam is advanced 2 deg already.
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XLR8  



Joined: 30 Mar 2016
Posts: 129
Location: Byron Bay, Australia

PostPosted: Mon Sep 14, 2020 5:43 pm    Post subject: Reply with quote

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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Mike9311  



Joined: 14 Dec 2004
Posts: 874
Location: Chicago-ish

PostPosted: Tue Sep 15, 2020 4:59 am    Post subject: Reply with quote

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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