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Timing Recommendation

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Old Nov 21, 2007 | 11:07 AM
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Default Timing Recommendation
I have a 73 L82 with a slightly more radical cam then a stock L82. Timing is currently set according to stock specs at 8 deg BTDC, and it's running a little rough. How far should I bump up the timing?
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Old Nov 21, 2007 | 11:19 AM
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Aggressive cams tend to have bad idles. I don't think timing will get you much of a better idle without affecting driving performance.
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Old Nov 21, 2007 | 11:48 AM
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Default vacuum advance
Do you have fulltime vacuum advance and verified that your vacuum advance unit is holding vacuum?
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Old Nov 21, 2007 | 11:52 AM
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Timing at idle - 15-18 degrees (Vaccum disconnected)
Total timing of 36 degrees, all in by 2500 -3000 rpm
Total with vaccum connected not to exceed 52 degrees
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Old Nov 21, 2007 | 12:24 PM
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Originally Posted by desi
Timing at idle - 15-18 degrees (Vaccum disconnected)
Total timing of 36 degrees, all in by 2500 -3000 rpm
Total with vaccum connected not to exceed 52 degrees


Factory idle numbers were set to pass emissions. I don't know about you but I don't drive my car at idle.

Here is a link to Lars' tuning paper:
http://www.corvettefaq.com/c3/HowToSetTiming2.doc
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Old Nov 21, 2007 | 12:56 PM
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Originally Posted by SteveG75


Factory idle numbers were set to pass emissions. I don't know about you but I don't drive my car at idle.

Here is a link to Lars' tuning paper:
http://www.corvettefaq.com/c3/HowToSetTiming2.doc
Follow Lar's paper to a tee...OHhhhh, and hang on Muddy
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Old Nov 21, 2007 | 03:43 PM
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Originally Posted by Durango_boy
Aggressive cams tend to have bad idles. I don't think timing will get you much of a better idle without affecting driving performance.
Yea, I pretty much have given up on getting my curb idle perfect, but I am concerned about the mild pinging (knocking) when I get into the excelerator hard. I bumped the timing up to 12 deg BTDC and it improved.
Last edited by c3andc5; Nov 21, 2007 at 03:49 PM. Reason: typo
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Old Nov 21, 2007 | 03:45 PM
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Originally Posted by 70ZZ3 96LT4
Do you have fulltime vacuum advance and verified that your vacuum advance unit is holding vacuum?
Yes to both. I have eliminated any vacuum issues and distributor problems (points, rotor, cap, etc).
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Old Nov 21, 2007 | 03:50 PM
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Originally Posted by desi
Timing at idle - 15-18 degrees (Vaccum disconnected)
Total timing of 36 degrees, all in by 2500 -3000 rpm
Total with vaccum connected not to exceed 52 degrees
What source do those numbers come from?
Thanks
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Old Nov 21, 2007 | 03:57 PM
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Originally Posted by SteveG75


Factory idle numbers were set to pass emissions. I don't know about you but I don't drive my car at idle.

Here is a link to Lars' tuning paper:
http://www.corvettefaq.com/c3/HowToSetTiming2.doc
That write-up from Lars makes sense to me and I had never considered setting the timing that way. I'll give it a shot.
Thanks
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