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Timing Advancement
Im about to tackle the tensioner upgrade on my 82 SC. I have heard of people advancing the timing to (I think) 1.4mm BTDC for better performance.
I was wondering what reference point you use to do this? What are the performance results? Does this produce a difference throughout or only at certain RPM's? Thanks in advance for your replies! Nick Shumaker. ------------------ __________ Nick Shumaker 1982 911SC Coupe [This message has been edited by Nickshu (edited 02-07-2001).] |
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02-07-2001, 07:55 AM
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Nick,
I don't think you really want to do that! Assuming a 'middle' setting, here is what the possible changes are, and the results: Advance the cams to 1.4 mm, emphasis goes to the top end, and you lose bottom-end torque! Retard the cams to 0.9 mm, and you increase bottom-end torque. But, since your '82 is supposed to be set at 1.0 mm (halfway between 0.9 mm and 1.1 mm) already, you would lose a lot of bottom-end responsiveness!!! You could set it at 0.9 mm for a slight increase, but I'm not sure it is worth the trouble if you find both sides already at 1.0 mm. Maybe just leaving it alone is the way to go. ------------------ Warren Hall 1973 911S Targa |
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02-07-2001, 09:41 AM
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Warren, thanks alot for the info. I think I'll just leave it alone. But, just for knowledge, what are the reference points used to advance/retard the timing?
Thanks again. Nick. ------------------ __________ Nick Shumaker 1982 911SC Coupe |
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02-07-2001, 11:49 AM
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Nick,
The Z1 mark on the crankshaft pulley. You turn the engine over until the distributor rotor is pointing at #1 or #4. Mount, preload by 0.5", and zero the dial indicator on the intake valve retainer, then turn the crank pulley a full 360 degrees and Z1 is lined up again ... that is the TDC 'overlap point' where both intake and exhaust valves are open a small amount. At this point you read the lift value for comparison with the spec book value. ------------------ Warren Hall 1973 911S Targa [This message has been edited by Early_S_Man (edited 02-07-2001).] |
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02-07-2001, 12:05 PM
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Thanks again Warren.
Nick. ------------------ __________ Nick Shumaker 1982 911SC Coupe |
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02-07-2001, 02:22 PM
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Warren, you made a mistake on the above post. Advancing cam timing will increase bottom end. Retarding cams will increase top end. I know you know that. I'm just pointing out that you got them backwards. I know it's counterintuitive, so I'll forgive you.
------------------ Tyson Schmidt 72 911 Cabriolet [This message has been edited by BRAINIAC (edited 02-07-2001).] |
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02-07-2001, 03:23 PM
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I thought that sounded a little wierd, but being inferior in knowledge to Warren, didn't want to say anything.
Thanks Tyson! Nick. ------------------ __________ Nick Shumaker 1982 911SC Coupe |
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02-07-2001, 05:26 PM
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Yes, Tyson, I did ... just call it brain fade while working on three things at once!
And, just two months ago, a mysterious power loss was attributed to a change to retarded cam timing after a tensioner replacement in the following thread: http://www.pelicanparts.com/ultimate/Forum3/HTML/004283.html So, Nick, you may want to reset the timing after all! This is one of those rare cases where I disagree with Bruce Anderson's beliefs! ------------------ Warren Hall 1973 911S Targa [This message has been edited by Early_S_Man (edited 02-07-2001).] |
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02-07-2001, 05:35 PM
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