advancing timing?
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Freshman User
Joined: Jan 2004
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advancing timing?
i am trying to understand about advancing my timing? i have a 1978, 400. 1405 carb, new rod/mains, new timing chain/gears and an hei distrib. new harmic bal also. timing cals for 12 btdc. if i advance it 4 degrees will it go to 8 or to 16 btdc? what is also the best way to set the vacuum advance. thanks for your help.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Set it around 10°BTDC. Advancing from 12° would be moving it to 16° which is WAY too much timing.
Some figures to start from:
1971 distributor & engine specifications for the 400
This was the GOOD year for the 400 engine before it was smogged to death.
=================================================
Distributor part #D00F-U
Centrifugal Advance Start: 0-0.5° @ 350RPM Finish: 14° @ 2275RPM
Vacuum Advance Start: 0-1° @ 5" Finish: 12.5° @ 25"
Point Dwell: 26-31°
Initial Timing: 10° BTDC, 6°BTDC California.
Vacuum given in inches of Mercury (Hg).
RPM specified as distributor RPM.
Degrees specified as distributor degrees.
Double those values for crankshaft figures:
Example: 0-0.5° @ 350RPM distributor becomes 0-1° @ 700RPM on the engine.
Some figures to start from:
1971 distributor & engine specifications for the 400
This was the GOOD year for the 400 engine before it was smogged to death.
=================================================
Distributor part #D00F-U
Centrifugal Advance Start: 0-0.5° @ 350RPM Finish: 14° @ 2275RPM
Vacuum Advance Start: 0-1° @ 5" Finish: 12.5° @ 25"
Point Dwell: 26-31°
Initial Timing: 10° BTDC, 6°BTDC California.
Vacuum given in inches of Mercury (Hg).
RPM specified as distributor RPM.
Degrees specified as distributor degrees.
Double those values for crankshaft figures:
Example: 0-0.5° @ 350RPM distributor becomes 0-1° @ 700RPM on the engine.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Are you talking about cam/valve timing, or spark timing?
You advance the cam/valve timing 4 degrees by using the '0' timing keyway on the timing chain sprocket. Most aftermarket timing set have three keyways. One being 4 degrees retarded (factory setting), the next being zero degrees, and the third being 4 degrees advanced.
Advancing the cam/valve timing improves the torque at low RPM. The factory retarded timing was done for emissions purposes.
You advance the cam/valve timing 4 degrees by using the '0' timing keyway on the timing chain sprocket. Most aftermarket timing set have three keyways. One being 4 degrees retarded (factory setting), the next being zero degrees, and the third being 4 degrees advanced.
Advancing the cam/valve timing improves the torque at low RPM. The factory retarded timing was done for emissions purposes.
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