Ignition timing set-up

[B.E. Herron]

At 10:48 AM 8/26/97 -0500, you wrote:
>> 
>> Help ... I've done a lot of work rebuilding a Ford 351W for
>> 
>> If I set the timing to give good low end response (requires
>> 20 to 25 degrees advanced at 600 rpm, no vacuum), I get
>> clatter under load at high rpm's.
>> 
>I've been battling much the same problem with my 351W 
>DuraSpark/MSD-6A combo.  I run a fairly warm cam (Comp-cams
>dual-pattern hydraulic), & recently switched from a Holley
>650 to an Edelbrock 750.  I've tried both ported & direct
>vacuum advance.  I've turned the vacuum advance adjustment
>screw to its limit for least advance, and run direct
>vacuum presently, with about 10 degrees idle advance (mech).  I 
>ended up setting the carb fairly rich to reduce pre-ignition(?)
>at part throttle accel (like trying to maintain speed on
>an uphill grade in 5th).  Then my O2 sensor says I'm a bit
>rich on level ground.  Playing with the timing light in 
>the garage, I see way beyond 30 degrees advance at 3000 RPM
>with the vacuum hooked up, causing pre-ignition.
>
>Like you, best idle is obtained with about 20 degrees 
>advance (vacuum + mechanical).  I wouldn't recommend
>setting idle mechanical advance beyond 12 degrees, or
>your total advance at 3000 will be over 30 (no vacuum),
>
>Realistically, most of my problems are due to attempting
>to operate the engine outside its optimum point.  I have
>a cam, carb, intake (Torker-II), and heads (Dart-II) that 
>are intended for 3000-6000 RPM, yet I want to cruise at
>2000 RPM in 5th. 
>
>-- 
>Matthew D. Sale,  IC Development Engineer, Delco Electronics Corp.
>msale at iquest.net   http://www.iquest.net/~msale
>'69 Mustang 351W 5-spd (13.464 at 103MPH using cave-man technology).
>
>All responses are my own and should not be mistaken
>for those of Delco Electronics or General Motors.
>

Mathew is correct.  Idle advance (mechanical only) should be 10 to 12
degrees, no more.  Idle advance (machanical+vacuum)) should be 20 to 25
degrees.  Total advance (mechanical) can be anywhere between 30 and 36
degrees for max power.  Your vacuum canister should be set to give total
advance (machanical+vacuum) in the same range for total mechanical advance
or detonation results.  


Bradley E. Herron
'66 Mustang Fastback	'73 Camaro RS