Timing

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My all time favorite vehicle is our 1969 Shelby GT500
I believe the stock timing is 6 degrees Before Top Dead Center (BTDC), which is a setting that is needed as part of the effort to help minimize emissions from an engine. If the timing is advance "too far"it could cause the engine to increase its NOx emissions due to increased internal combustion compression at the time a spark plug is fired. Often there is a point/counter-point setting the initial ignition timing setting where performance increases cause NOX output creation, something the 6 degree setting helps prevent - at the expense of performance. But going into too much initial advance will cause problems also. The objective for a dynamic timing setting is to get high performance out of an engine irrespective of the engine's emission output. So, for street engines a 6 degree initial timing setting is often correct.

The optimum initial timing will depend on a lot of things, to include compression ration of the combustion chamber in the engine, Octane level of fuel and any additive in the fuel (to include ethanol), Total in interim levels of (dynamic) timing advance whether caused by the vacuum advance, centrifugal, or aftermarket electronic advance sub-systems, engine load, timing gear stretch impact, engine RPM, temperature of the engine, air/fuel ratio, etc. With decent gasoline I find the initial timing being set to 12 degrees begins to wake up most engines. Setting your ignition up 12 degrees BTDC may, however, be too high if you are running a low octane of fuel, have relatively high compression in your engine. If you hear pinging you need to back off the timing until the ping is minimal or gone.

There are several "old school" ways of ascertaining your initial ideal timing. Some require the use of a "chassis dyno" that can add a load to the engine in a manner similar to road conditions. The way I used to do it is simple, and showed to be plenty good for "seat of the pants" timing adjustments.

I would leave the distributor hold-down clamp slightly loose so I could adjust ti, but not so loose that it would turn from the distributor housing on its own. Then connect a tachometer to measure engine speed. I would then leave the vacuum advance hose connected to the port vacuum source. Then using the chock high speed idle cam I would run the engine up to 2,500 RPM. At that point I would begin to advance the distributor position to increase (or decrease) the timing until I hit a maximum RPM reading. Once I hit the maximum RPM due to timing adjustments I would back off the timing advance enough to drop 200 RPM from the peak RPM.

Once the timing was set like that I would remove the distributor vacuum advance tubing, and check on the timing advance reading, For me it was consistently 12 degrees, but your engine may well be different.

Of course, I intend for this technique to be used for vehicles being run on a private race track. For engine on the public roadway you are going to have to comply with emission control requirements of your state and the federal government, to include engine tune settings. Many states no longer require any emission control equipment to actually function after the vehicle is 25 years old (check on your own state), but in some of those states the emission control components are not supposed to be removed or tampered with.

Also, please note, not all emission control items are "bad or will decrease performance. Positive Crankcase Ventilation (PCV) systems are good to have. Likewise the fuel evaporation control systems work well and do not rob horsepower from an engine. Some Thermal Vacuum Switches (TVS) units work well with engine vacuum advance systems, and in fact could be helpful in preventing engine overheating. I have a quick YouTube video explaining how those TVS units work, at the following web site:

 
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1973 Ford Mustang Coupe. 302cid 2v.

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I believe the stock timing is 6 degrees Before Top Dead Center (BTDC), which is a setting that is needed as part of the effort to help minimize emissions from an engine. If the timing is advance "too far"it could cause the engine to increase its NOx emissions due to increased internal combustion compression at the time a spark plug is fired. Often there is a point/counter-point setting the initial ignition timing setting where performance increases cause NOX output creation, something the 6 degree setting helps prevent - at the expense of performance. But going into too much initial advance will cause problems also. The objective for a dynamic timing setting is to get high performance out of an engine irrespective of the engine's emission output. So, for street engines a 6 degree initial timing setting is often correct.

The optimum initial timing will depend on a lot of things, to include compression ration of the combustion chamber in the engine, Octane level of fuel and any additive in the fuel (to include ethanol), Total in interim levels of (dynamic) timing advance whether caused by the vacuum advance, centrifugal, or aftermarket electronic advance sub-systems, engine load, timing gear stretch impact, engine RPM, temperature of the engine, air/fuel ratio, etc. With decent gasoline I find the initial timing being set to 12 degrees begins to wake up most engines. Setting your ignition up 12 degrees BTDC may, however, be too high if you are running a low octane of fuel, have relatively high compression in your engine. If you hear pinging you need to back off the timing until the ping is minimal or gone.

There are several "old school" ways of ascertaining your initial ideal timing. Some require the use of a "chassis dyno" that can add a load to the engine in a manner similar to road conditions. The way I used to do it is simple, and showed to be plenty good for "seat of the pants" timing adjustments.

I would leave the distributor hold-down clamp slightly loose so I could adjust ti, but not so loose that it would turn from the distributor housing on its own. Then connect a tachometer to measure engine speed. I would then leave the vacuum advance hose connected to the port vacuum source. Then using the chock high speed idle cam I would run the engine up to 2,500 RPM. At that point I would begin to advance the distributor position to increase (or decrease) the timing until I hit a maximum RPM reading. Once I hit the maximum RPM due to timing adjustments I would back off the timing advance enough to drop 200 RPM from the peak RPM.

Once the timing was set like that I would remove the distributor vacuum advance tubing, and check on the timing advance reading, For me it was consistently 12 degrees, but your engine may well be different.

Of course, I intend for this technique to be used for vehicles being run on a private race track. For engine on the public roadway you are going to have to comply with emission control requirements of your state and the federal government, to include engine tune settings. Many states no longer require any emission control equipment to actually function after the vehicle is 25 years old (check on your own state), but in some of those states the emission control components are not supposed to be removed or tampered with.

Also, please note, not all emission control items are "bad or will decrease performance. Positive Crankcase Ventilation (PCV) systems are good to have. Likewise the fuel evaporation control systems work well and do not rob horsepower from an engine. Some Thermal Vacuum Switches (TVS) units work well with engine vacuum advance systems, and in fact could be helpful in preventing engine overheating. I have a quick YouTube video explaining how those TVS units work, at the following web site:

I reckon my big question is what is the best way to open the engine to its full potential regarding timing. Because I run 87 or 93 in it usually. I know in the end of the last of the first generation the restricted the motors. Since it’s almost 50 years old I want to bring its performance up.
 

71coop

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I think mrgmhale's advice gets you off in that direction with a stock engine. My experience has also been that 10-12 degrees initial timing is a good baseline to start with when doing a performance timing curve on a stock motor. Make sure you pay attention to upper timing limits at higher RPMs.

Having your curve all in around 3K RPM is a good rule of thumb too. I would not go beyond 35/36 degrees max mechanical timing at 2800-3000 RPMs. If you have modern/aftermarket heads with efficient chamber design, you may need a little less. Play around with ported vs manifold and use whichever you engine likes. If you vacuum advance can is adjustable, make sure you keep the vacuum advance under 10 -12 on top of the initial/max mechanical timing.

Be prepared to play around with all of those "ballpark" settings - ONLY one at a time - to determine what your engine likes the most. Every engine is diferent and may repond differently, so be patient, make one change, drive the car, then adjust again, if needed. A dial-back timing light is a critical tool for this. My approach is to try to get those parameters into the ballpark like this:
  • Set initial mechanical advance
  • Adjust Max to 35/36 (if necessary, this can depend on the distributor setup)
  • Set rate of advance (springs in distributor)
  • Adjust amount vacuum advance (if it is adjustable)
  • Play with ported vs manifold
  • Drive and adjust one parameter at a time
 
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I think mrgmhale's advice gets you off in that direction with a stock engine. My experience has also been that 10-12 degrees initial timing is a good baseline to start with when doing a performance timing curve on a stock motor. Make sure you pay attention to upper timing limits at higher RPMs.

Having your curve all in around 3K RPM is a good rule of thumb too. I would not go beyond 35/36 degrees max mechanical timing at 2800-3000 RPMs. If you have modern/aftermarket heads with efficient chamber design, you may need a little less. Play around with ported vs manifold and use whichever you engine likes. If you vacuum advance can is adjustable, make sure you keep the vacuum advance under 10 -12 on top of the initial/max mechanical timing.

Be prepared to play around with all of those "ballpark" settings - ONLY one at a time - to determine what your engine likes the most. Every engine is diferent and may repond differently, so be patient, make one change, drive the car, then adjust again, if needed. A dial-back timing light is a critical tool for this. My approach is to try to get those parameters into the ballpark like this:
  • Set initial mechanical advance
  • Adjust Max to 35/36 (if necessary, this can depend on the distributor setup)
  • Set rate of advance (springs in distributor)
  • Adjust amount vacuum advance (if it is adjustable)
  • Play with ported vs manifold
  • Drive and adjust one parameter at a time
Good info and post 71coop.
I wasn't going to chime in on this as it's dealing with a 302 and I have no personal experience with 302's (other than my first Fastback in 1974 was a 302).
"Assuming" ( I hate that word!) your distributor is and will remain a stock Ford Autolite/Motorcraft, there is one HUGE part to look at and that is the slot plate. The width of the slot sets the amount of crank degrees that is on top of the initial number. e.g. 10 degrees initial with the slot plate in the 15L position, ( 15=30* on the crank) will add up to 10+ (15x2) 30 = a total mechanical advance of 40 degrees. That's too much as we know. This is why most base 351's and probably 302's had an initial of 6 degrees with a 15L slot, 6+30= 36 TMA and yes of course, back then emissions were a controlling factor. If your distributor has a 13L slot, that would be the one to use. That equals 10*+ 26* + 36 TMA which in turn equals pretty much the sweet spot.
Now, on my 351 4V M code 4 speed manual, it's sweet spot required a 10L slot (20* crank) plus 14 degrees initial for 34* TMA plus the vacuum can adds 4-6* on PORTED vacuum. The spring I have are 1 stock HEAVY spring set just loose and 1 Mr. Gasket 925D (I'm going from memory there??) set for all in around 3000rpm.
NOTE: I had to weld and recut an existing slot to make a 10L slot which is .410" wide. There is a quick fix for this and that is to add a small NYLON sleeve over the post and a 13L slot. This will cut the effective slot width and get the crank degrees lower, say around 22* at a guess.
Below is a pic of a slot plate and with a nylon sleeve.
EDIT: To change the slot you need to CAREFULLY punch out the roll pin on the dist. gear, but first MARK it so you replace it exactly as it came out. Make sure it is properly supported so as not to damage the shaft. While the shaft is out, insect for ware on it and bushing. Replace the bushing if needed or have it done. A reman distributor is an option if too bad.
 

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