Anyone happen to know what a good mostly stock street 300 six Duraspark II spark curve should be for best performance?
By this i mean:
(1) how much initial timing is a good setting?
(2) how much centrifugal advance should it have?
(3) at what RPM should it start coming in and when should it be all in?
(4) how much vacuum advance is correct and when should it start coming in and when should it all be in?
My truck weighs 3000 lbs and is not used for hauling. I am at sea level.
Many thanks to all...jack

 

The answer to any and/or all those depend on the vicissitudes of that particular engine, your manner of driving, the use you will put it too, etc...many other variables to deal with. In other words, there is no one-size-fits-all answer. Try starting here: Classic Inlines - Duraspark II Swap.
and here: http://www.gofastforless.com/ignition/advance.htm
and here:http://www.carbdford.com/viewtopic.php?t=5543

 

x2 on what Harte3 said...

but to get you at least in the ballpark-
~36 degrees mechanical advance, in by 2500-3000 rpm

how much of that is initial vs centrifugal will depend entirely on what your options are under the breaker plate (10L slot, 13L, 15L, 18L, etc).

you'll have to crack it open to find out.

 

UR best return for high RPM/Power return is camshaft lift/duration and dual plane intake manifold while still returning some midrange torque. Engine/ignition timing advancement/modifications, without addressing those first will mostly be a waste. The motors with VVT will jump the cam timing and ignition timing all the way to as high as 40 degrees +. Course they are overhead cam motors with multiple sensor signals to the ECU, much faster reactions to engine detonation or pinging. These 2 items are very costly to piston/head life. A new distributor would be the best return on investment/street performance of the old swayback truck, giving it life again.

http://www.reincarnation-automotive....ons_index.html


The following photo is a late 60's Ford distributor, with the breaker plate, springs, and weights removed. Not all Ford distributors are built this way. You will need to examine your engine's distributor to check for this feature.

As you can see, the slot labeled "15L" is engaged on the limit pin. This distributor is set up to provide 30 crank degrees of mechanical advance. It is 30 degrees of crank advance, because the distributor turns at half the speed of the crank, and whatever you do with the distributor, in degrees, is doubled on the crank.
On this next photo, the little clip beneath the rotor has been removed, and the breaker cam has been lifted up and rotated 180 degrees so that the "10L" slot is engaged on the limit pin.

This distributor now provides the engine with 20 degrees of mechanical advance at the crank.

IMPORTANT!!!
In order to perform this modification, the distributor must be removed from the engine, because moving the breaker cam 180 degrees to accomplish this task also moves the rotor 180 degrees, and the engine will be out of time. You must lift the distributor up enough to clear the cam gear, and rotate the whole rotating assembly by 180 degrees to get the rotor back to where it should be. Once you have reset the timing limiter, reinstall the clip that holds the point cam on the shaft, the advance weights, springs, and breaker plate. Restart the engine, and give it 12-15 degrees of advance at idle, and go for a spin. If it pings at high rpm, you may need to retard the timing a bit. You also may need to lengthen the 10L slot to provide a bit more advance at high rpm, but I think you'll be quite happy with the 10L slot as is.

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I'm not sure I agree- tweaking the ignition timing is FREE. very hard to beat that kind of return on investment.

to add to the links that Harte shared:
FORDMUSCLE webmagazine: Timing is Everything - Distributor Curving for Maximum Power

 

I assume once you turn the distributor 180, you have to change the plug wire order too

 

Papa Tiger mentions removing the distributor from the motor to do this, exactly to prevent this situation.
Pull the distributor, make the change, then you can drop it back into its original position.

Word of warning- the little c-clip you have to deal with to perform this operation is a GIANT pita.
Have some good needle-nose pliers ready, or maybe some surgical clamps.

 

So if I rotate the distributor the rotor button was pointing (red) number one, will be pointing at green number 1. I would not move the number one plug wire to the terminal that it is now in front of button? It’s at TDC in photo.

 

1. Rotate the engine to TDC, rotor pointing to #1 spark plug wire.
2. Remove the distributor, and disassemble.
3. Make the change to the weights, and reassemble.
4. Re-install the distributor with rotor pointing to #1 spark plug wire.

The position of #1 will not change, and neither will the spark plug wires.

 

��Ok thanks for replies and clearing it up for me, distributor was already out and I’ve read about wire rotation, but now I figure they didn’t rotate distributor but moved the wires out of order.

 

You can move the wires out of order, so long as the firing order is correct. The engine nor the distributor doesn't care, so long as there is clearance for the distributor itself to rotate when setting the timing.

A lot of people get hung up on the initial timing setting. It's the whole package that you're interested in. The only way to know is to run it up in neutral with a light and see where the mechanical (centrifugal) advance weights tops out at. The vacuum advance is always disconnected and plugged so as not to skew the reading on the damper. Even if you're not a drag racer you pretty much want as much advance as it will stand at all times, for best efficiency. If you're fussy you may well want to get inside the distributor and limit the amount of mechanical advance. This allows for a higher initial advance without too much on the far end. OEM advance curves were usually very slow curve and stiff. Somewhere between 10° and 15° initial and between 34° to 38° "total" mechanical is what you want to see. When you get it dialed in after a few test drives, engine starts well when hot (no kickback) then re-connect vacuum advance. These vaccuum cans are adjustable. It's important not to mess with the mechanical advance once that part of the curve has been optimized. If the vacuum advance is bringing in too much advance on the far end at part throttle then that is what needs adjusting, not the initial timing. Unless you are drag racing you always want vacuum advance, engine will run a lot cooler in hot weather and it adds better driveability. Plus about 15% better fuel economy.

 

Contact this man. He hangs out on the Fordsix Performance Forum and has an excellent reputation for re-curving distributors. He goes by: WSA111 on that forum.

billythedistributorman@live.com

 

Tedster is totally right on all points.

I try to keep the wires in stock location to minimize time spent troubleshooting (because my memory sucks and i'll forget that i moved them.)

 

Duraspark_distributor_recurve_instructions_index

Lots of recurving info there...

 

is if U have an ol Sun (dizzy recurve) machine U can dial it in perfect.
I agree w/everything said above but...using a Mr Gasket kit, tearing it apart, bending ur 'tabs', etc, etc.
Gather all the effecting factors together (use/application/80% of driving conditions, cam specs, carb, etc) & send it out to bill at ford six (see the fantastic resource cited above, it just another spot like this 1 here) or Farron, also on that site. But...have a tip top tune on 1st. Ur probs might B elsewhere. This is a final, cream w/a cherry on top.