Ignition timing:
Traditionally the Cleveland is set up with 20° of centrifugal advance, mostly because that was the least amount of centrifugal advance that could be attained with unmodified factory parts.
Ford of that era had two centrifugal advance cam plates, one marked 10L/15L and one marked 13L/18L. Using the smallest choice, marked 10L, resulted in 20° of centrifugal advance. Adding 16° to 18° of initial advance as recommended by Ford resulted in total ignition advance in the range of 36° to 38°. In 1970 they recommended having the advance curve all in by 3000 rpm (street motors) and in 1972 they recommended having the centrifugal advance all in by 2000 rpm (race motors).
The Cleveland generally likes lots of initial advance; I've found many engines would tolerate more than 18°. It is possible to modify a Ford cam plate, or to set up an aftermarket distributor for less than 20° of centrifugal advance, and dial in the "optimum" amount of initial advance. But too much initial advance will often make a motor difficult to crank-over when it’s hot, especially motors with lots of compression. So 16° to 18° is advanced enough for good low rpm pep and good vacuum at idle, without making the motor difficult to start when it’s hot, and doesn't require modification of a cam plate if you're using a Ford distributor.
That's more or less the logic behind Ford's settings.
Ford’s recommendation for 36° to 38° total ignition advance is a generally good recommendation for motors equipped with factory iron heads, flat top pistons and a reasonably “normal” amount of clearance between the piston’s dome and the cylinder head (i.e. squish); normal being in the range of 0.050” to 0.075” total clearance (total clearance = deck clearance plus compressed head gasket thickness). Motors equipped with piston’s having pop-up domes will usually require more total ignition advance, motors that have been zero decked and equipped with dished pistons will usually require less total ignition advance, and motors equipped with modern alloy heads having high swirl combustion chambers will also require less total ignition advance. Optimum “total” ignition advance is best determined on a dyno however.
It is possible to determine the “optimum” advance at idle if the marks on the crankshaft damper are reasonably accurate. Here’s how:
(A) Connect a manifold vacuum gauge, an accurate tachometer or an exhaust gas temperature (EGT) gauge to the motor. Leave the vacuum advance hose connected if the motor has vacuum advance. Loosen the distributor clamp bolt if the motor is equipped with a distributor, start the motor and allow it to warm up to full operating temperature.
(B) While the motor is running at idle speed in neutral (manual transmission) or in drive with an assistant firmly pressing on the brake pedal (automatic transmission), and assuming the initial advance is in a retarded setting; begin slowly turning the distributor clockwise to advance the initial advance setting. As you do the idle speed shall increase, the intake manifold vacuum shall increase and the EGT shall decrease.
(C) Continue advancing the initial advance until it reaches the setting where idle speed no longer increases, manifold vacuum no longer increases or EGT no longer decreases. The setting where the readings first stabilize is the optimum initial advance setting.
(D) You can tighten the distributor clamp bolt and leave it at this setting, or return it to the previous setting.
(E) If you leave the distributor at the new “optimum” setting, the idle speed will need to be readjusted (lowered) to the rpm where you normally set the motor’s idle; and the amount of centrifugal advance will require adjustment (less centrifugal advance) to attain the proper total advance.
High compression motors often have trouble hot starting with the ignition set at optimum initial advance. If your motor will not hot start after setting the initial advance as described above you have three choices to resolve the problem:
(A) Install a new or more powerful starter and/or a battery with more cranking amperage
(B) Install an ignition module that retards the ignition during starting
(C) Set the ignition for less initial advance and compensate by increasing the centrifugal advance.
Street motors should utilize vacuum advance for optimum efficiency during part throttle (high intake manifold vacuum) operation. Vacuum advance will more than improve fuel economy, it will prevent burning up the exhaust system during partial throttle (high manifold vacuum) cruising. The general consensus is to limit vacuum advance to about 10° to 12°.
I prefer not to enter into a debate over the superiority of either ported vacuum or manifold vacuum, rather I prefer to state that either method can be used, each has its advantages, the auto manufacturers used both. I think it’s important to keep in mind the sole reason the ported vacuum connection is provided on carburetors is to control the ignition’s vacuum advance, automotive engineers and carburetor manufacturers obviously think ported vacuum has merit. To state that only motors with emissions controls used ported vacuum is historically in error.
Ported vacuum sets a higher limit to how low the advance will be retarded under low rpm/low manifold vacuum conditions; it allows a race motor type ignition calibration while taking advantage of vacuum advance for cruising (high manifold vacuum, part throttle) conditions. It is the method I prefer and the method recommended by aftermarket ignition manufacturers such as MSD. This method results in peppier throttle response. Since there is no "ported vacuum" at idle, the ignition timing is not worsened by a lumpy idling camshaft. It should never cause a problem if a car is geared low enough and if a motor is in a good state of tune. However, the manifold vacuum method is useful when a high compression motor has trouble hot starting using the ported vacuum method, because the static/initial advance is significantly retarded. It is also useful for high geared or heavy vehicle applications in which the motor "pings" with the ignition tuned for ported vacuum.
For example:
Assuming a motor's optimum total advance is 36°, its optimum advance at idle is 16°, its vacuum advance is limited to 10°, and it idles at 1000 rpm.
Ported vacuum:
- 16° initial advance + 20° centrifugal advance = 36° total
- Centrifugal advance curve starts at 1200 rpm, ends at 2800 rpm (10° per 800 rpm)
- Advance at idle = 16° (16° initial setting, no vacuum advance)
- Advance gain above idle is a combination of centrifugal advance plus vacuum advance
- The vacuum mechanism always supplements total advance
Manifold Vacuum:
- 6° initial advance + 30° centrifugal advance = 36° total
- Centrifugal advance curve starts at 1200 rpm, ends at 3600 rpm (10° per 800 rpm)
- Advance at idle = 16° (6° initial plus 10° vacuum advance)
- Advance gain above idle is solely due to centrifugal advance
- The vacuum mechanism can either supplement or diminish total advance under various engine speeds and loads
Ignition advance can actually take a "dip" at throttle tip-in using the manifold vacuum method, because manifold vacuum will dip when the butterflies open; ignition advance will increase at throttle tip-in using the ported vacuum method, because ported vacuum is “zero” at idle and begins increasing as the butterflies open. This is why ported vacuum provides peppier throttle response. As motor speed increases the centrifugal mechanism increases advance while decreasing manifold vacuum results in the vacuum mechanism decreasing advance, therefore the advance mechanisms oppose one another using the manifold vacuum method, resulting in less advance during part throttle cruising compared to the ported vacuum method.
Here’s a universal ignition calibration for iron heads & flat top pistons based on Ford’s recommendation:
- 16° to 18° initial (i.e. static) advance
- 20° centrifugal advance
- 16° to 18° initial advance + 20° centrifugal advance = 36° to 38° total
- The centrifugal advance curve should start advancing a few hundred rpm above the motors idle rpm. I'm assuming the motors idle will be set around 800 rpm +/- 200 rpm.
- Centrifugal advance curve = 10° per 800 rpm to 10° per 1000 rpm. If the curve starts at about 1200 engine rpm it should end at 2800 to 3200 engine rpm
- Use ported vacuum for the vacuum advance
- Vacuum advance should be limited to about 10°
- Advance at idle = 16° to 18° due to the initial advance setting, there is no vacuum advance at idle with ported vacuum
Donor motors for a 351C compatible Ford Duraspark distributor are 1975 through 1982 351M, 400 or 460 V8s. The distributor’s centrifugal advance curve will require re-calibration.
To achieve a 20° advance curve the Ford distributor will require a 10°/15° centrifugal advance cam assembly (#C5AZ-12210-B; stamped 10L-15L) installed in the 10° position, and new advance springs from either Mr. Gasket (kit #925D) or Crane Cams (kit #99607-1). The Mr. Gasket kit includes one pair of springs, the Crane Cams kit includes 3 pairs of springs AND an adjustable vacuum advance canister. The Crane Cams kit is obviously the way to go as it will allow you to adjust the vacuum advance as well as the centrifugal advance.
The magnetically triggered MSD #8477 distributor is superior to the Ford distributor in my opinion; it is made of billet aluminum, it has better shaft bearings, and it has a centrifugal advance mechanism that will operate smoother and more accurately for a longer time than the advance mechanism in a Ford distributor. The MSD magnetic trigger is compatible with the Duraspark modules; the wires even have the same color coding. It is easier for the home mechanic to adjust the MSD centrifugal advance mechanism and the narrower/taller distributor has fewer intake manifold clearance issues.
To achieve a 20° centrifugal advance curve that is all in by 3000 rpm with an MSD distributor use the blue stop bushing and 2 blue springs included with the distributor.
Radiator fans & switches:
The replacement Pantera radiators sold by Hall Pantera and Fluidyne have one M22 fitting in the lower radiator inlet tank and one M22 fitting in the upper radiator outlet tank for fan control switches, one switch is used to control each radiator fan instead of controlling both fans with one switch. This is the same design as the OEM radiator. It is the experience of many owners that once the coolant temperature stabilizes one or both fans will run continuously, even when the car is traveling non-stop at cruise speed. If the engine is in a good state of tune and the cooling system is in good condition and vented properly the fans should turn-off completely when the vehicle cruises non-stop at higher speed. Constant running indicates (1) the motor is in a bad state of tune, (2) the cooling system has a problem, or (3) the reset setting of the fan switches is too low.
The M22 threaded fan switches used in the Pantera radiator tanks are a common style of temperature switch for controlling electric radiator fans in older European vehicles. They are manufactured by many aftermarket parts companies; Wahler and Intermotor are two companies whose switches are frequently used in motorsports because information regarding the settings of their various switches are readily available. The settings of the fan switches are expressed by two temperatures, such as 92°/87°; these temperatures are in degrees Celsius. The higher number is the temperature at which the switch closes its contacts to turn the fan on; the lower number is the temperature at which the switch resets (i.e. re-opens its contacts) to turn the fan off.
There is no reason to use individual temp switches for controlling the cooling fans. I recommend utilizing only one fan switch installed in the lower (i.e. inlet) tank to control both fan relays; this shall cycle the fans off and on simultaneously. Plug the M22 bung in the upper tank with an unused switch or an M22 plug. The ideal switch mounted in the lower tank, for use with a 192°F (89°C) thermostat is an Intermotor #50104 which has settings of 97°/92°. The ideal switch for use with a 180°F (82°C) thermostat will have settings of 90°/85°; however I am not aware of a switch with these settings having M22 threads. Alternative switches having M22 threads but slightly higher settings (92°/87°) are a Wahler #823.959.481.F or an Intermotor #50200.
-G