The issue is that this is one area I have never really understood. I can set the timing with a timing light but after read bits and pieces here I am sure I am missing something. Just hooking to cyl. #1 and shooting the balancer and moving distributor housing until the line flashs at about 6 degress BTDC is all I ve ever done. I ve worked on cars for years and even was a driveablity tech for Ford for years. I am embarrasest to say that I still don't know how to time an engine. I know there are weights inside the distributor and different springs will change the speed of the timing advance, but how do you measure total advance with out reving the engine to the max and dialing back the timing to zero the see the total. (I know this is not how its done, I just trying to so my ignorance in the area)
A brief outline or a link to how it is done for idiots would be great. A great book for me would be "Timing of Dummies)

_________________
67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Timing for Dummies
Another great book "Spelling for Dummies"

_________________
67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Timing by Dummies
By Reed

There are four main areas to consider when you are going to set up a custom distributor. (1) initial advance, (2) mechanical advance), (3) vacuum advance, (4) total advance. Total advance is perhaps the most important since this is the variable to which you ultimately calibrate the initial, mechanical, and vacuum advance variables. Slant sixes generally like a total advance setting of 32 BTDC by 2-2500 RPM (somebody correct me if I am wrong on this please).

Proper configuration of a distributor timing advance curve requires balancing of the first three variables.

(1) initial advance (also known as curb/idle timing). Initial advance is determined simply from the relationship between the rotor and the cap. This is the timing you set by turning the distributor housing.
Slant sixes came from the factory with base initial advance settings from TDC to 12 BTDC, there were even some smog motors that had timing setting ATDC. The proper setting for the initial base timing is largely determined by your selection of parts for the vacuum advance and the mechanical advance.

(2) Mechanical advance- Mechanical advance is a system of advancing the timing of the engine as engine RPM increases. This is accomplished by the use of weights, springs, and a slotted governor inside the distributor.

At idle, the distributor is rotating at about 750 RPM. Inside the distributor are a pair of weights , each weight being attached to a spring. The weights have a little peg on them which fits into a slot on the governor above. As engine RPM is increase, centripetal force makes the weights move outwards. As the weights move outwards, the peg on the weights slides in the slot in the governor and makes the governor turn the pickup plate in the distributor counter-clockwise, thus advancing the timing. The springs attached to the weights control the rate at which the weights will move outwards. Otherwise, the weight would just slam fully outwards as soon as you turn the engine on. The slots in the governor determin how much the weights will advance the timing.

Mechanical advance is therefore controlled by three variables, two of which are easily controllable. The first is the springs, the second is the governor, and the third is the weights. The weights are more difficult to work with since changing the weight of the weights is a more difficult variable to control and its effect on the timing advance is more difficult to quantify. it is far easier to replace the springs and replace the governor.

Distributor advance springs come in two main types- the heavy spring and the light spring. These springs are so named because the heavy spring is thicker and provides more resistance and the lighter spring is lighter and provides less resistance.

Changing the springs will change both the rate the weight will move and advance the timing and also the RPM at which the weights will start moving. Different thickness of weights are available from junkyard distributors and aftermarket suppliers.

The governor controls the total amount of mechanical advance which the weights will provide. The governor is stamped with a number indicating how much mechanical advance is allowed. Most governors are also stamped with a R. This is unimportant. It is essential to remember that this number must be doubled to convert it to the number of crankshaft degrees the timing will be advanced. For example, a governor stamed 9R will give 18 degrees of crankshaft advance. A governor stamped 12R will give 24 degrees crankshaft advance.

The total mechanical advance must be balanced with the initial advance to make sure that the initial advance plus the mechanical advance does not equal greater than the desired total advance. Or, intial+mechanical=32.

(3) Vacuum advance- Vacuum advance is a very helpful and desireable feature on a street driven car because it will improve both performance and fuel economy. The vacuum advance is controlled by the vacuum in the manifold. There should be no vacuum advance at idle, but as soon as the throttle is opened there should be full manifold vacuum supplied.

Vacuum advance allows for the advance of the timing based on engine vacuum. This is most useful in immediate off idle performance and light throttle cruising situations. Vacuum advance allows the timing to be advanced to where the motor will make more power, but before the mechancial advance alone will advance the timing to that point. As RPM increases the manifold vacuum generally will decrease thus reducing vacuum advance. but at the same time the mechanical advance is kicking and will keep the timing advanced where you need it. At light throttle highway cruise you actually will have high manifold vacuum which will advance the timing even more and provide better fuel economy.

Similar to the governor, most vacuum can arms are stamped with a number indicating degrees of advance, but this also needs to be doubled (11r arm = 22 degrees of advance). In addition to the amount of advance allowed, vacuum advance cans can also be adjusted in terms of at what vacuum reading the vacuum advance will begin. This is accomplished bu inserting the proper sized allen's or hex head wrench into the vacuum nipple on the advance can and turning it. (someone else jump in here with regards to which way = more or less advance and the proper size of wrench).

Too much vacuum advance can lead to pinging on unphill acceleration or at highway cruise. Similar to mechanical advance, vacuum advance my be calibrated with initial advance to avoid advancing beyond desired total advance.


So how do you use all this info?

First, pick the total advance past which you don't want your engine to go. This is your determinig factor. After that, you lookat your governor and the vacuum advance arm to see how much initial advance you can run. For example, assume you want 32 degree total advance and you have a governor stamped 9R. This means you can run 14 degrees initial timing. (18 mechanical advance+14 initial = 32 total). After you get initial advancre and total advance determined, you must slect the advance springs by trial and error and seat of your pants feel.

Total advance can be measured in two ways: with a dial back timing light or by marking the crank dampener. Remember, when measuring the total advance you must disconnect the vacuum advance. If you are going to measure total advance by using the crank dampener, set the dampener to TDC and using white paint or white out mark TDC on the timing tab and 5BTDC and 10 BTDC on the dampener. Rotate the dampener so the 10 BTDC mark is equal to the TDC mark and them mark the dampener at 15 and 20 BTDC. Do this again to get 25, 30, and 35 BTDC. This way you can use a normal timing light but still measure total advance faily accurately.

It is more important to get the mechanical advance curve established than it is to get the vacuum advance established, so do the mechanical advance first. Once you have the mechanical advance where you like, hook the vacuum advance up and begin tuning that.

I didn't go into the technique of selecting the advance curve. I am sure other folks can tell you how to do that.

I hope this helps.