Thread: Timing
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Old 07/13/2007, 10:46 AM   #2
robert campbell
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Location: Bremerton Washington
Joined: Apr 07
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Timing, as we all know, is critical to how each engine is built and how it runs. If you cam or carb them differently or add after market exhaust and such they engine will more than likely respond to a different approach to timing. Even stock engines will respond differently from engine to engine. I love the link that you posted and I did not know about! Another tool in the tool box!

I personally like to run as much initial timing as possible. The engine idles cleaner and creates more vacuum. Runs a bit cooler also. The downside is it is tougher on the starter during hot starts. But I have experienced little of that in 289’s and 302’s in stock to mile high performance builds.

My GT/CS has a 302-roller cam motor in it with Edlebrock RPM aluminum heads and intake. 670 Holley Street Avenger. JBA Shorty headers and 2 chamber “flows”. Cam is a crane retrofit roller in the .542 lift range. Mild lope, good vacuum and great mid range through top end. I am running a stock distributor with Pertronix ignition and coil. I run it a 12 BTDC degrees initial. No pinging great idle and power. Stock starter.

There are three types of timing. Initial, centrifugal/mechanical, and vacuum, on a stock application. One critical mark is total timing. The common mark for all V8’s is 38 degrees of total advance. Some can run a bit more some a bit less. 40/36. Every engine responds a bit different. Octane of gas will greatly affect these figures! To measure total, you either need a timing light with a degree dial, or a timing tape on the vibration damper. Tape is at any auto store that has some high performance stock. Get the engine warm and then with it in park and the e brake on, grab the carb linkage and run increase the rpm of the engine up to 3,000 RPM. You will watch the timing move as the RPM increase and the vacuum and mechanical throw in. Your goal is to set stuff up to get the 38 degrees total.

Now lets talk about ways to change the mecchanical advance. Try what the link says and then test it on your car with the light and see if it works. I think that would be a great way to alter a stock Ford distributor to shorten the mechanical advance to allow for more initial. Another way is change springs and weights. For that type of experimentation a “distributor machine” is best. Sunnen was and old company that made a machine you could drop your distributor in and customize the advance “curve”. Commonly called “recurving” your distributor. Some old hot rod shops still have them around.

Now lets talk vacuum advance. Many GT/CS cars have the dual diaphragm vacuum advance. They were part of the infant world of “smog” control. If you are not a purest, pull that distributor out and put in on the shelf. You can buy a replacement stock distributor for a 67 or 68 Mustang with a single diaphragm vacuum advance. The modern vacuum advance diaphragm has a stamp steel outer housing that is in the shape of a large hex nut towards the hose connection. You may already have this one in your engine. This type of diaphragm allows you to adjust the vacuum advance easily. Pull the hose off the diaphragm and insert a 3/32 allen wrench down the opening. You will engage an adjustment “screw”. Turning the wrench clockwise increases the amount of vacuum advance and adds to the total amount of advance. Turning counter clockwise decreases the amount of vacuum advance and decreases the total advance. The older “stock” Ford diaphragms have a removable nut on the end of the diaphragm that contains the hose connection. Removing this nut exposes a spring and spacers that can be altered to alter the advance. Lots of experimentation and a distributor machine is best.

So with this in mind you can increase the initial timing out to 10 or 12 and then decrease the total by turning the vacuum advance adjustment counter clockwise. Then you go for drives and see how it works. In an afternoon you may find a combination of more initial and less vacuum that works better. A dyno would be great for this. But you can do it seat of the pants. This is how I set up my GT/CS.

Do not let the car ping heavily under hard acceleration or hills. Also the type of gas is important. If you tune it running 92 and then grab some 87 it may not like you.

On my 67 with 13 to 1 compression and my 428 Cobra Jet in my 57 wagon with 11.7 to 1, I have Mallory unilights with no vacuum advance. I shorten up the mechanical and run them at 16 to 18 degrees BTDC and 40 total at 3,000 RPM. They are very radical and love lots of initial timing!

Another thought is ported and non-ported vacuum to the vacuum advance distributor. That will be another long response if anyone is interested. It can also help a car run cleaner and smoother at idle.

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