Sir read your brief and have some questions (in bold).
Vehicle in question is 68 L-79 Vette, 4spd, 3.07. Still has OEM dual point tach drive with Mallory blaster coil and Eldebrock model 1400, 650 mech secondary carb.

All questions will be assumed using non-adjustable timing light.

How to Set Your Timing for Peak Performance
by Lars Grimsrud
SVE Automotive Restoration
Musclecar, Collector & Exotic Auto Repair & Restoration
Broomfield, CO Rev. A 2-7-01

This tech paper will discuss setting the timing on a Chevy V8. This procedure also applies to other GM V8s.
The procedure outlined here differs from the Service Manual, and is based on my years of experience doing this work in the quickest, least painful, most economical way while keeping the level of quality high. It is recognized that other people will have different methods of doing things, and may disagree with specific methods and procedures that I use.

How to Set the Timing
When you think about it, setting the timing at idle speed makes no sense at all: You don’t operate your car at idle, and timing changes as the rpm changes. Fact is, the timing spec at idle speed is provided as a simple way for most people to set the timing, and is not a good procedure for optimum performance.
Small block Chevys (and most other GM performance V8 engines) perform best when the total timing (full centrifugal advance plus the initial timing setting with vacuum advance disconnected) is all in by 2,500 – 2,800 rpm and is set to 36 – 38 degrees. If you have an adjustable timing light, this is very easy to check. If you don’t, you need to scribe a 36-degree mark on your harmonic balancer. Here’s how:
Measure the circumference of your harmonic balancer using a sewing tape measure (or other flexible tape measure). Get it as accurate as you can. Take this measurement and divide by 10. The number you get is the distance to 36 degrees. Measure this distance CLOCKWISE from your existing harmonic balancer timing mark and place a clear mark on the balancer.

1. Once I have used the measuring tape on the circumference of the balancer and DIVIDED THAT NUMBER BY 10 do I go clockwise, more BTDC, as LOOKING FROM NOSE TO REAR OF CAR and then mark 36 degrees on the balancer? Will that new mark be the lone/ only mark I will refer to when setting timing whether 2,500 to 2,800 RPM or at idle curb speed. In other words the stock 0 degree mark on the balancer will no longer be of use to me for timing issues?

Remove your distributor cap and rotor. Remove the 2 centrifugal advance springs. Install the rotor and the cap (without the springs). Disconnect the vacuum advance.

2. Reference to vacuum advance disconnected means line pinched or plugged not actually disconnecting linkage inside distributor correct?


Start the engine. It may kick back a little due to the advance coming in immediately without the springs. If you’re using an adjustable timing light, set the light to 36 degrees advanced. Now rev the engine just a little while observing the timing marks with the light. It shouldn’t take much rpm to peg out the advance without the springs installed. With an adjustable light set at 36 degrees, align the stock timing marks with “0” when the timing is “pegged out.” With the non-adjustable light, align your new 36-degree mark with “0.”

3. With springs removed, vac advance disconnected running car to find where timing "pegs out" and reset timing to zero. Okay lets pretend that timing "pegs out" at 2100 RPM. Using new 36-degree mark I line that mark up to zero on the pointer while maintaining the car at 2100 RPM. As both hands are engaged with timing light/ distributor adjustment obviously an "assistant" is required here. Do you have assistant keep RPM steady using gas pedal or carb holding linkage? Any small movement by assistant or variation of a few RPM's will throw off timing. How did you do it?


Rev the engine a little to make sure the timing will not advance any further. Shut it down.
Pop the cap and rotor and re-install the springs. Put everything back together, but leave the vacuum disconnected. Start it up. For future reference, make a note of the timing setting at idle. This is your new curb idle timing spec. Now give the engine a few quick rev’s past 3,000 rpm and verify that the full timing (36 degrees) is coming in. If it’s not, you need to change to a softer set of springs until you get full 36-degree advance before 3000 rpm. (NOTE: A stock set of springs will usually not allow full centrifugal advance to come in before redline rpm. If you have stock springs installed, don’t rev the engine beyond its limits to try to force full advance in.)

4. Once total timing set I then re-install springs but leave vac. advance still disconnected to see if timing fully comes in 36 degrees before 3000 RPM. Again is this measured with the new 36-degree mark I made on the balancer? Is it okay to mix/ match springs? The shop that did my last Vette got advance in quickest with one blue one silver. Or is matching set the way to go?

Shut it down and hook up the vacuum. Now do a road test.
The 36-degree 2500 rpm advance curve is optimum for performance, but may require premium fuel. Lug the car around, and punch the throttle at low rpm while listening for detonation (“engine knock”). If you’re getting any audible knock, you MUST retard the timing. Retard the timing in 2-degree increments until engine knock stops. Engine knock will seriously damage engine components if not corrected. If you get no knock, you may see slightly improved performance at 38 degrees total timing. This is particularly true if you’re running at high altitude.

5. Now road test. with vac. advance re-connected I WOT from slow speeds to see if knock occurs. If knock does occur I retard timing 2 degrees. If I understand right retard timing 2 degree going more BTDC (clockwise looking FROM NOSE TO REAR OF CAR)

If you have no engine knock under acceleration, but the car “chugs” or “jerks” at cruising speed (light throttle application), you are getting too much vacuum advance on top of the mechanical advance. You may need to change out the vacuum advance diaphragm with an adjustable unit available from aftermarket sources. Adjust these units so that you get the most vacuum advance possible without any “chugging” or “jerking” at cruise speed.
Your timing is now set for best possible performance. Make note of the new setting, and use this for your future tune-up work.

Questions, Comments & Technical Assistance
If you have questions or comments regarding this article, or if you notice any errors that need to be corrected (which is quite possible since I’m writing this from memory…), please feel free to drop me an e-mail. Also, if you need any technical assistance or advice regarding this process, or other maintenance issues, feel free to contact me:

lars.grimsrud@lmco.com

 

Cali... you mean to tell me you cant get an adjustable timing light.
TTT

 

Sears sells them. (craftsman) They have a **** on the back to advance the flas so you can read it at the "0" mark. Worth the extra money.

 

Oh I can get one but I have a brand new non-adjustable I just bought before the 77 got crushed and used it for maybe 10 minutes. If I have to expend close to $100 in tools, light plus dweel meter I might as well take it to a professional. However I want to actually learn this stuff.


[Modified by Cali,68,L-79, 6:13 PM 11/13/2003]

 

Sorry Im not trying to change your topic... hehe... just wanted to keep you flying high till someone a little better suited to answer your questions caught it. TTT again! :cheers:

 

1. Yes, clockwise as viewed from the front of the engine. The TDC mark can still be used to set initial timing if you want to or if you're just curious as to what your initial is after setting total.

2. Disconnect vacuum line from canister and plug it. Nothing need to be done inside the distributor.

3. You can just turn the idle speed screw up until the timing marks stop moving. As long as rpm is at or above the point where total advance is achieved, it's not critical. Loosen the distributor just enough to turn with some pressure, but not loose enough to turn by itself. With timing light in left hand and right hand on distributor (watch out for the wires or you'll get zapped), turn distributor until the marks line up. Shut off engine, tighten down distributor, reinstall springs, recheck timing to make sure distributor didn't move while tightening.

4. Yes, increase rpm until marks no longer move (use idle speed screw if no assistant) and verify that the new mark aligns with 0º on the tab. If not, readjust so that it does. It's ok to mix springs if needed to get the curve you want. Once you have set total, changing springs will only affect the rate of advance and the rpm that is it reached but not how much.

5. To reduce timing 2º, disconnect vacuum advance, hook up timing light, start engine and let idle. Observe timing. Turn distributor until the timing mark has moved one notch towards you on the timing tab. Each mark indicates 2º. Pinging is probably less likely at wot than at partial throttle. Pinging might be the result of adance coming in too soon, too much total advance, or too much vacuum advance. If you do get pinging, make another post and describe the conditions in which it occurs and we will deal with it then.

 

Okay then I'm moving the timing from what ever setting lets say 18 degress BTDC to say 16 degrees, in other words the timing mark is going towards me, clockwise as seen from the front of the car or left front fender and going from say 18 BTDC to 16 BTDC correct?

Thanks

David

:cheers:

 

Yes, that's correct. Most tabs don't read past about 12-14 degrees so in your example you'd be guessing about 16-18 unless you used a timing tape or an adjustable light. Until you've established how much centrifugal advance you distributor is providing it's a moot point though. For example, if you are getting 26º centrifugal, setting total at 36º would put initial at 10º and that would still be within the range shown on the tab. To determine your true initial after setting total, check initial with the idle set a low as possibile. If the idle is high enough, and especially with light springs, centrifugal may have already started and you'll get a bogus reading. If you do find that optimum total results in too much or too little initial, you'll need to modify the amount of centrifugal the distributor provides. I think once you start playing with your timing and see how the marks move and such you'll understand it a lot easier.