I recently acquired a 69 Z28. While detailing the engine I discovered the distributor could be rotated even though the lock down nut was tight. Turns out the bracket was not fully seated against the shaft. Anyways I figured I'd better check the timing. The first thing I notice after starting and warming the engine is the smoother idle. In checking the timing I find it set to four notches advanced. Gee, that's great since I now think it is set correctly to 4degress BTDC. Later on I pull out a maintenance manual and discover the notches are not 1 degree but 2 degrees. Feeling like a dumbass I go back and retard the timing to two notches BTDC. However, the idle does not feel as smooth. Additionally there is a stumble on acceleration from idle. Therefore I ask what is the correct interpretation of the timing notches.

There are several things to consider when setting your ignition timing.
1) What is the engine? and its compression ratio?
2)What is the ignition system? Stock Chevy with vacuum advance? or is it aftermarket and full mechanical advance?
3)Has anyone changed the curve in the distributor?
4)If stock Chevy with vacuum advance, did you disconnect the vacuum to dist. and plug it?
5)Is the engine idling low enough to not be getting into the mechanical part of advance in the dist.?
6) If you are in Colorado and at high altitude, you can advance the timing more and not get into detonation as easy as you would at sea level.
7)What octane gasoline are you using versus the compression ratio of the engine?
8)I'd go for whatever feels and works best for you. Personally, I'd put as much initial (base) into it as possible, and make sure it doesn't crank hard or detonate.
9) You might also find a timing light that has the adjustable knob at the rear so you could check total ignition timing at a given rpm, say 2500-3500rpm's. Depending on compression ratio and octane of gasoline and cubic inches you're running, you should be able to run around 32-38 degrees total. Hope this helps some. Feel free to ask me any other questions. Rick

'68 Camaro SS427
'66 Yenko #YS-100

One other thing I forgot : If its a point type ignition, you want to remember to set the gap or dwell on the points BEFORE you set the ignition timing as 1 affects the other. If it also has a solid lifter camshaft, you want to make sure the valves are properly lashed before trying to fine tune anything else. I learned from a shop teacher long ago to always remember PTC, Points, Timing, Carburation. This is the order that you do the adjusting in. Rick

The factory setting of 4 degrees BTDC was pretty lame. My Z ran better with 10-12 degrees of initial advance, without the vacuum line connected. Set it to where the idle and off idle performance is good, and there's no pinging on acceleration.

Thanks for the replies. I'm seeing the same results as Dave described. The idle and off idle is much better when the timing is set to 8 degress BTDC at 900 RPM and the distributor vacuum advance hose disconnected and the hose plugged. Note, as far as I know the engine is original along with the distributor, etc. The only modification has been the addition of headers.

With 8 degrees of inital advance, what is your total timing running at? Say at 3000 rpm?

The reason that I ask is that I have been fighting a pinging problem with anything over 2-4 deg BTDC initial timing. My total timing is swinging to 36-38 deg at 2900 RPM.

[This message has been edited by mccorry (edited 11-30-99).]

mccorry
I set the timing Monday night (11/28) and took it for about a 10 mile ride. Didn't notice any pinging. Note, my garage is at an altitude of 7500 feet. Anyways I'll get back with any new information in a week or so. Got a snow storm coming in so I washed the car and put it away for some hibernation. This car is not going to see rain, let alone snow.
Colorado

Rule of thumb for early small blocks. Four degrees for two barrel engines, eight for four barrel engines, twelve for performance in any engine. Vacuum advance unhooked for setting timing.

If I run 8 deg initial advance, my total timing at 2800RPM swings all the way to 38 deg. Ping city.

I have switched springs and weights, but can't seem to get the excessive advance under control. Have to run TDC timing to get it to stop pinging. Any ideas? It is a stock 111169 dist. with points.

38 Degrees is way too much, I'd ping, too. To limit the advance, you have to limit the movement of the weights, by using weights with a different shape, or putting bushings on the limit stops in the distributor. Best bet would be to pull the distributor and have a speed shop with a machine check it and dail it in. You may have a wear problem, too.

I just want to know what you guys with 11:1 Compression 302's are running for gasoline? What octane is it? I know I owned a '69 Torino with a 351W 4barrel 290hp. 10.7:1 compression engine. This was in 1987. I found that at stock timing specs., with 92 octane premium, it would detonate alot. Retard timing to eliminate detonation = lost power and very lazy. I ended up buying an Edelbrock Vara-Jection water injection unit. I mixed 50/50 distilled water and alcohol. If you use tap water the brass nozzle will plug up. After adding this unit, I could run stock timing specs. and 87 octane gasoline. It ran great. Me and my Father drove the car to the Bonneville Salt flats, 650 miles in 9.5 hours. While driving at this pace the car averaged 20 m.p.g. for the trip. Through one tank I got 21.6 m.p.g. This was a 4000lb. car also. I think the Vara-Jection is a great unit. I don't work for Edelbrock either!! If I were to run a high compression engine on the street again, this would be my cure for detonation and save from buying $$$$ High Octane race gasoline. Rick
'68 Camaro SS 427
'66 Yenko Stinger #YS-100