Hey guys, I just set my ignition timing for the first time and I want to make sure I did it right. I have a Goodwrench 350 crate motor, and I was using a digital dial-back timing light.


First I let the car warm up and idle down (idles around 750 rpm). Then I loosened the distributor bolt and removed and plugged the vacuum line.


I then set my timing light at 10 degrees (I got this number as a good initial ignition timing setting off of a couple google searches. Is this a good setting for idle timing?) and aimed it at the crank pulley. Then I adjusted the distributor until the "0" mark on the pulley lined up with the pointer on the engine.


Then I set my timing light to 35 degrees (again, this is a number I found through some google searching as a good total timing number) and reved the engine up to 3000 rpm. Then I again adjusted the distributor until the "0" mark on the crank pulley lined up with the pointer on the engine.


Does that all sound correct?

 

Yes and no.

Yes, you did it correctly.

No, by doing it twice (at 750rpm and 3000rpm) you basically eliminated your idle setting of 10*.

By setting the timing to 35*@3000rpm (which is good), the timing at idle will fall where ever it needs to be based on your mechanical advance timing curve.

What you should do is, set the timing at idle (10*), then have someone hold the throttle at 2k, 3k, 4k, 5k rpm and check the timing at each interval. At each rpm level you will turn the dial on the timing light, to align the timing mark at "0" and record what the timing is. You need to go past 3k rpm to see if the mechanical springs are still stretching (advancing the timing). If they are, you need to use a lighter set of springs. The goal is to get all of the mechanical timing in (springs fully stretched out) by 3k rpm. Once you establish that, you set the timing to 35*@ 3k rpm and idle timing could be anywhere from 8* to 14*, it really doesn't matter.

 

That was actually my next question, I was wondering what the point of setting initial timing was if I was going to be turning the distributor more once I set the Total Timing. Thanks for clearing that up!

 

I would not be standing next to an engine revving to 5000 rpm though. I'd just check to see if the timing is still moving at 3000. if it is, then you could change the springs to lower the rpm that the mechanical advance stops advancing.

 

How does it run after you set the timing?

 

Honestly it runs about the same, the timing was fairly close.

That brings up my next question: how do you determine optimum ignition timing for your engine? I got that 35 degree number from a couple google searches, but some people reccomend more and some less. How do i figure out whats right for my motor?

 

Great question. I think vacuum can be used but I dont know how its done. Hopefully an expert can help us both out here.

 

email Lars and ask for his timing papers, they are the best.

 

Thanks for the great insight here! I was just searching this topic last night because I am not sure if my old original springs are doing the job.

 

The optimum timing is basically - keep advancing the timing until it starts to ping/detonate, then reduce the timing by 2*.

 

At idle?

 

Yes and No.

First you need to get the proper spring configuration set up so the mechanical timing is all in by 3000 rpm. Then set the timing to 35*@3k rpm. Once you have done that, the idle timing can be anywhere from 8* - 16* (or more). It is whatever it is. (it will depend on how much total mechanical timing your distributor has)

Go drive the car, floor it. If it doesn't ping or detonate, add a couple more degrees of timing. You can advance the timing using either the idle setting or advance it from the 3k rpm setting. It really doesn't matter. You can keep advancing the timing until you hear/feel it detonating, then back it down a couple of degrees.

In most cases, 36*@2.8k - 3k rpm is about right unless you want it on the razors edge of detonation.

Example - Lets say a distributor has a total mechanical advance of 20*. So basically you have a timing range of 0* to 20*.
With that being said, now the springs come into effect. Heavy springs will only let the timing advance from 0* to 20* once you reach 5000 rpm (this is slow). Softer springs will let the timing advance from 0* to 20* by 3000 rpm (this is more preferable).
Back to timing the car.
If you set the initial timing of the engine to 8*, (remember the distributor only has a 0*-20* range) so if you start at 8* and rev the engine to 3000 rpm, the distributor will advance a total of 20*. 8* initial timing + 20* total mechanical timing = 28*@3000 rpm.
Because you want 35*@3000 rpm, you need to advance the timing (twist the distributor) at 3000 rpm until you get 35*@3000 rpm. Since you effectively added 7* more timing (28*+7*=35*) once the engine goes back to idle you will have an additional 7* added in (8* initial timing + 7* advance = 15* at idle).
You can use the idle timing (15*) to retard or advance as much as needed to eliminate ping/detonation.

The above is all based on the mechanical settings only, with the vacuum advance plugged.
It really is a balancing act with the variables being, amount of total mechanical advance, how fast or slow that advance comes in, and if your distributor is using ported or manifold vacuum. Change one and the others need adjusted.

 

Look here at the third paragraph. You maybe surprised at what your initial comes in at.

http://www.burtonmachine.com/tech

 

Just because an engine isn't pinging doesn't mean timing is ideal. If it DOES ping, you want to decrease timing of course.

The optimum timing is found through measurements - specifically, looking for peak torque on a dyno cell.

For a small block Chevy running 70's heads, a typical "good" number is 36deg BTDC. As cylinder head chamber design improves, less timing is required as the burn happens more quickly.

Altitude has an impact as well - Lars' timing paper covers this well.

Basically, though, there are 3 components to timing:
Initial timing - what the advance rate is before the advance weights pull the rotor plate forward
Mechanical advance - the timing brought in as the weights spin
Vacuum advance - timing added by a vacuum canister which pulls the plate out.

The weights, springs and bushings impact the "curve" of timing advance, or how the amount of advance changes as rotation of the distributor increases as well as the maximum advance. Springs are the easiest part of the curve to modify - lighter springs get you to total advance more quickly. Really heavy springs can make it such that total advance exceeds the RPM capability of the engine.

Read Lars's paper, MSD also has some good docs w/ graphs on timing curves. Good luck!