Vintage Mustang Forums banner
  • Hey everyone! Enter your ride HERE to be a part MAY's Ride of the Month Challenge!

1 - 8 of 8 Posts

·
Registered
Joined
·
150 Posts
Discussion Starter · #1 ·
I was listening to two guys talking about ignition timing, last night One said it is better to time with a vacuum gauge (get the highest vacuum at idle and back-off one pound), the other said, use a timing light and stay with the factory specs.

Any thoughts on this?

Tom
 

·
Registered
Joined
·
21,376 Posts
Timing light! It's a far more accure way. Setting by vacuum is setting it by how it runs at idle. Conditions are going to change too much as rpm increases.
 

·
Registered
Joined
·
1,093 Posts
When I got my 428CJ carb back from Pony Carbs, they sent a video and said they did all of their timimg with a vacuum gauge. The reason for this is that as the older cars age, the harmonic dampner rubber gets old and can spin, causing the timimg marks to be off. Also, the timing chain can stretch causing the same problem.
 

·
Gone but never forgetten
Joined
·
25,239 Posts
I agree with both Huskinhano and mrgreene. First, you have to know if the harmonic balancer's timing marks are accurate, and use a combination of vaccum and the "back off until it doesn't ping" method if they are not. Or you could get some timing tape and MAKE the balancer accurate again.

If the harmonic balancer is accurate, it should definately be done with a timing light.

A lot of how the timing is set will depend on the motor. For a stock motor, set it to stock specs. If you have higher compression than stock, and especially if you have a non-stock cam, you won't want to use stock specs. For a performance engine, you want to determine you optimum total timing (usually around 38 degrees) and set your initial timing to obtain that. In other words, the initial is set to total timing less the total mechanical advance of the distributor. To do this, you must know the balancer is correct and use a timing light.
 

·
Registered
Joined
·
1,635 Posts
I disagree...Yes the vacuum method works BUT If theres ANY doubt that your balancer has a degraded rubber ring causing things to shift it should be replaced!!!!! Especially on a performance motor that sees higher rpms. Using a vacuum gage works but its nothing but a bandaid that youre using to mask another more critical issue that could destroy an engine....If in doubt, get a new balancer, use a dial indicator to verify TDC and use a timing light.
 

·
Registered
Joined
·
37,847 Posts
I'll be the general dissenter here. Setting timing with a light is a good baseline to start with, but here are some factors to consider:

1. No two engines are exactly alike.
2. Gasoline octane and vapor pressure varies between distributors and is seasonally adjusted.
3. Altitude is always a factor.
4. Engine deposits or wear are factors.

I always set timing on non-ECU controlled vehicles with a vacuum gauge, then road test and fine-tune accordingly.
 
1 - 8 of 8 Posts
Top