Set Timing Using Vacuum Gauge
- Thread starter ykf7b0
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lewtot184
Well-Known Member
setting the timing by using a vacuum gauge doesn't make sense to me. how do you know what the total is and it ignores the amount of centrifugal degrees built into the distributor.
BigBlock61
Well-Known Member
It's been awhile since I've done it this way and you know it's always best to set timing the correct way but here ya go.
1. Connect a vacuum gauge to a vacuum source directly on the intake manifold. Do not attach gauge to ports being used by any other device. Plug any vacuum lines you remove from manifold to make this connection.
2. Loosen the bolt securing the distributor so you can turn the distributor to adjust the timing.
3. Start the motor, let it warm up to normal operating temperature, and stabilize at normal hot idle. Using the idle speed adjustment at the carburetor, set the idle speed as low as possible without stalling the motor. Disconnect the distributor vacuum advance and plug the line.
4. Keep in mind when adjusting the timing, you have to turn the distributor clockwise to advance and counter-clockwise to retard.
5. While watching the vacuum gauge, slowly turn the distributor clockwise (advance timing) and look for a maximum reading on the gauge. For instance, if the reading on your gauge peaks at 18 inches of vacuum, that is the maximum for your engine. (The normal range could be from a high of 20 inches to a low of 15 inches, depending on the internal condition of your motor). The reading will drop off if you advance too far, so turn the distributor counter-clockwise (retard timing) to go back to the peak reading on your gauge.
6. Once you have established the peak reading, retard the timing (turn distributor counter-clockwise) to reduce the reading by about 1 inch to reduce ping. You may need to reduce the reading by 1.5-2 inches total, or even more, depending on the fuel available in your local area. Let your engine's performance guide you. If you had the same 100 octane fuel in your tank that was available when these cars were new, you would most likely leave the timing at the peak vacuum reading, but even when these cars were new, there were issues with fuel. Old Technical Service Bulletins (TSBs) exist that recommend retarding timing due to engine ping, so this was a concern even back when the cars were relatively new.
1. Connect a vacuum gauge to a vacuum source directly on the intake manifold. Do not attach gauge to ports being used by any other device. Plug any vacuum lines you remove from manifold to make this connection.
2. Loosen the bolt securing the distributor so you can turn the distributor to adjust the timing.
3. Start the motor, let it warm up to normal operating temperature, and stabilize at normal hot idle. Using the idle speed adjustment at the carburetor, set the idle speed as low as possible without stalling the motor. Disconnect the distributor vacuum advance and plug the line.
4. Keep in mind when adjusting the timing, you have to turn the distributor clockwise to advance and counter-clockwise to retard.
5. While watching the vacuum gauge, slowly turn the distributor clockwise (advance timing) and look for a maximum reading on the gauge. For instance, if the reading on your gauge peaks at 18 inches of vacuum, that is the maximum for your engine. (The normal range could be from a high of 20 inches to a low of 15 inches, depending on the internal condition of your motor). The reading will drop off if you advance too far, so turn the distributor counter-clockwise (retard timing) to go back to the peak reading on your gauge.
6. Once you have established the peak reading, retard the timing (turn distributor counter-clockwise) to reduce the reading by about 1 inch to reduce ping. You may need to reduce the reading by 1.5-2 inches total, or even more, depending on the fuel available in your local area. Let your engine's performance guide you. If you had the same 100 octane fuel in your tank that was available when these cars were new, you would most likely leave the timing at the peak vacuum reading, but even when these cars were new, there were issues with fuel. Old Technical Service Bulletins (TSBs) exist that recommend retarding timing due to engine ping, so this was a concern even back when the cars were relatively new.
Timing is everything when it comes to sucking like a vacuum.
69a100
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Also keep in mind on weather you have a big or small block as to which you turn the Dist., it will either advance or retard your timing. Just a FYI if you didn't know.
LOL, You funny, you speak from experience?
This technique is to set the initial timing to optimum so one can tune the ignition (mechanical advance) for best performance. It is the starting place for achieving the best possible performance timing. You need a great adjustable distributor to make this happen. Firecore, MSD, or modified MP etc...
72Fourspeed
Well-Known Member
The old mechanic who showed me this little trick said it was the best way to set base timing. He said it specifically eliminated any chance of a mismatched balancer or a broken off timing tab. Plus, if car was an oddball, he didn't need timing specs. He advanced for max vacuum, & then backed it off 2 inches. Sharp old guy, knew his stuff.
747mopar
Well-Known Member
I set my base timing off of throttle response, acceleration and clean idle, then I put a vacuum gauge on it and go figure that's where it made it's best vacuum as well so there must be something to it.
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