Setting timing with vacuum gage
- Thread starter ojh
- Start date
Michael Mayben
IHPA Tech Moderator - Retired & No Longer Online
Hey dude!
I know what you are talking about, but the vacuum gauge is not a substitute for a timing light (or seat-of-the-pants dyno ya already use!).
Once I've set or verified dwell (when appropriate, I always look at dwell on inductive-type electronic ignition systems also), then I go out and do the power timing deal:
http://www.forums.IHPartsAmerica.com/ignition-tech/2122-ignition-power-timing.html. Once that is snugged in for the particular octane grade of fuel on board at that point, I then shoot the timing with a "dial-back" timing light so I can verify proper distributor advance operation (vacuum and mechanical).
I don't have a micro-processor based dwell instrument or scope that I can read dwell on a capacitive discharge system (such as an msd or mallory "six" box)...so if I'm installing a cd box, I run the distributor first as inductive so I can verify dwell before moving ahead.
Actually...I do now have such a scope, a snap-on handheld "micro-scope" that will read that stuff, but it's on long-term loan now to bill usn-1, our resident efi dude here on the forum. He's using it to develop some scope patterns for use in doing the research on this stuff he's constantly trying to improve! I never gotta chance to really play with it before I hooked up with bill, and I knew it would help him, much more than me at the time!
So, once I get a visual on the actual base timing along with the advance numbers, now I know what the engine likes I'm dealing with. This is performance tuning as you know and bears no resemblance to smogtuning! Even though, the tailpipe numbers might actually improve! Likewise, I don't have a five gas analyzer for smog verification, though I do use an old analog a/f and co gas analyzer (two gas).
Then I set up with a "shop"-type vacuum gauge and see what the vacuum level looks like. That is used for finalizing the idle mixture adjustments (usually while watching the exhaust gas analyzer also).
Once all that is set, I then just start moving the distributor around to see if vacuum can be improved at all (ya gotta maintain the exact same curb idle speed when doing this!). Since I already have a bench Mark for "best" advance verified with the light, I can always put the timing back where I started from.
The whole idea is achieve best idle quality (by feel/sound), and best idle quality according to the gas analyzer numbers, with a base timing that provides best throttle response and tip-in. That of course must coordinate with optimum accelerator pump actuation. And...with the "average" actual octane of the fuel supply (it varies tremendously tank-to-tank!!) we have no ping or detonation throughout the operation rpm or load of the engine at any throttle plate angle!
That is why so many times the overall performance May be greatly enhanced with a fresh distributor with stable timing, and a tweeked advance curve!
Again, this is all performance stuff like you deal in, and May not be "on road" legal in your world!
Somehow I don't feel this longass verbosity actually answers the question, but that is what I do. After doing hundreds of these kinda setups on IH stuff, ya get a feel for it and it goes very quickly if ya have the tools and the test process down pat!
I know what you are talking about, but the vacuum gauge is not a substitute for a timing light (or seat-of-the-pants dyno ya already use!).
Once I've set or verified dwell (when appropriate, I always look at dwell on inductive-type electronic ignition systems also), then I go out and do the power timing deal:
http://www.forums.IHPartsAmerica.com/ignition-tech/2122-ignition-power-timing.html. Once that is snugged in for the particular octane grade of fuel on board at that point, I then shoot the timing with a "dial-back" timing light so I can verify proper distributor advance operation (vacuum and mechanical).
I don't have a micro-processor based dwell instrument or scope that I can read dwell on a capacitive discharge system (such as an msd or mallory "six" box)...so if I'm installing a cd box, I run the distributor first as inductive so I can verify dwell before moving ahead.
Actually...I do now have such a scope, a snap-on handheld "micro-scope" that will read that stuff, but it's on long-term loan now to bill usn-1, our resident efi dude here on the forum. He's using it to develop some scope patterns for use in doing the research on this stuff he's constantly trying to improve! I never gotta chance to really play with it before I hooked up with bill, and I knew it would help him, much more than me at the time!
So, once I get a visual on the actual base timing along with the advance numbers, now I know what the engine likes I'm dealing with. This is performance tuning as you know and bears no resemblance to smogtuning! Even though, the tailpipe numbers might actually improve! Likewise, I don't have a five gas analyzer for smog verification, though I do use an old analog a/f and co gas analyzer (two gas).
Then I set up with a "shop"-type vacuum gauge and see what the vacuum level looks like. That is used for finalizing the idle mixture adjustments (usually while watching the exhaust gas analyzer also).
Once all that is set, I then just start moving the distributor around to see if vacuum can be improved at all (ya gotta maintain the exact same curb idle speed when doing this!). Since I already have a bench Mark for "best" advance verified with the light, I can always put the timing back where I started from.
The whole idea is achieve best idle quality (by feel/sound), and best idle quality according to the gas analyzer numbers, with a base timing that provides best throttle response and tip-in. That of course must coordinate with optimum accelerator pump actuation. And...with the "average" actual octane of the fuel supply (it varies tremendously tank-to-tank!!) we have no ping or detonation throughout the operation rpm or load of the engine at any throttle plate angle!
That is why so many times the overall performance May be greatly enhanced with a fresh distributor with stable timing, and a tweeked advance curve!
Again, this is all performance stuff like you deal in, and May not be "on road" legal in your world!
Somehow I don't feel this longass verbosity actually answers the question, but that is what I do. After doing hundreds of these kinda setups on IH stuff, ya get a feel for it and it goes very quickly if ya have the tools and the test process down pat!