Oldschool Timing Adjustment
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
You don't set your idle mixture screws a certain number of turns out, or even to a certain A/F ratio, do you? No, you adjust them until you get the highest vacuum reading, at least that is one commonly accepted way of doing it. That's because a high vacuum reading at idle is a way of spotting an engine that is happy. Why wouldn't the same be true with ignition timing? I'd still check it with my timing light, just because...well, just because.
Scott
Scott
Thread Starter
Le Mans Master
Joined: Nov 2006
Posts: 7,215
Likes: 1
From: Orlando FL
attach a vacuum gage and disable the dist vacuum advance.
not the initial vacuum reading and adv the dist until you reach a peak and the it starts to fall off. If the rpm comes up take and idle it back so you are at say 800ish the entire time and the readings are not eschewed by the increase in rpm.
note the peak vacuum and them retard the dist about 1/2 in of HG vacuum from the peak. turn car of and try and restart. If it gives a fit back off again.
now you are at the optimum happy place for your cam and heads and you can tune the dist to limit or set the total advance to the 36 degrees or whatever number you like
I learned this trick many years ago and it has served well on non stock configurations.
I let my wife drive it after I did this and she swore I had changed hard parts on her car..
not the initial vacuum reading and adv the dist until you reach a peak and the it starts to fall off. If the rpm comes up take and idle it back so you are at say 800ish the entire time and the readings are not eschewed by the increase in rpm.
note the peak vacuum and them retard the dist about 1/2 in of HG vacuum from the peak. turn car of and try and restart. If it gives a fit back off again.
now you are at the optimum happy place for your cam and heads and you can tune the dist to limit or set the total advance to the 36 degrees or whatever number you like
I learned this trick many years ago and it has served well on non stock configurations.
I let my wife drive it after I did this and she swore I had changed hard parts on her car..
Thread Starter
Le Mans Master
Joined: Nov 2006
Posts: 7,215
Likes: 1
From: Orlando FL
You don't set your idle mixture screws a certain number of turns out, or even to a certain A/F ratio, do you? No, you adjust them until you get the highest vacuum reading, at least that is one commonly accepted way of doing it. That's because a high vacuum reading at idle is a way of spotting an engine that is happy. Why wouldn't the same be true with ignition timing? I'd still check it with my timing light, just because...well, just because.
Scott
Scott
tuning by vacuum may seem old and antiquated to some but that's the best way to do it IMOI bet that a car that is not vacuum tuned and let me tune it by vacuum and it will pic up in quarter mile and get better mileage. If you live in Central Florida give me a shout and we can do some theory to practice
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
One more thing to consider is computerized ignition systems. The computer has a timing map (lookup table) with spark advance values for all combinations of engine speed and engine load. A key load measurement is manifold vacuum. The MAP sensor feeds fuel metering and ignition timing.
Safety Car
Joined: Jan 2009
Posts: 3,736
Likes: 56
From: anchorage ak
I'm a fan of the timing light. But if you do it with a vacuum gauge, take it out to a rough grade asphalt and power brake it almost to the point of spinning the tires but not quite. If it pings regard it a hair and repeat.
Melting Slicks
Joined: Oct 2011
Posts: 3,453
Likes: 67
From: Midland Ontario
NCM Sinkhole Donor
Race Director
Joined: Feb 2006
Posts: 12,239
Likes: 19
From: Chino CA
attach a vacuum gage and disable the dist vacuum advance.
not the initial vacuum reading and adv the dist until you reach a peak and the it starts to fall off. If the rpm comes up take and idle it back so you are at say 800ish the entire time and the readings are not eschewed by the increase in rpm.
note the peak vacuum and them retard the dist about 1/2 in of HG vacuum from the peak. turn car of and try and restart. If it gives a fit back off again.
now you are at the optimum happy place for your cam and heads and you can tune the dist to limit or set the total advance to the 36 degrees or whatever number you like
I learned this trick many years ago and it has served well on non stock configurations.
I let my wife drive it after I did this and she swore I had changed hard parts on her car..
not the initial vacuum reading and adv the dist until you reach a peak and the it starts to fall off. If the rpm comes up take and idle it back so you are at say 800ish the entire time and the readings are not eschewed by the increase in rpm.
note the peak vacuum and them retard the dist about 1/2 in of HG vacuum from the peak. turn car of and try and restart. If it gives a fit back off again.
now you are at the optimum happy place for your cam and heads and you can tune the dist to limit or set the total advance to the 36 degrees or whatever number you like
I learned this trick many years ago and it has served well on non stock configurations.
I let my wife drive it after I did this and she swore I had changed hard parts on her car..
Thanks for posting! I'm gonna get a gauge and try it.
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Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
You believers can go ahead and trash your timing lights. The vacuum method gives you ball park timing only.
As for my question to Lars, he is a highly respected member of this forum along with some others who, imho, have exceptional knowledge in engine building and an acute understanding of how it all works. And then there are the others who think they do. I built my own engine and took the extra time and money to do it right using proper tools and double checking specs and tolerances. My engine won't be timed with a vacuum gauge.
Edit: My engine build does not need 36* mech'l and 52* total for optimum power. It requires a few degrees less timing. Again, someone explain how you accurately time an engine with a vacuum gauge so its bang on when verified with the more accurate method using a timing light.
As for my question to Lars, he is a highly respected member of this forum along with some others who, imho, have exceptional knowledge in engine building and an acute understanding of how it all works. And then there are the others who think they do. I built my own engine and took the extra time and money to do it right using proper tools and double checking specs and tolerances. My engine won't be timed with a vacuum gauge.
Edit: My engine build does not need 36* mech'l and 52* total for optimum power. It requires a few degrees less timing. Again, someone explain how you accurately time an engine with a vacuum gauge so its bang on when verified with the more accurate method using a timing light.
Last edited by resdoggie; Aug 24, 2013 at 09:14 AM.
Race Director
Joined: Feb 2006
Posts: 12,239
Likes: 19
From: Chino CA
You believers can go ahead and trash your timing lights. The vacuum method gives you ball park timing only.
As for my question to Lars, he is a highly respected member of this forum along with some others who, imho, have exceptional knowledge in engine building and an acute understanding of how it all works. And then there are the others who think they do. I built my own engine and took the extra time and money to do it right using proper tools and double checking specs and tolerances. My engine won't be timed with a vacuum gauge.
As for my question to Lars, he is a highly respected member of this forum along with some others who, imho, have exceptional knowledge in engine building and an acute understanding of how it all works. And then there are the others who think they do. I built my own engine and took the extra time and money to do it right using proper tools and double checking specs and tolerances. My engine won't be timed with a vacuum gauge.
I time by ear. And yes I know it's a crappy way, but my car runs pretty damn good thank you.
Yes, timing light are VERY accurate. No question about it.
Not trying to argue at all. Just saying there's more than one way to skin a cat
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I'm also saying that you can use a vacuum gauge but its not as accurate as a timing light. Imho, the use of a vacuum gauge on my mom's slant six is ok but not on a high performance engine worth thousands of dollars.
Race Director
Joined: Feb 2006
Posts: 12,239
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From: Chino CA
I can accept that.
Edit: P.S. the leaning tower of power (slant 6) was cool!
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
only thing about timing "til it pings" is detonation starts long before it becomes audible.
We used to do that as youngsters (by ear) thankfully there was good gas back then. Different strokes...
We used to do that as youngsters (by ear) thankfully there was good gas back then. Different strokes...
Tech Contributor
Joined: Jun 2004
Posts: 20,868
Likes: 961
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
You believers can go ahead and trash your timing lights. The vacuum method gives you ball park timing only.
As for my question to Lars, he is a highly respected member of this forum along with some others who, imho, have exceptional knowledge in engine building and an acute understanding of how it all works. And then there are the others who think they do. I built my own engine and took the extra time and money to do it right using proper tools and double checking specs and tolerances. My engine won't be timed with a vacuum gauge.
Edit: My engine build does not need 36* mech'l and 52* total for optimum power. It requires a few degrees less timing. Again, someone explain how you accurately time an engine with a vacuum gauge so its bang on when verified with the more accurate method using a timing light.
As for my question to Lars, he is a highly respected member of this forum along with some others who, imho, have exceptional knowledge in engine building and an acute understanding of how it all works. And then there are the others who think they do. I built my own engine and took the extra time and money to do it right using proper tools and double checking specs and tolerances. My engine won't be timed with a vacuum gauge.
Edit: My engine build does not need 36* mech'l and 52* total for optimum power. It requires a few degrees less timing. Again, someone explain how you accurately time an engine with a vacuum gauge so its bang on when verified with the more accurate method using a timing light.
Feel free to dismiss any of my knowledge and experience in engines and engine controls, but I have a simple question: How did you arrive at the correct timing curve for your engine?
Racer
Joined: Feb 2013
Posts: 386
Likes: 3
From: Clifton Virginia
Best vacuum reading minus 1 or 2 inches back will have older engines burn today s fuel much better. This method has been around for more half of century. My buddy's father is 40 year ASE master mechanic and he taught us to use vacuum method if it's an old old engine or if we didn't know if HB is is for fact line up with btdc.
Safety Car
Joined: Jan 2009
Posts: 3,736
Likes: 56
From: anchorage ak
I'm with ya there, but if your not going to use a timing light, I'd atleast try to make sure it doesn't ping and if it does, back it off. Like I said, I'm a fan of the timing light.
Last edited by bluedawg; Aug 24, 2013 at 02:13 PM. Reason: ****** spelling and 3rd grade punctuation
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
You are misunderstanding the difference between accurate and correct. For example, I could lock the timing at 10 degrees and confirm (with a timing light), accurately, that it is at 10 degrees. However accurate that might be, it would not be the correct timing to maximize combustion efficiency and power/mileage.
Feel free to dismiss any of my knowledge and experience in engines and engine controls, but I have a simple question: How did you arrive at the correct timing curve for your engine?
Feel free to dismiss any of my knowledge and experience in engines and engine controls, but I have a simple question: How did you arrive at the correct timing curve for your engine?
I think resdoggie is putting the cart before the horse in this situation. He's hung up on a number. It's like saying "Your idle mixture screws should be set at 1 1/2 turns out.", instead of setting them to the optimum level. Tuning the timing by using a vacuum gauge will help you find the sweet spot. That doesn't mean you should throw your timing light out in the trash, it's an important measuring tool.
When I was a kid, my dad used to set the timing on the family car by putting a glass of water on the air cleaner, and fiddle with the distributor and the idle mixture screws until the surface of the water in the glass was as smooth as he could get it. I'm not sure if this optimized performance, but it sure made for a smooth running engine.
Scott
Race Director
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From: Charlotte NC
SO ...worrying about a number or getting it to a specific number is pointless...when you have to take into account many variables. Which is why...using a vacuum gauge is giving you real world information...and then test driving it will let you know what may need to be done.
Then...hopefully you do not go and start using a lower grade of fuel if you got it to perform like you want with premium in it....because it will react differently.
I use the timing light to allow me to write down numbers that make some customers feel warm and "fuzzy" inside. I use it only for data...and this is under the assumption that the balancer is correct to allow correct information to be collected.
DUB
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From: Danville Illinois
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Yes, i also have a timing light, But.
Last edited by Mod75; Aug 24, 2013 at 08:15 PM. Reason: I cant spell