increased vacuum with increased ig timing
Moderator: Team
-
- Guru
- Posts: 4576
- Joined: Sat Mar 26, 2011 11:34 am
- Location: Belgium - Koersel
increased vacuum with increased ig timing
Can someone explain to me what causes the engine to pull more vacuum when ignition timing is increased ?
Thanks
Thanks
Re: increased vacuum with increased ig timing
Engine gets more power from air it's getting so it will rev higher at same throttle opening.
- John Wallace
- Guru
- Posts: 1511
- Joined: Tue Jan 04, 2005 10:20 am
- Location: was Central Illinois - Now in Sunny Florida!
- Contact:
Re: increased vacuum with increased ig timing
Put the engine idle rpm back to what it was with previously.
Is the vacuum still higher?
Is the vacuum still higher?
John Wallace
Pontiac Power RULES !
www.wallaceracing.com
Pontiac Power RULES !
www.wallaceracing.com
Re: increased vacuum with increased ig timing
At low rpm you have very little air for optimum fuel burn so if you ignite it sooner then you get a more complete burn so your intake system functions as it should...In that the chamber is clear to draw in the next intake charge at low rpm.Belgian1979 wrote: ↑Sun Dec 10, 2017 8:47 am Can someone explain to me what causes the engine to pull more vacuum when ignition timing is increased ?
Thanks
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Re: increased vacuum with increased ig timing
Yes, until you reach it's limit.John Wallace wrote: ↑Sun Dec 10, 2017 12:46 pm Put the engine idle rpm back to what it was with previously.
Is the vacuum still higher?
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Re: increased vacuum with increased ig timing
And at that advance limit, with some engines, idle is all it's good for. The timing will be so far advanced, in a vehicle with any weight and/or tall gears, the engine will ping trying to pull off idle. It takes a good computer controlled EFI/ignition/knock sensor to use max advance at idle and cruise and then immediately recognize when more power is signaled and pull back the advance. Distributors and carbs aren't usually able to handle that reliably.GARY C wrote: ↑Sun Dec 10, 2017 12:52 pmYes, until you reach it's limit.John Wallace wrote: ↑Sun Dec 10, 2017 12:46 pm Put the engine idle rpm back to what it was with previously.
Is the vacuum still higher?
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering
Studebaker-Packard V8 Limited
Obsolete Engineering
Re: increased vacuum with increased ig timing
I disagree and have done it with carb, HEI and adjustable vac advance (actually becomes a vac retard at load when hooked to full vac port), you end up with a curve that matches that of say a modern LS engine.PackardV8 wrote: ↑Sun Dec 10, 2017 12:58 pmAnd at that advance limit, with some engines, idle is all it's good for. The timing will be so far advanced, in a vehicle with any weight and/or tall gears, the engine will ping trying to pull off idle. It takes a good computer controlled EFI/ignition/knock sensor to use max advance at idle and cruise and then immediately recognize when more power is signaled and pull back the advance. Distributors and carbs aren't usually able to handle that reliably.GARY C wrote: ↑Sun Dec 10, 2017 12:52 pmYes, until you reach it's limit.John Wallace wrote: ↑Sun Dec 10, 2017 12:46 pm Put the engine idle rpm back to what it was with previously.
Is the vacuum still higher?
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
-
- Guru
- Posts: 1739
- Joined: Tue Jan 15, 2013 8:10 pm
- Location:
Re: increased vacuum with increased ig timing
"actually becomes a vac retard at load when hooked to full vac port."
Once the throttle plates are open a little bit, I'd figure the vac advance function is the same whether ported or manifold. More load = more open thottle = lower vacuum = less advance.
Something like this,
https://assets.hemmings.com/story_image ... .jpg?rev=2
Here is a link to some presumably stock Buick distributor curve, showing limits of cent plus vac advance under varying rpm and load. The lack of vac advance below 1000 rpm suggest ported vacuum is used.
The mpg plotted along with rpm suggests chugging around at pretty low speeds in high gear was an expected operating condition for a 1950 Buick.
Once the throttle plates are open a little bit, I'd figure the vac advance function is the same whether ported or manifold. More load = more open thottle = lower vacuum = less advance.
Something like this,
https://assets.hemmings.com/story_image ... .jpg?rev=2
Here is a link to some presumably stock Buick distributor curve, showing limits of cent plus vac advance under varying rpm and load. The lack of vac advance below 1000 rpm suggest ported vacuum is used.
The mpg plotted along with rpm suggests chugging around at pretty low speeds in high gear was an expected operating condition for a 1950 Buick.
Re: increased vacuum with increased ig timing
Hook up two vac gauges on your engine, one to ported and one to full and see what happens?Dan Timberlake wrote: ↑Sun Dec 10, 2017 1:45 pm "actually becomes a vac retard at load when hooked to full vac port."
Once the throttle plates are open a little bit, I'd figure the vac advance function is the same whether ported or manifold. More load = more open thottle = lower vacuum = less advance.
Something like this,
https://assets.hemmings.com/story_image ... .jpg?rev=2
Here is a link to some presumably stock Buick distributor curve, showing limits of cent plus vac advance under varying rpm and load. The lack of vac advance below 1000 rpm suggest ported vacuum is used.
The mpg plotted along with rpm suggests chugging around at pretty low speeds in high gear was an expected operating condition for a 1950 Buick.
If you plot the timing curve that can be created in the manner I presented vs the timing curve on a modern FI engine you will see the similarity.
It does require the correct spring and weight package along with an adjustable vac port and some actual work to get them in sink.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
-
- Guru
- Posts: 4576
- Joined: Sat Mar 26, 2011 11:34 am
- Location: Belgium - Koersel
Re: increased vacuum with increased ig timing
I maybe should explain a little more. I have tried several settings on my engine. It's an EFI engine equiped with maf sensors, ignition and fuel controlled by the ECU (fuel is ego controlled) and the rpm at idle is controlled by a closed loop IAC.
What I see is that when using more timing, vacuum goes up, while airflow through the mafs goes down. Power is up by the feel of it. In essence I would not have expected this effect. I was guessing at the reasons, but I was thinking that exhaust speed was up due to more pressure left in the cylinder when the exhaust valve open (in itself due to a better more complete burn and higher power stroke pressure) and this would scavenge the cyls better.
What I see is that when using more timing, vacuum goes up, while airflow through the mafs goes down. Power is up by the feel of it. In essence I would not have expected this effect. I was guessing at the reasons, but I was thinking that exhaust speed was up due to more pressure left in the cylinder when the exhaust valve open (in itself due to a better more complete burn and higher power stroke pressure) and this would scavenge the cyls better.
Re: increased vacuum with increased ig timing
All of the above, you see the same on a good ignition tune on a factory EFI, they are tuned for economy, emissions and smoothness not performance, a big part of what creates a performance tune is the timing curve to burn the fuel.Belgian1979 wrote: ↑Sun Dec 10, 2017 3:06 pm I maybe should explain a little more. I have tried several settings on my engine. It's an EFI engine equiped with maf sensors, ignition and fuel controlled by the ECU (fuel is ego controlled) and the rpm at idle is controlled by a closed loop IAC.
What I see is that when using more timing, vacuum goes up, while airflow through the mafs goes down. Power is up by the feel of it. In essence I would not have expected this effect. I was guessing at the reasons, but I was thinking that exhaust speed was up due to more pressure left in the cylinder when the exhaust valve open (in itself due to a better more complete burn and higher power stroke pressure) and this would scavenge the cyls better.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Re: increased vacuum with increased ig timing
Belgian1979 wrote: ↑Sun Dec 10, 2017 8:47 am Can someone explain to me what causes the engine to pull more vacuum when ignition timing is increased ?
Thanks
You're improving the efficiency going from insufficient timing to the correct timing.
Better efficiency means more work out and less heat.
That means more RPM from the same fuel which then means you can close the throttle to maintain original RPM from less throttle opening.
-
- Guru
- Posts: 4576
- Joined: Sat Mar 26, 2011 11:34 am
- Location: Belgium - Koersel
Re: increased vacuum with increased ig timing
OK, and how do you know when you've gone too far or are at a correct timing ? I mean, if vacuum keeps dropping this hardly looks like the factor to determine the correct ignition timing.
Re: increased vacuum with increased ig timing
Dropping? you OP said increasing?Belgian1979 wrote: ↑Sun Dec 10, 2017 3:45 pm OK, and how do you know when you've gone too far or are at a correct timing ? I mean, if vacuum keeps dropping this hardly looks like the factor to determine the correct ignition timing.
Can someone explain to me what causes the engine to pull more vacuum when ignition timing is increased ?
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
-
- Guru
- Posts: 4576
- Joined: Sat Mar 26, 2011 11:34 am
- Location: Belgium - Koersel
Re: increased vacuum with increased ig timing
Sorry, map drops (expressed in kPa) but this means that vacuum increases...my fault.GARY C wrote: ↑Sun Dec 10, 2017 3:49 pmDropping? you OP said increasing?Belgian1979 wrote: ↑Sun Dec 10, 2017 3:45 pm OK, and how do you know when you've gone too far or are at a correct timing ? I mean, if vacuum keeps dropping this hardly looks like the factor to determine the correct ignition timing.
Can someone explain to me what causes the engine to pull more vacuum when ignition timing is increased ?