Why did mazda retard timing at idle on carb'd 12A?
Lives on the Forum
Joined: Jun 2004
Posts: 11,359
Likes: 14
From: Grand Rapids Michigan
The think the whole problems is that some people think that the timing is supposed to retard as you throttle up, rather than advance. Anyway, I'm not about to start beating people over the head to get them to agree with me. I've made the needed changes to my setup and am extremely happy with the results. If others want to set theirs up so that it defeats the purpose of the whole system, then I wish them happiness. 
Registered Offender
Joined: Jul 2006
Posts: 689
Likes: 0
From: Bishopville, SC
Originally Posted by REVHED
Most of us understand the difference between venturi and manifold vacuum. The problem is you are working on a misconception and don't understand why the vacuum advance is designed to increase with manifold vacuum and decrease with load. You will never understand how the vacuum advance system works if you first don't understand why.
Let's get centrifugal advance out of the way first. As the engine rpm's increase there is less time to achieve a complete burn so the timing is advanced. We can all agree on that.
Vacuum advance is completely different. At low engine loads, such as idle and part throttle, combustion chamber pressures are low. As you accelerate and load increases combustion chamber pressures increase. The higher the combustion chamber pressure is the faster the flame front travels through the mixture. This means you need less timing advance to achieve a complete burn! In addition, having too much timing advance when combustion pressure increases can cause knocking. This is why you retard the timing on forced induction engines as boost (load) increases.
Let's get centrifugal advance out of the way first. As the engine rpm's increase there is less time to achieve a complete burn so the timing is advanced. We can all agree on that.
Vacuum advance is completely different. At low engine loads, such as idle and part throttle, combustion chamber pressures are low. As you accelerate and load increases combustion chamber pressures increase. The higher the combustion chamber pressure is the faster the flame front travels through the mixture. This means you need less timing advance to achieve a complete burn! In addition, having too much timing advance when combustion pressure increases can cause knocking. This is why you retard the timing on forced induction engines as boost (load) increases.
I'm not sure how your repeated attempts to introduce turbo into this thread are helping to explain anything. I think you're only further complicating the matter and making yourself out for a fool to boot. Pressure increases with the throttle opening alright, all the way up to atmospheric in an NA engine, which means vacuum is decreasing. How that transfers into a faster flame in your eyes, I have no idea as things move faster in vacuum conditions. However, higher RPM sure would do the trick.
Kentetsu has found the answer by working hands-on with his Nikki, that is good enough for me and should be enough to end this thread.
Absolute Power is Awesome
Joined: Mar 2001
Posts: 1,973
Likes: 5
From: Issaquah, WA
Originally Posted by djjjr42
Holy schnikies! We can now extrapolate and summarize from your posts that boost=load=rpm. WOW!
I'm not sure how your repeated attempts to introduce turbo into this thread are helping to explain anything. I think you're only further complicating the matter and making yourself out for a fool to boot. Pressure increases with the throttle opening alright, all the way up to atmospheric in an NA engine, which means vacuum is decreasing. How that transfers into a faster flame in your eyes, I have no idea as things move faster in vacuum conditions. However, higher RPM sure would do the trick.
I'm not sure how your repeated attempts to introduce turbo into this thread are helping to explain anything. I think you're only further complicating the matter and making yourself out for a fool to boot. Pressure increases with the throttle opening alright, all the way up to atmospheric in an NA engine, which means vacuum is decreasing. How that transfers into a faster flame in your eyes, I have no idea as things move faster in vacuum conditions. However, higher RPM sure would do the trick.
Last edited by purple82; Apr 19, 2007 at 11:38 AM.
Absolute Power is Awesome
Joined: Mar 2001
Posts: 1,973
Likes: 5
From: Issaquah, WA
Originally Posted by Kentetsu
The think the whole problems is that some people think that the timing is supposed to retard as you throttle up, rather than advance. Anyway, I'm not about to start beating people over the head to get them to agree with me. I've made the needed changes to my setup and am extremely happy with the results. If others want to set theirs up so that it defeats the purpose of the whole system, then I wish them happiness.
Hunting Skylines
Joined: Apr 2001
Posts: 3,431
Likes: 4
From: Brisbane, Queensland, Australia.
Originally Posted by djjjr42
Holy schnikies! We can now extrapolate and summarize from your posts that boost=load=rpm. WOW!
I'm not sure how your repeated attempts to introduce turbo into this thread are helping to explain anything. I think you're only further complicating the matter and making yourself out for a fool to boot. Pressure increases with the throttle opening alright, all the way up to atmospheric in an NA engine, which means vacuum is decreasing. How that transfers into a faster flame in your eyes, I have no idea as things move faster in vacuum conditions. However, higher RPM sure would do the trick.
Kentetsu has found the answer by working hands-on with his Nikki, that is good enough for me and should be enough to end this thread.
I'm not sure how your repeated attempts to introduce turbo into this thread are helping to explain anything. I think you're only further complicating the matter and making yourself out for a fool to boot. Pressure increases with the throttle opening alright, all the way up to atmospheric in an NA engine, which means vacuum is decreasing. How that transfers into a faster flame in your eyes, I have no idea as things move faster in vacuum conditions. However, higher RPM sure would do the trick.
Kentetsu has found the answer by working hands-on with his Nikki, that is good enough for me and should be enough to end this thread.
I have never said load = rpm and it's making you look stupid. Load can infact be refered to as manifold pressure ie, vacuum or boost. What do you think all aftermarket ECU's use for load sensing? A friggin MAP sensor. Do you know what that is?
Here's an excellent technical article that will teach you and Kuntsetsu all you need to know about ignition timing.
http://www.bristoldyno.com/tech/ignitiontiming.htm
Thats it. I've had enough of this thread going no where. It started out as a very simple question and has turned into a complete useless debate.
And no, don't pm me and ask me to reopen it.
And no, don't pm me and ask me to reopen it.
Thread
Thread Starter
Forum
Replies
Last Post
alphawolff
1st Generation Specific (1979-1985)
17
Nov 17, 2015 05:57 PM
