Distributor Timing Advance

Automotive powered airboat discussion.
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Rick McC.
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Distributor Timing Advance

Postby Rick McC. » Mon Jan 16, 2017 11:35 pm

If I'm understanding what I've read here correctly; why does everyone say it's best to disconnect the vacuum advance from the distributor, and run a static distributor timing when an automotive engine is used to power an airboat?

I'm pretty much lost on this...
Last edited by Rick McC. on Sat Jan 21, 2017 9:48 pm, edited 1 time in total.
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Re: Distributor Timing Asvance

Postby bkmail » Tue Jan 17, 2017 3:05 am

A search will result in lots of threads cover this topic.
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SWAMPHUNTER45
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Re: Distributor Timing Asvance

Postby SWAMPHUNTER45 » Tue Jan 17, 2017 6:34 am

Personally I think it is a bad idea to lock at full advance but the topic of much debate. As stated there are several threads to search.

The vacuum advance was designed for fuel economy in an automobile and is useless in a severe duty application.

What I find more appropriate is a properly curved mechanical advance. This allows for easy starts, no special switches or buttons and when done correctly a proper performance timing specification to match engine rpm.

Now this requires effort and resources (weights & springs) to get it right, could be why this best practice is avoided by some. Once set however it is a beautiful and simple thing.

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Deano
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Re: Distributor Timing Asvance

Postby Deano » Tue Jan 17, 2017 9:47 am

Rick McC. wrote:If I'm understanding what I've read here correctly; why does everyone say it's best to disconnect the vacuum advance from the distributor, and run a static distributor timing when an automotive engine is used to power an airboat? I'm pretty much lost on this...
You are trying to further your understanding of how the timing works, and there are those here that are willing to help toward that end. It may well only be my interpretation, but the way your question is worded makes it somewhat ambiguous. This subject can seem complicated to anyone on the front side, so don't worry about that. It is difficult in any case to pose the best question when your not familiar with what you are asking about. :wink:

There are basically three ways to set-up/alter/adjust the timing:

First . . . You could 'lock it out'. In other words, set your initial/base timing to a number that will NOT change, regardless of the RPMs. It is not variable, it is permanently fixed in one position. Consequently, it will only be optimal running in a SMALL rpm range, rather than across the board. This isn't generally recommended for that and other reasons.

Second . . . You could run 'mechanical advance' where the initial timing is set at idle, and the springs and weights in the distributor will add timing as the engine RPMs increase. This is overwhelmingly the recommendation by most people for most airboat applications running an automotive engine.

Third . . . You could run 'vacume advance' in addition to the mechanical previously mentioned. To oversimplify the purpose of vacume advance would be to say that it is to gain fuel efficiency when the engine is loafing around with only a partial load at lower RPMs. This generally doesn't happen on an airboat unless it is a very big engine on a very light hull, so generally it isn't used. It is worth noting that it can be beneficial in such a circumstance, but is generally not done due to the nearly non-existent difference it would make in most cases.

What wasn't really clear (to me anyway) about your question is exactly what you mean when you say 'run static distributor timing'. Depending on the context, "static" could be interpreted as fixed timing, or it would refer to the base/initial timing setting. Are you asking about running vacuum vs OPTION 1 or are you asking about running vacuum vs OPTION 2, or are you asking about OPTION 1 vs OPTION 2.

The first two responses figured you were asking about locked out (option 1) VS mechanical (option 2); but if that was your intended question, I'm not sure why you mentioned vacuum advance. If that was the case though, Swamphunter offers good advice and hits on the highpoints of the debate. Here is just one such recent thread: http://southernairboat.com/phpBB3/viewtopic.php?f=48&t=69593&p=675097

If this and/or the previous posts answered your question, then that's great.
If not, re-wording your question will allow us to get more specifically to what is it you are wanting to know.

If this was just my confusion, then just say so, excuse me, and I will quit trying to help. 8)
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
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glades cat
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Re: Distributor Timing Asvance

Postby glades cat » Tue Jan 17, 2017 2:29 pm

....the reason airboats don't benefit from the vacuum advance module is, they function during cruising RPMs and light throttle application. A vehicle can cruise down the road at highway speed and barely open the throttles...a light power demand. As a prop accelerates, it places increasing power demands on the engine. The engine therefore always sees high loads associated with high RPMS. The vacuum advance will stay retarded...except during idle and off-idle operation...
Which means...You do get a smoother idle with the additional timing.
A typical GM HEI distributor will give you about 20 deg of mechanical advance, plus 8-14 deg initial timing= your typical SBC 34deg total timing.
That is the problem with locking down a distributor on some engines. They don't like starting with too much base timing and can kick back or crank slowly, especially when hot. Some will diesel when shut down.
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Rick McC.
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Re: Distributor Timing Asvance

Postby Rick McC. » Tue Jan 17, 2017 11:06 pm

Deano wrote:
Rick McC. wrote:If I'm understanding what I've read here correctly; why does everyone say it's best to disconnect the vacuum advance from the distributor, and run a static distributor timing when an automotive engine is used to power an airboat? I'm pretty much lost on this...
You are trying to further your understanding of how the timing works, and there are those here that are willing to help toward that end. It may well only be my interpretation, but the way your question is worded makes it somewhat ambiguous. This subject can seem complicated to anyone on the front side, so don't worry about that. It is difficult in any case to pose the best question when your not familiar with what you are asking about. :wink:

There are basically three ways to set-up/alter/adjust the timing:

First . . . You could 'lock it out'. In other words, set your initial/base timing to a number that will NOT change, regardless of the RPMs. It is not variable, it is permanently fixed in one position. Consequently, it will only be optimal running in a SMALL rpm range, rather than across the board. This isn't generally recommended for that and other reasons.

Second . . . You could run 'mechanical advance' where the initial timing is set at idle, and the springs and weights in the distributor will add timing as the engine RPMs increase. This is overwhelmingly the recommendation by most people for most airboat applications running an automotive engine.

Third . . . You could run 'vacume advance' in addition to the mechanical previously mentioned. To oversimplify the purpose of vacume advance would be to say that it is to gain fuel efficiency when the engine is loafing around with only a partial load at lower RPMs. This generally doesn't happen on an airboat unless it is a very big engine on a very light hull, so generally it isn't used. It is worth noting that it can be beneficial in such a circumstance, but is generally not done due to the nearly non-existent difference it would make in most cases.

What wasn't really clear (to me anyway) about your question is exactly what you mean when you say 'run static distributor timing'. Depending on the context, "static" could be interpreted as fixed timing, or it would refer to the base/initial timing setting. Are you asking about running vacuum vs OPTION 1 or are you asking about running vacuum vs OPTION 2, or are you asking about OPTION 1 vs OPTION 2.

The first two responses figured you were asking about locked out (option 1) VS mechanical (option 2); but if that was your intended question, I'm not sure why you mentioned vacuum advance. If that was the case though, Swamphunter offers good advice and hits on the highpoints of the debate. Here is just one such recent thread: http://southernairboat.com/phpBB3/viewtopic.php?f=48&t=69593&p=675097

If this and/or the previous posts answered your question, then that's great.
If not, re-wording your question will allow us to get more specifically to what is it you are wanting to know.

If this was just my confusion, then just say so, excuse me, and I will quit trying to help. 8)


Thank you Sir.

I used the term "static" to imply a set timing advance that wouldn't change.
"Sights are for the unenlightened."
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jeepinocala1111
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Re: Distributor Timing Asvance

Postby jeepinocala1111 » Wed Jan 18, 2017 6:39 am

I run a locked timing distributer and it works great.

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Rick McC.
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Re: Distributor Timing Asvance

Postby Rick McC. » Wed Jan 18, 2017 10:30 pm

jeepinocala1111 wrote:I run a locked timing distributer and it works great.



Thanks!
"Sights are for the unenlightened."
Rick
http://guntipsandtalk.com


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