Vacuum advance question
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Does it respond quickly (neutral) when you blip the throttle fast? That's another easy test. A well tuned engine will be noticeably snappy, without a bog or flat spot hesitation. Revving up an engine in neutral isn't high on my fun stuff to do either, but 18 degrees indicated is about HALF of what you need, (assuming the mechanical advance is all in.)
Good deal, you may be on to something! You need to investigate further. Use a tach, and determine for sure what total timing is at, all the way up to 4000 or so. Be sure to disconnect vac advance for this check.
Likely your old distributor is gummed up and worn out, sticking, etc. How you achieve the 36 to 38 degree sweet spot is up to the tuner. Usually a stock engine and distributor has way too much mechanical advance, plus, that advance only comes all in at about 4500 RPM, (too late) something like that, and uses very little initial (crank) timing. This allows for hauling very heavy loads without detonation. Think dump truck on a mountain grade. But, it's a "dog".
By limiting the distributor mechanical advance and installing lighter springs, we still keep that same 36 to 38 degree total timing but the ratio and RPM is different. Instead of 4 or 6 degrees crank timing, we can now dial in say,12 or 14, and the advance will come in between 2500 and 3000 RPM. Makes for a lot better performance.
Good deal, you may be on to something! You need to investigate further. Use a tach, and determine for sure what total timing is at, all the way up to 4000 or so. Be sure to disconnect vac advance for this check.
Likely your old distributor is gummed up and worn out, sticking, etc. How you achieve the 36 to 38 degree sweet spot is up to the tuner. Usually a stock engine and distributor has way too much mechanical advance, plus, that advance only comes all in at about 4500 RPM, (too late) something like that, and uses very little initial (crank) timing. This allows for hauling very heavy loads without detonation. Think dump truck on a mountain grade. But, it's a "dog".
By limiting the distributor mechanical advance and installing lighter springs, we still keep that same 36 to 38 degree total timing but the ratio and RPM is different. Instead of 4 or 6 degrees crank timing, we can now dial in say,12 or 14, and the advance will come in between 2500 and 3000 RPM. Makes for a lot better performance.
Super Moderator
Joined: Apr 2004
Posts: 34,499
Likes: 2,811
Point taken on the 70 in a mile, clearly even a good 360 running on 6 cylinders will do that easily.
Once you sort out the timing, think fuel. You may be getting enough at idle and low revs, but it might crap out when you are under a good load. Had one do that--it would run ok till you got on it, then it would cut out after a little bit of acceleration.
Check the filter & see if it's clogged and maybe more junk in the tank.
Check the float level.
Once you sort out the timing, think fuel. You may be getting enough at idle and low revs, but it might crap out when you are under a good load. Had one do that--it would run ok till you got on it, then it would cut out after a little bit of acceleration.
Check the filter & see if it's clogged and maybe more junk in the tank.
Check the float level.
Elder User
Joined: Nov 2009
Posts: 891
Likes: 0
From: Mayfield, KY
Does it respond quickly (neutral) when you blip the throttle fast? That's another easy test. A well tuned engine will be noticeably snappy, without a bog or flat spot hesitation. Revving up an engine in neutral isn't high on my fun stuff to do either, but 18 degrees indicated is about HALF of what you need, (assuming the mechanical advance is all in.)
Good deal, you may be on to something! You need to investigate further. Use a tach, and determine for sure what total timing is at, all the way up to 4000 or so. Be sure to disconnect vac advance for this check.
Likely your old distributor is gummed up and worn out, sticking, etc. How you achieve the 36 to 38 degree sweet spot is up to the tuner. Usually a stock engine and distributor has way too much mechanical advance, plus, that advance only comes all in at about 4500 RPM, (too late) something like that, and uses very little initial (crank) timing. This allows for hauling very heavy loads without detonation. Think dump truck on a mountain grade. But, it's a "dog".
By limiting the distributor mechanical advance and installing lighter springs, we still keep that same 36 to 38 degree total timing but the ratio and RPM is different. Instead of 4 or 6 degrees crank timing, we can now dial in say,12 or 14, and the advance will come in between 2500 and 3000 RPM. Makes for a lot better performance.
Good deal, you may be on to something! You need to investigate further. Use a tach, and determine for sure what total timing is at, all the way up to 4000 or so. Be sure to disconnect vac advance for this check.
Likely your old distributor is gummed up and worn out, sticking, etc. How you achieve the 36 to 38 degree sweet spot is up to the tuner. Usually a stock engine and distributor has way too much mechanical advance, plus, that advance only comes all in at about 4500 RPM, (too late) something like that, and uses very little initial (crank) timing. This allows for hauling very heavy loads without detonation. Think dump truck on a mountain grade. But, it's a "dog".
By limiting the distributor mechanical advance and installing lighter springs, we still keep that same 36 to 38 degree total timing but the ratio and RPM is different. Instead of 4 or 6 degrees crank timing, we can now dial in say,12 or 14, and the advance will come in between 2500 and 3000 RPM. Makes for a lot better performance.
Cargo Master
Joined: May 2009
Posts: 2,587
Likes: 47
From: Eagle River, AK
http://www.fordmuscleforums.com/all-...stributor.html
Different engine, similar situation. The port you are not using needs to be open, not plugged. It is not allowing your vac advance to work properly.
Different engine, similar situation. The port you are not using needs to be open, not plugged. It is not allowing your vac advance to work properly.
Thread Starter
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Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
Mine is an old Holley 2bbl but the vac advance is connected to the pass side port. It doesn't have one on the drivers side.
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Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
Point taken on the 70 in a mile, clearly even a good 360 running on 6 cylinders will do that easily.
Once you sort out the timing, think fuel. You may be getting enough at idle and low revs, but it might crap out when you are under a good load. Had one do that--it would run ok till you got on it, then it would cut out after a little bit of acceleration.
Check the filter & see if it's clogged and maybe more junk in the tank.
Check the float level.
Once you sort out the timing, think fuel. You may be getting enough at idle and low revs, but it might crap out when you are under a good load. Had one do that--it would run ok till you got on it, then it would cut out after a little bit of acceleration.
Check the filter & see if it's clogged and maybe more junk in the tank.
Check the float level.
Thread Starter
|
Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
Does it respond quickly (neutral) when you blip the throttle fast? That's another easy test. A well tuned engine will be noticeably snappy, without a bog or flat spot hesitation. Revving up an engine in neutral isn't high on my fun stuff to do either, but 18 degrees indicated is about HALF of what you need, (assuming the mechanical advance is all in.)
Good deal, you may be on to something! You need to investigate further. Use a tach, and determine for sure what total timing is at, all the way up to 4000 or so. Be sure to disconnect vac advance for this check.
Likely your old distributor is gummed up and worn out, sticking, etc. How you achieve the 36 to 38 degree sweet spot is up to the tuner. Usually a stock engine and distributor has way too much mechanical advance, plus, that advance only comes all in at about 4500 RPM, (too late) something like that, and uses very little initial (crank) timing. This allows for hauling very heavy loads without detonation. Think dump truck on a mountain grade. But, it's a "dog".
By limiting the distributor mechanical advance and installing lighter springs, we still keep that same 36 to 38 degree total timing but the ratio and RPM is different. Instead of 4 or 6 degrees crank timing, we can now dial in say,12 or 14, and the advance will come in between 2500 and 3000 RPM. Makes for a lot better performance.
Good deal, you may be on to something! You need to investigate further. Use a tach, and determine for sure what total timing is at, all the way up to 4000 or so. Be sure to disconnect vac advance for this check.
Likely your old distributor is gummed up and worn out, sticking, etc. How you achieve the 36 to 38 degree sweet spot is up to the tuner. Usually a stock engine and distributor has way too much mechanical advance, plus, that advance only comes all in at about 4500 RPM, (too late) something like that, and uses very little initial (crank) timing. This allows for hauling very heavy loads without detonation. Think dump truck on a mountain grade. But, it's a "dog".
By limiting the distributor mechanical advance and installing lighter springs, we still keep that same 36 to 38 degree total timing but the ratio and RPM is different. Instead of 4 or 6 degrees crank timing, we can now dial in say,12 or 14, and the advance will come in between 2500 and 3000 RPM. Makes for a lot better performance.
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Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
Still have not acquired a tach.....I am at a fire chiefs conference this week out of town I will mess with it next week and hopefully be able to report some true numbers.
I was speaking to a mechanic friend and he was saying that I should only get about 8 degrees out of it which is way different than you guys. I just went on after that since you guys have more specific details with these engines than he does.
I was speaking to a mechanic friend and he was saying that I should only get about 8 degrees out of it which is way different than you guys. I just went on after that since you guys have more specific details with these engines than he does.
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Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
I am also starting to question my ignition, since I installed the pertronix II with their coil I have not seen much of a difference. I went with the II cause they had said that I could use the same wiring that came with the truck meaning I didnt have to bypass the resistor wire or whatever its called. Just to see if there is a difference where do i need to run a wire to from the positive side of the coil to see if it will in fact make a difference?
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Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
Stock distributor and as far as I know its the original 360 and its 43 yrs old.
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Laughing Gas
Joined: Jan 2013
Posts: 1,015
Likes: 4
From: Gulf Coast, MS
I did re read entire post. I do understand what you are asking for...I just wanted a tach so I can give accurate numbers. The most I have seen it advance while using a timing light with vacuum advance unplugged and capped off is about 15 degrees but I dont know what rpms were at.