Timing my 72 360
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Cargo Master
Joined: Sep 2004
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Timing my 72 360
I've recently installed a Pertronix Ignitor electronic ignition and and Flamethrower coil on my 72 w/360. I was expecting great things after reading all about those items in these forums but instead the truck still started and ran the same. Then kwanderi offered up that maybe I should increase the timing advance to 12-14 deg BTDC. I did so any the truck seems to start a little quicker and have a little more pep. When increasing the timing from 8 to 14, the engine started idling faster. I took this to mean running better. So for the heck of it I kept advancing the timing and it idled faster and faster up until about 25-30 deg BTDC at which point it started to get worse. Anyway, my question is:
1. why does increasing the advance so much make the engine run better? It would seem to me that the most efficient timing setting would be at TDC, not before or after. It seems to me that firing BTDC would have a negative effect on the efficiency.
2. And if increasing is better, then why shouldn't I set it at the 25 BTDC where it was running so much better?
1. why does increasing the advance so much make the engine run better? It would seem to me that the most efficient timing setting would be at TDC, not before or after. It seems to me that firing BTDC would have a negative effect on the efficiency.
2. And if increasing is better, then why shouldn't I set it at the 25 BTDC where it was running so much better?
Elder User
Joined: Mar 2004
Posts: 976
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From: SOUTH CAROLINA
the distributor has its own advance set up in it. as the rpms increase so does the timing . if you set it too far advanced it will fall on its face. also alot of advance will cause hard starting. almost like the starter is dragging. you have to find the happy medium. the sweet spot. the amount of set timing and the right amount of mechanical or vacume advance to get the best all around performance.
Hotshot
Joined: Feb 2004
Posts: 11,697
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From: Marengo, Iowa
another thing to look out for is the balancer. The later ones like that were 2 piece, and isolated with a rubber ring. sometimes that rubber ring disintergrates, and the outer ring starts to "walk" around, changing where the ring sits in relation to the crankshaft key. This condition will give you the wrong timing indication. The way I can tell if such has happened is to turn up the timing to the point it revvs nice. Then I shut it down, and see how it restarts. If it starts hard, I back it off a bit, revv test, then shut it down again and restart. After you do that a bit, you will find the sweet spot. Then you can check it with the timing light and compare the marks to see where you ended up.
Hotshot
Joined: Feb 2004
Posts: 11,697
Likes: 3
From: Marengo, Iowa
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Cargo Master
Joined: Sep 2004
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I found out why the advance is necessary. It turns out that the amount of time it takes for fuel to burn is pretty much constant no matter what the rpms of the engine. Therefore the timing is advanced so that the burn can begin before TDC and the power maximized at TDC. In other words, the downward forces of the burning fuel on the piston are maximized by starting the fuel burn early. This has now lead me to a new question.
I noticed that when I was setting my timing at idle, the engine rpms increased up to about 25-30 deg BTDC. After that it started getting worse. I think this means that 25 is an optimal timing at idle. I'm guessing that much advance is probably not good since at running speed the dist will advance it even further and make it run bad. My question to y'all out there is this:
Is there anyone out there with their timing advanced more than my 14, and if so how much is the advance?
I noticed that when I was setting my timing at idle, the engine rpms increased up to about 25-30 deg BTDC. After that it started getting worse. I think this means that 25 is an optimal timing at idle. I'm guessing that much advance is probably not good since at running speed the dist will advance it even further and make it run bad. My question to y'all out there is this:
Is there anyone out there with their timing advanced more than my 14, and if so how much is the advance?
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Elder User
Joined: Mar 2004
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From: SOUTH CAROLINA
qman, keep in mind the cam setup plays a big role in how the timing is set up and just because someone else is running a certain advance does not mean it will give you the best performance for your truck. if you have an aftermarket cam call the manufacturer of your cam and give them the particulars on your engine setup and they should be able to provide you with the proper numbers you want to run. they should at least get you close.
Freshman User
Joined: Oct 2003
Posts: 46
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From: Rockfield, KY
An old friend taught me how to set my timing years ago and it has worked for me ever since. I have a timing light but hardly ever use it. Set your idle up to about 2000 rpm then slowly advance the timing until the motor starts missing, bring it back until the miss stops and lock it down there. That's pretty much the most advance you can have. I use this method for setting the timing on all my vehicles with a distributor.
Senior User
Joined: Apr 2004
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From: I live in a warehouse in
I want to do the same in my truck and would like to know more about this. Qman, I often read and value your input on this forum. The efficiency of the engine is the important thing (fuel to output ratio). I need help with the numbers, but I think that burning a little more fuel to get a lot more output is the goal here. Overall, therefore, you gain in mpg. From what I have read, over and over, you won't see a giant burst of speed or performance, but rather a 10 to 15 % increase in efficiency over your previous performance (if that). From what I have read in previous posts, you seem to know your truck pretty well, and keep it properly tuned, and therefore might not see a giant increase in speed, performance,...etc. I would like to hear some others' answers to your #2, 'cuz I'm not qualified.
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Cargo Master
Joined: Sep 2004
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Kind words Knight. Here's an explanation of how an ignition system works and what timing is all about:
http://auto.howstuffworks.com/ignition-system.htm
After reading this, it now makes sense to me why you have to advance the timing. And as the engine speed increases the distributor will advance it even more. I'm just wondering how to determine the optimal timing setting. My goal is to get the most power (mpg) out of the fuel being burnt in my engine. With the pertronix ignition I am able to run the bigger jets and have real clean plugs. So I think my truck is being pretty efficient but it is still at 11-13 mpg around town as a daily driver. I also have a 92 F150. In that forum a while back there was a fella who put in performance iginition parts and increased his power and gas mileage from 15 to 22 mpg . But it cost him $400-500. Reading that got me thinking that most the cars/trucks we drive on a daily basis are not all that fuel efficient. I'm guessing that our catalytic converters burn up a lot of fuel that our stock engines are just wasting. I don't see why it should take a person all the time, energy, and money to get 22 mpg out of his truck when the manufacturer could have done it in the first place. I just don't know where to go for more info.
http://auto.howstuffworks.com/ignition-system.htm
After reading this, it now makes sense to me why you have to advance the timing. And as the engine speed increases the distributor will advance it even more. I'm just wondering how to determine the optimal timing setting. My goal is to get the most power (mpg) out of the fuel being burnt in my engine. With the pertronix ignition I am able to run the bigger jets and have real clean plugs. So I think my truck is being pretty efficient but it is still at 11-13 mpg around town as a daily driver. I also have a 92 F150. In that forum a while back there was a fella who put in performance iginition parts and increased his power and gas mileage from 15 to 22 mpg . But it cost him $400-500. Reading that got me thinking that most the cars/trucks we drive on a daily basis are not all that fuel efficient. I'm guessing that our catalytic converters burn up a lot of fuel that our stock engines are just wasting. I don't see why it should take a person all the time, energy, and money to get 22 mpg out of his truck when the manufacturer could have done it in the first place. I just don't know where to go for more info.
