Timing Advance Numbers
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
I run 12 to 14 initial and total of 34 to 36 and as much vacuum advance as she'll stand, all in by 3000 in the Y block. It has a very low compression engine, like 8 to 1 so it will take plenty of "lead" but all it takes is a tank of bad fuel and it will start to knock at cruise. It's still a doggy 292 but it will light the tires and has good low end torque. It has that one potato two potato lope that I like too. Almost as good as a flattie!
Light springs and plenty of timing early on makes a big difference. Dual exhaust helps a lot too, everything needs to breathe better.
Light springs and plenty of timing early on makes a big difference. Dual exhaust helps a lot too, everything needs to breathe better.
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Senior User
Joined: Oct 2012
Posts: 186
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I've made little progress. I'm being told by some that I don't want more than about 12degrees vacuum advance, and that total advance (with vacuum) should not exceed about 38.
I've been told that it could be detrimental to my new engine even though I don't hear it pinging, or notice it stumbling.
On the other hand I've been told that I shouldn't worry because I don't hear it pinging, or notice it stumbling.
I am trying to figure out how to limit my vacuum advance without having to try to install a new one. My plan is to call Pertonix and see if it is normal for their Flame Thrower distributor (D133700) to be adding 20degrees of just vacuum advance.
Until then I'm not driving it. :-( I'm taking the extra cautious route because I can't seem to get a consensus, and the thing took too much time and money to get this far.
I've been told that it could be detrimental to my new engine even though I don't hear it pinging, or notice it stumbling.
On the other hand I've been told that I shouldn't worry because I don't hear it pinging, or notice it stumbling.
I am trying to figure out how to limit my vacuum advance without having to try to install a new one. My plan is to call Pertonix and see if it is normal for their Flame Thrower distributor (D133700) to be adding 20degrees of just vacuum advance.
Until then I'm not driving it. :-( I'm taking the extra cautious route because I can't seem to get a consensus, and the thing took too much time and money to get this far.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It's all been laid out and documented long ago. The science here, really IS settled. Total timing numbers for V8 don't include vacuum advance. High performance motors, those distributors don't have vacuum advance because the engine is at full throttle all the time.
There are several distributor and timing publications and articles from the hot rod and performance racing crew available online going back 20 years. They all say the same thing. You want vacuum advance in a street motor. It's going to run cooler and get better mileage and driveability. You won't see 20 degrees vacuum advance under load but you might in the garage in neutral.
But under very lightly loaded conditions, cruising down the highway, an engine will only need about 50 horsepower, the fuel charge will be very lean. It's not unusual for the timing under those conditions to exceed 50 degrees BTDC.
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Senior User
Joined: Oct 2012
Posts: 186
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I have done zero "research". If by research we are talking about actual research, as in reading peer-reviewed published journals, white papers, etc. I have been scouring message boards and talking to anyone who wants to put in their 2 cents... trying to average all that information. If you have any research (even a link to a hot-rod mag article) I would really like to read it. It would be valuable for this message board as well.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Search "Distributor Curving", there's all kinds of information.
Each engine is a little different, and it depends on cam, compression ratio, etc but all V8s are going to run best somewhere around 34 to 38 degrees BTDC not counting vacuum advance. Let the initial fall where it may to get there, but generally something more than 10 is preferred. That's why limiting the mechanical advance is necessary, the stock curve is too slow and uses way too much mechanical.
Many people don't want to run high test or premium but if they've built a high compression engine with a rumpety rump cam it will not run well without it, common mistake when building a motor. But it doesn't make sense to leave performance and economy on the table after spending the money on distributor upgrades either, the folks with more stock engines who take the time to really dial in their distributor (and carburetor, another area of tuning importance) will be rewarded with excellent performance and surprisingly good fuel economy running only on 87 pump gas.
Each engine is a little different, and it depends on cam, compression ratio, etc but all V8s are going to run best somewhere around 34 to 38 degrees BTDC not counting vacuum advance. Let the initial fall where it may to get there, but generally something more than 10 is preferred. That's why limiting the mechanical advance is necessary, the stock curve is too slow and uses way too much mechanical.
Many people don't want to run high test or premium but if they've built a high compression engine with a rumpety rump cam it will not run well without it, common mistake when building a motor. But it doesn't make sense to leave performance and economy on the table after spending the money on distributor upgrades either, the folks with more stock engines who take the time to really dial in their distributor (and carburetor, another area of tuning importance) will be rewarded with excellent performance and surprisingly good fuel economy running only on 87 pump gas.
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
2X Ted. I'll just add one item. Spark knock starts Before you hear it. Minute but it could be there. Because of this I wouldn't set initial above 14*. Outside of this opinion I have full faith in Ted's words OP. Set your motor up as explained here then tweek it to perfection. I think there is a big O' smile in your near future.
Tried to REP ya Ted. Dang spread it around 1st ka ka.
Tried to REP ya Ted. Dang spread it around 1st ka ka.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Here's one article that explains it better than I can.
https://www.fordmuscle.com/archives/2000/03/timing/
And another
http://www.mustangandfords.com/how-t...-distributors/
https://www.fordmuscle.com/archives/2000/03/timing/
And another
http://www.mustangandfords.com/how-t...-distributors/
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Senior User
Joined: Oct 2012
Posts: 186
Likes: 1
A Quick Update:
I had very little time after work/before dark tonight, but advanced the initial from 6 degrees to 10. My total advance topped out at only 26 because I didn't have time to switch out my mechanical limiters (still at 16). Regardless, a quick test drive showed significant improved performance around town.
It DID notice a tiny bit of struggle from the starter.
I got a little worried because I finished installing a mechanical water temp gauge and it really heated up when I turned it off. (220-225) I've read that's normal because the water is absorbing the heat from the cast iron block. ??? My thermostat is 195 and while cruising around town I was somewhere between 188 and 198.
As for the articles posted above, I've read the first before and agree it does a great job of explaining. I'm going to use it for the curving info. I'm going to get to the second article soon.
Thanks for the direction.
I had very little time after work/before dark tonight, but advanced the initial from 6 degrees to 10. My total advance topped out at only 26 because I didn't have time to switch out my mechanical limiters (still at 16). Regardless, a quick test drive showed significant improved performance around town.
It DID notice a tiny bit of struggle from the starter.
I got a little worried because I finished installing a mechanical water temp gauge and it really heated up when I turned it off. (220-225) I've read that's normal because the water is absorbing the heat from the cast iron block. ??? My thermostat is 195 and while cruising around town I was somewhere between 188 and 198.
As for the articles posted above, I've read the first before and agree it does a great job of explaining. I'm going to use it for the curving info. I'm going to get to the second article soon.
Thanks for the direction.
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Senior User
Joined: Oct 2012
Posts: 186
Likes: 1
But, if say my initial timing sits at 10 degrees, and I switch to the highest mechanical limiters that came with the distributor (20 degrees) then my Total will still be only 30. Should I not use the limiters at all and see what happens?
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
Typical V8 numbers are maybe 10 to 12 initial and around 24 mechanical. "Total" timing is then usually 34 to 36 degrees BTDC "all in" before 3000 RPM. Finally, reconnect vacuum advance and back off till no ping at steady cruise or part throttle acceleration. This will result in around 50 degrees of timing at cruise highway speeds, lightly loaded.
Lead Driver
Joined: Jul 2011
Posts: 8,679
Likes: 191
From: On the Edge of the Desert
No, vacuum is not counted. And no, 50 is not too much while cruising.
Now on a race engine you can tune however the heck you want to. But vacuum advance on a race engine is pretty pointless.
Now on a race engine you can tune however the heck you want to. But vacuum advance on a race engine is pretty pointless.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Here's yet another link with some information on vacuum advance
http://www.onallcylinders.com/2015/0...y-you-need-it/
Yet another yet
"Total timing is the term given to the highest amount of advance. This is when the initial timing is added to the mechanical timing. For instance, if an engine has 10° of initial combined with 21° of mechanical, the total timing is 31° BTDC. Note that Total timing never includes vacuum advance."
https://www.msdperformance.com/support/set_your_timing/
Everything I can find data wise centers around 50 to 52 degrees timing BTDC for V8 cruising down the highway lightly loaded (the engine, not the driver). The reason for this is because the fuel charge is extremely lean requires lots of advance. Yeah thought it was nuts too the first time I read it, but thems the facts. I don't make this stuff up.
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