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Discussion Starter · #1 ·
Howdy,
If anyone is aware of a previous post here that details a procedure of how to measure/determine total timing, please post me the link, or post information here. Thanks, and appreciate it.

Mac
 

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The easy way is to either (1) install some timing tape on the dampener so you can read total timing with a regular timing light or (2) use a dial-back timing light.

-SM
 

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Discussion Starter · #4 ·
OLDMANRAM: I'm more interested in the actual procedure you use to get there, the steps you take to get the total timing.

SLANTEDMIND: Yes, I know that. I have a digital timing light but trying to wrap my mind around the procedure, the step by step .

Thanks,
Mac

 

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So you know how to physically measure it, are you looking for a procedure to determine what total advance/total timing should be?

If so, IMO trial and error. Every engine is different. A good starting point is 30-36* total timing. Set the total, and let the initial fall wherever it is with total timing set where you want it. From there you can adjust the amount of mechanical advance in the dist to get the initial timing where you want it.

For max total, the method I use is to take the truck out and make some hard pulls up a steep hill (the one I use is an 8% grade) If I don't have any predetonation, I advance 2*, make another pull. When I finally do get some predetonation, I back the timing off 2* and it is set.

IMO this is the best way to tune for your particular engine. If this method leaves you with retarded initial timing, you have too much mechanical advance in the dist. Curing too much mechanical advance can be done several ways, including welding up the advance slots or installing set screws to limit the amount of mech advance. If it is an aftermarket dist limiting mech advance is easy using the limiters from the manufacturer.

Hope that is at least somewhat what you are looking for....

-SM
 

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Discussion Starter · #6 ·
SLANTED MIND: This has to do with that other post I have about the RC that runs hot that belongs to my buddy. I am going over to his place this weekend and taking my timing light and wanted to check out the total timing as it is now, and see about retarding it a bit and hopefully that will cool her down a little. Just wanted to be sure I understood what I was doing before then. Thanks again.

Mac
 

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http://ramchargercentral.com/boards/index.php?board=3;action=display;threadid=36123;start=0 I explained how to do it in this thread. Small block mopars like 35 degrees total timing and big blocks like 38. Thats pretty much a standard plus or minus 2 degrees. That part has to do with combustion chamber design and how fast of a burn the chamber allows. How fast of an advance an engine likes varies from engine to engine and depends on compression, exhaust, temp and fuel.
 

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You can get a rough idea of what the total timing is by setting the idle speed at around 3000 rpm, with the vac adv disconnected, then use a hand held vac pump on the vac adv to adv the timing until it maxes out. This would give you the max timing the engine can see. Then if you know what vac your engine runs at, only put that much on the vac adv. and see what the timing is, but you will need a inductive timing light that can be dialed in.

The difference between the reading with and without vac adv is how much the mechanical timing is, and you can adj the vac adv part to get what you want, or you can adj the mech too.

The diff between the idle reading and the 3000 rpm reading with no vac adv is the mech adv and you can determine how fast it comes in by taking readings at diff rpm.

vac adv is only for acceleration, and once the engine is at a given rpm for a period of time, it has no effect.

am I helping, or am I telling you somethign you already know ?????
 

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Discussion Starter · #10 ·
THERAMCHARGERMAN: The info you gave helps me a lot as well. I'm the type that needs to get all this info together in my head then it all clicks together and it is clear to me. What you said gives me another perspective on it. I am eager to get this show on the road. I'm gonna get one of those advance timing lights tomorrow - maybe with a digital read out if I can find a deal on one. I've screwed around with timing tape before and I never liked it.

Thanks,
Mac
 

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I wouldn't worry about the vacuum advance. Its preset on how much it will advance. Generally its 18 or 22 degrees. Total timing is initial + mechanical timing. Vacuum advance isn't included in that. So find your total timing first set it about 35 degrees. If it pings at part throttle then there is an adjustment inside the vacuum module. You can stick an allen wrench in the vacuum nipple and adjust how much vacuum has to be applied before it will advance.
 

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I mentioned the vac adv because on mine, the only time it ever pinged was when the vac adv was in. You can adjust how much vac adv you get inside the distributor, but to adjust how soon you get it is inside the vac canister/module
 

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Until you get the timing/overheating issues resolved, I would disconnect and plug the vacuum advance for now. You don't need it, as it is mostly a fuel mileage/drivability device, and it leaves one less thing to worry about (for now). Once you get your problems solved, then work on dialing in the vac advance.

-SM
 

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vac adv is only for acceleration, and once the engine is at a given rpm for a period of time, it has no effect.
Huh?? Just the opposite is true. When you are accelerating (hard) vacuum is low, so little or no vacuum advance is applied. When you are cruising, vacuum is high again, and since the throttle is open somewhat, the ported vacuum is applied to the vacuum advance canister. This pulls in that additional 18-22 degrees of timing, when the engine isn't heavily loaded, to improve mileage. Total timing, plus vacuum will be over 50 degrees at that point.

true...or just run the vac adv off the intake manifold and have it in all the time. I know people who swear by that method.
This doesn't make much sense to me either. If you're running that 18-20 degrees of vacuum all the time, and have your typical 22-25 degrees of mechanical advance, then you're going to need to set base timing ATDC to get back to your 35 total. Having vacuum pull in your base timing makes tuning a bit dicey. And gas mileage will suck.

Mac - at your 3000 RPM on the freeway, you'll be over 50 degrees total time including vacuum advance. This is normal. But if it's pinging, back it down a couple degrees on the base timing and try again, and again, etc, as has been suggested. If you get much below that 50 or so mark, your gas mileage will go in the toilet. Trust me, I know. I used up about 35 gallons of gas in 200 miles by pulling the vac advance line because it was pinging at cruise.

If you get your total timing - base timing plus mechanical advance - in the 35 degree ballpark, then timing will not be the cause of your heating problem.
 

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Discussion Starter · #17 ·
SLANTEDMIND: Yup, on by buddies truck which is overheating, we capped off the vacuum advance until we get things squared away. Odd thing on this particular vehicle is that capping off the VA has never made a noticeable difference anyway.

Ok, so the Total Timing is the base timing PLUS mechanical advance = Total Timing?

GUNPILOT: I heard just the opposite of your statement below yesterday too. Just trying to enlighten myself here cause I am no expert. Logically, you want high vacuum at acceleration to increase the vacuum advance, right? At cruising, it is the mech advance that takes over and there is little or no VA. That is what I always understood to be true.

" Just the opposite is true. When you are accelerating (hard) vacuum is low, so little or no vacuum advance is applied. When you are cruising, vacuum is high again, and since the throttle is open somewhat, the ported vacuum is applied to the vacuum advance canister. "


Mac
 

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vac adv is only for acceleration, and once the engine is at a given rpm for a period of time, it has no effect.
Huh?? Just the opposite is true. When you are accelerating (hard) vacuum is low, so little or no vacuum advance is applied. When you are cruising, vacuum is high again, and since the throttle is open somewhat, the ported vacuum is applied to the vacuum advance canister. This pulls in that additional 18-22 degrees of timing, when the engine isn't heavily loaded, to improve mileage. Total timing, plus vacuum will be over 50 degrees at that point.
I have to disagree with you one this GP... When you are accelerating...yes, INTAKE vacuum is low, but PORTED vacuum is very high. The vac adv is run off ported vacuum, and since ported vacuum is the difference between intake manifold vacuum and the vacuum across thru the venturi in the carb, it is 0 at idle and 0 at constant throttle position. When you accelerate, the vac across the blades (thru the venturi) goes up, and the intake vac drops, so the difference is the signal going to the vac adv. Once it evens out again, the vac adv goes away.

Hook up a vac gage to the ported vac and rev the engine...it will go up with rpm, (or increase). Do the same thing to a manifold vac source, and it will drop (or decrease) with rpm.

true...or just run the vac adv off the intake manifold and have it in all the time. I know people who swear by that method.
This doesn't make much sense to me either. If you're running that 18-20 degrees of vacuum all the time, and have your typical 22-25 degrees of mechanical advance, then you're going to need to set base timing ATDC to get back to your 35 total. Having vacuum pull in your base timing makes tuning a bit dicey. And gas mileage will suck.

Mac - at your 3000 RPM on the freeway, you'll be over 50 degrees total time including vacuum advance. This is normal. But if it's pinging, back it down a couple degrees on the base timing and try again, and again, etc, as has been suggested. If you get much below that 50 or so mark, your gas mileage will go in the toilet. Trust me, I know. I used up about 35 gallons of gas in 200 miles by pulling the vac advance line because it was pinging at cruise.

If you get your total timing - base timing plus mechanical advance - in the 35 degree ballpark, then timing will not be the cause of your heating problem.
I didn't say I did this. I have in fact had some extended arguments with a good friend over this, cuz he refuses to do anything else.

It works fine, IF yer engine is tuned to run this way. Most people's engines aren't.

When you run like this, you actually loose timing when vac drops in the intake (acceleration), and run at high timing when vac is high (cruise or idle).

Hook vac gage to your intake and put it where you can watch it when you drive. Vac will not be as high during cruise as it is at idle, but it will be fairly decent. Now, do the same thing with ported vac. It will be high during acceleration and throttle movement, but will drop to near zero at a constant speed and throttle position.

The vac adv comes in to help the engine speed up and to get the mech timing (which is rpm related) in faster so you accelerate faster, and burn less gas. IF you disconnect the vac adv without changing the distributor to compensate (people do run with no vac adv and still have quick cars/trucks), you will be slow at accelerating, and WILL burn more gas (hence yer lousy mileage). I have run my truck both ways, and it gets way worse mileage with no vac adv. Like half as much almost.

I'm not saying I am 100% correct, but I know from some testing I did on my truck, using a holley carb, ported vac is only present when there is a difference between the intake manifold vac and the vac across the throttle blades.

I did this to try and prove to my friend that running his vac adv off the intake is not a good idea. Well, we did the same testing on his, and he got the same results I did. That is why I say IF your engine is set up to run this way, it will do so well. Just like if it is set up to run with no vac adv, it will run well.
 

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TheRamChargerMan said:
I have to disagree with you one this GP... When you are accelerating...yes, INTAKE vacuum is low, but PORTED vacuum is very high. The vac adv is run off ported vacuum, and since ported vacuum is the difference between intake manifold vacuum and the vacuum across thru the venturi in the carb, it is 0 at idle and 0 at constant throttle position. When you accelerate, the vac across the blades (thru the venturi) goes up, and the intake vac drops, so the difference is the signal going to the vac adv. Once it evens out again, the vac adv goes away.
I agree, sorry George. ;D
 

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Ok, so the Total Timing is the base timing PLUS mechanical advance = Total Timing?
Correct.

When you accelerate, the vac across the blades (thru the venturi) goes up, and the intake vac drops, so the difference is the signal going to the vac adv. Once it evens out again, the vac adv goes away.
This hasn't been my experience. When I hook my vacuum gauge to ported vacuum, and jab the throttle open (from something off-idle, say 2000 rpm or so) , and sustain it at, say, 2500-3000 RPM, it will definitley initially drop the vacuum signal. Then, it will come back up as the rpms level off. I identify a ported signal as one that has little or no vacuum at idle, and plenty at some degree of off-idle setting.

It is not 0 at a constant throttle setting. It is only 0 at idle, because the port is above the throttle blades. It will be 0 or near 0 at WOT, because there is no intake restriction. If it isn't 0 at WOT, then you need a bigger carb (a topic for another discussion.) As you open the throttle, the signal drops, because the intake restriction is being removed, and RPMs aren't high enough to build the vacuum back up. As RPMs increase, the vacuum will build again, pulling the advance back in.

If this isn't the case, they explain to me why you would want 20-22 degrees more timing under heavy load? Wouldn't this be ping city? Wouldn't it make sense to mometarily reduce timing under heavy load, then bring it back up as the load, identified by a low vacuum condition, decreases?

I didn't say I did this. I have in fact had some extended arguments with a good friend over this, cuz he refuses to do anything else.
I understand you didn't do this. I really don't think it would work fine, though, because of my argument above. It will make idle and off-idle tuning a nightmare.

Think about it - if you have to set your base timing at 10 ATDC - what is your timing going to be like while you are cranking? And what's the point of having the timing pulled in all the time? Why not just set that much more base timing in?

Here's a page about timing. Coincidentally, it supports my position on vacuum advance: http://www.2quicknovas.com/happytiming.html

I agree, sorry George.
You don't have to apologize for agreeing with me, Kendall! It's OK to take the easy road sometimes.
 
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