Timing made easy - i hope - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 12-11-2013, 04:27 PM Thread Starter
 
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Timing made easy - i hope

So I built a full roller 468 with KRE heads and Dave @ SD said they like 32 degrees total timing. I am running a stock HEI. The short of it is, anyone know which advance kit gives a nice 32-34 all in by 3000? My initial will be like 14 so i need 20 in by 3000. Most kits are less or in way later than 3000. Id imagine by now the Pontiac community has a spring and weight combo they like to run in HEI with alum heads no?

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post #2 of 7 (permalink) Old 12-11-2013, 10:50 PM
 
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You need to go on PY forum and talk to the author of performance Pontiacs and he can get you the correct setup. I think it's Jim Hand. He doesn't come on here much. I think the DUI distributor has a good curve in it, but sounds like you are beyond that.

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post #3 of 7 (permalink) Old 12-13-2013, 06:36 PM
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Hokay.... need to understand some basics here first.

An "advance curve kit" (springs and weights) does NOTHING to control "how much" advance you have. Such a kit only changes "how fast" the advance you already have comes in.

Take the cap off your distributor - and if it's not already installed in the car, then secure the "gear end" in a vise or something to immobilize it. Now, using your hand, grab the rotor and (gently) turn it from side to side. Notice that you can feel some springiness in there and that you can turn it a little bit each way before it hits "something solid" and won't turn any farther. How far it turns from one stop to the other is how much "mechanical advance" is "in" the distributor. Underneath the cap and rotor there's a set of springs and weights. The springs will hold the rotor (and the points cam or trigger if it's an HEI) up against one of the stops when it's not spinning. As it spins, and as rpm increases, the weights tend to "fly out" and will overcome the spring tension to begin moving the rotor and cam/trigger towards the other stop until it reaches the stop. The heavier the weights and lighter the springs, the "sooner" this will happen -- but you're still limited by the stops at "both ends".

So..... in your case, what you need is a good timing light that's capable of measuring total advance on a running engine (something like one of these: Innova/Heavy duty housing pro timing light with tool case, test up to 9990 RPM (INN5568) | Timing Light | AutoZone.com or one of these: Actron/Digital timing light (CP7529) | Timing Light | AutoZone.com)

Or, as an alternative you can use a timing tape on your balancer, but make CERTAIN you get the right tape for the size of balancer you have.

Next, disconnect your vacuum advance hose from the distributor and plug it so that you don't have air leaking into your intake manifold.

Loosen the distributor clamp nut just enough so that you can turn the distributor with some effort - you don't want it really loose.
Start the engine, hold it at a steady 3500 rpm (at least).

Use the light to set advance to 32-degrees - while the engine is running and maintaining at least 3500 rpm.
Shut it off, tighten the distributor clamp, then start it up again and measure, again at 3500, to make sure nothing moved and you're still at 32-degrees.

NOW - let it idle (leave the vacuum disconnected and plugged), and use the light to measure what the timing is at idle. You're not going to change anything, all your adjusting is already done. All you're doing at this point is finding out what setting AT IDLE corresponds to 32 degrees at 3500, so the next time you need to set it you can do it at idle and not have to be fussing with the distributor while the engine is sitting there spinning at 3500 (which can be a little disconcerting if you're not used to it). Record this setting somewhere so you'll have it when you need it.

Reconnect your vacuum advance, and you're done. You now know that your engine will have 32 degrees advance at rpm, under load. (Remember that when you've got your foot in it, there's no manifold vacuum so you won't have any vacuum advance at that point).

Run it like this for awhile and see how it goes. If it's hard to turn over/start when it's warm, then maybe you'll need to modify the distributor advance mechanism (fiddle with the stops) so that you have MORE dynamic/mechanical advance travel in the distributor - which will allow you to still have 32-degrees when you need it yet with less "initial" timing. If you get pinging/knocking at low rpm under load, then you might need to "slow down" the advance curve some (use lighter weights and/or heavier springs) so that you don't reach 32 degrees advance "as soon".

Hope this helps...


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post #4 of 7 (permalink) Old 01-03-2014, 09:06 AM Thread Starter
 
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That makes total sense Bear and thats what I needed to know. Now when you say "fiddle" with the stops, are they adjustable on a stock pontiac hei or is a kit required? What am i expecting to see or deal with if i need to move the stops? Im guessing the stops will allow for more than 32 degrees timing with an acceptable idle / start up is why I ask. I also have a power bond street damper with up to 60 degree marks on it so were good there.

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post #5 of 7 (permalink) Old 01-03-2014, 09:29 AM
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Here's a link to a good photo that shows how the mechanical advance limits work on both a factory points distributor and also an HEI.



Another photo with the shaft removed from the advance/"cam" plate:



To get more mechanical advance, replace the bushing on the pin with a smaller one, and/or elongate the slot that the pin fits into. To reduce the amount of advance, use a fatter bushing and/or weld up the slot to make it smaller.

Note that these operations will almost always require removal and disassembly of the distributor: use a punch to push on the pin that holds the drive gear onto the end of the shaft, then pull the shaft out from the top of the unit.

On aftermarket units, I've seen some variance in how the advance mechanisms work. Some have the pin/bushing in different places, some instead use the shape of the "tails" on the weights as the limits. Once you get it apart and have a look through you should be able to see how yours is designed.

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post #6 of 7 (permalink) Old 01-05-2014, 09:25 AM
 
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Originally Posted by BearGFR View Post
Hokay.... need to understand some basics here first.

An "advance curve kit" (springs and weights) does NOTHING to control "how much" advance you have. Such a kit only changes "how fast" the advance you already have comes in.

Take the cap off your distributor - and if it's not already installed in the car, then secure the "gear end" in a vise or something to immobilize it. Now, using your hand, grab the rotor and (gently) turn it from side to side. Notice that you can feel some springiness in there and that you can turn it a little bit each way before it hits "something solid" and won't turn any farther. How far it turns from one stop to the other is how much "mechanical advance" is "in" the distributor. Underneath the cap and rotor there's a set of springs and weights. The springs will hold the rotor (and the points cam or trigger if it's an HEI) up against one of the stops when it's not spinning. As it spins, and as rpm increases, the weights tend to "fly out" and will overcome the spring tension to begin moving the rotor and cam/trigger towards the other stop until it reaches the stop. The heavier the weights and lighter the springs, the "sooner" this will happen -- but you're still limited by the stops at "both ends".

So..... in your case, what you need is a good timing light that's capable of measuring total advance on a running engine (something like one of these: Innova/Heavy duty housing pro timing light with tool case, test up to 9990 RPM (INN5568) | Timing Light | AutoZone.com or one of these: Actron/Digital timing light (CP7529) | Timing Light | AutoZone.com)

Or, as an alternative you can use a timing tape on your balancer, but make CERTAIN you get the right tape for the size of balancer you have.

Next, disconnect your vacuum advance hose from the distributor and plug it so that you don't have air leaking into your intake manifold.

Loosen the distributor clamp nut just enough so that you can turn the distributor with some effort - you don't want it really loose.
Start the engine, hold it at a steady 3500 rpm (at least).

Use the light to set advance to 32-degrees - while the engine is running and maintaining at least 3500 rpm.
Shut it off, tighten the distributor clamp, then start it up again and measure, again at 3500, to make sure nothing moved and you're still at 32-degrees.

NOW - let it idle (leave the vacuum disconnected and plugged), and use the light to measure what the timing is at idle. You're not going to change anything, all your adjusting is already done. All you're doing at this point is finding out what setting AT IDLE corresponds to 32 degrees at 3500, so the next time you need to set it you can do it at idle and not have to be fussing with the distributor while the engine is sitting there spinning at 3500 (which can be a little disconcerting if you're not used to it). Record this setting somewhere so you'll have it when you need it.

Reconnect your vacuum advance, and you're done. You now know that your engine will have 32 degrees advance at rpm, under load. (Remember that when you've got your foot in it, there's no manifold vacuum so you won't have any vacuum advance at that point).

Run it like this for awhile and see how it goes. If it's hard to turn over/start when it's warm, then maybe you'll need to modify the distributor advance mechanism (fiddle with the stops) so that you have MORE dynamic/mechanical advance travel in the distributor - which will allow you to still have 32-degrees when you need it yet with less "initial" timing. If you get pinging/knocking at low rpm under load, then you might need to "slow down" the advance curve some (use lighter weights and/or heavier springs) so that you don't reach 32 degrees advance "as soon".

Hope this helps...


Bear
this is a very good "how to" on timing.
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post #7 of 7 (permalink) Old 01-16-2014, 07:22 PM Thread Starter
 
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Perfect advice. I got my 32 degrees with 14 initial. Id like 10 initial with 32 total for easier starting though.

You outta see her on a road course, or a quarter mile
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