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  #31 (permalink)  
Old 07-13-2010, 10:49 AM
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Quote:
Originally Posted by kyle86
Oh also made a little J looking limiter plate out of some scrap kind of like the pic Cobalt327 posted. I took about half the travel out. I'll drive it some and see if that helps any.

Just as a note on this to point something out, if the current setup is working for you then so be it but...

Your limiter plate is on the opposite side of the can push rod than the crane part, the crane limiter sits under the other screw and limits the amount that the rod can travel back thus shortening the total travel which equates to less advance added when in operation (this effects your base timing so you need to reset it after installing the crane part) With what you have you are in effect limiting the travel of the can push rod however the can will start to add vac advance at the same time as it did before. Since you do not have an adjustable vac can set screw it would be advantageous to put the limiter on the back side as the crane one does, this will raise the effective start point of the vacuum advance coming in because the spring is preloaded by the limiter plate and therefor it will drop out sooner as well so when the engine vacuum drops on light trottle the vac advance will disappear sooner which may help a pinging issue.

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  #32 (permalink)  
Old 07-13-2010, 10:51 AM
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Quote:
Originally Posted by bubbahotep
Is 15' intial and 32' total correct for your engine? I thought a 383 would be at 20' idle 36-38' total.

Edit: the reason I ask is because I had my 383 at low timing once and that forced me to have my idle-speed screw on the carb set too far down (to raise my rpm). I had similar issues as you. This board solved all that
It's been higher. I've ran 22 initial and 36 total before with good results. That was in the winter though, during this heat, I've been having to run around 19 initial and 36 total. What happened was I got bad gas a couple weeks ago and had to back off the timing 4 degrees to stay out of destination in this 90 degree weather. I figured I would just leave it at 15/32 for street driving in case it happens again.

I did have to idle up the screw to compensate for the lost rpm. I've been contemplating on pulling off the carb and using the secondry throttle blade adjustment to let more air in at idle. Never messed with that before tho.
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  #33 (permalink)  
Old 07-13-2010, 10:58 AM
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Quote:
Originally Posted by kyle86
It's been higher. I've ran 22 initial and 36 total before with good results. That was in the winter though, during this heat, I've been having to run around 19 initial and 36 total. What happened was I got bad gas a couple weeks ago and had to back off the timing 4 degrees to stay out of destination in this 90 degree weather. I figured I would just leave it at 15/32 for street driving in case it happens again.

I did have to idle up the screw to compensate for the lost rpm. I've been contemplating on pulling off the carb and using the secondry throttle blade adjustment to let more air in at idle. Never messed with that before tho.
you could try using manifold vacuum instead of ported, this would add the extra timing at idle lost by backing down the base timing then you can back down the idle screw so as not to expose the transfer slots too much. Again this is were an adjustable can comes into play as well cause you can tinker with how much advance is added at idle by the vacuum can.
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Old 07-13-2010, 12:28 PM
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Quote:
Originally Posted by Custom10
you could try using manifold vacuum instead of ported, this would add the extra timing at idle lost by backing down the base timing then you can back down the idle screw so as not to expose the transfer slots too much. Again this is were an adjustable can comes into play as well cause you can tinker with how much advance is added at idle by the vacuum can.
Thanks. I've already tried that though. The rpm drop from being in park and then into gear was just too much and it jerked the car. It would be like 1000 in park down to 550 in gear because of this vac can. I get 11" in park and 6-8" in gear. I think I'm going to pull the carb off and look at the transition slots and see if they're open too much.
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  #35 (permalink)  
Old 07-13-2010, 12:32 PM
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Quote:
Originally Posted by Custom10
Just as a note on this to point something out, if the current setup is working for you then so be it but...

Your limiter plate is on the opposite side of the can push rod than the crane part, the crane limiter sits under the other screw and limits the amount that the rod can travel back thus shortening the total travel which equates to less advance added when in operation (this effects your base timing so you need to reset it after installing the crane part) With what you have you are in effect limiting the travel of the can push rod however the can will start to add vac advance at the same time as it did before. Since you do not have an adjustable vac can set screw it would be advantageous to put the limiter on the back side as the crane one does, this will raise the effective start point of the vacuum advance coming in because the spring is preloaded by the limiter plate and therefor it will drop out sooner as well so when the engine vacuum drops on light trottle the vac advance will disappear sooner which may help a pinging issue.
That is a good idea, I didn't think about that. I might just have to buy an adjustable vac can then. I don't think this one works very well with my combo.

Or maybe I'll try welding a hook type deal on my little limiter plate that will limit it from the back side. I don't know if it's more trouble then it's worth though to mess with it. OR maybe I can fab something else up to work kind of like the crane limiter.

Last edited by kyle86; 07-13-2010 at 12:42 PM.
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  #36 (permalink)  
Old 07-13-2010, 01:10 PM
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the crane limiter plate is very inexpensive and is fully adjustable so you can change its effective range, but it seems like you like to fabricate things up yourself...OK then, I would buy both the plate and the new adjustable can if it were me but I like to spend $$ on my truck it seems...just ask my wife. Good luck
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  #37 (permalink)  
Old 07-13-2010, 01:17 PM
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The Crane limiter plate is an easy fab- the last one I did in about 5 min. out of a quarter coin. But I cheated by using a real one as a template.
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  #38 (permalink)  
Old 07-13-2010, 05:30 PM
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It's still pinging going uphill. I know it's the vacuum advance because I disconnected it and it stopped. I guess I'm going to have to buy an adjustable can.

Last edited by kyle86; 07-13-2010 at 06:09 PM.
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  #39 (permalink)  
Old 07-13-2010, 06:14 PM
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You shoulod want around 52 degrees total timing. Since most factory vacuum cans make 15-16 degrees of ADVANCE (not vacuum), 36 degrees of inital and mechanical would put you in the ball park with 15 degrees of vacuum ADVANCE. To solve your pinging, either reduce your initial, limit your mechanical, or adjust your vacuum advances. Your engine is no different than any other when it comes to timing.
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  #40 (permalink)  
Old 07-13-2010, 07:43 PM
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Quote:
Originally Posted by cool rockin daddy
You shoulod want around 52 degrees total timing. Since most factory vacuum cans make 15-16 degrees of ADVANCE (not vacuum), 36 degrees of inital and mechanical would put you in the ball park with 15 degrees of vacuum ADVANCE. To solve your pinging, either reduce your initial, limit your mechanical, or adjust your vacuum advances. Your engine is no different than any other when it comes to timing.
I dont agree with adjusting the mechanical. If you limit your mechanical you're never going to get the TOTAL timing youd need if you do a wide open throttle run (WOT). I think the only thing that needs correcting is the vac advance limiting. If you take anything away from the mechanical advance you'll never get proper TOTAL TIMING which is 36'
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  #41 (permalink)  
Old 07-13-2010, 07:52 PM
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yes, you do. You increase the initial. If you run 18-20 initial you are gonna have to reduce the amount of mechanical either by throwing a larger bushing on (when using a distributor with adjustable mechanical advance) or you're going to have to shorten the slots on the advance mechanism. Of course, limiting the mechanical is the most difficult to do if you don't have a distributor that is adjustable but sometimes you gotta do what you gotta do.
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  #42 (permalink)  
Old 07-14-2010, 12:06 AM
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Quote:
Originally Posted by cool rockin daddy
yes, you do. You increase the initial. If you run 18-20 initial you are gonna have to reduce the amount of mechanical either by throwing a larger bushing on (when using a distributor with adjustable mechanical advance) or you're going to have to shorten the slots on the advance mechanism. Of course, limiting the mechanical is the most difficult to do if you don't have a distributor that is adjustable but sometimes you gotta do what you gotta do.
That's not the problem. I've already disassembled the distributor, welded up and ground my advance slots 3 times already. I got the initial and mechanical timing dead on it's nuts. We think the problem is the vacuum advance isn't dropping out soon enough causing it to ping when I lightly tip in the throttle. Custom10 pointed out in an above post that the adjuster plate I made for my vacuum advance is limiting the advance from the wrong side. I made another limiter to mount on the opposite side same as the crane one that I'm going to try tomorow.
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  #43 (permalink)  
Old 07-14-2010, 12:25 AM
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Quote:
Originally Posted by kyle86
That's not the problem. I've already disassembled the distributor, welded up and ground my advance slots 3 times already. I got the initial and mechanical timing dead on it's nuts. We think the problem is the vacuum advance isn't dropping out soon enough causing it to ping when I lightly tip in the throttle. Custom10 pointed out in an above post that the adjuster plate I made for my vacuum advance is limiting the advance from the wrong side. I made another limiter to mount on the opposite side same as the crane one that I'm going to try tomorow.
At light throttle cruise, the vacuum is as high as it is going to get. There's no way to lower the vacuum, or to set the vacuum advance to not be fully advanced at the maximum amount of vacuum that it will ever see, short of at idle. This is going to be the case, no matter what side the limiter is on.

The difference in where the limiter is (in front or behind like the Crane), has NO effect on how much vacuum it takes to first move the vacuum advance rod on the can I'm testing right now. Intuitively it may seem that it would be otherwise, but for that to be the case, the spring inside the vacuum advance can would have to be a progressively wound spring.

At least in the case of the can I just tested, this is not the case- but the real test would be on the one that you're using. What MY cans do or don't do won't help you either way, other than to see if there's a trend. So before assuming anything- check your can w/a MityVac like I just did. My can's marked AR16, BTW.

On my can, the same amount of vacuum causes the initial movement of the rod. Same amount of vacuum to begin the decrease of advance. This is whether the rod has had 1/2 of its travel taken up by a spacer placed in front or behind the rod. The same ~4 in/HG moves the rod, either way.

If there's a reason to, I have numerous vacuum advance cans out in the shop that I will be happy to test tomorrow to see whether they behave the same or not.

In any event, I believe if limiting the total vacuum advance amount that the can is set to provide doesn't do it- then nothing involving the vacuum advance will do it, period.

Last edited by cobalt327; 07-14-2010 at 12:59 AM.
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  #44 (permalink)  
Old 07-14-2010, 10:56 AM
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Quote:
Originally Posted by cobalt327
At light throttle cruise, the vacuum is as high as it is going to get. There's no way to lower the vacuum, or to set the vacuum advance to not be fully advanced at the maximum amount of vacuum that it will ever see, short of at idle. This is going to be the case, no matter what side the limiter is on.

The difference in where the limiter is (in front or behind like the Crane), has NO effect on how much vacuum it takes to first move the vacuum advance rod on the can I'm testing right now. Intuitively it may seem that it would be otherwise, but for that to be the case, the spring inside the vacuum advance can would have to be a progressively wound spring.

At least in the case of the can I just tested, this is not the case- but the real test would be on the one that you're using. What MY cans do or don't do won't help you either way, other than to see if there's a trend. So before assuming anything- check your can w/a MityVac like I just did. My can's marked AR16, BTW.

On my can, the same amount of vacuum causes the initial movement of the rod. Same amount of vacuum to begin the decrease of advance. This is whether the rod has had 1/2 of its travel taken up by a spacer placed in front or behind the rod. The same ~4 in/HG moves the rod, either way.

If there's a reason to, I have numerous vacuum advance cans out in the shop that I will be happy to test tomorrow to see whether they behave the same or not.

In any event, I believe if limiting the total vacuum advance amount that the can is set to provide doesn't do it- then nothing involving the vacuum advance will do it, period.
Have you found that the preload on the spring doesn't cause it to drop out faster if limited from the back (Crane) verses the front?

Say on the AR16, around 4" the arm starts to move and it's total advance is in around 15". If it's limited to 10 degrees the way I did mine, wouldn't the advance start to move around 4", but hit the limiter around say 8" vacuum instead of the total 15" needed to move the whole arm then entire distance?

Then if it's limited to 10 degrees the crane way from the back side of the arm, you would think that it would have to make it all the way to that 15" before all the advance was in regardless of where it started since the arm has to move all the way to it's factory stop right? I don't have access to a vacuum pump right now so I don't know.

Last edited by kyle86; 07-14-2010 at 11:03 AM.
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  #45 (permalink)  
Old 07-14-2010, 11:48 AM
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"The difference in where the limiter is (in front or behind like the Crane), has NO effect on how much vacuum it takes to first move the vacuum advance rod on the can I'm testing right now".

I am quite sure that changing the springs nominal position or position without any vacuum will effect the point at which it starts to move due to a vacuum force applied to the diaphragm. The limiter plate on the back side as I stated will push against the rod which in turn will put some preload on the spring. This should effectively raise the pressure that is needed to begin to move the rod. However I am not the one doing this with a dist so I don't doubt your findings cobalt but I will try it myself. This is a cut from the crane instruction sheet that states that changing the springs nominal position with the limiter plate at the back of the rod may require an adjustment to the cans spring set screw in-ward or clockwise which on my dist anyway causes the vacuum to come in sooner, so the nominal spring pressure must have an effect on the start point of the movement...or so it seems "intuitively"

As vacuum timing is decreased it will automatically increase tension on the vacuum diaphragm spring. It may be necessary to decrease tension
by turning the allen screw adjuster inside the vacuum port of the canister clockwise.
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