Timing adjustment - 455 pontiac - Pontiac GTO Forum
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post #1 of 11 (permalink) Old 01-08-2018, 02:50 AM Thread Starter
 
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Timing adjustment - 455 pontiac

Hello everyone,

Im rebuilding the 455 and now just adjusting the timing,

The car is for street strip, edelbrock intake , long tube headers, a big cam!

I set the timing to 14 initial timing and 36 total timing.

Should i set it the same or maybe lower it to 12 initial and 34 total.

Recommendations?

Thanks!
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post #2 of 11 (permalink) Old 01-08-2018, 07:00 PM
 
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Originally Posted by TheGoatFather1965 View Post
Hello everyone,

Im rebuilding the 455 and now just adjusting the timing,

The car is for street strip, edelbrock intake , long tube headers, a big cam!

I set the timing to 14 initial timing and 36 total timing.

Should i set it the same or maybe lower it to 12 initial and 34 total.

Recommendations?

Thanks!
I would go with the 12/34 to start. Might even go with 10/32 to begin with and then jump it up once I knew the engine did not "ping." Have your timing light in hand when you fire up the engine to break it in and basically listen to it and watch your water temp. If it should run a little warm, then bump it up a little. Retarded timing will cause the engine to run hotter, but too advanced will make the engine ping under load -unless you are running racing gas. So you will have to judge for yourself on this one and find the best initial timing setting.
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post #3 of 11 (permalink) Old 01-09-2018, 04:51 AM Thread Starter
 
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I would go with the 12/34 to start. Might even go with 10/32 to begin with and then jump it up once I knew the engine did not "ping." Have your timing light in hand when you fire up the engine to break it in and basically listen to it and watch your water temp. If it should run a little warm, then bump it up a little. Retarded timing will cause the engine to run hotter, but too advanced will make the engine ping under load -unless you are running racing gas. So you will have to judge for yourself on this one and find the best initial timing setting.
PontiacJim,

The car is now running fine i set it at 14 intial and 35 total, i might re-set it because i set these without hooking up distributor vacuum advance.

I had a vacuum leak in the hose so thats why i set it like this temporarily until i find me a proper hose.

This means i have 21 mechanical advance right, so if i say set it to 12 im going to get 33 of total timing.
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post #4 of 11 (permalink) Old 01-09-2018, 09:35 AM
 
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Hey - seeing is how I just went through this a few times, I'll pay it forward....

Your vacuum advance should be disconnected and the port on the carb plugged. That vacuum is only present under very light load - idle/cruising. The timing should be set with this disconnected and plugged, so that when you move up through the RPM ranges, you're simulating WOT out on the road (no vacuum advance).

Here's a link that helped me: http://outintheshop.com/faq/Lars%20timing%20.pdf

And....channeling my inner PontiacJim, use the search feature in this forum and you'll find the topic has been covered extensively. :-)
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post #5 of 11 (permalink) Old 01-09-2018, 10:00 AM Thread Starter
 
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Hey - seeing is how I just went through this a few times, I'll pay it forward....

Your vacuum advance should be disconnected and the port on the carb plugged. That vacuum is only present under very light load - idle/cruising. The timing should be set with this disconnected and plugged, so that when you move up through the RPM ranges, you're simulating WOT out on the road (no vacuum advance).

Here's a link that helped me: http://outintheshop.com/faq/Lars%20timing%20.pdf

And....channeling my inner PontiacJim, use the search feature in this forum and you'll find the topic has been covered extensively. :-)
Hello bredfan,

When i was adjusting the timing it was as said, for it to read correctly I disconnected the vacuum from the distributer side and covered it on the carb side.

When i reinstall the vacuum hose will i get the same timing or will it change?

The link you posted explains that point ill read about it.

Thanks alot!
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post #6 of 11 (permalink) Old 01-09-2018, 08:01 PM
 
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Originally Posted by TheGoatFather1965 View Post
Hello bredfan,

When i was adjusting the timing it was as said, for it to read correctly I disconnected the vacuum from the distributer side and covered it on the carb side.

When i reinstall the vacuum hose will i get the same timing or will it change?

The link you posted explains that point ill read about it.

Thanks alot!
If the vacuum line from the distributor is connected to a manifold source, the timing will advance additionally once you hook up the line (initial 12 degrees at the crank PLUS your vacuum advance which is typically about 12 degrees for a total of 24 degrees).

If the vacuum line from the distributor is connected to a "ported" source on the carb (typically a fitting above the throttle plate) it will remain the same as what you timed it at UNTIL the carb is cracked open in part throttle to expose the ported source to manifold vacuum.

At wide-open-throttle, there is no manifold vacuum to speak of. This is where mechanical advance comes in and takes over.
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post #7 of 11 (permalink) Old 01-10-2018, 01:38 AM Thread Starter
 
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Originally Posted by PontiacJim View Post

If the vacuum line from the distributor is connected to a manifold source, the timing will advance additionally once you hook up the line (initial 12 degrees at the crank PLUS your vacuum advance which is typically about 12 degrees for a total of 24 degrees).

If the vacuum line from the distributor is connected to a "ported" source on the carb (typically a fitting above the throttle plate) it will remain the same as what you timed it at UNTIL the carb is cracked open in part throttle to expose the ported source to manifold vacuum.

At wide-open-throttle, there is no manifold vacuum to speak of. This is where mechanical advance comes in and takes over.
Hello PontiacJim,

Then i should be alright as im going to plug in the vacuum line on the distributer side and the vacuum port on the carb side.

Then it shouldn’t change i will re-check the timing. I usually check my total timing at 4000rpm, would this give me an accurate degree?


Thanks PJ!
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post #8 of 11 (permalink) Old 01-10-2018, 10:52 AM
 
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Originally Posted by Bredfan View Post
Hey - seeing is how I just went through this a few times, I'll pay it forward....

Your vacuum advance should be disconnected and the port on the carb plugged. That vacuum is only present under very light load - idle/cruising. The timing should be set with this disconnected and plugged, so that when you move up through the RPM ranges, you're simulating WOT out on the road (no vacuum advance).

Here's a link that helped me: http://outintheshop.com/faq/Lars%20timing%20.pdf

And....channeling my inner PontiacJim, use the search feature in this forum and you'll find the topic has been covered extensively. :-)
FYI, Lars (the author of the link article) used to be a member here, very knowledgeable, there are several stickys written by him on this forum.
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post #9 of 11 (permalink) Old 01-10-2018, 04:02 PM
 
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Originally Posted by TheGoatFather1965 View Post
PontiacJim,

The car is now running fine i set it at 14 intial and 35 total, i might re-set it because i set these without hooking up distributor vacuum advance.

I had a vacuum leak in the hose so thats why i set it like this temporarily until i find me a proper hose.

This means i have 21 mechanical advance right, so if i say set it to 12 im going to get 33 of total timing.
Correct....

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #10 of 11 (permalink) Old 01-10-2018, 07:12 PM
 
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Originally Posted by TheGoatFather1965 View Post
Hello PontiacJim,

Then i should be alright as im going to plug in the vacuum line on the distributer side and the vacuum port on the carb side.

Then it shouldn’t change i will re-check the timing. I usually check my total timing at 4000rpm, would this give me an accurate degree?


Thanks PJ!
Total can be in at a number of RPM's ranges based on the mechanical advance weight/springs - that is how you tailor your advance curve.

Do not know what timing light you are using or if you have a timing tape on your balancer. I like to use a dial back timing light as it is a bit easier to use because when you hit the timing advance you set the dial to (ie 34 degrees), your timing mark on the balancer will be at zero. Using a regular timing light, you need a timing tape to accurately get your reading for full advance so you can read off of it. With a dial-back timing light, set it at the desired "all-in" advance and bring the RPM's up slowly and watch the RPM's. When the advance stops, that is the total RPM number full advance is realized. Could be anywhere from 3,200 to 4,000 RPM's.

You can also watch to see when the mechanical advance begins to kick in and your timing begins to move up from the Initial setting on the balancer, which may be from 1,000 - 1,500 RPM's.

Disconnect your vacuum advance to get total advance - Initial (balancer) + Mechanical (Distrib. weights). This will also tell you how many degrees your mechanical advance is simply by knowing what you set the Initial advance on the balancer minus your total advance number. If you had 12 Initial minus 34 Total, your Mechanical Advance would be 22 degrees.

Keep in mind that these numbers can change once you get the car on the road and the engine is under load, and it is a 95 degree summer day. You may need to retard the timing if you hear any kind of engine pinging.
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