Another Distributor/Timing Question....
Thread Starter
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Another Distributor/Timing Question....
My 69 427/390 has the original motor and is stock except for a mild roller cam. The original distributor has been converted to Pertronix from points and these are the numbers I get with my timing light.
Initial advance of 16 degrees with a mechanical or centrifugal advance of 17 degrees for a total of 33 degrees. Idle is set at 800 rpm and mechanical advance starts at 1200 rpm and is all in by 3000. The vacuum can produces another 16 degrees and at idle the vacuum is 17.5"hg.
My shop manual says that the stock mechanical advance from the factory was 24 degrees so my question is why would someone reduce it which then requires such a high initial advance? Are there any pros or cons to running it like this? The engine starts easily, runs strong and smooth with no hesitation anywhere, no pinging or knocking on 91 octane and I have no complaints. Just wondering what the pros and cons are to running such a low centrifugal advance requiring that high an initial. If I wanted to run 36 total I would have to bump up the initial to 19 degrees....
Thanks guys!
Initial advance of 16 degrees with a mechanical or centrifugal advance of 17 degrees for a total of 33 degrees. Idle is set at 800 rpm and mechanical advance starts at 1200 rpm and is all in by 3000. The vacuum can produces another 16 degrees and at idle the vacuum is 17.5"hg.
My shop manual says that the stock mechanical advance from the factory was 24 degrees so my question is why would someone reduce it which then requires such a high initial advance? Are there any pros or cons to running it like this? The engine starts easily, runs strong and smooth with no hesitation anywhere, no pinging or knocking on 91 octane and I have no complaints. Just wondering what the pros and cons are to running such a low centrifugal advance requiring that high an initial. If I wanted to run 36 total I would have to bump up the initial to 19 degrees....
Thanks guys!
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
My 69 427/390 has the original motor and is stock except for a mild roller cam. The original distributor has been converted to Pertronix from points and these are the numbers I get with my timing light.
Initial advance of 16 degrees with a mechanical or centrifugal advance of 17 degrees for a total of 33 degrees. Idle is set at 800 rpm and mechanical advance starts at 1200 rpm and is all in by 3000. The vacuum can produces another 16 degrees and at idle the vacuum is 17.5"hg.
My shop manual says that the stock mechanical advance from the factory was 24 degrees so my question is why would someone reduce it which then requires such a high initial advance? Are there any pros or cons to running it like this? The engine starts easily, runs strong and smooth with no hesitation anywhere, no pinging or knocking on 91 octane and I have no complaints. Just wondering what the pros and cons are to running such a low centrifugal advance requiring that high an initial. If I wanted to run 36 total I would have to bump up the initial to 19 degrees....
Thanks guys!
Initial advance of 16 degrees with a mechanical or centrifugal advance of 17 degrees for a total of 33 degrees. Idle is set at 800 rpm and mechanical advance starts at 1200 rpm and is all in by 3000. The vacuum can produces another 16 degrees and at idle the vacuum is 17.5"hg.
My shop manual says that the stock mechanical advance from the factory was 24 degrees so my question is why would someone reduce it which then requires such a high initial advance? Are there any pros or cons to running it like this? The engine starts easily, runs strong and smooth with no hesitation anywhere, no pinging or knocking on 91 octane and I have no complaints. Just wondering what the pros and cons are to running such a low centrifugal advance requiring that high an initial. If I wanted to run 36 total I would have to bump up the initial to 19 degrees....
Thanks guys!
Thread Starter
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Thanks guys. I'm going to bump it up a couple of degrees so I have 35 total and see how it works. I just couldn't get past the idea of running so much initial but I guess it's the total that really matters as it starts and runs really nice. I thought it might be a little slow cranking on hot starts with that much initial but it's no diff from cold.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
My 69 427/390 has the original motor and is stock except for a mild roller cam. The original distributor has been converted to Pertronix from points and these are the numbers I get with my timing light.
Initial advance of 16 degrees with a mechanical or centrifugal advance of 17 degrees for a total of 33 degrees. Idle is set at 800 rpm and mechanical advance starts at 1200 rpm and is all in by 3000. The vacuum can produces another 16 degrees and at idle the vacuum is 17.5"hg.
My shop manual says that the stock mechanical advance from the factory was 24 degrees so my question is why would someone reduce it which then requires such a high initial advance? Are there any pros or cons to running it like this? The engine starts easily, runs strong and smooth with no hesitation anywhere, no pinging or knocking on 91 octane and I have no complaints. Just wondering what the pros and cons are to running such a low centrifugal advance requiring that high an initial. If I wanted to run 36 total I would have to bump up the initial to 19 degrees....
Thanks guys!
Initial advance of 16 degrees with a mechanical or centrifugal advance of 17 degrees for a total of 33 degrees. Idle is set at 800 rpm and mechanical advance starts at 1200 rpm and is all in by 3000. The vacuum can produces another 16 degrees and at idle the vacuum is 17.5"hg.
My shop manual says that the stock mechanical advance from the factory was 24 degrees so my question is why would someone reduce it which then requires such a high initial advance? Are there any pros or cons to running it like this? The engine starts easily, runs strong and smooth with no hesitation anywhere, no pinging or knocking on 91 octane and I have no complaints. Just wondering what the pros and cons are to running such a low centrifugal advance requiring that high an initial. If I wanted to run 36 total I would have to bump up the initial to 19 degrees....
Thanks guys!
Does it look like the stock flyweights have been removed and replaced with zinc-plated aftermarket flyweights? Perhaps a previous owner put a kit into it at some earlier time. If so it could account for the less mechanical advance. And the mechanical advance does not "require" a higher initial advance to achieve a certain total. If I remember correctly most stock distributors didn't exceed 30 degrees total but rather somewhere in the high 20's. The 36 degree figure is a desired figure for racing applications for maximum power using high octane gasoline.
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Thanks guys. I'm going to bump it up a couple of degrees so I have 35 total and see how it works. I just couldn't get past the idea of running so much initial but I guess it's the total that really matters as it starts and runs really nice. I thought it might be a little slow cranking on hot starts with that much initial but it's no diff from cold.
Thread Starter
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Does it look like the stock flyweights have been removed and replaced with zinc-plated aftermarket flyweights? Perhaps a previous owner put a kit into it at some earlier time. If so it could account for the less mechanical advance. And the mechanical advance does not "require" a higher initial advance to achieve a certain total. If I remember correctly most stock distributors didn't exceed 30 degrees total but rather somewhere in the high 20's. The 36 degree figure is a desired figure for racing applications for maximum power using high octane gasoline.
Intermediate
Joined: Jul 2019
Posts: 30
Likes: 9
First, don't assume that what a factory manual says for the timing to be gospel, or even accurate. Especially on a 50 year old distributor. The only way to know is to actually check it. Factory GM distributors were normally around 24-26 degrees advanced, but way up around 4000 to 4500 rpm fully advanced with their big heavy springs.
If you are wanting the best performance, I would suggest any one of the aftermarket distributors out there where you can choose how fast the timing curve comes in and how much total mechanical advance it will give. Just changing the springs and weights on a stock distributor will not change the total advance. Only when it will happen.
A distributor like a MSD 8360 will allow you to dial in your curve exactly like you want. Like others have said, 18 degrees initial, plus 18 degrees of mechanical for a total of 36 would be great on your 454. Big blocks like less mechanical and more initial, especially with big cams that bleed off cylinder pressure.
If you are wanting the best performance, I would suggest any one of the aftermarket distributors out there where you can choose how fast the timing curve comes in and how much total mechanical advance it will give. Just changing the springs and weights on a stock distributor will not change the total advance. Only when it will happen.
A distributor like a MSD 8360 will allow you to dial in your curve exactly like you want. Like others have said, 18 degrees initial, plus 18 degrees of mechanical for a total of 36 would be great on your 454. Big blocks like less mechanical and more initial, especially with big cams that bleed off cylinder pressure.
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