Help with the right timing vacuum can selection, please?
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Help with the right timing vacuum can selection, please?
Just received my all dancing all singing HEI MSD Distributor (p.n. 8365) and set my initial and total timing however, now I need a help to pick a correct vacuum can for my application.
My 383 with roller cam is running 12.5HG of vacuum at idle and my initial timing is set to 16* with total of 34* at 3050RPM. (I can go to 18 initial and total 36, but for now I am happy with my setting)
All good, so far.
The supplied MSD vacuum can when connected directly to the MANIFOLD vacuum port advances my timing by 19* which is too much!
Could you please recommend a suitable vacuum can, please?
Also my Holley SA 770CFM carb comes with 6,5 HG power valve as standard, should I keep it with my 12.5HG idle vacuum, or should I change it to a different one?
Thank you
Paul
My 383 with roller cam is running 12.5HG of vacuum at idle and my initial timing is set to 16* with total of 34* at 3050RPM. (I can go to 18 initial and total 36, but for now I am happy with my setting)
All good, so far.
The supplied MSD vacuum can when connected directly to the MANIFOLD vacuum port advances my timing by 19* which is too much!
Could you please recommend a suitable vacuum can, please?
Also my Holley SA 770CFM carb comes with 6,5 HG power valve as standard, should I keep it with my 12.5HG idle vacuum, or should I change it to a different one?
Thank you
Paul
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
I don't think its way too much for the way you have your car set up. You should have a max of 52-54 degrees with everything all in. With 34 deg total mechanical advance, you can tolerate 18-20 deg of vac advance. You're not that far off. You have any detonation?
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
34 + 19 = 53, which should be just about perfect. If you advance your timing any more, say up to 36 or 38 all in, you will probably need a vac can which pulls a few less degrees, in which case, an email to Lars will hook you up with a document which will make everything clear.
Scott
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
I have read few articles about timing and they all suggest to run no more than 52* .
With my 34* and 19* I am getting 53*, but would like to be on safe side and run 50* all in.
Ideally I would like a can with 16* of advance which will leave me room for 2* of advance should I need to.
With my 34* and 19* I am getting 53*, but would like to be on safe side and run 50* all in.
Ideally I would like a can with 16* of advance which will leave me room for 2* of advance should I need to.
Last edited by C3Paul; Feb 17, 2013 at 06:24 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,392
From: At my Bar drinking and wrenching in Lafayette Colorado
C3P -
With current pump gas formulations, the previous 52-54 degree total combined timing number at elevated rpm cruise is no longer a good number: It can cause "trailer hitching" and jerking with a little too much vacuum advance. For that reason, we're now recommending vacuum advance be limited to 12 - 14 degrees. Unfortunately, very few vacuum advance control units have a 12 - 14 degree curve with the desirable "all-in" vacuum number, so you have to modify what's available to get what you want.
If your current vacuum advance control unit pulls all the way in at your 12.5" of vacuum, keep the can, but shorten it just a tad. You can do this in one of 2 ways:
1. Following the instructions in my Vacuum Advance tech paper, you can calculate how much to shorten the "stroke." Weld a little dab into the end of the limit slot on the vacuum can and grind it to the right length to get the 12 - 14 degrees.
-or-
2. Slip a piece of hard rubber tubing over the "pin" on the vacuum advance control unit - this will limit its travel in the slot. A rubber "sleeve" the same diameter as the width of the slot will shorten the curve perfectly. Trim the sleeve to length so it stays sandwiched under the breaker plate attach hole.
Lars
With current pump gas formulations, the previous 52-54 degree total combined timing number at elevated rpm cruise is no longer a good number: It can cause "trailer hitching" and jerking with a little too much vacuum advance. For that reason, we're now recommending vacuum advance be limited to 12 - 14 degrees. Unfortunately, very few vacuum advance control units have a 12 - 14 degree curve with the desirable "all-in" vacuum number, so you have to modify what's available to get what you want.
If your current vacuum advance control unit pulls all the way in at your 12.5" of vacuum, keep the can, but shorten it just a tad. You can do this in one of 2 ways:
1. Following the instructions in my Vacuum Advance tech paper, you can calculate how much to shorten the "stroke." Weld a little dab into the end of the limit slot on the vacuum can and grind it to the right length to get the 12 - 14 degrees.
-or-
2. Slip a piece of hard rubber tubing over the "pin" on the vacuum advance control unit - this will limit its travel in the slot. A rubber "sleeve" the same diameter as the width of the slot will shorten the curve perfectly. Trim the sleeve to length so it stays sandwiched under the breaker plate attach hole.
Lars
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,392
From: At my Bar drinking and wrenching in Lafayette Colorado
The paper posted on that website is grossly out of date and completely obsolete - don't use it. E-mail me for current information and papers.
Lars
V8FastCars@msn.com
Lars
V8FastCars@msn.com
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Do not change the PV unless you have a flat spot when accelerating just prior to the PV opening - if you did, an 8.5 would enrichen the mixture sooner. Conversely, if it is too rich while accelerating at between 6.5 and 4.5" Hg, try a 4.5 PV. Most likely the 6.5 will work best!
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Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
The paper posted on that website is grossly out of date and completely obsolete - don't use it. E-mail me for current information and papers.
Lars
V8FastCars@msn.com
Lars
V8FastCars@msn.com
Paul, How is it running?
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Still a little rich and therefore I am trying to set the timing bofore I start adjusting the carb.
I am very interested to hear about the change in timing setting however, I have few questions.
I live in the UK, 5 miles from the sea. Nice! This means that the average temperature is about 19*C, there is no issue with altitude AND I am using 98(GB) RON Octane fuel which is 93-94US (AKI)
How does this affect my timing?
2, I am thinking of buying this vacuum can and modify it if need be:
VC1843 AR15. 3-5 7.5 @ 9-11
Good choice?
3, Sorry, but this may be a little strange question.
This is my digital timing light and when I use it, I always connect the power supply to the ALTERNATOR, rather than Battery, Is this OK?
http://www.iequus.com/Product/Detail...0-3D36BC2E44BE
And lastly, this is what I do not understand at all!!
The timing is set to 16* initial and for this picture the balancer is dead on 16*.
I have marked the timing rotor with the distributor housing, but when I put the cap on, the rotor arm is beyond the #1 terminal post and not directy under the terminal.
WHY?
So, what I am trying to understad is that if I move the ballancer to TDC, the rotor arm will be even more further away from the #1 terminal?
I am very interested to hear about the change in timing setting however, I have few questions.
I live in the UK, 5 miles from the sea. Nice! This means that the average temperature is about 19*C, there is no issue with altitude AND I am using 98(GB) RON Octane fuel which is 93-94US (AKI)
How does this affect my timing?
2, I am thinking of buying this vacuum can and modify it if need be:
VC1843 AR15. 3-5 7.5 @ 9-11
Good choice?
3, Sorry, but this may be a little strange question.
This is my digital timing light and when I use it, I always connect the power supply to the ALTERNATOR, rather than Battery, Is this OK?
http://www.iequus.com/Product/Detail...0-3D36BC2E44BE
And lastly, this is what I do not understand at all!!
The timing is set to 16* initial and for this picture the balancer is dead on 16*.
I have marked the timing rotor with the distributor housing, but when I put the cap on, the rotor arm is beyond the #1 terminal post and not directy under the terminal.
WHY?
So, what I am trying to understad is that if I move the ballancer to TDC, the rotor arm will be even more further away from the #1 terminal?
Last edited by C3Paul; Feb 18, 2013 at 11:28 AM.
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
So when when you rotate the distributor to change the timing, you are moving the base and cap. The rotor stays in its place in relation to the cam via the gears.
Many people put a mark on the housing exactly where the #1 terminal is. Then, when you bring the motor to TDC the rotor should point right at that mark on the housing. **This is a reference starting point. ** TDC points at #1
As soon as you change the timing by rotating the distributor housing, the rotor will not line up with your TDC mark on the dist. when the crank is lined up with TDC
So, if you were to move your black mark in pic #2 over to the right so that it is exactly below the #1 terminal, then set the balancer to TDC, you would see a difference. The difference would be the amount of initial timing you have set.
Or, TDC is actually back directly under the #1 terminal. The gap represents the 16* timing you set.
Many people put a mark on the housing exactly where the #1 terminal is. Then, when you bring the motor to TDC the rotor should point right at that mark on the housing. **This is a reference starting point. ** TDC points at #1
As soon as you change the timing by rotating the distributor housing, the rotor will not line up with your TDC mark on the dist. when the crank is lined up with TDC
So, if you were to move your black mark in pic #2 over to the right so that it is exactly below the #1 terminal, then set the balancer to TDC, you would see a difference. The difference would be the amount of initial timing you have set.
Or, TDC is actually back directly under the #1 terminal. The gap represents the 16* timing you set.
Last edited by johnt365; Feb 18, 2013 at 09:12 AM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Well and this is why I am confused.
I have set the initial timing to 16* and the total to 34* with my timing light, changed the springs......
Later on, I wiped off the original mark on the housing and then scribed a new mark on the rotor and the housing. see pic 1
Turned the engine by hand expecting to see the mark on the rotor arm and the housing to line up with the cap at 16*, but imagine my surprise when the rotor passed the cap at 16*.
Basically, my timing light is reading 16* however, in reality the rotor lines up with the cap at 22-24* !?
I have set the initial timing to 16* and the total to 34* with my timing light, changed the springs......
Later on, I wiped off the original mark on the housing and then scribed a new mark on the rotor and the housing. see pic 1
Turned the engine by hand expecting to see the mark on the rotor arm and the housing to line up with the cap at 16*, but imagine my surprise when the rotor passed the cap at 16*.
Basically, my timing light is reading 16* however, in reality the rotor lines up with the cap at 22-24* !?
Last edited by C3Paul; Feb 18, 2013 at 10:01 AM.
Drifting
Joined: Aug 2005
Posts: 1,443
Likes: 65
From: Wauconda IL
I've just been going through this with my distributor and found out that my adjustable Crane vacuum canister totally threw off my distributor rotor phasing to the point that the rotor tip was already PAST the #1 tower by about a 1/4" at the beginning of my advance curve!!
That explained my poor idling and plug fouling issues.
The rotor position will change over the entire advance range-
So theoretically, the rotor should start before the #1 tower and migrate past the #1 tower during the entire advance range. The rotor should be directly under the #1 tower at it's mid-point of your total advance curve (in a perfect world).
In my case (OEM points distributor with Pertronix module), the advance limiter on the Crane Vacuum can is poorly designed and messed up the rotor phasing (in my case) to the point that my rotor tip was closer to the next cylinder on the cap than to #1 at full advance. Not good-
With an HEI, I'm not sure if the issue is as pronounced since the diameter of the cap is much larger, but on the smaller points style distributors, this is crucial. I was able to get my rotor phasing dead-on by modifying the vacuum can limiter to work correctly and by using a MSD adjustable rotor.
That explained my poor idling and plug fouling issues.
The rotor position will change over the entire advance range-
So theoretically, the rotor should start before the #1 tower and migrate past the #1 tower during the entire advance range. The rotor should be directly under the #1 tower at it's mid-point of your total advance curve (in a perfect world).
In my case (OEM points distributor with Pertronix module), the advance limiter on the Crane Vacuum can is poorly designed and messed up the rotor phasing (in my case) to the point that my rotor tip was closer to the next cylinder on the cap than to #1 at full advance. Not good-
With an HEI, I'm not sure if the issue is as pronounced since the diameter of the cap is much larger, but on the smaller points style distributors, this is crucial. I was able to get my rotor phasing dead-on by modifying the vacuum can limiter to work correctly and by using a MSD adjustable rotor.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
I think, I have installed the distributor incorrectly?
Last edited by C3Paul; Feb 18, 2013 at 03:20 PM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
I was trying to be clever and set the balancer to 16* and than set the rotor to match the 16* however, when I started with adjusting the timing I have set my timing light to 0* wheres I should have set it to 16*, shouldn't I?
I think I am 16* out on my timing!
Last edited by C3Paul; Feb 18, 2013 at 03:35 PM.
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
I have eaten entire meals of humble pie on this forum, but I still like to try and be helpful. Moreover, there are usually two ways to skin a cat and troubleshooting is difficult over distance anyhow.
Were it my car, I would start fresh. It sounds like you have a nice dial back light, let the light do the work. Set your light for 16*, then move the dist. till the mark on the balancer lines up with the 0 on the tab.
Were it my car, I would start fresh. It sounds like you have a nice dial back light, let the light do the work. Set your light for 16*, then move the dist. till the mark on the balancer lines up with the 0 on the tab.
