Neighbor.
Total Advance Reading - how to
Thread Starter
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
Total Advance Reading - how to
Steer me in the right direction if I'm wrong. To determine total advance, I set my timing mark at 0. Using my dial back light I ran the engine up to 2400 RPM and and brought H-balancer mark back to zero using the light. I showed 36 degrees on light dial-back. Is this correct.
Next question, If I need to take timing out of an engine, say I need 28 degrees vice 36, how do I do that? Using the stock HEI distributor.
Next question, If I need to take timing out of an engine, say I need 28 degrees vice 36, how do I do that? Using the stock HEI distributor.
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
That is the correct way to do it, 36 is correct if there's no vac. advance, then it is spot on. To take timing out you can adjust the base timing or get a recurve kit & replace the springs and/or weights to modify the advance curve to give less. Why would you want that? (fuel economy?)
Last edited by Twin_Turbo; Jul 12, 2004 at 12:53 PM.
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
Sounds sorta OK assuming you're interested in checking your mechanical timing advance. Just for clarification, here are the steps to check mechanical and total advance:
1) disconnect vacuum line to distributor and plug
2) attach timing light to number 1 spark plug wire
3) start engine and rev to 2400-2500 RPM
4) turn timing advance **** on light until zero is showing on the balancer. The degrees now showing on your timing advance **** is now indicating your total MECHANICAL advance. Most folk say 36 is about optimum. Now, if you're wanting to set to 28, then you'd loosen the bolt holding your distributor and turn it until your balancer is zeroed with 28 showing on your timing light ****.
5) reconnect the vacuum line to the distributor.
6) rev engine to 2500 rpm
7) turn the timing light **** until zero is showing on the balancer The amount now showing on the timing light **** is your TOTAL advance. This number is probably going to be 45,46 or more degrees.
Now, when you say that you're wanting 28 degrees, are you sure you want 28 MECHICANICAL or TOTAL?
1) disconnect vacuum line to distributor and plug
2) attach timing light to number 1 spark plug wire
3) start engine and rev to 2400-2500 RPM
4) turn timing advance **** on light until zero is showing on the balancer. The degrees now showing on your timing advance **** is now indicating your total MECHANICAL advance. Most folk say 36 is about optimum. Now, if you're wanting to set to 28, then you'd loosen the bolt holding your distributor and turn it until your balancer is zeroed with 28 showing on your timing light ****.
5) reconnect the vacuum line to the distributor.
6) rev engine to 2500 rpm
7) turn the timing light **** until zero is showing on the balancer The amount now showing on the timing light **** is your TOTAL advance. This number is probably going to be 45,46 or more degrees.
Now, when you say that you're wanting 28 degrees, are you sure you want 28 MECHICANICAL or TOTAL?
Racer
Joined: Oct 2001
Posts: 271
Likes: 0
From: St Louis MO
Disconnect the vacuum line from the vacuum advance.
Idle the car below 800 rpm.
Read the advance on the indicator using a variable advance timing light (set at 0). This initial advance will probably around 6-10 degrees.
Rev the engine and follow the mark until it advances no further (usually 3000-4000 rpm).
Turn the variable advance **** until the timing mark until it gets back to the original initial timing mark (ie 6-10 degrees).
The reading on the **** is the total mechanical advance built into the distributor. Add that to your initial and that's your total advance. Hooking up the vacuum advance will add to this under low load conditions.
To change total advance, you can simply back down the distributor, decreasing the initial and total. If you change it too far it may decrease idle quality and may not pass emissions.
You can also recurve the distributor to change total mechanical advance by changing the springs and weights. Recurve kits are available through Summit, Jegs, etc.
Idle the car below 800 rpm.
Read the advance on the indicator using a variable advance timing light (set at 0). This initial advance will probably around 6-10 degrees.
Rev the engine and follow the mark until it advances no further (usually 3000-4000 rpm).
Turn the variable advance **** until the timing mark until it gets back to the original initial timing mark (ie 6-10 degrees).
The reading on the **** is the total mechanical advance built into the distributor. Add that to your initial and that's your total advance. Hooking up the vacuum advance will add to this under low load conditions.
To change total advance, you can simply back down the distributor, decreasing the initial and total. If you change it too far it may decrease idle quality and may not pass emissions.
You can also recurve the distributor to change total mechanical advance by changing the springs and weights. Recurve kits are available through Summit, Jegs, etc.
Pro
Joined: Sep 2002
Posts: 690
Likes: 1
From: near Memphis TN
Originally Posted by Hvymtlc5
Steer me in the right direction if I'm wrong. To determine total advance, I set my timing mark at 0. Using my dial back light I ran the engine up to 2400 RPM and and brought H-balancer mark back to zero using the light. I showed 36 degrees on light dial-back. Is this correct.
Next question, If I need to take timing out of an engine, say I need 28 degrees vice 36, how do I do that? Using the stock HEI distributor.
Next question, If I need to take timing out of an engine, say I need 28 degrees vice 36, how do I do that? Using the stock HEI distributor.
For question 2 - You turn the distributor clockwise to take timing out of the engine, this will retard the total as well as the initial. If what are you asking is you want to limit the total amount of mechanical advance travel then you may have to modify the distributor itself. I'm not sure how to do that on a stock distributor - this may involve welding over a portion of the slit that the weight pins travel in, or maybe changing the pin bushings. Just changing springs or weights won't do it.
Pro
Joined: Sep 2002
Posts: 690
Likes: 1
From: near Memphis TN
Originally Posted by Hvymtlc5
Need to retard for Nitrous application. Lots of good info - Thanks!
I purchased something from Jegs for $150 called an MSD adjustable timing mechanism. It works with HEI stock ignitions, you don't need any other MSD external boxes, and simply involves clipping on three wires, attaching a box to the engine compartment, and sticking on a dial in the dash. With this little gem you can advance or retard ignition 7 1/2 degress plus or minus on the fly! I get a bad tank of gas on a hot day and get some pinging? No problem - I move the dial back a few degrees. I put in a half a tank of race gas at the track? No problem - I move the dial forward a few degrees. I want to expirement with different total timings at the track - no problem, just play with the dial during each run. If and when I put in nitrous - no problem, move the dial back for a nitrous run. The device is super accurate, I tested it, moving the dial back 5 degrees WILL decrease your timing 5 degrees in each RPM point.
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Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Originally Posted by SpyderD
For question 1 - That is incorrect. You are assuming that your timing stops advancing at 2400 RPM. A stock distributor with a stock curve usually has a slow curve and advances WAY past 2400 RPM. The correct way is just to increase the RPM and watch that timing light until you are sure the mechanical advance stops. Of course, disconnect and plug up the vacuum advance.
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Some stock distributors don't reach full advance unitl over 5,000 rpm!. Setting total timing at a point before centrifugal advance is all in gives a bogus reading that results in way too much total once once it is all in.
