Mike
Well-Known Member
This tech article was provided by Wild Mango
Price of gas being what it is makes us aware of the importance of a correct tune. (down here $2:00 a litre is common) I have used this little trick for years on HEI's, it works for other similar systems as well.
What we really want to know is that all the timing is in when we want it. Setting the idle timing and assuming we will get another 20-22 degrees after that is a bit haphazard. This way we know what the full advance setting will be without all that revving.
Now the HEI is a great piece and the only parts that really wear are the weights and pivot pins, the weights tend to wear little trenches in the pins while elongating their own holes. The collar the whole lot pivots on can get sticky with old grease too. Just make sure everything works freely before we start the exercise. Checking the TDC mark is accurate is important as well.
Measure the circumfrence of the balancer and divide your answer by 10. Measure that value from the TDC mark against the direction of rotation
and make a mark which is, of course, a 36 degree advanced mark. As a rule of thumb most SBC's like about 36 degrees.
Fire her up and warm. Shut it off, and taking the cap and the rotor off, remove the springs (carefully, its easy to stretch the little buggers) from the advance flyweights. Put the cap and rotor back on, plug the vacuum line, hook up the timing light and fire her back up. Now, she might buck a bit, because as soon as things start to turn she'll get the whole centifugal advance, and you might have to crank up the idle a bit to keep her going.
Set the timing (by turning the distributor body) to your 36 degree mark you just put on. Shut it off, lock the distributor and replace the springs. Fire her up again, still vacuum line plugged and note the timing for future reference. If everythings healthy it should now be about 12 deg BTDC - or close. If it ain't the springs could be stretchy or just weak.
Put the vacuum line back and note the timing. With a normal sort of cam and connected to manifold vacuum, you should see about 8 -15 degrees added to the idle setting with anything up to 18" of vacuum. Don't be tempted to do away with the vacuum advance, your engine needs it to burn the weak idle mixtures and also when cruising at part throttle openings.
Tuning the mechanical and vacuum advance is another topic in itself!.
Price of gas being what it is makes us aware of the importance of a correct tune. (down here $2:00 a litre is common) I have used this little trick for years on HEI's, it works for other similar systems as well.
What we really want to know is that all the timing is in when we want it. Setting the idle timing and assuming we will get another 20-22 degrees after that is a bit haphazard. This way we know what the full advance setting will be without all that revving.
Now the HEI is a great piece and the only parts that really wear are the weights and pivot pins, the weights tend to wear little trenches in the pins while elongating their own holes. The collar the whole lot pivots on can get sticky with old grease too. Just make sure everything works freely before we start the exercise. Checking the TDC mark is accurate is important as well.
Measure the circumfrence of the balancer and divide your answer by 10. Measure that value from the TDC mark against the direction of rotation
and make a mark which is, of course, a 36 degree advanced mark. As a rule of thumb most SBC's like about 36 degrees.
Fire her up and warm. Shut it off, and taking the cap and the rotor off, remove the springs (carefully, its easy to stretch the little buggers) from the advance flyweights. Put the cap and rotor back on, plug the vacuum line, hook up the timing light and fire her back up. Now, she might buck a bit, because as soon as things start to turn she'll get the whole centifugal advance, and you might have to crank up the idle a bit to keep her going.
Set the timing (by turning the distributor body) to your 36 degree mark you just put on. Shut it off, lock the distributor and replace the springs. Fire her up again, still vacuum line plugged and note the timing for future reference. If everythings healthy it should now be about 12 deg BTDC - or close. If it ain't the springs could be stretchy or just weak.
Put the vacuum line back and note the timing. With a normal sort of cam and connected to manifold vacuum, you should see about 8 -15 degrees added to the idle setting with anything up to 18" of vacuum. Don't be tempted to do away with the vacuum advance, your engine needs it to burn the weak idle mixtures and also when cruising at part throttle openings.
Tuning the mechanical and vacuum advance is another topic in itself!.
