Ignition Base Timing and Advancing Timing, How to set it and what it should be set at for better performance.
Setting the base timing is the only control we have
over the timing on the ECM controlled HEI ignition. The stock base timing on all 307s is 20 degress before TDC. If it is set
too retarded it will be a wimp, if its too advance you will experiance some pinging (pre ignition). GM has designed and tuned
these cars from factory to run on fuel octang rating as low as 87 octang but if you are planing on using better higher octang
fuel like 91 or higher than you can advance your ignition timing to take advantage of the higher octang, results
are smoother running engine, more free reving top end and better sharper throttle responce. I have played with the base
timing alot on these 307s and I have learned that 3 to 4 degrees advanced from stock for a total of 23 to 24 before TDC
is the best for street performance as long as you use 91 octang or higher but feel free to play with different settings
yourself as long as you stay away from pinging. Here is how you set the base timing.
1. On a fully warm engine you
must bypass the ECM so that the engine is running on its base timing heres how, on a cutlass or regal under the radio by the driver's right knee you'll see a connector with two rows of
pins, on all other 307 powered cars it will be under the steering wheel just above your knee. That is the ALDL (Assembly Line
Diagnostic Link) connector. Pin A is in the upper right-hand corner (as you're looking at it), Pin B is right beside it. Bend
a paper clip or small piece of wire into a U shape and insert it into both pins A and B so that they are connected together.
this may cause the "service engine soon" light to flash error codes while the pins A and B are connected together but its
2. Hook up your timing light, restart the engine, and check
the timing by aiming the timing light at the harmonic balancer from the drivers side of the car just over the alternater.
Use one hand to move the throttle and bring the RPMs up a bit, to about 1500RPM while watching the balancer with the light
(the indicater on the balancer might be hard to see so cleaning might be needed if so) and noting the base timing.
3. If the timing needs to be adjusted, shut off engine,
loosen the hold-downbolt at the base of the distributor were it meets the engine block. It's a 9/16th's bolt. A socket followed
by a U-joint, then an extension makes it easiest. Restart engine and turn the distributor a few degrees while operating the
timing light to get the timing just right where you want it (sometimes they might be hard to turn in this case you can grab
the distributor in the middle of its neck with an 1 inch wrench to turn it). Shut off engine. Tighten the distributor bolt
back down, recheck timing, and remove the ALDL jumper to un bypass the ECM.
|This is your timing indicater located by your harmonic balancer
Sometimes the numbers are hard to see because of the dirt and grease covering them so I put this
picture above here to help give you an idea, by counting the teeth you can know that your timing is it even if you cant see
the numbers. The top of the picture is the passinger side of the timing indicater, going from top or passinger side as follows
24-20-16-12-8-4-0, so they jump 4 degrees per tooth on the indicater.
Indexing your plugs will
slightly increase your powers responce and economy. Indexing is just marking the plug from the side of the plug that the cap goes on so
that when you screw the plugs in you can tighten them to a position that will allow have the plugs to spark
(gap) more open toward the valves and center of the cylinder (plugs sit in the corner of the cylinder on a Olds). That little
thingy that you bend to adjust the gap called the ground strap (look at the picture below to see a thingy/ground strap), well
you want that ground strap to be furthest away from the center of the cylinder so that the center of the cylinder sees all
the spark without that ground strap in the way. Just imagine the cylinder that has to spark and then the flame must
first run around that ground strap before gettin to the center, what a sorry burn! Thats were indexing comes
into play, if all the cylinders have the ground strap faced into the corner of the cylinder and the spark gap open
to the center of the cylinder(all plugs sit on the exhaust port side of the cylinder on olds) then you will have all cylinders
firing the same and getting a good hot spark. That makes an engine smoother and more accurate. Its added confidence! what
I do is I take a hack saw and just cut a tinny slit on the top of the plug where the cap goes onto it, (but you can also use
a dab of nail polish) well I cut a mark on that part on just one side, the side that that ground strap is on so that when
I screw the plug into the engine as soon as I start to feel the plug tighten on to its washer then I pull the
socket off and look at the plug for the mark I cut and then tighten slowly till the ground strap is in the corner of
the cylinder using the mark as my indicater, sometimes you might have to try a plug on a different cylinder to get it right
so dont be afraid to swap the plugs around from cylinder to cylinder till they all find a cylinder that allows them to be
in the right postion. now that thats done the spark will be open to the center of the cylinder. I hope you can understand
this it was not easy to explain. Ohh just incase you dont know the plugs are on the same corner of the cylinder of
the exhaust port is so face the "thingy" toward the exhaust mainfold on each cylinder and you'll be fine,let me know how it
works for you! Visit my "Contact Me" page if you have any questions.
|Picture above shows the "thingy"
This is the combustion chamber of a 307s heads. Notice the spark plugs "thingy" is on the far side
of the valves so that the cylinder see's the whole spark without the thingy in the way
Cam Timing, Advanced or Retarded?
I know this has nothing to do with your ignition ok but if you are using the stock Vin Y or Vin 9 cam than DO NOT advance
the cam timing unless you like losing power, Let me explain. Advancing the cam will shift the basic RPM range downward. Four
degrees of advance (from the original position) will cause the power range to start approximately 200 RPM sooner. Retarding
it this same amount will move the power upward approximately 200 RPM. When you retard a Cam a few degrees the engine is then
fooled into thinking that it has a slightly larger cam, when you advance the cam a few degrees the engine is then fooled
into thinking it has a slightly smaller cam. The reason you hear of some many builders advancing the cam timing is because
of two reasons
1. They are looking forward to the timing chain wearing in and droping the cam timing back
some. but on most after market cams now in days they grind in 4 degrees advancement just to compensate timing chain wear so
there is no need to advance a after market cam anymore
1. When you hear storys of someone that advanced his cam timing and gained a chunk of power
thats because the cam he was using was TOO LARGE for his setup so advancing the cam fooled the engine into
thinking the cam was a little smaller and improved his power.
As for us 307 guys that are using a Vin Y or Vin 9 cam there is no reason to advance the
cam timing because these cams are already wimpy as is so if anything you might want to fool the engine into thinking it has
a slightly larger cam by retarding the cam a few degrees to get more power. The Vin Y cam loves to be about 3 degrees retarded
for a strong powerband but if you advance the Vin Y you will have a big wimp. The Vin 9 is good right on but can be improved
with just 2 degrees retarded for a healthier breathing engine. I have heard of people getting higher, slower E.T,s
at the track just from replacing a worn out stock chain for a new one. So if you have a Vin Y or 9 cam and the chain is got
just a little slack dont sweat it because most likely a new chain will just make your car a little slower and dont
let a builder advance your cam timing, if he trys to advance your cam timing hes just proving to us how old school and out
of date he is, school him in , if he dont want to listen than call him an old timer and find someone else. One more thing
if you change your cam timing always check your ignition timing afterward because it will need to be readjusted