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Performance Olds 307
Ignition & Spark
Understanding The ECM & System
Cold Air Induction
Ignition & Spark
Tuning The Q Jet
Carburetor & Intakes 1
Carburetor & Intakes 2
Intake Manifolds
Great Links
Who's The Man!!!
Contact Me!

The HEI ignition that the 307 uses is a very good design. Using performance parts for your HEI is useless unless you have already purchased them (then you dont want to hear that they are useless do you, sorry) or unless you are spinning RPMs higher then 6000 which I doubt unless you have done major work to your 307. The HEI already has a strong spark and is very dependable, it has only two weak spots in the system that I have noticed one is the ignition module, if your car runs fine while cold but after a while of driving it starts to die under heavy peddle and the problem gets worse as it gets hotter to the point that the car bearly takes off without trying to die but after a cool down period its back to normal again intill it gets hot again then you might have a bad ignition module. This part is located just under the cap and rotor, it has two small hex screws holding it in and 3 terminals, 1 terminal on one side and 2 on the other side of the module. The other weak spot is the cap, between the coil and rotor is a spring loaded contact that delivers the jolt from the coil the the rotor, well the cap holds the spring loaded contact in place but after some miles the plastic cap will crack and break right in the spot that it holds the spring loaded contact, leaving you with a weak spark. There is a "pick up coil" just under the rotor, it has two wires running from the module to the pick up coil, the pick up coil lets the ECM know what position the crank is in so the ECM knows when to signal the spark, if this goes bad you will get no spark at all. Before replacing the pick up coil make sure you check it with a digital volt meter.

 Arrow 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 ok.
 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.

Lightbulb  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. cool

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


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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 Wink 

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